I agree with Anatech 100%. My advice would be the same. Don't touch it. Also unerstanding how circuit works is one thing and whole another is how it performs in reality. Just look at those amps. Wires are thin, traces are thin and long, you see twisted wires there and so on. Start to mess with it and you might find yourself in bad situation. My other hobby is HAM radio, I do fix and modify old radios and RF power amplifiers. Don't ask how I know what will messing with the design cause. It is schematic and layout in reality. Those two work together.
Of course I'm also aware that whatever advice you give to people they will still try to ''improve'' the circuit. You can't stop it. People ''roll'' op amps and even more common practice they ''roll'' the tubes like crazy all the time without even remotely understanding the circuit or tubes datasheets. I'm also aware it's their gear to which they can do whatever they want, they can even ''modify'' it using angle grinder if they feel so. That is why sometimes, though really rare even respond on the forums. I do fare more reading.
I also understand frustration which comes from experienced service engineers when they are asked about such things. Such guys have seen unthinkable damage to all sorts of devices, fixed various ''modifications'' and sloppy jobs after other people and so on. I can understand various angles of the situation.
That's why again I will give you best advice of all of them, it probably comes from HAM radio, KEEP ONE HAND IN THE POCKET when working on those.
Of course I'm also aware that whatever advice you give to people they will still try to ''improve'' the circuit. You can't stop it. People ''roll'' op amps and even more common practice they ''roll'' the tubes like crazy all the time without even remotely understanding the circuit or tubes datasheets. I'm also aware it's their gear to which they can do whatever they want, they can even ''modify'' it using angle grinder if they feel so. That is why sometimes, though really rare even respond on the forums. I do fare more reading.
I also understand frustration which comes from experienced service engineers when they are asked about such things. Such guys have seen unthinkable damage to all sorts of devices, fixed various ''modifications'' and sloppy jobs after other people and so on. I can understand various angles of the situation.
That's why again I will give you best advice of all of them, it probably comes from HAM radio, KEEP ONE HAND IN THE POCKET when working on those.
Absolutely !!!!
With these amplifiers, you have well over 200 VDC across the two high supplies. Keep your left hand in your pocket for sure! Also, because of the high voltage, there are failure modes not normally seen in lower powered transistor amplifiers.
Yes, I can get extremely frustrated. I try really hard to keep people from doing things that may cause very expensive or unrepairable damage. I don't need more work, there is enough. What I need are normal repairs and lower charges as I typically lose money on these types of jobs trying to help people.
My advice comes from a place of trying to help. I've seen poor work and the resulting damage now for over 4 decades, and it is getting worse.
Re: "rolling op amps" or "rolling tubes". Absolutely, people often have no clue. Tube heaters can demand higher current than the original type, or the plate may not be rated as highly. Op amps can cause oscillations or high DC offset when you don't get it right. Never mind distortion. Parts work with the circuits they are in - together.
Hi Tajzmaj,
I also repair old radios and also test equipment. Pure hobby, although I am trained.
With these amplifiers, you have well over 200 VDC across the two high supplies. Keep your left hand in your pocket for sure! Also, because of the high voltage, there are failure modes not normally seen in lower powered transistor amplifiers.
Yes, I can get extremely frustrated. I try really hard to keep people from doing things that may cause very expensive or unrepairable damage. I don't need more work, there is enough. What I need are normal repairs and lower charges as I typically lose money on these types of jobs trying to help people.
My advice comes from a place of trying to help. I've seen poor work and the resulting damage now for over 4 decades, and it is getting worse.
Re: "rolling op amps" or "rolling tubes". Absolutely, people often have no clue. Tube heaters can demand higher current than the original type, or the plate may not be rated as highly. Op amps can cause oscillations or high DC offset when you don't get it right. Never mind distortion. Parts work with the circuits they are in - together.
Hi Tajzmaj,
I also repair old radios and also test equipment. Pure hobby, although I am trained.
@anatech
This look like a good cap replacment?
Edit:
Forgot to add link 🤦♂
https://www.ebay.com/itm/2207668041...U7rHPFrDx5XzgX7jEjyC7WIA==|tkp:Bk9SR7D8sb-vZQ
The pins look too skinny, but it looks better than most.
Also, no insulation between the caps and the PCB, you would need to remove the capacitors and put the insulation in.
Also, no insulation between the caps and the PCB, you would need to remove the capacitors and put the insulation in.
