Unknown Tube Amp

[ThSpeakerDude88]

no you should be ok, however monitor your caps and make sure they are not getting hot . Most of the time amps were made with 117v primaries, and todays wall voltage is 120. This causes a 10-20% rise in B+ voltage, and can cause old electrolytics to fail.

Now I would notleave the amp on unmonitored for any length of time... You really should replace those caps, especially if you have any hum. You will be astounded at how much better the amp sounds. Not only that , your B+ will be higher and you will have more power output.

[allyourzigg]

I do plan on replacing them, but I'm going to do so when I take the amp apart to make a new chassis. This way I don't wind up taking it apart twice and confusing myself

[Jim McShane]

Originally posted by SY
The tube looks like a 5879.

It sure does, it isn't an EF86 I don't think, although as Tom Bavis says that would have been a "typical" tube for that application. But since the 5879 is kind of an RCA "clone" of the EF86, and the 5879 has that solid metal looking internal piece that's what I would say it is.

There are some 3 mica 5879 RCAs that are FINE tubes, BTW. And they are not expensive.

On the caps, the can cap you have will not be available since no new production caps have the 50 volt section. What I'd recommend is you replace the 20/10 with a dual section 500 volt modern cap - I have some LCR 32/32 at 500 volt that would work well if you need a source or you can search around - and get a discrete 50 uf cap to replace that section. An LCR, a mounting clamp, and a 50/50 is a lot cheaper than a new production can cap too.

Were it me I would also replace the "top hat" diodes and the 100 uf 250 volt caps. And just for safety's sake I'd replace the .01 green AB cap from the fuseholder.

I see the amp has 12 watts per channel as continuous power, but with only one output trafo it must be mono now. So it does appear to be a homebuilt that was done on a commercial chassis.

[ThSpeakerDude88]

for the Diodes, 1n4007's should work just fine. They will have these at yourlocal radio shack , and they will be cheap too ( 97c for two if I remember correctly) Btw, that 50uf cap is most likley your cathode bypass capacitor on either the input or the output stages, most likley output stage if the amp is cathode biased. If you wanted to kill two birds with one stone, RS will have what you need there too. You won't be able to find a 50 uf at RS, but a 47uf 50v will work just fine.

[pchw]

Originally posted by ThSpeakerDude88
no you should be ok, however monitor your caps and make sure they are not getting hot . Most of the time amps were made with 117v primaries, and todays wall voltage is 120. This causes a 10-20% rise in B+ voltage, and can cause old electrolytics to fail.

Sorry for a stupid question, why a 3% increase in primary will cause improportionally more increase in the B+? I observed this scenario while restroing my old gears but couldn't quite figure what I did wrong :-)

[Jim McShane]

Originally posted by pchw

Sorry for a stupid question, why a 3% increase in primary will cause improportionally more increase in the B+? I observed this scenario while restroing my old gears but couldn't quite figure what I did wrong :-)

Because the power transformer steps up the primary voltage. The ratio between primary and secondary windings determines the amount of step up (or down in other cases), so a 3 volt increase in the primary will increase the secondary 3 volts x the step up ratio. That added AC voltage on the secondary will increase the B+ too; how much depends on the type of rectification in use and some other factors.

Also, not all utilities provide 120 volts. It's been my experience that under normal circumstances I see a lot of 122-124 volts; also the voltage is not absolutely constant, it varies. For that reason it is unwise to build gear that won't withstand a somewhat higher than "normal" line voltage, say 10% or so.

Finally, a 1N4007 diode are no more expensive than a UF4007 which is a much higher quality part. I never use 1N****series diodes in audio gear anymore.

[allyourzigg]

Ok, I just got the new tubes today and OH MY GOSH I got a volume jump of atleast 50%! This sucker screams now! Also, thank for identifying the unknown tube I really appreciate that. The new tubes brought out allot more bass and definition than the old ones, I think the old ones were run quite hard when it was last used. I can't wait to get in the shop and make a new chassis and replace those components which I'm very thankfull for the part numbers for. I like the look of the can caps so I'm going to get atleast one of those (they look neat I can't help it). Later on I will lug out my old scope (1966 Tek 422 with Nuvistors) and see how a few signals look through it. Thanks again!

P.S. --you haven't heard the last of me yet! just wait till I start building it's replica! (yay! stereo)