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Stereo Tube Amp Question

Discussion in 'Shock Brother's DIY Amps' started by robrob, Jan 2, 2021.

  1. Paul-T

    Paul-T Tele-Holic

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    I know very little about this, but I have been keeping half an eye out for circuits. There tend to be one or two recommended, but I know one good one is the Mullard Circuit. The 5 10 is the most often mentioned, 5 tubes, 10 watts. Bigger versions too.

    Lots of stuff online including this:

    http://www.r-type.org/articles/art-003e.htm

    Google it and you'll also find a booklet on Mullar, available on the Primary Windings site. Their blog features some Mullard builds and they also do a number of the necessary transformers. https://primarywindings.com/product-category/mullard/

    There might be better versions, but the Mullard circuits are well documented, and there are a good number of Brit companies that supply transformers, including Primary Windings, Sowter and Majestic. I suspect Edcor do too.

    In short, the 5 10 seems almost to be the 5E3 of audio amps.

    Would be very interested to see your progress on this.
     
    Last edited: Jan 3, 2021
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  2. Squawker

    Squawker Tele-Holic

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  3. dougsta

    dougsta Tele-Meister

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    Here's document by Mullard in the 1950s is an excellent resource for building audio amps, including circuits with descriptions, BOMs, board layouts and chassis drawings (in inches).

    The power amps use EL84's (10Watt) and EL34's (20Watt) pentodes with UL taps on the output transformers for low distortion.

    If your music source is digital/line out I would just try a simple single dual triode tube driving 2 x 6V6 for each channel (and why stop at 3 when you can have 5 channel surround sound!) into a larger than usual OT to get a reasonable bass response.
    It will retain the 'valve' sound. Another option is to use triode strapped pentodes (EF86, EF80, EF184) for a linear preamp/PI stages.

    I built something simple to play audio in my lab, the source is an old mobile phone with a 128gb sd card, also used for EQ settings so no need for a tone stage.
    The whole stereo amp is 3 tubes in total! 1 x 12ax7 for a single triode preamp stage with master volume per channel and 2 of the rather exotic ECLL800 tubes for the dual channel power amp, 10 watts per channel. From the name of the tube you can see E=6,3v C=a triode L=a pentode L=another pentode and 8=B9A socket, a push-pull amp in a single bottle.

    http://primarywindings.com/wp-content/uploads/2017/04/Mullard-Circuits-for-Audio-Amplifiers.pdf

    Doug.
     
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  4. Squawker

    Squawker Tele-Holic

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    Thanks Doug. That saved me some scanning :)
     
  5. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    My living room amp is a simple beast. A 6n2p-EV drives a pair of 6p1p-EV ( one triode and one pentode per channel, you can see where this is going ). It's a 'power' amp with a volume control, suitable for line level signals. Switch out the valves for a 12AX7 or 12AY7 and a pair of 6V6 and you have essentially a 5F1 monoblock pair that's missing a gain stage.
    It sounds utterly glorious. OK, so my late Victorian/early Edwardian tiny terrace has a living room about the same size as an American fridge ( :) ) but it fills the room with wonderful sound. Think back to tabletop radios, early, low power gramophones et al and you're there in an instant. That first Watt is magic, the second one?, icing on the cake.
    Feed it with a signal from a modern DAC, allow your favourite chair to mould itself around you and relax into the sonic atmosphere that surrounds. Marvellous.
    I think there's mileage in a super Champ ( 6L6/KT66 ) single ended, super simple 6~8 Watt per channel if you like the Class A artefacts. Personally, I love 'em.


    ps. The huge, chunky, ALPS potentiometers are heartily recommended.
     
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  6. tubelectron

    tubelectron Tele-Afflicted

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    @robrob,

    Design it ! :cool:

    It's not so difficult, particularly if it is a SE UL cathode bias type : in two stages, with a 10dB NFB and a correct OPT, you're done ! ;)

    In these conditions, a 6V6 driven by a 12AX7 (RL = 100K or SRPP operation, like below) will give you circa 2W RMS 8R at onset of clipping, with a plate voltage at 270V, Rk = 270R + 470µ//, RL = 5K, 43% tap.

