Using Inexpensive Line Transformers For Vacuum Tube SE or PP Output Transformers
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- Опубликовано: 27 авг 2024
- Using the inexpensive audio line transformer for SE and PP vacuum tube audio amplifiers and how to determine the plate-to-plate load and center tap.
For reasonable plate load impedance values these types of line transformers are going to be low wattage.
These transformers might be ideal for headphone amplifiers and similar applications where low wattage is adequate.
Here is a very nice article that includes schematics posted below by a viewer. www.ozvalveamps...
More further reading at the bottom of the article: www.bunkerofdo...
Keep in mind that in most of his examples he uses a 100 volt line transformer rather than the 70.7 volt transformer that I used in my video. When working with these transformers keep in mind that squaring 70.7 gives 5000 (as I used) and squaring 100 gives 10,000 so a 70.7 volt line transformer at the 5 watt tap would be 1000 ohms but the 100 volt line transformer at the 5 watt tap would be 2000 ohms, etc.
Update: 7/24/2021 - I have learned a little more about these line transformers and they are not gapped and are not meant to have any DC current flowing in the primary winding as they would saturate easily. To use them as a SE transformer they should be capacitor coupled to eliminate any DC in the primary winding. However, they can be used in push pull as the two halves of the primary have opposite DC polarity current flowing in them which adds up to zero if perfectly balanced and they should work quite well in push pull. In the case of the examples in this video, the power would be low and from what I have seen in the higher wattage line transformers, the available taps are usually very limited. They could work nicely if you are lucky enough to find one with the impedance values you need at the power level you require.
Here you go, all the taps on a 10W or smaller line match transformer. First column is the markings, second column is the resulting impedance, third column is what to connect.
I actually opened the wrap-around clamp on a pair and took a rotary tool with a cutoff disc to cut a gap into the core, and the pair works dandy for a single ended stereo amp with EL84 tubes.
BEWARE that there are some of these, where the wire gets thinner on the higher impedance side. Use only those for tube output, that have constant wire thickness!
70V match Rpri(Ohm) = (70V^2)/Ptap
Uin = 70V Rsec = 8 Ohm Usec = sqrt(P*Rsec) = sqrt (P*8)
Ptap Rpri Rpri plate-plate Usec Uin/Usec Rin/Rsec
(Uin/Usec)^2
0 0 plate-plate 4K,8K
10W 490 8.94 7.82 61.15
5W 980 B+ 4K 6.32 11.07 122.5
2.5W 1960 B+ 8K 4.47 16.65 277.2
1.25W 3920 plate-plate 4K 3.16 22.15 490.6
0.62W 7840 plate-plate 8K 2.23 31.39 985.3
As Eli Duttman says, these small transformers were/are used in the Bottlehead single-ended Para-Feed power amplifiers. So you get a big choke, say 10 Henrys, that is the DC plate load/plate supply. You then feed off of the plate with a large signal cap, say 3uF, into the little line transformer. Since there is no DC , the line transformer handles only the pure AC signal and is loaded by the speaker. Great and cheap method of building a 2a3 or 45 or any low-watt single ended tube amp.
They work excellent for low power PP-headphone amps! Used one for a 12AU7 PP-Amp. Nothing to complain about till one watt of output power.
I really like the videos that bring us back to basics. No, these transformers probably don't have interleaved windings, they probably aren't balanced from CT to each end but they are a great lesson in what you can do with what you have. Knowing the basics like this allows the designer to make compensations for something less than perfect and brings expectations back into reality. Great video David.
I agree that they probably don't have a gap and may not be very good for SE amps but for PP we don't need the gap so maybe they will turn out good in that application. I surely have to build one now and test it. :-) I have several different brands and the better brands as I showed in the video are very balanced to its calculated CT. The cheaper one I have are not as well balanced.
Thanks for the great info.. Cheers from UK.
Thanks - Came at just the right time. Restoring an RCA CONSOLE radio circa 1947.
The only place I've seen 'line transformers' is in old Bogen P.A. amps! I never knew what the whole 70.7-volt line was all about.
Thanks for very informative video, you just helped me to get out of confusion about this 70.7 V audio transformers, always learning, from the first until your last breath.
Experiences with these awhile ago although not as a plate loading output.Right now,using a little Stancor 5w unit to match the 600 ohm output of the Hammarlund SP-600 I am restoring to an 8 ohm speaker.Still has a slight mismatch but WAY better than without the transformer! Good job! You make an excellent Elmer!! 73's.
I use one of these transformers on my Collins R-390 as it has a 500 ohm output. It surely makes a huge difference. BTW, I use the R-390 as my main receiver. The audio is so superior to the high pitched receivers as it sounds like my contact is in the same room with me. Love it.
