Alternate power supply for SSS driver stage

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ToneMerc
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Re: Alternate power supply for SSS driver stage

Post by ToneMerc »

dreric wrote: The question is does having the plates with 700Vac make for a good sounding amp? I have heard the 6550 sound great with these voltages.

Eric
I'm quite fond the ODS clones that I have built with 700+ volts on the plates. I've only used the El34, 6L6 and 6CA7 though.

TM
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dreric
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Re: Alternate power supply for SSS driver stage

Post by dreric »

Martin,

I'm in the process of a build using your new power supply.

I'm confused by one connection on your layout "HT CT" at the 200uf cap. Is this the center tap of the PT?

You wouldn't possibly have made a schematic?

Thanks
Eric
Eric
1949 Zenith, Zenith Toggle Recoil, Zenith 55 & 440
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martin manning
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Re: Alternate power supply for SSS driver stage

Post by martin manning »

Yes that's correct, it's the PT CT and the reservoir cap ground.
larsvictor
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Re: Alternate power supply for SSS driver stage

Post by larsvictor »

Martin,

can you explain why the entrance of your cf driver has a different design ? (compared to the published #002 cf driver circuit). In your schematic the grid leak resistors are 470k ( 1M in #002) and you have 220k grid stoppers (#002 has no grid stoppers there). I do understand the 100k for the Rk. This one can be calculated by the voltage and maximum plate dissipation of the triode. The voltage divider for the bias is also clear to me.
Can I use the two 1M and no grid stoppers as well ?

Thanks
Lars
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martin manning
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Re: Alternate power supply for SSS driver stage

Post by martin manning »

I can't recall where I got the 220k value for the grid stoppers, and looking back through the earlier thread it's not mentioned there either. The value is not critical, and neither is the 470k grid leak. I believe that came from another SSS schematic. A small grid stopper is a good idea to prevent oscillation, so I would use something like 1k at least. Much larger values are fine since there is no Miller capacitance. It might be worth some experimentation to see if there is any tonal effect.
Aaron
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Re: Alternate power supply for SSS driver stage

Post by Aaron »

I built an amp with the 160PS transformers. 700v on the plates and 350 on the screens with a pair of KT88's. It is LOUD and clean. I don't think I've ever had the pre and master past 2.

Did I mention it is loud? :D
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dreric
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Re: Alternate power supply for SSS driver stage

Post by dreric »

Aron, I know you did and your build has been an inspiration to use the PS 160 transformer I have. The thing is that I don't have the PT just the PT.

I had Heyboer made up a OT with the 6600 primaries. Now I'm torn between using a twin PT with the Sunn OT or the PS 160 with the new OT.
Eric
1949 Zenith, Zenith Toggle Recoil, Zenith 55 & 440
larsvictor
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Re: Alternate power supply for SSS driver stage

Post by larsvictor »

Ok, Martin. I´m convinced. :D
Build this tiny board for the +/- 160VDC CF-power supply. Curious wether it makes a difference soundwise.

Lars
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martin manning
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Re: Alternate power supply for SSS driver stage

Post by martin manning »

Cool! looking forward to reading your report on the sound, especially since you have direct experience with the other bias supply.
larsvictor
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Re: Alternate power supply for SSS driver stage

Post by larsvictor »

The new circuit works fine: B+ for the plates is +198 VDC, grids of the CF have -50.3 VDC and Cathodes -48.6. Less stress for the tube with ~250V plate to cathode.
PT somehow delivered higher voltages than I expected (+/- 206 VDC without load). I had to adjust the values of the resistors in the bias string. Range is -40 to -77 VDC.
The rest of the amp is again "under construction" - so I had no possibility to hear, if there is a dfference to the old circuit.

Lars
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martin manning
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Re: Alternate power supply for SSS driver stage

Post by martin manning »

Here's another tweak to the alternate negative power supply: Moves the driver stage bias trimmer to the chassis for easier access, and adds a balance trimmer.

Lars, glad it worked out for you! The regulation on small transformers is generally pretty poor. I got about the same output voltage from a similar unit when it was lightly loaded.
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martin manning
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Re: Alternate power supply for SSS driver stage

Post by martin manning »

Here is an eyelet board that combines the 60V tap-powered bipolar bias supply and HV rectifier on the same footprint as the CE chassis/J Boarders PCB. This is pretty tight, so I think I'd stuff and solder it from the middle out.
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Last edited by martin manning on Mon Nov 29, 2021 12:12 pm, edited 1 time in total.
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dorrisant
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Re: Alternate power supply for SSS driver stage

Post by dorrisant »

There must be something intense buried in this doc... It locks up Corel when I try to import it. Any way it could be exported as a different file type? I hate to lose the vector though.
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martin manning
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Re: Alternate power supply for SSS driver stage

Post by martin manning »

dorrisant wrote: Mon Nov 29, 2021 10:07 am There must be something intense buried in this doc... It locks up Corel when I try to import it.
I've recreated the .pdf. Maybe that will solve it.
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