Symmetric Reichert 300B push-pull

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

Post by IslandPink »

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.
I would have suspected more - on the basis that poor valves sound like they have more odd-order distortion - that won't cancel out in PP ?
But I know you did a lot of tinkering and measuring with the DAC in that sort of area. I do remember the Aurora amps were much happier with 5687's than ECC99's.

Somewhere upstairs I have a box of some nice things that are like a 6SN7 with only one section per bulb, and two top-caps ( bunny ears ) , I've forgotten what they are called, 2d22 ? ... will check later.
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#17 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Well, seems 12J5's (single triode equivalent to 12SN7) are REALLY cheap.

I'm starting to think, just have done with it and wire up 12V heaters from a separate transformer, 1x 12SN7 in the input position and 2x 12J5's in the driver stage. That would be do-able for even less than buying all-new manufacture 6SN7s.

Edit - just realised I'll be able to use a thinner gauge wire for the heater wiring. Wins all round.
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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#18 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

steve s wrote: Fri Jul 24, 2020 9:10 am 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
Pm if intersted
Noted, and thank you very much Steve, you're a gent! Per the above, I'm leaning towards 12SN7 and 12J5 types at this point.
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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#19 Re: Symmetric Reichert 300B push-pull

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Thermionic Idler wrote: Fri Jul 24, 2020 3:13 pm Well, seems 12J5's (single triode equivalent to 12SN7) are REALLY cheap.

I'm starting to think, just have done with it and wire up 12V heaters from a separate transformer, 1x 12SN7 in the input position and 2x 12J5's in the driver stage. That would be do-able for even less than buying all-new manufacture 6SN7s.

Edit - just realised I'll be able to use a thinner gauge wire for the heater wiring. Wins all round.
Yep, and if the world runs out of 12v valves, you could always leave space to add a small torrid as a 2:1 step down either in the primary or secondary of the heater transformer.
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#20 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Ray P wrote: Fri Jul 24, 2020 7:07 am
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?
I think on balance i'm probably going to do that. When I plan these things, I tend to think about long-term sustainability, and there is always a worry that if I lock myself in to a particular kind of valve variant that is no longer being manufactured, sooner or later they will become unobtanium.

However, the prices of 12SN7's and 12J5's seems to suggest we're a long way from that scenario with those variants, and I can't sensibly pass up the opportunity to enjoy NOS 6SN7 performance at a fraction of the price. And how often does one need to replace input and driver valves anyway?

Plus this solves another niggle I had - I really hate this thing about only using half a double-triode - the engineer in me really baulks at that. So if I want to use a single triode equivalent, I'd have to go NOS anyway as no one is making 6J5's any more.
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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#21 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

A question to the knowledgeable:

I'm building up a list of parts required to build this. The circuit diagram calls for a 5Hy 80mA choke in the power supply for the input and driver stage. The nearest I can find in the Hammond range of chokes is the 156L, which is rated for 5H at 75mA. According to the circuit annotations the maximum current draw should not exceed about 55mA so as far as I can see this should still be okay, do we agree or should I go for a bigger one?

Similarly for the output stage power supply which calls for a 5Hy 200mA choke, the closest I'm getting is the 159R, 6H at 200mA. Presume I should be okay with this one too?

Thanks in advance.
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'
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#22 Re: Symmetric Reichert 300B push-pull

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Thermionic Idler wrote: Fri Jul 24, 2020 4:56 pm

Plus this solves another niggle I had - I really hate this thing about only using half a double-triode - the engineer in me really baulks at that.
Understandable, but if you wire each monoblock double triode differently (assuming both parts are identical) then you effectively have two spares. If one goes wrong, or wears out, just swap them over.
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#23 Re: Symmetric Reichert 300B push-pull

Post by IslandPink »

Bear in mind he's using the driver valves at 3.65W dissipation per plate - too much for 6SN7 or 6SN7GT ( and 12v equivalents ).
It needs the higher dissipation GTA or GTB models, I remember this from the Reichert article.
You'll need to make sure which ever alternative you choose can take at least 4.5W per section, for some lifetime.
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#24 Re: Symmetric Reichert 300B push-pull

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IslandPink wrote: Fri Jul 24, 2020 2:44 pm
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.
I would have suspected more - on the basis that poor valves sound like they have more odd-order distortion - that won't cancel out in PP ?
But I know you did a lot of tinkering and measuring with the DAC in that sort of area. I do remember the Aurora amps were much happier with 5687's than ECC99's.

