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You wrote recently, either here or in an email that you would like to be able to rebuild my two Stereo 20s with FILM caps for the PSU.I'm quite happy with the bass now with 4 big 470Uf caps. But am aware that setup is 'stressing' the OEM PT.
Four caps?
And I'd be guessing a choke, or chokes?
The caps would need to be no larger in size than the 470 uf 400V Nichicons we used. The amps aren't here, so I can't measure the Nichicon's dimensions.
And, which choke (ESR, current and L) OR chokes, as IN CLCLCC or LCLCCC - plus bleed / discharge Rs?
So, TIA for cap and choke specs / suggestions.
Once I have those we can cost the bits in Australia plus the work.
While I may not be able to pay for the bits and the work straight away, you do keep on about how good and fast the bass is - with a film cap PSU - even though I can see that the energy storage would be a bit lower.
So I'd like to give it a try, can't hurt. As I do like how a mixture of film caps sound in audio stages. :-).
One more thing? I believe there's CL thermistor in the primary to the PTs - in both amps. Is there value in having another one on the 'HT' or 'B plus' secondary, so as to give heating a bit more time?
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 08/19/16 08/19/16 08/19/16Follow Ups:
Tim
If you decide you use film caps,they won't be anywhere near the 470uf in value..You would only need a 50uf off the GZ34 rectifier and after a choke if you decide to use one you can put a 60uf after the choke or the resistor if you don't have a choke. The original capacitance in those amps are a pair of dual 32uf..For the other two section cap just use a pair of 50uf films..I'm giving you these values because I know they will physically fit and sound awesome,
Your 470uf caps won't hurt the power transformer because but, unless you use diodes in place of the rectifier tube,you can mess up a GZ34.
One more thing? I believe there's CL thermistor in the primary to the PTs - in both amps. Is there value in having another one on the 'HT' or 'B plus' secondary, so as to give heating a bit more time? It won't hurt but if you are using a GZ34,it isn't really necessary..I would be using Schotky diodes instead of the GZ34 as they are so quiet and have no switching noise or ugly spikes at turn on.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 08/19/16 08/19/16
There's an article at Elliot Sound Products that strongly cautions against the use of thermistors for audio equipment. Might be worth reading when you have time.
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Buy Chinese. Bury freedom.
I know what the original caps were, I bought the amps in OEM condition. ? Nice amps but they hummed and farted, due to poor replacement NoS caps and 'not wonderful' new 'GZ34' s - which weren't within a bull's roar of a real GZ34. We measured! And there was no OOMF to the sound. No slam either.Good real NoS GZ34s which are the ONLY good GZ34s around now, and back then, were silly money.
(That experience put me off VRs, and my experience since has confirmed for me that VRs are a waste of time and money.)
So we ditched them and could and did use the big caps, 'cause we now could.
As I've mentioned before, in this series of posts about using the LEAKs to drive the QUADs, there are 4 Soft Recovery SS diodes in a bridge in each amp. Lots of OOMPH and slam and valve sound, to boot!
What about adding a choke or two and cutting down from four big caps to two, or three, say LCLCC? or even LCLCLC? Chokes store energy too, don't they?
TIA
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 08/19/16
"Good real NoS GZ34s which are the ONLY good GZ34s around now,"
Did you try the recent releases - the Genalex U77, or the Tung-Sol or Mullard branded 5AR4/GZ34s?
This was back in the mid 90s, and we put a third Nichicon 400V 470uf cap where the octal socket was. The bass duty amp had a 4th cap underneath. Click below.I briefly used a DH VR, a 5AS4?, whose heater current draw was too high for the PTs.
And both amps sound fine. Slam, nuance, etc.
And, in their new role driving 63s strapped to mono blocks (40W pentode) and filtered 150Hz 1st HP, they won't be working all that hard.
We've replaced some valves.
I am happy.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 08/24/16 08/24/16
There are a lot of people who don't realize how good the 3 rectifiers I mentioned are, so I thought I'd ask if you knew of them.
A VR tube must be used where it's appropriate. Saying only that they're a waste of time and money is way off base. VR tubes reduce distortion when used to regulate screens, and they can stabilize preamp circuitry with much less complexity than active regulators.
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Buy Chinese. Bury freedom.
not valve regulators.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
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