It depends. It depends on the particular make and model of cap, the physical size of the cap, its dielectric type, etc. There is no one-size-fits-all answer.
That said, there might be a good answer in a particular case. Or maybe not.
Its also true that no matter what you do reproduced audio will never sound exactly like a live event. So, the answer, if there is one also depends on your goal.
Chances are the orange drop cap is a fake so replacing it won’t hurt. Don’t waste money on a Duelund cap for this amp, a Clarity Cap or Solen is good enough. Measure all the voltages in the amp with speakers connected. Use sacrificial speakers just in case. I’d be willing to be the output transformers aren’t that great and might be much of the issue. Replacing the pots is a nice upgrade. The Alps pots will be better matched left to right and less noisy than junk pots. As has been said, do one channel and one change at a time and listen to compare the channels. If you are pushing the amp into high distortion with low efficiency speakers it will definitely sound like something is wrong. Remember, a low powered amp runs out of power quickly on inefficient speakers. Does the amp sound ok on other speakers at low volume levels? Tube amps don’t like difficult loads where the impedance is all over the place. Especially in the bass! Think of this as a learning experience!
FWIW, an ordinary Sprague "orange drop" type 716P capacitor is about as perfect a coupling capacitor as can be made, costs little, perfectly reliable, made by folk who've made a few over the years, no surprises, no drama. If uncomfortable about the existing devices, buy a pair from Mouser or Digikey or the folk in Tempe, and Stop Compulsing! It's bad for your health.
All good fortune,
Chris
All good fortune,
Chris
Last edited:
Modern components made by monster sized commercial companies by the Millions are incredibly well made.
Literally NASA quality.
Whatever went to the Moon in 1969, is nothing compared to modern stuff, simply because technology-has-advanced.
As of "custom handmade boutique caps" read what user limono posted:
Compare that to "cheap china/India made"
TDK/EPCOS factories in China and India, two of 20 or so they have in the region:
While Duelund bragged about having inherited 80s technology old Jensen caps machinery 🙄
You can't even compare them.
Literally NASA quality.
Whatever went to the Moon in 1969, is nothing compared to modern stuff, simply because technology-has-advanced.
As of "custom handmade boutique caps" read what user limono posted:
So much for handmade expensive technology.
Compare that to "cheap china/India made"
TDK/EPCOS factories in China and India, two of 20 or so they have in the region:
While Duelund bragged about having inherited 80s technology old Jensen caps machinery 🙄
You can't even compare them.
When the US military wanted vacuum valves, they bought them, as possible, from big production lines. They wanted reliability, and it came from experience, corrections on the production line, and evolution in action. It was OK to throw away a lot from the beginnings and the endings of production, but reliability, when lives depend on it, comes from a winnowing. Audiophile capacitors tend to let the winnowing happen at the customer level.
I'm sorry if this sounds harsh, but calls em as I sees um.
Chris
I'm sorry if this sounds harsh, but calls em as I sees um.
Chris
@Chris Hornbeck , just to make sure, you are saying is to do smt like this?
Distortion messures (performed by Stephe) where really good as it is now, lower than 2% at 4W:
PS: Too bad I bought an AN Kaisei cap for replacing the driver bypass cap...
****. I actually bought a JDM 0.1uf Pure Copper (not Tinned) to bypass the coupling cap. It was "cheap" enough to give it a try...
Thanks for the comments also @Positron !
I do need to add to my last comments that I also bought a Jantzen Superior Z 0.1uf 1200V (they don't come at 630 or 400V) for bypassing the output bypass cap. I read somewhere that it's a must (literally) to bypass the output bypass electrolytics (also got the ELNA's ROA Cerafine for replacing actuals) with some Polyxxx ones.
But I promise I'll stop here. Only after getting tha 5AR4 rectifier tube that seems important to be there.
Sorry @Chris Hornbeck . On my previous schematic picture I crossed out the coupling cap by mistake 🤦♂️, but I got what you meant. Removing this bypass cap:
0.22uF (220n) is a small value cap, so just buy a decent replacement.
Almost any polyester or polypropylene one of the correct/higher voltage will be fine.
The cheap ones that look like boiled sweets work fine for me.
Then change the cap, and listen.
