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- Опубликовано: 2 окт 2024
- Brief review and checkout of a Boonton model 92C RF Millivoltmeter from the early 1980s that I recently found at a hamfest. Nice to find this meter in good shape at a local hamfest, and that it includes the original probe and adapters - because these meters were calibrated together.
Always enjoy your videos. yes that sure is a great find. I"m finding it difficult to find one with probes.
Looks like a nice meter that could be useful for RF measurements, very nice find. Boonton Electronics is still around, they are in Parsippany, NJ about 45 minutes from me.
Watching your equipment videos is like a trip down memory lane for me. I spent 10 years in a metrology lab repairing and calibrating stuff like the Boonton. Lots of Tek scopes, too, even a fair number of the older, large tube rigs. Love your stuff, keep it up!
Do you know the difference between the 92A, 92B and 92C? I just picked up a nice 92A for cheap, but I'm curious. Can't find much online. I see the 92C listed in the 1971 Boonton catalog with a price, cheaper than the 92A, but there’s no other details on it in that catalog.
I don't have any additional info. Boonton is still in business, maybe one of their application engineers can get you the answer.
Now, you have the correct meter to calibrate wattmeters, though you'll need a precision attenuator for any large power (measuring voltage across 50 Ohms) measurement. This was how many amateur wattmeters were calibrated at the factory.
I have two Millivac RF Voltmeters with the probe sets, and they're how I do wattmeter calibrations.
Have not used one of these since the days I worked for EF Johnson. I always wanted one at home but never found one that had the original probe or was not beat up. Very nice score on this unit Alan. Thanks for sharing.
Nice find, I have a MOTOROLA S1052B that has an RF probe.
The diode is open in the RF probe, would you know what kind of diode would work in that probe?
There is no service manual nor any schematic on this meter.
Thanks for any information you can provide.
I would think that it is some kind of schottky or zero-bias diode, but I really don't know for sure.
Thanks Alan, it looks like a glass diode like a 1N60, etc.
Thanks again Allan
I would like to see a video on calibrating one of these - for us that do not get as lucky and have to find & combine meters & probes ;)
Subbed to your channel.
Boy there is the kinda things lucky to find in a HamFest , maybe I should start going to NJ or like Paul goes to lol lol Yes Alan Yes had one in the old school years working .Always wondered what was inside of the Beast !! Thanks for sharing Alan 73's Dale
I have one of those and a matching Boonton green signal generator. That thing is a beast. Back when equipment was built to last.
Do you use it much?
w2aew
The meter I use pretty regularly. The signal generator only gets used occasionally these days. Use on days I'm feeling green. Like my old 1950's HP equipment. Use it when I'm feeling grey and tan. :-)
We will have to wait 30 years to see if any of the modern stuff lasts as long! With all the plastic in new stuff, probably not nearly as long.
Nice solid piece of test equipment. Thanks for sharing! Dan
What an absolutely great video, thanks Allan. Definitely will shop for one of these as I align the vintage equipment for my shack and some service manuals specify the use of an RF millivoltmeter, such as the Yaesu FRG-100 and Icom R7100 manuals.
Hello sir, great demonstration, I also have the same millivoltmeter I am looking to manufacture the test point, can you send me the measurements of the part, difficult to find in the market. with my thanks
Hi Alan ,
I'm studying a circuit for mounting an RF Millivoltmeter like RF instrument assemblies....Thank you very much, your videos are very good
Nice piece of test instrument. How can we build one of these with a D. C. Digital multi-meter and a circuit? It would be fun little project.
Great find and thanks for sharing Alan. Earlier this year I purchased a Boonton 92E from the USA and imported it to Australia. Unfortunately I didn't know at the time the probes were calibrated for the unit. So I tested the 92E and 50 ohm probe with my HP8640B and Tek MDO 3012. It's fine at 10 & 20 mHz, and is acceptable for the typical HF testing a Ham would need. The big meter looks great on the bench too!
Nice find, Alan! With the matching probe it is well worth the $60 you paid. It also looks well cared for. I muddle by with an HP 403 and an HP 3400A - both restored and pristine. Good to 2 Mhz and 10 Mhz respectively but OK for QRP HF.
71/72
Bill, k6whp
Dit dit.
Ahh i have encountered a few service manual's where they want a Milli-voltmeter i just use the scope to peak but when they want a exact measurement i am stuck, So some tips would be great thanks and thanks for great vids very informative.
