Hi Stee
With my limited knowledge I already see some problems.
A pair of 6V6 in pentode delivers, lets say, 15W into 8 ohms. This is about 10V RMS, which won't drive the 6S33S to full output, as for full output you need rather 50V RMS, or more.
Much care with fixed bias on a 6S33S, it can and has been done, but is not recommended by the manufacturer.
You have global feedback, which does not (always) go well with an interstage transformer. You may experience oscillation...
And then there is the driver stage with the ECC82. It will probably work, but won't do more than that. The ECC82 ain't a good tube, and the choice of the phase splitter is even worse. Expect high distortion from it!
Good luck, Erik
With my limited knowledge I already see some problems.
A pair of 6V6 in pentode delivers, lets say, 15W into 8 ohms. This is about 10V RMS, which won't drive the 6S33S to full output, as for full output you need rather 50V RMS, or more.
Much care with fixed bias on a 6S33S, it can and has been done, but is not recommended by the manufacturer.
You have global feedback, which does not (always) go well with an interstage transformer. You may experience oscillation...
And then there is the driver stage with the ECC82. It will probably work, but won't do more than that. The ECC82 ain't a good tube, and the choice of the phase splitter is even worse. Expect high distortion from it!
Good luck, Erik
Ciao Stee,
I second Erik.
The basic problem when driving those lo voltage tubes is that you invariably need more B+ for the driver than for the power stage.
You did that ... but lost in the step down IT !
What about a single Hi Gain stage ?
http://www.dissident-audio.com/SE_845/Amp.gif
Yves.
I second Erik.
The basic problem when driving those lo voltage tubes is that you invariably need more B+ for the driver than for the power stage.
You did that ... but lost in the step down IT !
What about a single Hi Gain stage ?
http://www.dissident-audio.com/SE_845/Amp.gif
Yves.
Hi Stee
If you want to go PP in the driver stage you can use a differential amplifier loaded with an interstage transformer. The Raven by Lynn Olson is an example, but you want a 1+1:2 or 1+1:1+1 interstage transformer, and not the step down one used in the Raven.
Still have to look if you will have enough gain, though.
Erik
If you want to go PP in the driver stage you can use a differential amplifier loaded with an interstage transformer. The Raven by Lynn Olson is an example, but you want a 1+1:2 or 1+1:1+1 interstage transformer, and not the step down one used in the Raven.
Still have to look if you will have enough gain, though.
Erik
Jeb-D. said:
Why are you using an output stage to drive another output stage?
'cause it works well.
I'll second the idea to rid yourself of the step-down TX. A 1+1:1+1 IT with enough primary inductance to load a 6V6 pentode stage would be quite nice here. For that matter 6AQ5 or EL84 would do just as well. The 12AU7 is not worthy of designing around. 12BH7 at minimum, and there are many others better...
Phase split with a LTP twin triode( or perpahs pentodes, 6AU6 maybe? ).Also, mu of the 6C33 is more like 3. Cathode bias leaves need for a B+ supply to cover bias voltage, and plate-cathode voltage which is good for the driver stage too.
cheers,
Douglas
ray_moth said:
Actually, it's a self-adjusting paraphase, IIRC.
When a signal goes through the top tube, it'll be voltage-divided between the 470K resistor (between the top tube input line and the line to the second grid of the 12AU7) and the resistor from there to ground. This will induce a voltage on the grid, which will drive the second half of the 12AU7... causing output to the lower 6V6.
However- since there's also a resistor from the bottom 6V6 input BACK to that same node (going to the grid of the second 12AU7 stage), it'll act to CANCEL OUT a lot of the gain. In fact, the second 12AU7 will act almost like an op amp at unity gain... the gain of the second half of of the 12AU7 will be set to right at -1... in theory, it'll be in perfect gain balance with the top side, just in opposite polarity...
IIRC, H.H. Scott used this topology on some of their amps, back in the old days. Seemed to work well for them, AFAIK...
Regards,
Gordon.
I didn't notice there was a resistor between the right-hand grid of the ECC82 and ground - it looked like a grounded grid.
Hi Stee
Though the 12BH7 is similar to the ECC82, you can not just substitute them and keep the same values for the other components: the gain of both tubes is different and using same components will cause imbalances in the phase splitter.
I see you still have the global feedback loop which does not inspire very confidence due to possible oscillations.
As you already decided for a heavy and expensive IT on the EL84's, why you just don't go with another simples IT in front of that? I am thinking along the lines of the Karna
http://www.nutshellhifi.com/triode2.html
You could probably also get away with the first stage if you use triode strapped D3a's feeding into the IT (instead of the EL84).
Though the 12BH7 is similar to the ECC82, you can not just substitute them and keep the same values for the other components: the gain of both tubes is different and using same components will cause imbalances in the phase splitter.
I see you still have the global feedback loop which does not inspire very confidence due to possible oscillations.
As you already decided for a heavy and expensive IT on the EL84's, why you just don't go with another simples IT in front of that? I am thinking along the lines of the Karna
http://www.nutshellhifi.com/triode2.html
You could probably also get away with the first stage if you use triode strapped D3a's feeding into the IT (instead of the EL84).
Re: YES WRONG
hey-Hey!!!,
Try a long-tail-pair for the input stage. It will need a small negative supply and a CCS, but it will allow you to switch in any pin-compatible tube without wrecking the OP. It will also have very nice PSRR, though it isn't likely that you'll deliver much ripple to that stage.
cheers,
Douglas
Stee said:
hey-Hey!!!,
Try a long-tail-pair for the input stage. It will need a small negative supply and a CCS, but it will allow you to switch in any pin-compatible tube without wrecking the OP. It will also have very nice PSRR, though it isn't likely that you'll deliver much ripple to that stage.
cheers,
Douglas
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