73 WA4QGA David
ElPaso TubeAmps R-390 is an amazing piece of engineering. The 600 I am using was quite the tough dog! Typical problems were it being WAY out of alignment in the RF and the 1st conversion LO would just stop dead above 7 Mhz.After exploring everything I could think of,with all voltages spot on and swaping 6C4 osc. tubes from the variable to xtal. LO,in desperation I tried a brand new RCA N.O.S. tube and it kept on tickin right up to 11m!!About 27.50Mhz.Been using it alot with the line trans on the output.Watch alot if what you do.Can tell you're into it! I love the test equipment you have.Should have invested in stocking my bench! Have a great New Year! 73's back to you. Charlie N2VUW.
Interesting discussion. Just for "Fun" I built a 6AU6 (small signal pentode) ->6AQ5 using a 10W line matching transformer in single ended mode. Yes, I expected a lot of saturation and biased the 6AQ5 really really cold (like 5W). The "el cheapo" guitar amp was a success! Of course the amp's output was compressed and distorted, but it still sounded great, for what it is..
That is good to hear. You are one of the rare few that will actually build it... I might guess that putting a capacitor in series with the plate of the 6AQ5 to the line matching transformer and putting a choke of at least 10H on the plate side of the transformer for DC to the 6AQ5 might improve it ?? I don't know that but it would take the saturating DC off the line transformer. Thanks for letting everyone know.
I never thought of this....... Great idea!
Dave, I agree with the not air gapped assessment. I recall Dan Schmalle, AKA Doc B., using that sort of "iron" in a "parafeed" setup. IMO, an interesting experiment would be "parafeed" PP 6BM8s, with constant current source (CCS) loads and the "line" trafo priamary across the plates. Regulate g2 B+, for max. open loop linearity. As incorporating those little cores in a GNFB loop is almost certain to cause saturation, use short loop NFB. Heat sinked 10M45S ICs should be OK for the CCS loads.
Eli D.
Great video. That's a good explanation of line (100V, 70V, 25V etc.) transformers.
The last pair are low level signal transformers so are not suitable for handling any power but for low level signal impedance matching. They seem to be general input/output impedance matching transformers, i.e. probably designed for both tasks, whereas most low level transformers are specifically designed to work as either input or output but not both for optimum performance.
Thank's, every bit of info helps. I am going to build a mini twin reverb 2x8" at 8ohm , 2x6V6 push/pull low wattage portable Guitar amp. Like Valve powered boogie box with spring reverb...I hope. All this because the speakers have a really good clean tone and they look too well made to just throw in the bin..
Transformers, especially those with mulitple taps, are really under-appreciated these days. Thanks for sharing.
Have in mind that this transformers do not have appropriate insulation, remainding you that if tube circuit works on 250V (DC) AC value can be as high as 250 + 100 or more.
Not good for high DC bias though, they are not gapped much and are really intended for AC only use. But if you have a small DC bias and low power use they will work fine, good enough for interstage coupling at low power. Simplest is to look for the primary winding triplet that has equal DC resistance side to centre, as the primary is always going to be wound with the same wire gauge.
You can delaminate them and restack with a gap though, but you will lose at least 1 set of laminates getting the first one out, then stack as all E and I with the centre leg ground down slightly.
Voice of music amplifiers use them especially the v-m 1428 great integrated tube amp
Why don't we take the whole dc problem (both insulation and saturation) out of the equation and use them merely as impedance matching devices? We can design a single ended para-feed with a plate load resistor or, even better, an inductor. We add a capacitor for coupling (pretty cheap these days) and we get rid of all the dc saturation. That should make up for the poor low frequency response on those things. The famous REDD 47 preamp uses an arrangement pretty similar to the one I'm describing here and it's one of the holy grails of tube sound. If that was good enough for Sir George Martin and The Beatles, then it sure as heck should be good enough for me ;) Thanks for another great video and also for such a great idea, I just threw so many of those things away...
Common to 70volt Intercom systems to drive speakers.
Hi David Happy New Year, I'm not positive as these are before my time, but I thought these type transformers were used in office buildings at the speaker...for matching different speakers to a PA type amp or intercom system. Most PA's have a 70 volt output tap, and then you would put one of these transformers at each speaker....to match it @ 4,8,16 ohms no?
That is true what they were originally designed for. The taps are to control the volume as you would not want the same volume in a bathroom as you would in a much larger area so the taps are there to limit the volume. They could be soldered or have a switch on the speaker for volume control. I have to build an amp and test these transformers but some people report that they have been using them for years.
There still used today.. we install them all the time
I seem to remember a 6V rms ( 0-115 0-115 ) torodial can work OK. I think 10 kHz if no correction used. EL84 comes to mind ( usually 8K ohms A-A ).
I suspect the downside is probably suppressed response at the low and high end frequency ranges. I searched a few old Stancor catalogs and found no specs listed. I did find that Thordarson still has the 24S71 shown in their current online catalog. Sadly indeed, the response is stated as 100 - 10kHz. For headphone amplifier output impedance matching, the story may be different - only way to know is to build one and see what happens.
I agree that they are not likely to have a FR from 20 to 20KHz but, as you say, I bet they will be very good for headphone amps. I have to build an amplifier and test one now.