Somewhere upstairs I have a box of some nice things that are like a 6SN7 with only one section per bulb, and two top-caps ( bunny ears ) , I've forgotten what they are called, 2d22 ? ... will check later.
Absolutely, them Micky mouse ears are 6j5 curves with less capacitance I think.

I held my tongue about 5687 too but it always sounded a lift to that type of circuit, for me. May not hear it in PP though.
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#25 Re: Symmetric Reichert 300B push-pull

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National Union 7193's they are, just had a look.
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#26 Re: Symmetric Reichert 300B push-pull

Post by Nick »

Or you could increase the current a bit and run both sections in parallel.
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#27 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

IslandPink wrote: Fri Jul 24, 2020 8:18 pm Bear in mind he's using the driver valves at 3.65W dissipation per plate - too much for 6SN7 or 6SN7GT ( and 12v equivalents ).
It needs the higher dissipation GTA or GTB models, I remember this from the Reichert article.
You'll need to make sure which ever alternative you choose can take at least 4.5W per section, for some lifetime.
Ah - so the 12J5 is probably a no-no then, as I don't think that GTA or GTB versions of those were ever produced.
Nick wrote: Fri Jul 24, 2020 10:29 pm Or you could increase the current a bit and run both sections in parallel.
The Sun Audio SV300B uses that trick, I saw it in the Harvey Rozenberg write-up when I was researching different circuits. That would seem to be the logical way forward, given they were suggesting using separate *SN7 valves anyway. Am I right in thinking that the mod required is to double those CCS's from 10.8mA to 21.6mA each and parallel everything up?
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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#28 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Thinking about it though, that could also impact stage 1 as I think the Miller capacitance would double?

I should stop overthinking this and just build the thing as designed. As Phil suggested, if I wire it up such that V2 uses Triode 1, and V3 uses Triode 2, they can simply be swapped to use the other halves.
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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#29 Re: Symmetric Reichert 300B push-pull

Post by Nick »

Am I right in thinking that the mod required is to double those CCS's from 10.8mA to 21.6mA each and parallel everything up?
Well, I would have reduced the current so the valves were then inside their dissipation limits. Altered the current source and the series resistance to match.

Or as you say, you could just build it.
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#30 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

OK, I need some assistance from the collective again please, as I'm struggling to spec the capacitors. See annotated schematic below:

Image

Firstly the power supply and output stage caps. The Mundorf Tubecap range is the closest range of non-electrolytic capacitors I've been able to find available which might fit the bill, so the first thing I want to check is whether my 'nearest match' should be okay, as some of the voltages are a little derated, but not less than the in-circuit values.

1) Pi-filter caps circled in red. Spec calls for 40uF, 630V. Closest TubeCap match: 47uF 600V. (500V DC in the circuit).
2) Pi-filter caps circled in orange. Spec calls for 5uF, 1000V. Closest TubeCap match: 10uF 1000V
3) Output stage caps circled in green. Spec calls for 80uF, one rated at 630V, the other unknown rating. Closest match: 100uF 550V (485V in-circuit).

(Ignore the one circled in blue as I've just found the Tubecap at that value is rated 750V, more than enough).

Secondly, there are some capacitors which have not been specified with a value, and I"ve searched through the DIY audio thread to no avail:

1) Shared cathode capacitor between the driver *SN7s paralleled with 500R resistor, circled in purple. The *SN7 datasheet specifies a cathode bypass cap value of 1.4uF but I'm not sure if that applies here? Any idea of what the ballpark value should be?

2) Two capacitors connecting the input stage B+ line to ground, looks like a bit of RCRC smoothing with 500 ohm resistors. I've circled those in brown. Any ideas on value / type? (looks like they should be at least 600V rated).

At least I know what to use for the coupling caps and I shuold be able to work out the resistor ratings with Ohms law.

Many, many thanks in advance.
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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