    Here's what I tested with re-use parts ;) :
    upload_2021-1-3_12-52-44.png

    [​IMG]

    Of course, you can go much further in power and fidelity : cost will rise quickly... o_O

    But it's me, OK ? :D

    -tbln.
     
    Last edited: Jan 3, 2021
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  7. DuckDodgers

    DuckDodgers Tele-Meister

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    The original Sunn amps used Dynaco amplifier chassis. I think they used a Dynaco Mk-IV mono power amp.

    Leo and other amp maker took their first circuits right out of the RCA Tube Manual, so that’s a good place to start. So is The Tube Book, by Austen Pittman.
     
  8. mooncat

    mooncat TDPRI Member

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  9. Wally

    Wally Telefied Ad Free Member

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    https://www.ampslab.com/vintage1.htm

    I have a couple of stereos that I need to get back in action. One is a little Harmony Kardon. The other is a Voice of Music. Iirc, both run EL84/6BQ5 power tubes. I also have the transformer set form a Sherwood stereo that also ran EL84s.
    I have two power amps from Baldwin organs that would set up well for stereo. Iirc, they have enough Noval sockets for preamps to be built in them.
     
  10. Mongo Park

    Mongo Park Tele-Afflicted

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    Rob. RH 84 is a singe end tube stereo. It was designed to be able to use inexpensive parts and sounds great. It is single end it has sweet tones and is not complicated or expensive. It is not new and been around a while with variations on tubes. So builds with bigger tubes can found if that is what you want.
    Do check it out it is a simple great sounding amp. This is the Champ of the stereo world.

    http://rh-amps.blogspot.com/2013/02/rh84-amplifier-revision-2_26.html?m=1
     
    Last edited: Jan 3, 2021
  11. FenderLover

    FenderLover Poster Extraordinaire

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    I'd suggest you look at the Lexicon Signature 284 Recording Amp. I've done stereo before and find that dual preamps are a lot of extra baggage. The best solution I have found is a mono preamp > FX send > stereo FX returns > dual outputs. The Lexicon is simple and can be simplified further, as far as the preamp gain stages are concerned. It has SE EL84 outputs and can obviously be changed as well. If you do a little search on this forum, I have posted the schematic and gut shots of mine.
     
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  12. schmee

    schmee Doctor of Teleocity

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    Yeah!
    I was thinking: Left channel, right channel, sub woofer. Those amps have 6 EL84's, two for each channel IIRC.
     
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  13. FenderLover

    FenderLover Poster Extraordinaire

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    Curious why you don't just cut and paste another schematic together with a 5F1 preamp and dual outputs?
     
  14. Junior Little

    Junior Little Tele-Meister

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    IMG_1409.jpg
    A guy I was conversing with built this. Single PT, SS rectified, but 2 completely different 5F2A circuits.
     
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  15. David Barnett

    David Barnett Doctor of Teleocity

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  16. David Barnett

    David Barnett Doctor of Teleocity

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  17. schmee

    schmee Doctor of Teleocity

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    [​IMG]
     
  18. archetype

    archetype Fiend of Leo's

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    Here's an example schematic. It's a CHA-33. Later ones used a 5U4GB.

    upload_2021-1-3_13-7-44.jpeg
     
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  19. dankilling

    dankilling Tele-Afflicted Silver Supporter

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    Very interested in this thread- I regularly build guitar amps, but the hi-fi designs I’ve seen do some things I don’t really understand
     
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  20. telemnemonics

    telemnemonics Telefied Ad Free Member

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    Here’s pics of one old stereo amp chassis I pulled from a big console that had the original 1961 receipt inside and I believe said high fidelity somewhere in the name on the pretty cabinet.
    I find this doubly interesting in this discussion because I have a second of the same chassis that was turned into a guitar amp by a Detroit builder, and voiced like an early Marshall AKA tweed Fender.
    Not a tweed circuit but supports the spirit of the idea that records can sound good through amps not that different from old tweeds

    6EA21C69-BC53-4055-96DE-D949079487FD.jpeg F07569B2-DB75-4A81-A8E9-2C763E9314AF.jpeg
     
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