Alternate power supply for SSS driver stage

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martin manning
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Alternate power supply for SSS driver stage

Post by martin manning »

For TAG member bcmatt’s Traynor YGL3 to SSS conversion project, I proposed a bipolar supply fed by a small flat-pack transformer for the CF driver stage. Since the Traynor PT used a FWB rectifier, the usual means of deriving the negative voltage for the driver tube from the HT would not work. Matt built it, and it worked fine: http://ampgarage.com/forum/viewtopic.ph ... 489#361489

I’m still not a fan of the driver tube power supplies seen in the various SSS schematics because they have very high voltage across the driver tube (even if another RC branch is created), and the negative voltage develops quite slowly. So, here's another idea: If there is an existing bias winding or tap, it can be used to feed a voltage quadrupler to create a ±170VDC bipolar supply. This solution requires about the same number of components as the later SSS HT-derived supply, but it operates with a very reasonable 340V from the plates to the bottom of the cathode resistors, and both the positive and negative voltages come up very quickly. This circuit will work using a FWB rectifier where there is a separate bias winding (as in the Traynor YGL3 PT), or with a FW rectifier where there is a 60VAC bias tap (as in the Dumble-standard Fender Twin Reverb/Dual Showman PT). Below is an example of how this design could be laid out on the SSS main power supply board.
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Last edited by martin manning on Tue Feb 07, 2017 11:05 am, edited 1 time in total.
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dreric
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You must be psychic

Post by dreric »

Martin,

I am the early stages of a Hartman build. I'm using a Fender PS 160 PT which has a dedicated 47V bias tap. The PS 160 was a 2 6550 amp and I want to run the amp with it because I have a nice Dynaco / Sunn OT for a 2 6550 build.

Would to suggest this bias arrangement for a build like this?

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

Post by martin manning »

I don't see why not. The schematic shows the bias winding at 49VAC, which should get +/- 135V for the driver. Are you going to use the 700V plate/350V screen as in the 160 PS power supply? Is the Dynaco OT expecting that combination of plate and screen voltage? What is it's Zpri?
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dreric
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ptot

Post by dreric »

Well Martin, truthful I hadn't planned that far ahead and I was planning on asking your advise. The Sunn 3-60 is an ultra linear OT I'm nto clear on how it would interact with the Fender PT. I would like to get the voltages out of the PT.
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martin manning
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Re: Alternate power supply for SSS driver stage

Post by martin manning »

If you are going to run the Sunn OT in UL, then I would look for another PT that would keep the plate voltage at ~485V as shown on the Sunn schematic, and which has a -60V bias tap to use with the quadrupler bias supply. A 100W Twin PT would probably be fine too. If not, find out what the primary impedance is and see if the PS 160 plate and screen voltages (700/350) are compatible.
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Re: Alternate power supply for SSS driver stage

Post by dcribbs1412 »

Brilliant!
Thanks for your work Martin
Will implement this in the next SSS style build

D
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dreric
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primary

Post by dreric »

Martin,

Thanks for your feedback.

You said that if I wanted to run the Sunn PT in ultra linear then the PT wouldn't be a good match. What if I didn't run it in UL but just hooked up the primaries to the plates?

I looked into how to determine the primary impedance and the impedance ratio. I'm unsure if I did this right and more uncertain as to the meaning. If you would indulge me:

Primary @ 16AC Secondary (16ohm tap) @ 1 VAC
= 16/1 turns ratio, = 256/1 impedance ratio
Into 16ohms primary impedance (16 x 256) = 4096 ohms

Primary @ 24 VAC Secondary (8ohm tap) @ 1 VAC
= 24/1 turns ratio, = 576/1 impedance ratio
Into 8ohms primary impedance (8 x 576) = 4608 ohms

Primary @ 32AC Secondary (4 ohm tap) @ 1 VAC
= 32/1 turns ratio, = 1024/1 impedance ratio
Into 4ohms primary impedance (4 x 1024) = 4096 ohms

Is there a way to make this transformer combo work?

Thanks
Eric
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dreric
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??

Post by dreric »

Would this OT be a better match?

I have the 1650R
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dreric
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Re: Alternate power supply for SSS driver stage

Post by dreric »

wasn't there a picture?
Eric
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martin manning
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Re: Alternate power supply for SSS driver stage

Post by martin manning »

Yes, one of the 47u caps was marked 470u. Fixed now :^)
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Re: ??

Post by martin manning »

dreric wrote:Would this OT be a better match? I have the 1650R
To run 700V you will need 6k6.
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dreric
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Re: ??

Post by dreric »

martin manning wrote:
dreric wrote:Would this OT be a better match? I have the 1650R
To run 700V you will need 6k6.
Meaning to run 700 volts on the plates of the 6550s I would need a OT with a primary impedance of 6600 ohms?
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martin manning
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Re: Alternate power supply for SSS driver stage

Post by martin manning »

Yes correct. And screens at ~350V like the Sunn.
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dreric
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Re: Alternate power supply for SSS driver stage

Post by dreric »

So I have a dilemma................

If I use the PS 130 PT with it's high plate voltage it seems I would need to get a OT made up with a primary of 6600 ohms.

If I use a twin PT then I could use the Sunn 3-60 as the plate voltages would be good but the screens are too high as the twin iron has 458v on the screens. Seems I could increase the value of the screen resistors to drop the voltage to 350V..............would this work?

Trying to avoid buying a transformer, I have too many laying around.

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.

Your thoughts
Eric
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dreric
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Re: Alternate power supply for SSS driver stage

Post by dreric »

Or ................it seems this Dynaco mark 3 PT would work as it's matched to the Sunn OT

I need to check it there is enough heater current. And I could use the 5V tap for a Fet and Reverb relay!

http://triodeelectronics.com/mq782.html
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