Thanks for this! Exactly what I needed to revive a Classic 30 that was eating output tubes! Unlike a couple other tube amp channels, you don't hide the details! And the devil is in the details!
Thanks mate. The long format and lack of flashy lights and controversy doesn't suit the short attention span of the masses, but this channel is for the nerds. Glad to have you on board and if you subscribed and shared it around I'd appreciate it.
Thanks for these videos! I bought a Delta Blues 115 a couple of weeks ago. I'm loving it, but I want to get it to a tech for service to make sure that I can keep it a while. Your video is a great resource.
Clean faceplates like this one with Nev-R-Dull polishing wadding. Should be perfectly safe for the silk screening because it is the only thing I have found that you can safely use on vintage McIntosh hifi equipment without removing the silk screening on those.
These amps sound great when healthy and with a speaker upgrade. Nice work, Brad. It's nice to know there's a Brad amp tech out there not using gardening or rusty hand tools on amps 😂.
If an amp has a tube rectifier and I want to bring up the voltage slowly with a Variac, I usually replace the tube rectifier with a plug-in solid state rectifier temporarily, and stop the Variac at about 80 to 100 volts (that's 160 to 200 volts AC in Europe or Australia), keeping the input voltage towards the lower end if the output tubes aren't installed in the amp. The reason for using the solid state rectifier is because a tube rectifier is very non linear and won't deliver much voltage to the circuit until you get at least halfway up to the normal AC input voltage with the Variac and the rectifier tube heater begins to warm up. The solid state plug in rectifier delivers a linear B+ voltage rise to the circuits inside the amp, in relative lockstep with the Variac setting. The reason for stopping the Variac at about 3/4 of the normal wall voltage is because the solid state plugin does not have the voltage drop inherent to a tube rectifier, and also because, as Brad notes, without the output tubes in place to load the B+ and drag it down, the voltage to the filter capacitors could go significantly above their voltage rating. PS, why is your Variac marked "Shitbox"? And shouldn't it be "Shite-box" down under? 😁
What role does the 400 ohm, 5 watt resistor play in these amps? I believe it's R58 on both the Classic 30 and 50. I've read some analysis suggesting that this acts as a screen grid and the 100 ohm resistors are only there to prevent oscillation. But I don't see how a single 400 ohm resistor could act as an effective screen grid for the entire power tube board?
The 400R resistor along with the following capacitor form a filter node which supplies the screen grids. The screen grid stoppers are primarily there to limit screen grid current to within datasheet specifications of the output valves.
Really, really interesting. I own a Delta Blues which is going on for 20 years old. I haven't played it for 10 years plus, so I'm accumulating a list of things to replace in addition to the electrolytic caps. I noticed that you didn't bother to replace the links - would you suggest using flexible wire to replace them? Again, I loved it!
You can bend the links once or twice, but they get sketchy at thrice. I just use 22 AWG solid tinned buss wire. Stranded might not hold it's shape and short to surrounding wires if not tinned. And if it is tinned, you negate the advantages of using stranded wire.
In future it might be a good idea to put a thin silicone transistor insulator under each of those additional screen resistors that you added on the back side of the board near the tube sockets, just to protect the traces underneath the resistor in case the resistor runs hot or starts to burn a little before it fuses and goes open.
@@onefastmini , silicone *transistor insulators* conduct and dissipate heat. They're commonly used in place of old-fashioned mica insulators and heatsink grease for thermally coupling power transistors to a heatsink without electrically bonding them to the metal. A hole or series of holes in the circuit board to provide air flow around the resistor is a great idea but not always practical unless you're designing the board that way from scratch. Also, although perching the resistors up off the board is good for dissipating heat, it might cause problems with the solder joints breaking or the foils lifting as the resistors are vibrated by the speaker when the amp is played at high volumes.
