Checkink an old Ampeg and finding strange things...

Hi everyone!
Yes I've been away for a long time.
Anyway, I often have some funny problems to tell, and here's the last one.
After a long time, a month ago I decided to switch my old Ampeg V4 on again. Sadly, switching the stanby off caused immediately bad noises (thumps, wobbles, and so on), and after few seconds, plate on a power tube started to glow. Switched the amp off in a rush and left it there for some time.
Today I decided to open the beast, to see if I could find something clearly broken-burnt-dead, but did not find anything like that. I found three strange things instead (assuming I know the previous owner had made some work on the amp, and the power tubes were really old and from different brands-ages):
1) on one power tube (the one that started to glow actually) there were 2 47ohm resistors wired from pin 7 to pin 8, and from pin 8 to pin 2. No trace of this on the schem, so no idea what it was made for.
2) in what I think to be the bias section, there are two resistors, R49 and R50 (respectively, 75k and 56k). The first one is around 100k instead: I was wondering if this could cause early breakup (not something the V4 was originally famous for)
3) there are two extra electrolytic caps in there, wired in series, linked to one end to one pin of the main filter capacitor, and on the other somewhere else I could not find (didn't want to take the amp completely apart for now). The value is unknown since it's covered by the body of the caps, in a place hard to reach.
Does anyone have any ideas?!?
I'm at the point were I can track parts from an amp to the schem now, but these things are pretty obscure!

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:) , riz. I have strange sleep patterns, all incompatible with my work. As you say, 7027s can be found at a higher price than 6L6GCs usually go for. I was getting mixed up with 8417s, which are even more expensive than NOS 6550s. With fresher glass and replaced caps (you can parallel caps, if that helps), it should sing. Again, putting up a message in "Miscellaneous American Amps" on Plexi might help you locate a source for the correct caps.

I'm in the North West of England, midway between Manchester and Liverpool; either are easy enough for me to get to if you ever fly in :D

I've actually been up there some months... Well it was Harrogate to be more precise. I'll save some cash to come back some day...

Talking about the amp... I ordered some parts yesterday: tubes, C9 (small cap), some resistors (including the 4 10ohm/5watters), the two electrolytics in the bias circuit, and that's it for now. I'll try to put everything back to specs and see what happens.
I'll change the filter caps later, since hum was really low and looking at them, they seemed fine (this is my average degree of accuracy :? )

I'll keep you updated!!!

If there's no hum and the filter caps are neither bulging nor powdering out, then I'd keep them in. I've got 40+ year old amps with their original filter caps. Not bad, considering they were designed to last maybe 10. Let me (and Tim) know if you're in the area again and we'll make an effort to say hello.

Best for now :)

1bassleft wrote:
Let me (and Tim) know if you're in the area again and we'll make an effort to say hello.

Yeah, would be good. Maybe imbibe a beverage or two...

Well the new parts arrived today. Obviously, I found out I ordered the wrong resistor for the bias circuit (1/4 watt - not 1/2 :cry: ) - I'll try to find that on monday. Hopefully, I'll put them in the amp before next weekend, and let you know what happened.
I bought a couple of 15ohm/5w resistors.. can you tell me WHY?!?!!?
ah, I'm too young to already behave like this.

Yep, as the schem says, "all resisitors are 1/2W 10% unless otherwise stated". As for your 15ohm resistors; sorry, I have no idea :lol: I know we talked a lot about 10/5W but I don't recollect 15ohm and I can't see them on my schem. HST, it's printed on an A5 size piece of paper so I get funny eyes looking at it too hard...

ok, I must be too tired really. I knew they had to be 1/2 watt... simply wans't careful enough in that moment.
and the other two resistors are not 15ohm but 15Kohm... Still no idea about what I had in mind when I placed the order. Weird. 5W seem to be a specific choice too. Who knows!
As for the eyes... I can't imagine how you can decipher that, my schem is printed A4 and still a nightmare to look at!
mmm... those resistors... I need a check-up.

(by the way... some OT rage: protools is good when it works, a nightmare when it doesn't - damn. I hate it.)

Yes, I've got a book full of A5 schems. That probably explains why I like Champs and 5E3s :lol: . I don't remember seeing 15kOhm, either. What would be really good is if something like schematics heaven on the web had a facility to search + locate caps, resistors etc on a schem; a bit like the "search and replace" function in Word. That'd be a Godsend.

A 5 watt resistor could be a grid resistor . My jtm I think is 470 ohm 5 watt and the jmp50 (didn't tell you about that one 1b :) ) are 1k 5 watt.

Just read the whole thread and it looks like it's not a grid resistor .Sorry :(

Yeah, I need some holidays.
I bought the two 15k resistors to build a cap discharge tool...

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