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There are a number of tweaks for the power supply of the M60 amplifiers published by paul speltz some years ago.
Is there somebody who knows where to get the schematics ?
I cannot find it anymore on the web
Wayback machine has the original article.
IMO, the CL30s hurt nothing and help every aspect of safety of the transformers and the circuit. Perhaps some people are paranoid about the very small amount of residual resistance in a current limiter, once it takes itself out of the circuit by heating up. Otherwise, I don't get it.
"Not seeing the need to limit the current to either the filament or driver transformers, I left the CL-30 connected to only the output supply transformer fuse"
Inrush current on heaters is MASSIVE relative to their quiescent current. I wouldn't be surprised if a single 6336 wanted 10A of inrush current on the heaters. I suspect that the CL-30 is there to help mitigate that. I would also not use Hexfreds, they are obsolete/inferior technology.
What's always missing from write-ups like this is the report 2-5 years down the road regarding reliability.
In addition, Paul was using the 6336; the filament transformer circuit *definitely* would have benefited from an inrush limiter!
There have been other improvements in the circuit since Paul did his article; the link below is more up-to-date.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
This Asylum is a descendant of the "Atma-sphere Owners Group", aka "ASOG". If you search on that title, you might find an archive with Speltz's tweaks. I know I could find it 4-5 years ago, when last I looked for it. Further to that, you can contact Paul Speltz the man; he is the proprietor of "Anti-Cables" a thriving internet business located in Minnesota. Paul is a very nice guy, and he may be willing to forward to you the info.
One tweak that I remember well, because I use it, is to insert very small value resistors between the capacitors in the LV power supplies to the output stage. Thus you convert what was a pure capacitor filter into a CRC filter. For all I know, that practice may be standard now for Atma-sphere. The end result was a CRCRC or CRCRCRC filter, where the first R was 0.5 ohms, the second R was 0.21 ohms, etc. Each C was about 2000uF, with a much higher amount of C at the last stage. Another tweak was to convert the Cathode Follower driver stage to a version of late Allen Wright's "Super Linear Cathode Follower" (SLCF). That's described in AW's "Preamp Cookbook". But Paul had a schematic that suits the Atma-sphere topology.
Thanks, I already emailed with Paul but he says it is too long ago and he dont have the information.
I did look at the internet archive wayback machine and found the articles of Paul in the ASOG website but only the text, no figures are shown.
It would be convenient to have the schematics of the changes in powersupply and bias metering etc.
Thanks a lot, I now have the schematic I was looking for, I will build the ampifiers this year hopefully
Glad to know that, because so far I have not been able to find my print-outs. And I do seem to recall that while thinning out the mountain of audio-related paperwork I keep in my workshop, I may have tossed the Speltz schematics. But I do have his schematic of a solid-state SLCF (Super Linear Cathode Follower). Paul even made a few for me, but I never used them.
I printed out some of Paul's schematics. I will check and see if I still have them. I can draw the schematic for the CRCRC mod to the LV power supplies; that's easy.
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