You didn't show how and where you added the previously missing grid stoppers. By the way, in my experience a brass brush is too soft to clean tube pins well, so I use a steel brush. Tube pins on vintage tubes usually aren't plated anyway, though modern tubes might be, perhaps with "gold" (mostly as a marketing ploy); tube pins are supposed to be made of a metal that has the same expansion coefficient as glass ---- a nickel alloy called Monel was the industry standard back in the day ---- in order to minimize cracking or air leaks; and therefore plating the pins would be counter-productive from the standpoint of reliability (you'd have to plate the pins *after* the tube, or at least it's glass "button base" was assembled, in order to avoid having a glass-to-plating junction). No idea what kind of crap metal they might use to make the tube pins these days.....and the gold alloy they use for plating the pins on some tubes is probably so adulterated with baser metals and applied so thinly that it likely does no good whatsoever. ( Lots of 70s/80's hifi gear with plug-in boards suffer intermittent operation because of "gold" plated contacts that oxidize). By the way if you look up Monel metal you will find that there are numerous alloy variations of it, most with excellent anticorrosive properties properties, far better than even stainless steel but also much more expensive, and difficult to machine or cold work. Some high-end brass instruments use Monel in the plunger mechanisms, and some guitar and bass strings use Monel alloys.
Nice one mate. Always an education to be had in your work. Mate can I ask where you got that component lead crimping tool/pliers from? I can't find them anywhere for less than a silly amount of money! Australian supplier? Cheers again for the lessons fella.
Scotty! They've changed a little bit but they still do the job: www.mektronics.com.au/piergiacomi-c-type-preforming-tool.html email me with your address and I'll chuck a pair on the next order and ship em out to ya. Save you starting an account and whatnot.
Ok: inspired your video, I have the circuit boards pulled out of my Delta Blues. I took it slow, took photos and it all went easier than I expected. Everything looks in excellent condition - no burn marks, no bad-looking solder joints. My amp must be about 25 years old, but it's been in storage for the last 16 years (shame, I know). I'm assuming all the big electrolytic caps have to go, but there about about a billion small electrolytics as well. What's your advice with them? Replace? Thanks again for your channel. It's somehow great to see a fellow Aussie working in this area and doing it right.
Being about 25 yo, I'd be doing them. They're not expensive in the scheme of things. Not sure whether I changed these ones before placing it back in the chassis, but this amp was a lot younger and the budget was tight, so maybe not. In hindsight, it'd be a full re-cap on these things or nothing, considering the labour involved in the disassembly and reassembly.
@@BradsGuitarGarage 😂 i have just become so accustomed to seeing you with your beard, I had to be a wanker. i wanted to watch these, because I have a Delta Blues 210, from 2003. Just got it back from a tech actually! No issues, just dirty sockets and time for a check up.
@@BradsGuitarGarage Ah, got it. If you ever think on selling it, please keep me on your list. Last night I was doing the 1K screen grid mod, forgot to trim the leads on one of them, they touched the chasis and blew up the 390 ohm 5W. I ordered some, they will be here on thursday.
@@BradsGuitarGarage I did all four. The one on V5, where the jumper is on the other side. Put the leads thru and idiotically forgot to clip them. I think everything else is fine, just that 390 ohm that feeds the screen grid of all 4 valves burned out.
Thanks for this! Exactly what I needed to revive a Classic 30 that was eating output tubes! Unlike a couple other tube amp channels, you don't hide the details! And the devil is in the details!
Thanks mate. The long format and lack of flashy lights and controversy doesn't suit the short attention span of the masses, but this channel is for the nerds. Glad to have you on board and if you subscribed and shared it around I'd appreciate it.
Thanks for these videos! I bought a Delta Blues 115 a couple of weeks ago. I'm loving it, but I want to get it to a tech for service to make sure that I can keep it a while. Your video is a great resource.
Love watching your vids. Always a fan of people who care about the quality of their work👊😎
Clean faceplates like this one with Nev-R-Dull polishing wadding. Should be perfectly safe for the silk screening because it is the only thing I have found that you can safely use on vintage McIntosh hifi equipment without removing the silk screening on those.
!!!!
excelente trabajo !!!!
