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Grommes 10PG amp problem.

inperson

inperson

Active Member
I bought this mono amp at a record shop today, $10.00. It was dusty but looked okay. I took it home cleaned it up and plugged it in and turned it on long enough to see if the tubes lit up (I know I shouldn't do that, I don't have a variac) and all the tubes lit up except the 5Y3 GT tube. I had a spare and put it in and it lit up but after hooking up a speaker and playing a cd for about 1 minute that 5Y3 GT tube lit up way too much and the volume started to drop quickly so I turned her off. Except for my lack of patience, what's the problem?
 
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Shorted filter capacitor. I think you caught it before any serious damage... MAYBE would have survived for a little while if you'd brought it up slowly enough. I MIGHT have a schematic - I'll look.

<later>

The good news - I have the schematic. The bad news... a mouse ate the middle of it...
 
It was already on its way out and now it's toast, just get a new cap can or put in individual electrolytics of same or slightly higher values.

It's easy, only need a soldering iron, solder, needlenose piers, wire cutter. If putting in individual electrolytics, might want to epoxy them in place under chassis.
 
Nirky said:
It was already on its way out and now it's toast, just get a new cap can or put in individual electrolytics of same or slightly higher values.

It's easy, only need a soldering iron, solder, needlenose piers, wire cutter. If putting in individual electrolytics, might want to epoxy them in place under chassis.
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Will do or at least get someone else to do it:thmbsp: I'd like to use it for my dedicated mono set-up.

Oh! BTW does the last value on a replacement cap can have to be the same as the original? The first three values are the same on a NOS cap can I have, however the last value is 50 25 but the original one is valued 20 25. Can it be used?
 
Yes, I don't see an issue using a 50uF 25v in place of a 20uF 25v. If I'm wrong, somebody will chime in.

Just make sure that the voltages on your NOS can are the same or higher than the voltages on the old cap can. For instance, you don't want to use a 350v cap when the original was 450v!
 
I had someone check out the amp and they told me the output transformer needs to be replaced. Is this a difficult search? What do I need to know when looking for a suitable replacement? Money IS an issue. I only paid $10.00 for the amp and I don't want to put $100 in a transformer.
 
I'm just curious, who said the output transformer was bad? If you had sound for a minute, it may still be good. Your main repair would be to the filter capacitor first. get it up and running without the 5Y3 overglow and go from there.
 
Well, half the primary could be open, and it would still produce SOME sound... a quick check with an ohmmeter will tell. It could also be breaking down inside (B+ to core), and that might not show up until it's powered.

The through-chassis type will be a bit harder to replace, though you can sometimes take the end bell off the old transformer and use it on another one.
 
cademan said:
I'm just curious, who said the output transformer was bad? If you had sound for a minute, it may still be good. Your main repair would be to the filter capacitor first. get it up and running without the 5Y3 overglow and go from there.
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Good question. I can only say what I was told. The owner of this place told me it was the OP transformer.

http://www.opera-consonance.com/company/company.htm

The amp does put out some music but it is very weak and if I turn up the volume it is very, very distorted. I was using a very sensitive speaker.
 
Nirky said:
Yes, I don't see an issue using a 50uF 25v in place of a 20uF 25v. If I'm wrong, somebody will chime in.

Just make sure that the voltages on your NOS can are the same or higher than the voltages on the old cap can. For instance, you don't want to use a 350v cap when the original was 450v!
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Those low-voltage sections are used for output tube cathode resistor bypass... and yes, in that application, a bigger cap generally won't hurt anything.

The only issue with increasing cap size, is the potential for overloading a power transformer, or more commonly, overloading a rectifier tube. Many rectifier tubes have STRICT limits on how much cap they can handle hooked up directly to their outputs. I tend to either a) look up the specific rectifier tube and find out EXACTLY how much it's rated for and use that value or smaller or b) leave it original, if I can't find good data on the rectifier tube.

But, that's only a potential issue with the high-voltage sections of the cap. As I said, the low voltage sections are usually much more readily subject-able to change, generally without upsetting anything...

Regards,
Gordon.
 
inperson said:
Yes, I am. I am friends with the guys at Opera Consonance. Very nice people.
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Wow your a world away from me lol. Welcome to AK. Not to hijack your thread here but have you been able to listen to any of there tube amps, and if so what was your impressions?



REGARDS JIM
 
jim3860 said:
Wow your a world away from me lol. Welcome to AK. Not to hijack your thread here but have you been able to listen to any of there tube amps, and if so what was your impressions?



REGARDS JIM
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Yes, sure I have. I think they have great sounding stuff and good quality. Some of the design styles, such as the droplet series I am not so crazy about. I love their M-15 speakers (which I have) and they have some new ones coming out that are M-18's. Look and sound great!
 
inperson said:
Yes, sure I have. I think they have great sounding stuff and good quality. Some of the design styles, such as the droplet series I am not so crazy about. I love their M-15 speakers (which I have) and they have some new ones coming out that are M-18's. Look and sound great!
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Yes I have read good things about the M-15's and the M-18'S must be even nicer but out of my price range.



REGARDS JIM
 
The good news - I have the schematic. The bad news... a mouse ate the middle of it...
Click to expand...
Man do I hate it when that happens...:D How do those rodents know just exactly what part of the schematic your going to need.:scratch2: I guess the mouses name was murphy..
 
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