Greetings from Simon in UK
I used to have one on my bench when I worked for Motorola. Worked great for troubleshooting all the way from front end to IF. You got a real good find AND price. Not every tech liked using one, but I relied on it a lot. Craig -- N8CA
Nice find Alan, always great when you can find a piece of test gear with all the original pieces. My HP437 was looking a little concerned over at the bench as it saw me so interested in the Boonton! 73 - Dino KL0S
I have one but missing the Tip, any of you guys knows where to get one or make one?
Occasionally I have to use one of these at work, they are quite unique and useful. Thanks for sharing your nice find. Super price on that by the way. Best Wishes n Blessings. Keith
Old timers had all the fun. Now it's all "anritsu this" "OTN analyzer that" 🙄
Does this voltmeter have thermocouple inside like HP RMS voltmeters? Teardown! Teardown! Teardown!
No, they are using 2 diodes for the voltage sensing in the probe.
The "magic" is done inside the voltmeter.
Sverre is correct.
Nice piece of kit in very good nick. Thanks for sharing.
Nice meter, still accurate and working!
I almost managed to get a hold of a Hickok crystal-controlled millivolt RF source which I believe was made in the early 1950s.
Interesting how the green color match that of Brüel & Kjaer equipment.
Like the B&K 2425 www.acoustilog.com/forsale/bk2425a.jpg
Wonder if there is any relation between the two companies.
Nice introduction to RF-millivolt metets.
Will be nice to watch a follow up video with some real life measurements for us "dummies"..
Thanks!
I have a "helper rf milivoltmeter" but received it without a probe. Have been watching for probes but no luck so far.
+w2aew
I'm no RF expert, but is there a reason why the negative scale goes down further than the positive scale goes up?
(i.e. only up to 20dBm but down to -40dBm?)
It's just the range of the meter. +20dBm is 100mW. On the meter scale itself, 0dB is closer to the max end of the scale to give good accuracy (analog meters are most accurate at the high end of the scale).
Great work Allan, your are one of the greats in this medium and remind me of the days of Forest Mims.
I recently obtained one of these as well. Was tickled to death to see Alan do a video on this unit! Mine had two problems from the start: (1) The meter stayed pegged and was unresponsive. This was caused by an LM301 that had a railed output. Replaced, meter now responds. (2) The tip of the calibrated probe is broken off, about 5/8" back from the tip. I have the pieces, but I need a way to reattach the two halves of cast aluminum. Been watching for a replacement probe at hamfests and E-Bay, but nothing so far. Any suggestions for repair???
Replying to my own post... Since the earlier post I have found that elusive replacement probe out there on E-Bay and am waiting for it to arrive via "Snail Mail". Alan brought up a good point about having the matched serial number probe and meter, and it seems like instead of just replacing the probe, it might be better to use the coming replacement probe as a donor for the broken pieces of the original--in other words, pull the calibrated components out of the original probe and use these in the "donor". This would effectively replace the structure and retain the components used to calibrate the meter originally. Just a thought...Another thing: I noticed another video (credit: AERVBlog) where the fellow who posted also had a broken probe which was repaired with solder. That's a possibility, but the darned thing had been broken in the same way mine was. What gives? I'm thinking that this points to a design weakness: that the threaded end of the probe corrodes forcing the user to use excessive torque to remove the accessory--and *SNAP* another broken probe. Looks like it might be wise to do some corrosion mitigation on the screw threads.
Great video. In fact, all of your videos are so educational. I'm slowly adding test equipment to my shop/lab and I would love to have an RF Millivoltmeter. You picked up a true jewel there with that Boonton 92c. I would love to add an RF Millivoltmeter to my shop, but it seems hard to find one at a entry level price. And many of the 92a,b,c don't have probes, and look pretty rough. Are there any decent mid-level meters around? Even DIY? Thanks again. Greg
Depending upon what frequency you need to go up to, you might find some of the designs for RF millivoltmeters that amateur radio operators have designed may be suitable.
Wow this was a great score Alan, congratulations! And as always thanks for a great video. I just scored what looks like the Motorola version of this. The layout of buttons, placement of the zero know, box size, meter face are all identical. Looks like they just painted Boonton where older models say Motorola. I wonder how close they really are? I wonder because mine seems to work but is wildly out of cal. I've been trying to find the manual for the Motorola and had little luck. I wonder if the Boonton would get me close...