Well, the application here is performance with headphones - most are around 30 to 35 ohms. The winding resistance of most 70V line transformers is pretty low. The output impedance if the vacuum tube amp is >>> greater than a typical 70V line amp. The combination of operation below 1/2W with significantly higher I/O impedances "might/may" yield better FR performance. That said, it's worth testing both ways. Surprises happen.
You have me thinking about connecting the transformer, as you say, with a load and driving it with another high quality amplifier that can deliver enough power to test it at its power rating. The test transformer would be driven (by the amplifier) at the low impedance side and I would have to have a resistor equal to the high impedance side to load it and measure it ... I will have to think about it. I have tested transformers with just the few volts output from the oscillators and checked it with the HP 8903 and they all turn out fabulous, including filament transformers so, testing them at a few mW doesn't seem to mean much as how it will operate close to maximum levels.
Oh well, it was worth the thought. The only bogey not modeled by the simplified physics & math is the core material/construction behavior - sounds like you already have a pretty good idea that the affect on FR is minimal.
Great tip - Thanks very much!
Those are my main PP OTs for 6AQ5's - 6V6's - 6BM8's. I often get them for $5 or less delivered watching on Ebay. The ones I have are 10W max. I got about 10 in stock. LOL But you are giving away my secrets. Prices may be rising now! LOL ;^)
I certainly agree with you comment of unnecessary complexity. I often times find the best answers in the first books that were written on a subject, likely written between the 1940's and 1970. After something is discovered or designed, academia gets into it and regurgitates complicated versions of it. We also have the advertisement community putting all kinds of flowery words all over it to increase sales. The most common one is "RMS power". No one wants "average" power... but mathematically, RMS power does not come from multiplying RMS voltage times RMS current. We know it is called average power. I hope this video helps builders find and put to use some of these line transformers that have been laying around for decades. Unfortunately, the power levels are going to be pretty low but I am confident even the lower power rated windings of these transformers will be able to deliver up to 10 watts (depending on the size of the transformer, of course) and there may be some concern about the max voltage these transformers can withstand.
I bought some lots of transformers on Ebay for cheap. I then had to identify what I bought and what I might be able to use them for. LOL That is how I too stumbled into using these line transformers as output transformers. I make mainly guitar amps so a certain level of distortion is actually desirable in these designs. I also use cheap Chinese converter boards with DC inputs to light the heaters and switching boost boards to get the HV B+ of +250VDC I use with the 6AQ5/6V6/6BM8s. This keeps the output wattage down near the 10 W my line transformers claim. They absolutely work with lower B+'s at around 10W output for ROCKING little guitar amps!
Yeah, the Data Sheets for the tubes I use have clear specs for +250V operation. I've pushed it up to +300V just to see how it worked with no problems. +250VDC from my cheap Chinese DC PS design works very well with 6AQ5/6V6/6BM8! With this type of design I can build a nice bedroom volume level guitar amp for less than $50 in parts. I can't get a new traditional OT for these tubes delivered for that price! LMAO
No, PP
Great !
Now I need to go find me some of these 😀👍
Nice video's... Subbed !
i already use 100 volt line transformers in my valves as you there cheap. 30 HZ 25 K the one i use i find they work well in hi fi and guitar
can you tell me more?
@@zxttgg pa line transformers
@@zxttgg www.ozvalveamps.org/optrans.html
@@moodyga40 Thats very helpful. thanks!!!
i have a old 1961 5watt 6v6 harmony amp with a dead OT transformer. locally i can only find a small line matching transformer its the right 8ohm 15watt 70v could i realistically use it?
A 70.7 volt primary rated at 15 watts would be 5000/15 = 333 ohms. Certainly a bit low but it will probably "work" in that it will output power but will likely not do low frequencies very well. I assume your amplifier is SE (a single ended 6V6) or is it push-pull 6V6's ? You should be able to find a SE transformer on Ebay to replace the one you have. It should be about 8000 ohm primary to your 8 ohm load. Here is one I found for you to look at. www.ebay.com/itm/165490843444?hash=item268805df34:g:JesAAOSwiChffRkH
@@ElPasoTubeAmps thanks yes a single ended 6v6 abs 5y3 rectifier. Just looking over old schematics at work.
@@ElPasoTubeAmps just picked one up. It's rated in wattage on the primary leads. 5/10/15_common. Now just to figure out which one to the output tube and the other wire is going to the rectifier on my stock
Hello. Can I use 100V / 300W step up line transformer as Tube amp output transformer ? Transformer has 70V and 50V tabs on secundar and primar 8 ohm ( and 4 ohm tab) ( 100W NF output).
Genius . So glad i kept all mine now!
Hey is there any way to use these in ultra linear?
Thanks again.
Thanks so much for that great video. I am not sure if I fully understood one thing: can those take any B+ from the power supply or is there a limit?
There would be a limit but I personally would not worry about anything 500 volts or less.
Perfect, that’s more than enough for my project. Thanks!
Also, Am I thinking right? Using them, no matter what, if I need a 5000 ohm impedance, say for a 6L6, I can only ever have 1 watt of output?