People love chatting about audio caps, but I do know from personal experience that it's possible to buy a tube amp from China, and have a simple looking coupling cap turn the sound totally muddy, as if it was actually an inductor inside.
So just change it, to see if that's the cause. Change all of the small caps, in fact, I'd advise, it's cheap and easy.
That 220uF is upping the gain for you above the very low bass.
It's harmless to try the sound without it.
To replace, use a lowESR replacement of a reasonable (branded) make, and bypass with a film cap, from 56n to 1000nF should be fine, it really just has to act as a low impedance AC path.
I feel like I've grabbed aholt of a TarBaby, which is a DeepSouth American way of saying I've bit off more than I can chew, which is an even stranger idiom. I'll stop before it gets worse.
Shunt feedback around the output stage has become popular because it's applied at the exact best location, and is fairly forgiving in the normal small quantities, but isn't ideal because it must penalize the driving stage (by heavy loading) to benefit the output stage. Tradeoffs.
Bringing the feedback further back, to the driver's cathode, removes the loading penalty and keeps the advantage of lowered source impedance to the OPT and the resulting transformer performance advantages (both distortion and frequency response) of the shunt (I refuse to call it "Schade" - it's not his fault) feedback, voltage sensing negative feedback at the primary, for lower transformer distortion and better frequency response (less effect of both lumped leakage inductance and lumped winding capacitances).
But! We can't just move the feedback resistor to the cathode - it conducts DC and so changes the driving valve's bias. Resistor values need to be juggled to get everything optimum. Not rocket surgery, but definitely a thing.
My hope is that this older way of doing feedback over two stages will return, if only for its performance advantages. Of course, I'd also hope the same for phono equalizers, but nobody's interested there either, so there we are.
All good fortune,
Chris
Shunt feedback around the output stage has become popular because it's applied at the exact best location, and is fairly forgiving in the normal small quantities, but isn't ideal because it must penalize the driving stage (by heavy loading) to benefit the output stage. Tradeoffs.
Bringing the feedback further back, to the driver's cathode, removes the loading penalty and keeps the advantage of lowered source impedance to the OPT and the resulting transformer performance advantages (both distortion and frequency response) of the shunt (I refuse to call it "Schade" - it's not his fault) feedback, voltage sensing negative feedback at the primary, for lower transformer distortion and better frequency response (less effect of both lumped leakage inductance and lumped winding capacitances).
But! We can't just move the feedback resistor to the cathode - it conducts DC and so changes the driving valve's bias. Resistor values need to be juggled to get everything optimum. Not rocket surgery, but definitely a thing.
My hope is that this older way of doing feedback over two stages will return, if only for its performance advantages. Of course, I'd also hope the same for phono equalizers, but nobody's interested there either, so there we are.
All good fortune,
Chris
I'm guessing here is that the pictures I posted show the correct thing, but I'd have to play around with values for the feedback resistor. It was mentioned that 820k was maybe to high, smt around the 400's?
And @Chris Hornbeck I really look forward to doing so, but I do need confirmation on the changes I got to understand from you here:
and here pls:
And @Chris Hornbeck I really look forward to doing so, but I do need confirmation on the changes I got to understand from you here:
and here pls:
Thanks again!
I'll try removing it as Chris said, but I also bought some ELNA ROA Cerafine 220uf 35v and AN Kaisei polars 220uf 16v for testing replacements.
I haven't bought bypass caps for the driver stage's cathode bypass, only for the output. So, I could try those Jantzen Superior's (0.1uf) on either and see where it has more impact?
I think you'll quickly reach the area of 'belief > what your ears hear' type comparisons, I would guess the only real way of seeing if they make a difference is with frequency and swept distortion measurements. But why not try, it's DIY, all good, careful of the voltages.
I'm not a fan of 'audio grade' parts, perhaps that's just me being stubborn, but for me I've seen too many times when cleaning and oiling an RCA socket has made more difference than any esoteric changes inside
I despaired when 'HiFi' became some occult religion involving special cables and HifI fuses LOL, so perhaps I'm a little jaded
There's no harm in bypassing electros, unless they are hugely inductive it should always improve things, especially power rails and cathode bypass, feedback bypass etc.
I've never bypassed a film cap, but if they are faulty or terrible quality it may 'fix' them