Symmetric Reichert 300B push-pull

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Thermionic Idler
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#1 Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Well, for no sensible reason that I can identify yet, I still have a hankering to build a 300B push-pull amplifier - probably monoblocks now, given how my system is configured. Meredith was right - I'll always need a project.

I was always attracted by the Lynn Olson designs as the all-differential circuits seemed so elegant, but the reality of building stuff with so much iron and power supply demands just put me off after a while.

Having searched around for a simpler circuit that I felt able to cope with, both from a build and budget perspective, I came across a more recent Olson-designed circuit called the Symmetric Reichert. It's apparently based on Herb Reichert's single ended Flesh and Blood design: http://www.enjoythemusic.com/diy/0709/flesh_blood.htm . Lynn himself writes further about it here: https://www.diyaudio.com/forums/multi-w ... ost4409732

The circuit is below, and it looks relatively straightforward to achieve in monoblock form, and doesn't use any exotic or difficult to source valves - 6SN7 and 300B, and the TV diodes can be replaced by GZ34's. Scratch building the OTL Beasts has given me more confidence to tackle something like this.

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Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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#2 Re: Symmetric Reichert 300B push-pull

Post by IslandPink »

Interesting - nice find. That would be worth hearing.
These days you'll have more chance of getting good 6SN7 types if you go for other filament voltages. The 6SN7's are awful prices for the good ones.
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Ray P
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#3 Re: Symmetric Reichert 300B push-pull

Post by Ray P »

Did you consider the Transcendent Pinnacle Dave?

And Mark is right about 6SN7s; I recently bought a pair of NOS RCA 12SN7s a lot cheaper than similar 6SN7s.
Last edited by Ray P on Wed Jul 22, 2020 9:30 pm, edited 1 time in total.
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#4 Re: Symmetric Reichert 300B push-pull

Post by Nick »

Trying to work out how the second stage works without a way to share current across the to anodes. I guess maybe through the coupling caps.

Ignore that, the anode voltage can move, just not the current.
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#5 Re: Symmetric Reichert 300B push-pull

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IslandPink wrote: Wed Jul 22, 2020 6:56 pm These days you'll have more chance of getting good 6SN7 types if you go for other filament voltages. The 6SN7's are awful prices for the good ones.
Well, I did want to ensure it could use valves in current production. However, it should be easy enough to make the heater supply switchable (note to self, use a locking switch) between 6v and 12v, seems 12SN7s are still quite thick on the ground. That way I can use either.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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Thermionic Idler
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#6 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

The output iron will likely be sourced from here: http://npacoustic.com/en/product-and-price

Amorphous core, bandwidth up to 80kHz, that'll do for me.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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#7 Re: Symmetric Reichert 300B push-pull

Post by IslandPink »

Thermionic Idler wrote: Thu Jul 23, 2020 11:25 am Well, I did want to ensure it could use valves in current production. However, it should be easy enough to make the heater supply switchable (note to self, use a locking switch) between 6v and 12v, seems 12SN7s are still quite thick on the ground. That way I can use either.
Well I was just thinking about the current production ones I tried about 15 years ago, and assuming you'd go for NOS. Those Russian ones 'instantly converted the sound into wishful thinking' as Romy would say. Maybe things have changed. There must be loads of great NOS Loctal 6SN7 equivalents around.
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#8 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

IslandPink wrote: Thu Jul 23, 2020 10:01 pm
Thermionic Idler wrote: Thu Jul 23, 2020 11:25 am Well, I did want to ensure it could use valves in current production. However, it should be easy enough to make the heater supply switchable (note to self, use a locking switch) between 6v and 12v, seems 12SN7s are still quite thick on the ground. That way I can use either.
Well I was just thinking about the current production ones I tried about 15 years ago, and assuming you'd go for NOS. Those Russian ones 'instantly converted the sound into wishful thinking' as Romy would say. Maybe things have changed. There must be loads of great NOS Loctal 6SN7 equivalents around.
Yeah, the ones that came with my 2A3PSE in 2003 weren't great, I remember replacing them with some Sylvanias and hearing quite an improvement. I think current manufacture have got better since then but if I can give myself the option of switching to 12v heaters and trying NOS at a fraction of the price then why not.

Of course, nothing is straightforward - Lynn recommends that the driver valves use one half of a 6SN7 because of the power dissipation. So each chassis would have three 6SN7s, so not just a matter of being able to switch the heater supply between series and parallel unless one were to use a wasteful dropper resistor. I've contacted Primary Windings about how much custom mains transformers would be - the heaters need to be centre tapped to ground, requiring a secondary of 0v - 3.15v - 6.3v - 12.6v to get the switchable voltage. Waiting to see what they come back with.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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#9 Re: Symmetric Reichert 300B push-pull

Post by Ray P »

Thermionic Idler wrote: Fri Jul 24, 2020 12:01 am Of course, nothing is straightforward...
It would be a lot more straightforward if you just choose to run a single filament voltage - do you really need the flexibility to be able to run either 6SN7s or 12SN7s?
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#10 Re: Symmetric Reichert 300B push-pull

Post by simon »

If you're only using half of the 6SN7 perhaps try 7A4s, a well regarded loctal keeping with Mark''s suggestion? They look to still be 10 bucks each.
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#11 Re: Symmetric Reichert 300B push-pull

Post by steve s »

I don't have many 6sn7s, most went years ago, I sold a large box of b65 ecc32/33/35s last year, I have quite a few l63/6j5 types, and I think I have a few b36 and 12sn7, I can test and match them all. Let me know what other type you think of as I still have quite a few 1000 valves
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#12 Re: Symmetric Reichert 300B push-pull

Post by Nick »

You could just breadboard it and see how sensitive it is to valve choice. Being push pull I suspect less than you think.
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#13 Re: Symmetric Reichert 300B push-pull

Post by steve s »

Nick wrote: Fri Jul 24, 2020 9:35 am You could just breadboard it and see how sensitive it is to valve choice. Being push pull I suspect less than you think.
That's an idea, but it still means having a selection to test.
Steve in his push pull days, brought his kt66 amp round to mine to test valves it was easy to tell the differences between makes/types of output valves
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#14 Re: Symmetric Reichert 300B push-pull

Post by Nick »

Yes, but we were talking about input valves here.
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#15 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

simon wrote: Fri Jul 24, 2020 7:49 am If you're only using half of the 6SN7 perhaps try 7A4s, a well regarded loctal keeping with Mark''s suggestion? They look to still be 10 bucks each.
Ooo... with a 7N7 dual triode equivalent at the input. Thanks for the heads-up on those Simon.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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