I'm looking for some ideas for a suitable stereo tube amp to build that will ideally deliver around 15 Watts of power per channel. I have some (loose) constraints:
I realize that it's perhaps a bit odd to start with the transformer!
- I'd like to base it around a massive Paeco mains transformer I have (photo in attachments): this has secondaries of 289V 200mA, 207V 125mA, and four 6.3V heater secondaries for a combined total of 15 Amps heater current.
- I'd like to use 6080 tubes in the final stage, as I have about ten of them looking for a purpose.
I realize that it's perhaps a bit odd to start with the transformer!
Attachments
If you will only use that power transformer . . .
1. Each 6080 filament is 2.5A
You can power 5 each 6080 tubes, and have 2.5A left over for the input tubes and driver tubes.
. . . 6 each 6080 does not leave any filament current for the input tubes and driver tubes.
2. Add a couple of output transformers, and you can build either a Parallel Push Pull 6080 stereo amplifier, or a Parallel Single Ended stereo amplifier.
Either of those will work very well. The output transformer primary can be a very low impedance, and so the turns ratio will be low to get to 8 or 4 Ohms output tap (real good primary to secondary coupling, and very good high frequency response).
. . . As you said, a stereo OTL 6080 amplifier is not practical or reliable with that power transformer. No free lunch.
3. OTL:
RMS Power into 8 Ohms speaker load . . .
(((200mA)Squared) x 8 Ohms) / 2 = 0.16 Watt (160mW).
Just my opinions.
1. Each 6080 filament is 2.5A
You can power 5 each 6080 tubes, and have 2.5A left over for the input tubes and driver tubes.
. . . 6 each 6080 does not leave any filament current for the input tubes and driver tubes.
2. Add a couple of output transformers, and you can build either a Parallel Push Pull 6080 stereo amplifier, or a Parallel Single Ended stereo amplifier.
Either of those will work very well. The output transformer primary can be a very low impedance, and so the turns ratio will be low to get to 8 or 4 Ohms output tap (real good primary to secondary coupling, and very good high frequency response).
. . . As you said, a stereo OTL 6080 amplifier is not practical or reliable with that power transformer. No free lunch.
3. OTL:
RMS Power into 8 Ohms speaker load . . .
(((200mA)Squared) x 8 Ohms) / 2 = 0.16 Watt (160mW).
Just my opinions.
Great - thanks so much for the ideas! I was mistaken about the 6080 heater current: I thought it was 2A, but it is 2.5A as you say.
I wonder if 15W is feasible in push pull and/or single ended with two paralleled 6080s?
You might get close, 12 watts? Have a look thru this old thread: https://www.diyaudio.com/community/threads/idea-for-a-2-tube-6080-pp-amp.76820/
jeff
Maybe start with a power supply built around that transformer, in its own chassis. Then you can connect to a variety of amplifiers' chassis you may build down the road.
Thanks so much for the excellent ideas! Right now I'm thinking of a parallel SE setup with two 6080s fed by a 6SL7 and a 6SN7 for each channel. Just doing some Spice simulations ...
I'm sitting on a very similar stack of parts.
Same power transformer and a box full of big regulator triodes including 8080, and 6336x4
Been thinking about doing something fun but it hasn't materialized yet.
I'll be watching with great interest and perhaps building a copy cat amp.
One thing I think is fun about those big "dual triodes" is the possibility to make a "spud" push pull amp.
Meaning a push pull amp with both devices in one bottle. People will not immediately know weather its single ended or push pull, and you can play with their heads a little before you tell them.
Anywho, you may have a copy cat, co-developing this along side you if I find the time...
Very fun.
Same power transformer and a box full of big regulator triodes including 8080, and 6336x4
Been thinking about doing something fun but it hasn't materialized yet.
I'll be watching with great interest and perhaps building a copy cat amp.
One thing I think is fun about those big "dual triodes" is the possibility to make a "spud" push pull amp.
Meaning a push pull amp with both devices in one bottle. People will not immediately know weather its single ended or push pull, and you can play with their heads a little before you tell them.
Anywho, you may have a copy cat, co-developing this along side you if I find the time...
Very fun.
I found a couple of transformers that may work as outputs for the amp - they measure 15 Henries on the primary and 1 mHenry on the secondary, but I've no idea what their power capability is. I'll post the in-progress schematic for the amp later.
jjbunn,
Push Pull output transformers?
or
Single Ended output transformers?
For a single ended output transformer, an important factor is the 'Amp x Turns / lamination volume' and how much quiescent current it can take before the laminations saturate.
6080 like to run with lots of current.
Push Pull output transformers?
or
Single Ended output transformers?
For a single ended output transformer, an important factor is the 'Amp x Turns / lamination volume' and how much quiescent current it can take before the laminations saturate.
6080 like to run with lots of current.
Single ended. They are probably not beefy enough, but I'm not sure how to check given that I don't have their specifications.
Those output transformers might work well with a single triode of a 6080, so stereo with the pair of triodes in one glass envelope.
Parallel Single Ended is going to be a problem at some point, with 2, 3, 4 triodes running all that current in a single primary winding.
Parallel Single Ended is going to be a problem at some point, with 2, 3, 4 triodes running all that current in a single primary winding.
I found out what model those transformers are: they are 3W types for Fender Reverb amps, 8 Ohm secondary, and not nearly beefy enough. Back to the drawing board.
With the tranformer you have I think the max is 2x10W (stereo) out for music only.
The 6080 is ment for low voltages, 290V gives a 400V supply, suitable for setial PP with 200V on each tube.
Problem is the high voltage of 500Vpp to drive the upper tube but with a mosfet and bootstrap from the output is looks doable.
I am to old to fiddle around with simulators, so this idea is done with pencil and paper. Has an input of somewhat like 0,7V (0dB) and a feedback of ~12dB.
Mona
The 6080 is ment for low voltages, 290V gives a 400V supply, suitable for setial PP with 200V on each tube.
Problem is the high voltage of 500Vpp to drive the upper tube but with a mosfet and bootstrap from the output is looks doable.
I am to old to fiddle around with simulators, so this idea is done with pencil and paper. Has an input of somewhat like 0,7V (0dB) and a feedback of ~12dB.
Mona
Attachments
Wow, this looks phenomenal! Thanks for the schematic. I will try to enter this into LTSpice and see what I get. Would there be any advantage in doubling up the 6080 output tube, i.e. running two in parallel?
Phenomenal in the sense that it is explicitly geared to the transformer and tubes I have.
With a OPT of 500Ω in place of 1k and twice the 6080 it could give 20W out. But not with your power transformer, 200mA is barely enough for the 10W version.
Mona