Symmetric Reichert 300B push-pull

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IslandPink
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#46 Re: Symmetric Reichert 300B push-pull

Post by IslandPink »

Thermionic Idler wrote: Tue Jul 28, 2020 12:09 am Also, I think I"m going to use 6AH4 for the driver valves,
That's an obscure one ! Have you got a datasheet or curves - i couldn't find much with TDSL.
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#47 Re: Symmetric Reichert 300B push-pull

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IslandPink wrote: Tue Jul 28, 2020 11:55 am
Thermionic Idler wrote: Tue Jul 28, 2020 12:09 am Also, I think I"m going to use 6AH4 for the driver valves,
That's an obscure one ! Have you got a datasheet or curves - i couldn't find much with TDSL.
http://oldradio.qrz.ru/tubes/foreign/01/6AH4.gif

There is more info on the 6AH4-GT

https://frank.pocnet.net/sheets/093/6/6AH4GT.pdf
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#48 Re: Symmetric Reichert 300B push-pull

Post by IslandPink »

Thanks Phil, hadn't seen the GT datasheet.
Are they linear enough below 40ma ?
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#49 Re: Symmetric Reichert 300B push-pull

Post by Nick »

Looks nicely linear with a CSS load.
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#50 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

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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#51 Re: Symmetric Reichert 300B push-pull

Post by Nick »

Valves made for TV deflection amp tend to be nice and linear.
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#52 Re: Symmetric Reichert 300B push-pull

Post by IslandPink »

It's not quite as linear as a 6SN7 ( which looks like a DHT on the traces ) but I take your point about CCS and how that helps.
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#53 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

The plan is to use the K&K audio cascode CCS's - I'm in touch with Kevin Carter about getting hold of 4 of them.
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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#54 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Another question, my preamp delivers a true differential balanced output via XLR, so I don't think I actually need that line input transformer?

Granted, the power amplifiers are plugged into different mains sockets near the speakers, but as long as I leave Pin 1 (shield) unconnected at the power amp end, I can't see that causing any issues as it would with an unbalanced connection. The first *SN7 stage will cancel any common mode noise, as far as I can see.

EDIT just found this article https://www.tubecad.com/2018/09/blog0440.htm which suggests if I put a CCS between the grids of the first *SN7, it should reject common mode noise properly. Ferrite beads near the grids should kill any RFI.

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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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#55 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

I'm having second thoughts about the 6AH4 as driver. Re-reading Morgan Jones this morning, he claims that sample-to-sample variations can be more variable for valves not designed for audio use. He apparently tested 30 6BX7's (similar to the 6AH4) and found the distortion performance varied by a factor of 4.

Further research seems to indicate that a triode-connected 6V6 is linear enough to do the job, and won't result in the amp having too much gain. Plus there are cheaper 5 volt and 12 volt versions.
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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#56 Re: Symmetric Reichert 300B push-pull

Post by Cressy Snr »

I’ve used the triode connected 6V6 to drive a JJ, 2A3-40. It’s excellent.
The PCL86 is also good as a self-contained, voltage amp and driver. The nine-pin noval, PCL86 is basically a 12AX7 and EL41 in the same bottle. They sound great triode strapped.

It has a 13V heater, but it works perfectly well on 12.6V, as myself and MikeH can testify. Langrex are virtually giving them away at a fiver each. https://www.langrex.co.uk/products/pcl8 ... nos-boxed/

Four of them, and (including the 300Bs) you’ve only got 8 valves on your top plate. Watch out for oscillation though. Grid stoppers are a must.
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#57 Re: Symmetric Reichert 300B push-pull

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Thermionic Idler wrote: Sun Aug 02, 2020 12:31 pm I'm having second thoughts about the 6AH4 as driver. Re-reading Morgan Jones this morning, he claims that sample-to-sample variations can be more variable for valves not designed for audio use. He apparently tested 30 6BX7's (similar to the 6AH4) and found the distortion performance varied by a factor of 4.

Further research seems to indicate that a triode-connected 6V6 is linear enough to do the job, and won't result in the amp having too much gain. Plus there are cheaper 5 volt and 12 volt versions.
sounds like a plan, Stephie said same about the original first stage valves in matrix, 1 out of 10 good enough, so valve was changed but not on schematics. its in 813 version text.

if you go 6v6 why not splash out for 10. or not forgeting 1619 dht in the position? Nothing wrong with 6v6.
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#58 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

@Steve - thanks for that, I remember your 2A3 build, I just pulled up the thread to remind myself about it. I'll borrow your 6V6 operating points for the Spice sim if you don't mind! :D

@Paul - I have to say having the DHT driving the DHT has crossed my mind many times, but it's also going to add complication in terms of the heater supply, I won't be able to get away with running AC heaters on the driver valves. This way, I can run all AC and not worry.

Basically, I'm trying to minimise the spend and simplify as much as possible up to the output stage, to allow as much budget as possible for the output transformers.
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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#59 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Spice model so far. The output stage isn't finished yet because I've run into some problems with modelling the output transformer, but I should be able to sort that out.

I've got the 6V6s operating at the recommended settings in the RCA datasheet for Class A1 push pull operation (although I'm still not certain about the C3 value or whether it even needs to be there). According to Spice, the input to the 300Bs will swing over 200V peak-to-peak before clipping. I believe 300Bs need about 80V to reach full output, so that should do nicely.

Might want to right click and view image to be able to see it properly - it's quite a high rez screen shot.

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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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#60 Re: Symmetric Reichert 300B push-pull

Post by IslandPink »

Nice ! What happened to the CCS's ?
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