Symmetric Reichert 300B push-pull

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Thermionic Idler
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#61 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

IslandPink wrote: Sun Aug 02, 2020 7:07 pm Nice ! What happened to the CCS's ?
Circuit seems to be working well without them so at the moment my approach is not to include anything that doesn't need to be there. No regulation, no silicon CCS's. Just two separate, simple power supplies to keep things clean and a really good amorphous OPT.

I'm sort of committed to this now, just pulled the trigger on 5 x 5V6GT's (NOS, NIB) from the US. All I need is dropping resistance off the 12V power supply and connect in series for 4.7V each.
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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#62 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Duh! Well unless I want to add an input transformer, I'm going to need at least one CCS, on the first stage cathodes. Spice just told me a plain resistor does nada to cancel common mode noise - which I probably should have realised if I'd had my wits about me. Sure it gets summed in the OPT but probably don't want it going through the whole amp in the first place.
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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#63 Re: Symmetric Reichert 300B push-pull

Post by pre65 »

I make my CCS from Ixys 10M43s chips, and I used DN2540n5 X 2 as cascade on the GK71 driver valve.

A small heatsink, or mount on the amp casing is enough. Only other things are a current set resistor and a 1K gate stopper.
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Nick
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#64 Re: Symmetric Reichert 300B push-pull

Post by Nick »

Spice just told me a plain resistor does nada to cancel common mode noise
Well, it will do some, but not as much as the longer tail a CCS provides. But as long as you feed a real balanced input it should be ok without the CCS in the tail.
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#65 Re: Symmetric Reichert 300B push-pull

Post by Ray P »

Dave, I have four K&K Compact Cascode Current Source Board kits that I will no longer need - I've been planning to post them on the Buying and Selling topic for £5 each (plus shipping & PP fees) but haven't got around to it.

Ray
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#66 Re: Symmetric Reichert 300B push-pull

Post by Paul Barker »

Erm if they’re on a long tail they’re current sinks, whatever Kevin calls them.
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#67 Re: Symmetric Reichert 300B push-pull

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Paul Barker wrote: Mon Aug 03, 2020 7:52 pm Erm if they’re on a long tail they’re current sinks, whatever Kevin calls them.
Well, topologically I guess it depends where it is it relation to the load its feeding. There are normally two terminal devices so can be viewed either as source or sinks, but CCS covers them both. And in a tail, well, depends if you mean in terms of conventional or actual current flow.
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#68 Re: Symmetric Reichert 300B push-pull

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"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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Thermionic Idler
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#69 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Ray P wrote: Mon Aug 03, 2020 7:33 pm Dave, I have four K&K Compact Cascode Current Source Board kits that I will no longer need - I've been planning to post them on the Buying and Selling topic for £5 each (plus shipping & PP fees) but haven't got around to it.

Ray
I will very likely take you up on a couple of those Ray - they need to sink 23mA which should be well within their capability. Thanks.
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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#70 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Woke up early this morning, so spent a little time before work tweaking the coupling cap and grid leak values for the 6V6 and 300B, and seeing what effect they had on the frequency sweep results.

This is what I ended up with, the grid leaks are about 60% of the maximum values specified on their respective data sheets, going higher gave a diminishing return in terms of bandwidth. The 10 degree bass phase shift point seems to happen at about 26Hz.

My OPT model is for the Monolith Magnetics product but to be honest I probably haven't the budget for that, so in reality the bandwidth may end up being a touch less. However, this configuration has extended the bandwidth considerably over the original design. Screen captures below (I have yet to set a final value for C3 by the way):

Image

Image
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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#71 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Latest circuit iteration.

I've restored the I/P transformer (the 7m leads from the preamp mean I want to kill as much common mode noise as possible right at the start). I've selected a low impedance transformer to take advantage of the very low impedence output on my preamp (66 ohms balanced) and the resultant superior phase accuracy.

I've also restored the CCS's on the driver stage - they are needed, without them, I only have 2dB of headroom between the output stage and driver stage clipping. With CCS, I have 6dB. That said, the plate dissipation on the 6V6's is still close to maximum (11.5 watts or so) and as I'm intending to use NOS tubes (5V6's in fact) I'm going to play with the operating points to try and dial that back a bit without affecting my available headroom too much. The CCS's I just bought off Ray will do the job perfectly.

Picking up Neal's Sowter U082's tomorrow. And the anodised samples arrived from Schaeffer AG for the chassis top plate - choosing between dark green or gold.

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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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#72 Re: Symmetric Reichert 300B push-pull

Post by Nick »

Not sure I understand your 6v6 numbers. Looking at the plate curves I would have expected about 200v on the anode which is only 8W so lots of scope. And I would have thought loads of headroom to drive the 300v grid.
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#73 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Nick wrote: Fri Aug 07, 2020 6:51 pm Not sure I understand your 6v6 numbers. Looking at the plate curves I would have expected about 200v on the anode which is only 8W so lots of scope. And I would have thought loads of headroom to drive the 300v grid.
I based them on this: https://frank.pocnet.net/sheets/084/6/6V6GT.pdf - page 2, push-pull amplifier (triode connection) class A1. But that was without factoring in the CCS of course. As you say,the curves on the last page suggests a rework might be in order.
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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#74 Re: Symmetric Reichert 300B push-pull

Post by Nick »

I was looking at 200v, 40ma -10v on the grid. 30ma amd 250v may be better.
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#75 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Nick wrote: Sat Aug 08, 2020 10:18 am I was looking at 200v, 40ma -10v on the grid. 30ma amd 250v may be better.
Thanks Nick - all operating point suggestions gratefully received! I'll be poring over the datasheets tomorrow.

Picked up Neal's quite large output transformers today - these things are about 3x the size of the ones in my old 2A3PSE amp, and that was single-ended!
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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