These amps sound great when healthy and with a speaker upgrade. Nice work, Brad. It's nice to know there's a Brad amp tech out there not using gardening or rusty hand tools on amps 😂.
Very skilled amp technician and guitarist 🎸! Bravo 👏
Thanks for watching, mate!
I am adding the 1k screen grid resistors on one of these and i just went back and redid my work after seeing this
That was an awesome watch, cheers
If an amp has a tube rectifier and I want to bring up the voltage slowly with a Variac, I usually replace the tube rectifier with a plug-in solid state rectifier temporarily, and stop the Variac at about 80 to 100 volts (that's 160 to 200 volts AC in Europe or Australia), keeping the input voltage towards the lower end if the output tubes aren't installed in the amp. The reason for using the solid state rectifier is because a tube rectifier is very non linear and won't deliver much voltage to the circuit until you get at least halfway up to the normal AC input voltage with the Variac and the rectifier tube heater begins to warm up. The solid state plug in rectifier delivers a linear B+ voltage rise to the circuits inside the amp, in relative lockstep with the Variac setting. The reason for stopping the Variac at about 3/4 of the normal wall voltage is because the solid state plugin does not have the voltage drop inherent to a tube rectifier, and also because, as Brad notes, without the output tubes in place to load the B+ and drag it down, the voltage to the filter capacitors could go significantly above their voltage rating. PS, why is your Variac marked "Shitbox"? And shouldn't it be "Shite-box" down under? 😁
Great job..Lots of info and tips..Thanks for sharing..Cool playing too..Ed..uk..😀
I enjoy you videos, as I learn so much, thank you 😊
Thanks for watching, mate!
Hey Brad.... where do you find little tubes of silicone like that? Thx!
5-Stars! ★★★★★
What role does the 400 ohm, 5 watt resistor play in these amps? I believe it's R58 on both the Classic 30 and 50. I've read some analysis suggesting that this acts as a screen grid and the 100 ohm resistors are only there to prevent oscillation. But I don't see how a single 400 ohm resistor could act as an effective screen grid for the entire power tube board?
The 400R resistor along with the following capacitor form a filter node which supplies the screen grids. The screen grid stoppers are primarily there to limit screen grid current to within datasheet specifications of the output valves.
Really, really interesting. I own a Delta Blues which is going on for 20 years old. I haven't played it for 10 years plus, so I'm accumulating a list of things to replace in addition to the electrolytic caps. I noticed that you didn't bother to replace the links - would you suggest using flexible wire to replace them? Again, I loved it!
You can bend the links once or twice, but they get sketchy at thrice.
I just use 22 AWG solid tinned buss wire.
Stranded might not hold it's shape and short to surrounding wires if not tinned. And if it is tinned, you negate the advantages of using stranded wire.
In future it might be a good idea to put a thin silicone transistor insulator under each of those additional screen resistors that you added on the back side of the board near the tube sockets, just to protect the traces underneath the resistor in case the resistor runs hot or starts to burn a little before it fuses and goes open.
Keeping an air gap will allow enough airflow to keep the resistor from burning the board, but silicone will trap the heat and may cause a failure.
@@onefastmini , silicone *transistor insulators* conduct and dissipate heat. They're commonly used in place of old-fashioned mica insulators and heatsink grease for thermally coupling power transistors to a heatsink without electrically bonding them to the metal. A hole or series of holes in the circuit board to provide air flow around the resistor is a great idea but not always practical unless you're designing the board that way from scratch. Also, although perching the resistors up off the board is good for dissipating heat, it might cause problems with the solder joints breaking or the foils lifting as the resistors are vibrated by the speaker when the amp is played at high volumes.