Anyway, thank you for what you do for our community! W1CBD
I would imagine that Boonton made a special version for Motorola (not the other way around). I bet the Boonton manual would be close.
Muito bom, eu gostaria de adquirir um RF Millivoltmeter!
Why would they not mark the dBm scale below -10? They marked the full scale for volts so I would assume it would be accurate down there. Yes, you should switch down when below -10 but if you are already on the lowest scale you can't.
They did as an option for extra money. - - marketing
what would be a proper probe setup for probing tube if's at 455 and 10.7 using solid state detectors without blowing them from high b+ as you move around
The probe is rated for up to 400Vdc. Beyond that, you may have to use additional isolation means.
❤🌷🌟🌷🌟🌷🌟🌷🌟🌷
I've got some 'modern' analog multimeter as a present. Why are they still being manufactured? Is there some special use for them?
When you are doing things like radio alignment, where you're making adjustments looking for a peak or a dip in a voltage or current - it is much easier and more intuitive to watch for this on an analog meter movement than with a digital display or bargraph on a DMM.
NICE VIDEO
Here goes a question that should probably be obvious, but here it is: I assume this RF Millivoltmeter is necessary because a standard bench top DVM wouldn't read the correct voltage at Radio Frequencies. I'm now guessing that the specs on a standard DVM would tell a user as to a maximum frequency in order to make accurate measurements using the DVM? (I guess that's why Alan mentioned he used an oscilloscope in the past to get by with making alignment measurements - I think I'm quoting Alan accurately here. ) Also, Alan mentions loading effects at the end of this video: I think the probe has 5k ohms at 100k HZ - if even possible, a bench top DVM's loading input impedance would be a problem at RF, as well.
Correct, a DVM or DMM is typically limited to measuring AC voltage on signals well below RF frequencies. Often, the maximum is limited to audio frequency ranges.
@@w2aew I found one of these millivoltmeters model 92B at my local electronics surplus store with the probe cable but it is missing the tip end.
i do not know what the difference is between yours and the one i saw.
Will it be worth it to buy it even though is missing the probe tip? how hard would it be to find the tips?
I could use one of these millivolt meters when i am working on my stereos or reel to reels.
Thank you.
@@SDsailor7 does it have the probe, and just missing the tip, or is the probe also missing?
@@w2aew It has the part that you are holding in your hand at the beginning of the video the part that has the serial number . And it was missing the rest, so is it hard to find those other pieces? to be able to use it? I did not buy it due to missing the complete probe. It is probably still at the store. How hard is it to find/get the rest of the probe?
Thank you for replying back.
@@w2aew It did not have the 50 Ohm adapter or the browser tip.
Just the cable and the probe at the end.
question, for example, when you say, this is 0db, whats the reference power? I thought db is 10log10(p1/p2). If your estimate target p1(from your signel gen) is x, then how do i know the value of p2? Sorry, i know my question is native.
Good question. The absolute value is given by the switch selection. If you hit the +10dBm switch, then 0dB on the scale is +10dBm, -3dB on the meter would be +7dBm, etc. The "m" refers to "1 milliwatt" as the value of P2.
I think I didnt make clear my question. e.g. in a signal analyzer, the PSD shows that the peak height is 5dB, then, my question what the value of p1 and p2 are? p1 is the reference or p2 ? If p2 is a given value, and p1 is the target estimation, where to find out the p2? Thank you. Sir
A signal analyzer *should* be measuring power in an absolute unit, like dBm. If it is showing just dB, then it has to be a relative measurement. Without seeing what specifically you are talking about, then I can't comment on what the reference (p2) is.
w2aew thank you sir. I will study more then.
What a great find!
GOLD!
No peek inside? ;)
Just trying to keep the video on the shorter side...
I have an aeroflex 8300 so this is completely useless hahaha! U need to get new equipment bro! And go digital.
Alcrats
Absolutely nothing beats an old analog meter for peaking RF/IF circuits. Digital equipment is completely useless for peaking circuits.
The problem today is that people wants that the equipment do their jobs .....
Digital in these area means just a reading from an analog like these ... just a pretty face ..
Beautiful Equipment. Quick question, Is it possible to make a LM386 type Opamp with just transistors, resisters and capacitors?
ありがとう。
Sure it is - you can even find the basic schematic in the LM386 datasheet.
Thanks for pointing me towards the right direction. I will try to make one with BC 547 and 1n4007. Thanks again