Building on my comment earlier, I would think that in a PP circuit where DC is opposite and essentially canceled in the push-pull configuration and in a perfect balanced output circuit there is no DC biasing current to lead to saturation (assuming tubes are nicely balanced) I think they would work great. These transformers are rated at different levels of power up to 20 watts or more so I don't see a limitation on power as long as the transformer is big enough and rated for some higher power level. I haven't slowed down on building but my passion moves around between RF and AF and then astronomy and who knows what else, and I have been stuck on RF lately. I do want to get back to audio amplifier building with some of the magnificent UTC transformers I have. Thanks for your comment and always good to hear from you...
@@ElPasoTubeAmps You do have some nice transformers!
I order one of these off ebay and it was from china and it has the 4 and 8 ohm and both are measuring 4 ohms for speaker. People might want to watch the chinese ones. That is ok though. I have a cab that is 4 ohms. This one appears to be new. I'm going to use it, No more money than I gave for it, not worried. I just gave 8 dollars for it. Thanks for the info.
What if one uses a battery tube? Plate current is typically 2-4 mA…
I see no issue with the battery type tubes. Probably would work quite well at the 2-4 mA current levels as it will not magnetize the core
@@ElPasoTubeAmps thanks. I hope to resume working on these again in the near future.
Nice video. Thanks for sharing! What do you think about these transformers if they are used in the old fashion way as interstage transformers where the primary side is driven by simple push-pull circuit for example using 12AU7 and secondary side goes directly to for example 6V6 grids without the usual 220k grid leak resistors. I suppose you get the center tap for secondary if you use 0&16ohm for grids and 4ohm for CT right? There’s not much data about the behaviour of the interstage transformers where their secondary is left open like basically they were left that way in old radios and Gibson amps.
I never thought about using the secondary side (low z side) to drive grids but it might work for the 12AU7 and 6V6. The 6V6 only takes about -15 volts bias so open-circuit, as you mention, might deliver enough to drive them to a reasonable level. Sure wouldn't be picking up much hum at the low Z value. Yes, impedance levels for CT would be 1/4 (or 4x) from a side instead in the middle. Common and 16 and 4 ohm CT - makes sense to my head right now 🙂
@@ElPasoTubeAmps yea i’ve been trying to find cheaper alternatives to the usual interstage transformers that seem to be designed for class A2 operation. It doesn’t make much sense using a 5W bulky transformer to drive pentodes where they don’t deliver any extra output when they are driven into grid conduction. At least this is how i understand it. Hopefully someone corrects me if i’m wrong that with pentodes there’s not practically such thing as class A2 🙂
I've got an old Sony tube amp with just a 6BM8/ECL82 triode pentode in it. The output transformer is open circuit. Could I use a line transformer in its place?
There is a good chance that you can. You will need to get a line transformer that has a primary impedance that is high enough for your 6BM8 circuit. I assume it is around 10K or so. That should work.
I see a lot of talk about how cool this is, but no demos on how it sounds and if its reliable.
I agree with you. I have little doubt they will work in push pull. In PP the effective magnetizing primary current is canceled by the opposite direction of current flow to the two output tubes (assuming they are balanced) but as for a direct SE transformer I have some serious doubts. It has been brought up a few times that these transformers are meant to be used in a distribution system with no DC flowing in the windings (especially the primary) so there is probably no gap in the core and with that said, in a standard SE amplifier design, I suspect the core will saturate very easily, the primary inductance will drop to virtually zero and it will be a big flop with the bass sounding horrible. However, there are solutions suggested in the comments below that sound reasonable to me if one wants to use these transformers for SE operation. Just below where I am typing, a suggestion by Joseph Mooney, his solutions sounds good to me. Maybe I can get around to it some day but I am still charmed by big RF and AF push pull amplifies at the moment.
Interesting! I recall thinking about that many years ago, but never ran the numbers. Most of these small transformers are very low wattage, I'm wondering how far they can be pushed before they develop heating problems? Could a 10 watt transformer handle 30 W push-pull?
I don't think you could push a 10 watt to 30 watt just by looking at the size of it. I am hoping that even at the lowest wattage numbers stamped on the transformer, indicating what it will do for what it is mean to do, it will perform at the highest rated power of the transformer - but I don't know for sure.
Instructive!
Could I use microwave transformers to feed two 816's in a push pull amp?
A microwave oven transformer (MOT) is a power transformer around 2000 volts output on the HV secondary but it has no center tap. It also has one end of the high voltage winding connected to the metal core of the transformer which is grounded to the case of the microwave oven. It has one "hot" terminal and two other wires to light the filament in the magnetron. Sometimes people "lift" this connection off the grounded core but a MOT is s deadly high voltage device and I do not recommend using one in a power supply. People have definitely been killed messing with microwave high voltage transformers. One was a college professor here in El Paso a few years back. If you did lift the grounded end of the secondary off the core of the transformer and insulate it properly, then you could put it into a bridge and get around 2600 volts or you could put it into a voltage doubler with two 816 MV rectifiers and you would end up with about 5200 volts. I don't think you want to do that. MV rectifiers may be very pretty glowing blue in a power supply but that should be taken as a warning of high voltage that can kill. That would likely be Death On Contact with voltage at either of those levels. In any case, a MOT plugged into a wall outlet is a deadly device. Otherwise you could cut all the wires off and wrap it in nice cloth and use it as a door-stop... Stay safe and alive...