You didn't show how and where you added the previously missing grid stoppers. By the way, in my experience a brass brush is too soft to clean tube pins well, so I use a steel brush. Tube pins on vintage tubes usually aren't plated anyway, though modern tubes might be, perhaps with "gold" (mostly as a marketing ploy); tube pins are supposed to be made of a metal that has the same expansion coefficient as glass ---- a nickel alloy called Monel was the industry standard back in the day ---- in order to minimize cracking or air leaks; and therefore plating the pins would be counter-productive from the standpoint of reliability (you'd have to plate the pins *after* the tube, or at least it's glass "button base" was assembled, in order to avoid having a glass-to-plating junction). No idea what kind of crap metal they might use to make the tube pins these days.....and the gold alloy they use for plating the pins on some tubes is probably so adulterated with baser metals and applied so thinly that it likely does no good whatsoever. ( Lots of 70s/80's hifi gear with plug-in boards suffer intermittent operation because of "gold" plated contacts that oxidize).
By the way if you look up Monel metal you will find that there are numerous alloy variations of it, most with excellent anticorrosive properties properties, far better than even stainless steel but also much more expensive, and difficult to machine or cold work. Some high-end brass instruments use Monel in the plunger mechanisms, and some guitar and bass strings use Monel alloys.
Nice one mate. Always an education to be had in your work. Mate can I ask where you got that component lead crimping tool/pliers from? I can't find them anywhere for less than a silly amount of money! Australian supplier?
Cheers again for the lessons fella.
Scotty! They've changed a little bit but they still do the job:
www.mektronics.com.au/piergiacomi-c-type-preforming-tool.html
email me with your address and I'll chuck a pair on the next order and ship em out to ya.
Save you starting an account and whatnot.
@@BradsGuitarGarage Ah man that would be fantastic! Very kind mate! Email sent.
Ok: inspired your video, I have the circuit boards pulled out of my Delta Blues. I took it slow, took photos and it all went easier than I expected. Everything looks in excellent condition - no burn marks, no bad-looking solder joints. My amp must be about 25 years old, but it's been in storage for the last 16 years (shame, I know). I'm assuming all the big electrolytic caps have to go, but there about about a billion small electrolytics as well. What's your advice with them? Replace? Thanks again for your channel. It's somehow great to see a fellow Aussie working in this area and doing it right.
Being about 25 yo, I'd be doing them. They're not expensive in the scheme of things.
Not sure whether I changed these ones before placing it back in the chassis, but this amp was a lot younger and the budget was tight, so maybe not. In hindsight, it'd be a full re-cap on these things or nothing, considering the labour involved in the disassembly and reassembly.
@@BradsGuitarGarage thanks, Brad - I really appreciate your reply.
Tremolo sounds quite good; the reverb (digital?) not so much....
Reverb is spring and sounds decent. Better if the tank is upgraded.
Who is this man, and what have you done with our Brad?!?
No beard?
@@BradsGuitarGarage 😂 i have just become so accustomed to seeing you with your beard, I had to be a wanker.
i wanted to watch these, because I have a Delta Blues 210, from 2003. Just got it back from a tech actually! No issues, just dirty sockets and time for a check up.
This repair service how many bucks can take 💵 ?
Quite a few, but the amp will likely last decades more, now.
Greetings, where do you sell those boards?
I don't sell them, sorry.
@@BradsGuitarGarage Ah, got it. If you ever think on selling it, please keep me on your list.
Last night I was doing the 1K screen grid mod, forgot to trim the leads on one of them, they touched the chasis and blew up the 390 ohm 5W. I ordered some, they will be here on thursday.
Whoops!
Did you do the 1 screen grid resistor per valve mod, or just replace the 2 x 100 ohm ones from the factory circuit?
@@BradsGuitarGarage I did all four. The one on V5, where the jumper is on the other side. Put the leads thru and idiotically forgot to clip them. I think everything else is fine, just that 390 ohm that feeds the screen grid of all 4 valves burned out.
@@BradsGuitarGarage I meant all 4 one per valve with the lam cut between V5 and V6.
The weird angle of those pots really triggers the fuck out of me, like they couldn't straighten those fucking things out, it's a PCB.
Dude you’re always having to deal with glue wtf
I know, right!? I have a few tricks to make it much easier up my sleeve these days, though.