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Upgrade capacitors in tube amplifier?

I have upgraded crossovers with very good results.  I now have a "very good" IMO chinese tube amplifier that can probably be improved with a couple of capacitor upgrades.  

I don't have a schematic, but I have a picture and I expect some of you knowledgeable folks can point me to/confirm the ones to change.  My thought is to change the two large silver ones first and then maybe the four smaller silver ones (on the circuit boards). 

Would probably replace with something like Jantzen Superior Z-Cap or comparable and go with a higher voltage if space permits.  

https://imgbox.com/rtBfoyg0

Thoughts?


chinook9
atmasphere's avatar
atmasphere
11,967 posts
 
There are three coupling caps. The first is at the top of the photo, one in each channel. To the far left and right beside the power tubes is a small circuit board; the coupling caps for the output tubes are mounted on that circuit board; they should be matched for best results.
oldhvymec
5,101 posts
 
Yup I see 6 decouping caps also. They look like they are directional. But they look to be good caps.. IF there is NOT a problem, leave it alone. 
I don't think it's broke in yet, is it? 1000 hours or so...
Your one of those guys.. LOL Because it's there.....Right...

Is something missing, a valve roll won't cure? Why do you want to mess
with a new unit? Highs not high enough, lows not low enough...?
What do you want to change? Sound wise.

100.00 will buy some real nice sounding Green EH EL34 for under 100.00. Rubys, ReIssue, Mullard, 100.00 or so..

12ax7 or 12au7s, 100.00 no more.. don't get crazy.. Tellies, PVANE, GEs, Mullards, Volvo, Mazda, RCAs. BE CAREFUL with all the NOS stuff, a LOT of rip offs... I test EVERYTHING...MATCH the valves it will make or break the SQ, in both small and large valves..

Regards..


audioman58's avatar
audioman58
4,222 posts
 
In a tube circuit the higher the voltage the better 600v is optimum 
the vh Odam is a excellent cap ,the VH Cu Teflon caps even better 
if it will fit and can afford.
brockwired's avatar
brockwired
53 posts
 
I know this not a tube rolling thread, but I would suggest swapping the 12ax7 and 12au7 tubes first. I recommend trying some 1950's vintage Raytheon black plates. Try to stay around $70 for each tube. For the power tubes you could get some 807 tubes with an adapter.
blvdre
11 posts
 
My advice is, if you’re going to change coupling caps, stick with the various film and foil types, rather than a metallized film. They’re generally more expensive (but not always, depending on mfgs), but are of better construction, especially in regards to lead attachment. In a film & foil cap, the foil protrudes at each end of the rolled cap, and the lead is soldered or welded directly to the foil . Metallized caps have the dielectric protruding at each end, so a conductive paste is applied, which makes contact with the plate. The lead is then attached to this paste (a less reliable form of construction).

 Be aware that, for equivalent voltage ratings, film & foil types are generally larger in overall size.
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