Bill, for reasons I can not understand, I can not always see comments in my RUclips videos so I will try to answer one of your other questions here. The comments only show up in my email.
You asked about balancing grid voltage vs balancing cathode current. If all tubes were perfect, then balancing the grid voltage would balance the cathode current. But in any case, the objective is to balance the cathode currents and that is done by, most likely, unbalancing the grid voltage by a small amount. For example, one tube might need -36.4 volts for 50 mA of current while the other tube might need -36.7 volts for 50 mA of current. There are just math examples to illustrate that the objective is making the cathode currents the same at 50 mA in this example. Hope this helps.
How would you install a pentode to triode switch in a 6l6 push pull guitar amp?
Here is what is suggested.
www.premierguitar.com/articles/24181-ask-amp-man-reduce-power-with-a-pentodetriode-switch
In essence, you are disconnecting the wire or resistor from the screen grid (pin 4 of the 6L6 family of tubes) and then connecting the screen (pin 4) directly to the plate (pin 3). This would connect it in Triode mode. In other words, remove the wire or resistor from pin 4, whatever might be there and then jumper (short) pin 3 (the plate) to pin 4 (the screen). This is what they call Triode mode. In the link above they use a switch, which is known as a double-pole, double-throw (DPDT) so you can go back and forth between the Pentode and Triode mode. DPDT switches come as toggle switches or as rotary switches. There will be a total of six (6) contacts on a toggle switch. An example of this type of switch is shown below on Ebay. I hope this helps.
www.ebay.com/itm/2-pack-Waterproof-6pin-DPDT-Momentary-Toggle-Switch-Boot-Cap-ON-OFF-ON-Amp/401623319313?hash=item5d829d8311:g:KCEAAOSwPXFcI2EN&frcectupt=true
hi sir thankyou for make this video...sir i have a problem designed a pre amp with 12au7 but i want to know how can i calculate output impedance i mean (Zoutput) please lead me sir and thankyou
As unscientific as this may sound, you do not need to calculate output impedance. There are the characteristic curves of the tube and there is the empirical "design" which is contained in the many examples over the decades of amplifier builds. I recommend studying the designs of the Williamson design like the Heathkit W-5M or the UTC schematics. They are easy to find on the Internet. "Designing" an amplifier is like designing a car. We use metal, tires, motors, ignition systems, fuel systems, ad infimum, that are already designed and available to us to use to make a complete product. We do not need to reinvent the wheel. About as low into the design as you can get is the RCA tube manuals, free off the Internet, where they recommend resistor and capacitor values for voltage amplifiers like the 12AU7 and others. Their advice on component values is hard-learned from real life experience and is available to us for free. Hope all this makes sense. Some links are below. The vintage 6SN7/6J5 and 12AU7 are basically interchangeable in audio amplifier building.
www.elektronikjk.pl/Elektroakustyka/wzmacniacze/wzmacniacze_lampowe/UTC_W-20_Williamson_Amplifier_Kit.pdf
www.vintage-radio.info/heathkit/
Again hi sir..at first I must say you thank you for answer my request..and then sir you said the output impedance it isn't very important but sir I design a pre amp when I want connect this pre to amp..if my pre to have low output impedance I take normal quality on output amp but when respect impedance and I use high impedance I get good quality on the output..((absolutely when I change the impedance I pay attention to don't change my output watt))) i mean all the parameters are the same when I use low or high impedance except impedance..but we have a lot of chane quality on the output
So because of that I need to know how we can calculate output impedance
And again thank you sir for answer my question..thank you sir
Maybe I am just a bit lazy when I build amplifiers and use values of components like high-end vintage amplifiers and preamps. 🙂 I assume you like the higher level output you get from your preamp when you use a higher impedance load on the output (?)
Since a 12AU7 is a medium mu triode, most circuits have load resistors ranging from 22K to as high as 100K. A 12AX7 being a high mu triode, uses higher value resistors up to 1 meg to get lots of gain. I suppose it just depends on how much gain you need. I hope I am understanding what your goal is and am helping. Best regards...
Please add more topic why power transformer can not be replace interstate transformer in Single End amplifier . For example 2 : 3.5 can not be replace by 220V : 385V power transformer with the same ratio. Thank you in advance.
You very well may be able to use a power transformer for an audio transformer if the turns ratio is reasonably correct. I don't think I have ever used them in interstage coupling but I don't see why not as long as the turns/impedance ratio is close. I have tested power/filament transformers at very low power levels (mW level) and the frequency response is very good. Not so good when using a power transformer as a output transformer running higher (20 watts or so) of power. If you select your transformer carefully, you may find one where you can use the CT HV secondary as the plate-to-plate winding and use the filament windings to drive the speakers. It can work - maybe not 20Hz to 20KHz but it can work.