Looking closer that replacement doesnt look like they're snap caps.
I wonder if factory replacements are even available anymore.
Edit:
In fact, it sort of looks like these, only assembled.
https://www.ebay.com/itm/143127890183
I wonder if factory replacements are even available anymore.
Edit:
In fact, it sort of looks like these, only assembled.
https://www.ebay.com/itm/143127890183
No, I bought the last of them from Carver way back before they went under. Carver service probably had a large stock as well when they went under, but Carver service became it's own business.
From the originals I bought (the last one), I took it apart and designed a new PCB using heavy copper. I build them exactly the same way with same dimensioned square pins. I use only snap-in caps. Normal leaded capacitors are not something I would use unless there was no alternative. You do need to insulate the capacitor bases, and trim down the post leads, I use a dremel to grind them smooth.
From the originals I bought (the last one), I took it apart and designed a new PCB using heavy copper. I build them exactly the same way with same dimensioned square pins. I use only snap-in caps. Normal leaded capacitors are not something I would use unless there was no alternative. You do need to insulate the capacitor bases, and trim down the post leads, I use a dremel to grind them smooth.
I was actually just sitting down taking measurements on the one I have and teaching myself KiCad to attempt to make my first PCB.
I was looking up replacement caps and was a bit put off by the drastic size difference in modern caps. My 80v caps are 1" x 2", and when I looked up a replacement it was only about 1" x 1", a whole inch shorter.
Is that correct? Is this a acceptable replacement for the 80v cap? https://www.digikey.com/en/products/detail/nichicon/LLS1K222MELA/2548912
Newer capacitors tend to be smaller, but you can get the same value in a larger can. Those tend to be better but more expensive.
The one you found would work. Look for larger ones. I haven't checked in a while. It is better than the dual capacitor. I'll never know why they went to those dual caps, unless the snap types were just too large back then. Bad choice in any case.
The one you found would work. Look for larger ones. I haven't checked in a while. It is better than the dual capacitor. I'll never know why they went to those dual caps, unless the snap types were just too large back then. Bad choice in any case.
@anatech
I'm having trouble sourcing them insulator pads. Can you provide a link or something to where you get them from?
Thanks.
It's just "fish paper" (grey in colour) cut to size, poke the cap leads through. It's easier to push the pins down then use a PCB poker or nail to make the holes.
It isn't thermally conductive. It is oil or wax impregnated paper, Cambric would also work (yellow in colour). I didn't find it at Digiley, but other places would sell it. www.tubesandmore.com may have it.
Here it is ... https://www.tubesandmore.com/products/insulation-gc-electronics-fibroid-fish-paper
It isn't thermally conductive. It is oil or wax impregnated paper, Cambric would also work (yellow in colour). I didn't find it at Digiley, but other places would sell it. www.tubesandmore.com may have it.
Here it is ... https://www.tubesandmore.com/products/insulation-gc-electronics-fibroid-fish-paper
Hello again.
I'm making progress.
I got my custom circuit boards in for the capacitors and its a perfect fit! Its a good feeling when things work the first time.
I am now going through reassembling and replacing the fried components with new ones and came across a few more I failed to locate.
I have Q17 (MPS8093) and Q14 (MPSA43) that were bad and I cannot locate them.
The MPS8093 I think I might be able to use 2N4403 but I am not sure. The MPSA43 I cannot find one what is a good match.
Not really knowing their usage, I dont know if one having a different gain would mess things up.
Does anyone know of replacements for these two that are known to work?
Thanks again for all the help getting me this far.
I'm making progress.
I got my custom circuit boards in for the capacitors and its a perfect fit! Its a good feeling when things work the first time.
I am now going through reassembling and replacing the fried components with new ones and came across a few more I failed to locate.
I have Q17 (MPS8093) and Q14 (MPSA43) that were bad and I cannot locate them.
The MPS8093 I think I might be able to use 2N4403 but I am not sure. The MPSA43 I cannot find one what is a good match.
Not really knowing their usage, I dont know if one having a different gain would mess things up.
Does anyone know of replacements for these two that are known to work?
Thanks again for all the help getting me this far.
I'd have to look them up. The beta won't change much unless it is far off. Mostly look at capacitances and Ft values as well as breakdown voltage and power/current ratings.
Look up the part, then check on Digikey's parametric search. Watch for pin out changes.
Look up the part, then check on Digikey's parametric search. Watch for pin out changes.