I think that halving the voltages would be sum-optimal, although 6922s don't mind low voltages too much. The performance, especially the THD, will likely suffer.
You can buy 120VAC Triad transformers really cheap. You would only need two of them to provide +/- 100V and the +200V could be had from a voltage doubler. You can even use VR tubes to regulate. 0B2 will regulate at about 108V. Close enough for this amp.
You can buy 120VAC Triad transformers really cheap. You would only need two of them to provide +/- 100V and the +200V could be had from a voltage doubler. You can even use VR tubes to regulate. 0B2 will regulate at about 108V. Close enough for this amp.
Hmmm, I think I can make do using multiple surplus transformers.
I was planning to use CLC regulation. Is that OK?
And what kind of transformer current draw would I be looking at for 2 channels (3 tubes)?
Lastly, if I only get close with voltages, which would be better: under (-85, +85, +170) or over (-115, +115, +230)?
I was planning to use CLC regulation. Is that OK?
And what kind of transformer current draw would I be looking at for 2 channels (3 tubes)?
Lastly, if I only get close with voltages, which would be better: under (-85, +85, +170) or over (-115, +115, +230)?
I'll post the diagram again with voltages and currents, but as I recall each tube is running a little over 2mA. This would be 12mA total, but this is divided up over three supplies, so each supply doesn't have to supply very much current.
Volume pot goes right at the input where the 1M grid leak resistor is located. In fact, you can remove the grid leak resistor. It was just a place holder in the diagram. I'll add this when I re-post later.
Do you mean the voltage of the transformer secondary? If so, then choose the 115V secondaries. This will rectify to a little over 160V (probably more given the light load on the transformers) giving you enough drop to use a choke and some resistors in a multi-stage filter that will be quite good and will lite the VR tubes.
+200V can come from a full-wave voltage doubler on the +100V supply and two VR tubes in series. Four glowing VR tubes altogether, two small transformers, some chokes and a few resistors. Relatively painless!!
If you want to get more sophisticated you can put tube CCSs on the CFs. This will reduce their contribution to the distortion. Many diyers on this forum would recommend this, but then that's a total of 5 tubes instead of 3.
Volume pot goes right at the input where the 1M grid leak resistor is located. In fact, you can remove the grid leak resistor. It was just a place holder in the diagram. I'll add this when I re-post later.
Do you mean the voltage of the transformer secondary? If so, then choose the 115V secondaries. This will rectify to a little over 160V (probably more given the light load on the transformers) giving you enough drop to use a choke and some resistors in a multi-stage filter that will be quite good and will lite the VR tubes.
+200V can come from a full-wave voltage doubler on the +100V supply and two VR tubes in series. Four glowing VR tubes altogether, two small transformers, some chokes and a few resistors. Relatively painless!!
If you want to get more sophisticated you can put tube CCSs on the CFs. This will reduce their contribution to the distortion. Many diyers on this forum would recommend this, but then that's a total of 5 tubes instead of 3.
As promised, here's the new diagram with volume control and bias currents.
I forgot to talk about the gain. The gain of each leg is less than 1, about 0.9. That is, measuring from either the + or - outputs to ground the gain is 0.9.
But, the gain when measured between the +/- outputs is twice that, or 1.8.
So, if your balanced amp needs 1Vp balanced signal input between the rails, then this guy will easily do the trick for less than 1Vp into the preamp.
So you want a tone control section? That can be switched in or out?
I forgot to talk about the gain. The gain of each leg is less than 1, about 0.9. That is, measuring from either the + or - outputs to ground the gain is 0.9.
But, the gain when measured between the +/- outputs is twice that, or 1.8.
So, if your balanced amp needs 1Vp balanced signal input between the rails, then this guy will easily do the trick for less than 1Vp into the preamp.
So you want a tone control section?
That can be switched in or out?Attachments
You're right Frank, I forgot to add the VR tube currents, say 10mA each.
The way this actually breaks down is, preamp only, both channels:
+200V - 8.6mA
+100V - 4.5mA
-100V - 8.8mA
or thereabouts.
So, add 10mA to each one for the VR tube and everything will regulate ok.
+200V - 18.6mA
+100V - 14.5mA
-100V - 18.8mA
Can be done with really simple supplies.
The way this actually breaks down is, preamp only, both channels:
+200V - 8.6mA
+100V - 4.5mA
-100V - 8.8mA
or thereabouts.
So, add 10mA to each one for the VR tube and everything will regulate ok.
+200V - 18.6mA
+100V - 14.5mA
-100V - 18.8mA
Can be done with really simple supplies.
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