@@ElPasoTubeAmps in audio forum they said something about gap. Power transformer does not have gap. Is it relevant?
@@nuttyl283 Power transformers only operate at one frequency in the USA, 60 Hz. In audio amplifiers operating at low frequencies, as low as 20 Hz, the core can saturate much more easily so single-ended (SE) transformers need the gap to help prevent core saturation. Push pull transformers do not need a gap as the current in the two halves of the primary are in opposite polarities so the core does not saturate.
@@ElPasoTubeAmps Thank you very much. I plan to build 4P1L SE as a schematic use interstate T. Due to interstate T. is expensive. I change schematic to a Japanese guy version using Transistor to drive 4P1L PSE 4 watts instead to save cost. However I already have 6N2 4P1L Push Pull amp 10 watts. I don't know is it good Idea to make SE 4 watts just for JAZZ and audiophile voice music. I don't have much knowledge about different of SE and PP but my friend tell me that SE is more proper for audiophile voice. That make me want to build 4P1L SE 4 watts
@@nuttyl283 The SE amplifier is going to be easier to build but it will not deliver the power of a push-pull (PP) amplifier. That may be OK. Amplifiers with low amounts of negative-feed-back (NFB) tend to sound very "alive" and is probably why audiophile's like it, especially with string instruments like the violin and the human voice. However, the fact that SE amplifiers are usually low power (3-5 watts) they do not do bass very well. Best of luck with your project.
Vgood sir.kindly make video about audio out put transformer compliant design ..500wt input out4.8.16ohm...100v line...with..bobin size ...truns ..formula
I am not familiar enough with transformer design so I am not able to make a video on that aspect of transformers. However, I can recommend a book title "Practical Transformer Design Handbook" that I have and reference occasionally.
ISBN 0-672-21657-4
www.amazon.com/Practical-Transformer-Design-Handbook-Lowdon/dp/0830632123
You know that you just raised the price of them!!!!!!!!!!!!!!!!!!!!!!!!!!!
Yep... they are probably $250 each on Ebay nowadays. :-)
A few years ago I posted a video on using hot water heater elements as 16 and 8 ohm dummy loads and we joked that there would be a world-wide shortage of hot water heater elements after my video. Fortunately, that didn't happen and they are still about $15 at Lowe's. However, you never know what can happen on Ebay. Here is the dummy load video: ruclips.net/video/5gAUuLkc1ik/видео.html
Check out the link provided above by the viewer, Hayruss www.ozvalveamps.org/optrans.htm
I actually bought a similar line transformer off eBay. It was advertised 8k but when I put it on my signal generator and measured voltages, both with volt meters and digital oscilloscope, I got closer to 5.2k. Have you measured the line transformers to see how close to theoretical they are? Is there a better way than my method, assuming the mentioned items and maybe excel? Thanks for the video I think they would do great in 1-5 watt push pull amps.
I haven't actually measured Z yet but now that you mention it, I will and let you know what I find.
I did measure the larger of the two transformers I showed in the video and the 10K secondary read 11.7K with the GR bridge (I used 8 ohms on the 8 ohm secondary)
Thanks for the reply. I wonder how balanced they are, more a general curiosity than a request. Always fun to get new information. Thanks again for the update.
Do you think common or garden switched mode psu transformers be used for the same thing ?
I sure don't know but I kind of doubt it. I am not sure of the frequency that SMPS operate at but I think it is 15KHz or so (??) and I would assume that the FR of these transformers would not do well at LF and I have no idea of the primary to secondary impedance values. Maybe some other viewer can comment and provide more information.
ElPaso TubeAmps Thanks for that,it was just a though -maybe later I will do some experiments and let you know
Thanks again !
Anyone know if a hammond 117f2 could be used for something like this? Im thinking about a 1w SE guitar tube amp.
I looked it up and it has primary power taps of 4 watts, 2, 1, 0.5, and 0.25 watts. This is a good universal transformer. This corresponds to a primary Z of 1250, 2500, 5000, 10,000 and 20,000 ohms as a SE transformer. No guarantees how it will handle quiescent current concerning core saturation as an SE transformer. You could also use it as a PP output transformer as a 5000 ohm (1 watt tap) (and C as the other end), plate to plate, with the CT at 2500 ohms (2 watt tap), 10,000 ohm plate to plate with 5000 ohm (1 watt tap) as the CT etc. The primary Z is from the common tap, C, to the power tap in watts. The Z point of the primary is between the (C)ommon wire and is determined by dividing the power number into 5000 (which is 70.7 squared). Hope this helps.
Thanks! Yeah i calculated the impedance like you did in the video and it seems to work out, im just worried about the wattage. I was thinking using a pair of 12au7 (both halves of each) to drive it in paralell SE. I could use a higher wattage hammond, 4w model for instance but im thinking it wont saturate as nicely.
Looking at the 12AU7 data sheet I would personally do PP and use the 20K end of the transformer with the CT at the 5K tap. That would probably give you 2 watts or so with 300 volts on the plate of the 12AU7. Just my thoughts. Best of luck with your project.
Well, im trying to keep the wattage down on this build so im going to stick with a SE design, but PP would probably be better. My power supply is only going to have a little over 200 volts for the plates. If it fails then atleast i learned something right :)
If OPT is 10K : 600R, can I put 38r headphone in serial with 560R resistor (38r+560r = 598r) to connect with 600r?
You could do that but the majority of the voltage drop (93%) will be across the 560 ohm resistor so it may not be very loud in the headphones but that could be OK.
@@ElPasoTubeAmps Thank you very much, From your teaching about center tab I see that the 10K : 600R transformer has 2 groups is it equals to 600 /4 = 150R? to be easy explain 2 groups comprise of wire 1 and 2 for Group A and wire 3 and 4 for group B. I am not sure if I am correct. for 600R you need to solder wire 2 and wire 3 together and measure 600R at wire 1 and wire 4? If I am correct so Group A (wire 1 and 2) will be 150R and another Group B (wire 3 and 4) is also 150R. Hence If I use either wire 1+2 for 150R or 3+4 also 150R for my 38R headphone, I just need about 100R resistor in serial (100R+38R). Or another method is to make 150R of to group to drop to 75R by Parallel by connect wire1 (Group A) to wire 3 (Group B) and wire 2 (Group A) to wire 4 (Group B). If I am correct may be I just add 31R to my 38R Headphone and voltage will drop by 45% instead of 93.6% of 560R drop of 600R secondary side. I can't find transformer of 38R in secondary in local market. 150R (2 Groups) is the best I can find for OPT of headphone amp. Please advise any alternative for my 38R OPT headphone. Thank you very much
@@nuttyl283 You are correct in understanding how inductance and impedance is calculated. Impedance of a 600 ohm output in your transformer is comprised of two 150 ohm coils in series because they not only add in series but also in magnetic coupling by the same amount. You could put the resistor in series with one half and your headphones for technical reasons or you could put a pot of 600 ohms or even 1000 ohms across the 600 ohm output of the transformer (capable of handling the power level) and then put your headphones across the ground connection and pot wiper connection. I know this will vary the load resistance and reflected impedance as you vary the volume level but it will work out perfectly well. Matching impedance is a real thing but at the power levels we generally operate at (less than 20 watts) impedance mismatch can be off by factors of at least two times or more with no noticeable difference and no significant measurement difference. At high power levels of around 250 watts and more, impedance matching becomes critical. You could connect your headphones directly across the 600 or 150 ohm windings and see how it sounds or you could use the series resistor for proper technical matching.
ElPaso TubeAmps thank you very much, transformer seller give me 2 specs which one is better and what are reasons? He offers The primary is about 11H, the secondary is about 618mH
100HZ test. Leakage inductance is about 60 mH
Distributed capacitance is about 1.9nF primary 17H,. secondary 7508mH
100HZ test leakage inductance is about 57 mH
Distributed capacitance 2.6nF both are 10k : 0-62-300R which he said I can use parallel for 51R headphone output. Does Henry affect sound?
@@nuttyl283 You have some interesting data. Inductance ratio is the same as impedance ratio so 11/0.618 = 17.8 so, if you put 51R on the secondary, the primary would be 907.77 ohms or call it 1K. Is that what you are looking for?
A good quality PP OPT is 20H plate to plate so that is 5H plate to CT so, that is why I say 11H is good for SE.
What's the frequency response?
At its rated power output is it probably pretty poor compared to high-end output transformers. I would assume something in the range of 100 Hz to 5 KHz but if it is used as an interstage transformer where the power is very low at fractions of a watt, it can be very good and do 20-20KHz.
Great tutorial! What percentage of power would one lose because of the air gap? I am looking for around 10K p-p for a couple of 6GW8s at around 10watts output?
Have you tried using these?
No, actually, I have not built anything with them. After some of the lengthy comments that have been posted about these little transformers and the fact that some say they have used them very successfully in SE amps (with current thru the primary) I have a feeling that they would do best on the DC isolated side of a blocking capacitor as a driver transformer. I still have reservations about using them as a legitimate SE output transformer. I have been very involved in my ham radio equipment and have neglected my audio hobby but I seriously do have a project that I will start on "any day" using a pair of Svetlana SV752-10's. I have a nice 10K Tridad transformer that should be a good match. I have not decided on how to drive the grids of the 572-10 yet. I don't think the standard Williamson driver will deliver enough voltage swing so I may have to go with the choke drive (also known as impedance drive) or maybe some of these line transformers or whatever that interstage transformers that I have that seems best.
When you say 70v are you speaking of 70v public address speaker transformers
Yes, these are the small public address type matching transformers that might be found in an office setting. I suppose this 70.7 volt and 100 volt and even 25 volt (8 ohm) rating was to keep things simple but in my opinion, it made things more complicated to use them for anything but their primary purpose. To find a use for them, as builders might want to use them, it is a simple procedure to use a formula, Z = E^2/W In this case 70.7 squared is always equal to 5000. So to find the impedance of the high impedance side, we divide 5000 by the power rating stamped next to the terminals. For example a 70.7 (or just 70) volt transformer with a power tap of 0.5 watts would have a primary impedance of 5000/0.5 = 10K ohms. The CT of that would be 1/4 of the whole value or 2500 ohms. So if you have a nice transformer with lots of "power" taps, you can do the math and see if you have a transformer that you can use in a vacuum tube amplifier. These transformers are not meant to have DC flowing in the primary winding or it will saturate the core so they can not be used in single-ended amplifiers, but if the output tubes are balanced in a push pull circuit, they could probably be successfully used maybe with a pair of 6AQ5 or 6BQ5 or maybe even 6V6 tubes to match the output to speaker voice coils.
ElPaso TubeAmps I wish I could get you and a sharpie together at my shop.... I certain in 2beers or less All my stockpile would be marked and labeled....
I’ve yet to run a part number through google that led to any discovery.
I need a variac... Tell me why couldn’t I wrap 22ga wire about 140 single layer isolated turns down an iron bar, hook each end up to the 124 (that’s what my shops running so EVERYTHIINGS running a bit hot so I need several of these) clean out a small track and drag a piece of carbon up and down it tied to the output line?
ElPaso TubeAmps I wish I could send you pictures I have just scored a mother load of Peerless Altec Lansing 70v type 15066 USA
Have 32 16 8 &4 hm taps with common... for free from a buddy... they were all pulled with horns an speakers from the casino... only installed 2yrs... need any?
@@thespiritof76.. That is a very kind offer and I thank you very much. I don't need any at the moment as I have gone down the rabbit hole of SET amplifiers, as one gentleman put in. As mentioned above, if there are lots of power-taps, then there will be lots of high impedance connections on the primary side so there can be many uses for them. If the taps go down to the 0.25 and 0.125 watt level then I can see them possibly being used as input driver transformers for high power amplifiers where the grids of a set of large tubes like a pair of 810's can be driven directly with them. The Peerless transformers are nice so you scored a nice one.
ElPaso TubeAmps really?
There even marked 4-8-16-32 U so there’s no guessing.....
I have 12 in hand and prob at least 12-20 more I gotta go pick up....
My Q is will they run a pair of 6550? Those are abouf 40watt each from what I gather.... they are exactly 4” tall and 3” wide
Hi A couple of guys worked this out in Australia years ago and I use them for push pull guitar amps all of the time based on the info in this site. www.ozvalveamps.org/optrans.htm Hope this provides a bit more info for you on the subject. Cheers Haydn
Very nice article.
Recommended reading for anyone getting into these transformers with lots of excellent examples in the link.
I copied and pasted the link www.ozvalveamps.org/optrans.htm to the top of this video in the description block. I also mentioned that some of the transformers used in the article are 100 volt and not the 70.7 volt as I used in this video and this changes the primary impedance by a factor of two just to help prevent confusion that might come from the different transformer values. Many thanks for your information.
This transformer winding formula call me
Yes i came up with the same idea .But you want to be sure that those transformers can handle high voltage
Also i had one idea to design OTP amplifiers and used them to match 800 ohms to 8 ohms output
I just used two of these type transformers in series to get 600 ohm CT to drive a class-B pair of 3-400Z modulators for an AM transmitter. The 3-400Z require 26 watts of drive. They worked great. Also, as I think about these matching transformers, I doubt they have a gap to allow DC in the primary windings so the core will saturate very quickly but they can be used with a blocking capacitor to match a plate load to speaker impedance. I use this method in a SET amplifier using 300B where I have a plate load using a 10H choke and separate the plate potential from the matching transformer with the blocking capacitor. Works good. Thanks for your comments and information on using them in an OTP design.
@@ElPasoTubeAmps GOOD JOB .. I was wondering if this could be done ..To increase output power !
@@ElPasoTubeAmps The more i think in OTP designs you could use several of those transformer to drive an individual speaker each one
@@ladronsiman1471 As mentioned, I put them in series, taking into account phase and came up with 600 ohm CT for driving the grids and 4 ohms on each side of the secondary in series for 8 ohms and it works. I did make measurements with an impedance bridge so I confirmed what I was getting was correct. This is just my thoughts on it at the moment - I might consider loading the anode of a 6AS7 (I assume you are using a low mu triode like this) into a 10H choke for a plate load and separate that with a non-polarized coupling capacitor (two electrolytics back-to-back) into the line transformer(s) at some low impedance (250 ohm, 600 ohm, etc. - experiment around) and then the 4/8 ohm side to the speakers. Transformer separation would ensure no DC can get to the speakers. Just thinking - I have not tried anything like this yet. 🙂