Long title but I hope it will provide helpful for future searches.
So what am I asking?
I've been reading a bit on UL and Schade feedback and in particular “An Ultra Linear Amplifier feedback Including UL” by Hafler and Keros,
And “ULTRA-LINEAR DISTRIBUTED LOAD AUDIO AMPLIFIERS”
ultra-linear
I'm also interested in trying transformer cathode feedback
In looking at this transformer, last page bottom right :
http://www.the-planet.org/pdf/transformer.pdf
… it seems to me that the use of the separate winding for Screen taps is great for tubes that have much lower screen voltages wrt plate voltage. However, I’m confused by the alternate use for cathode feedback.
Wouldn’t that provide an awfully lot of cathode feedback (40% of plate voltage) ?
Most of the commercial schematics I’ve seen with cathode feedback use the output windings with the 4 ohm tap tied to ground and one cathode to the common terminal, and the other cathode to the 16 ohm tap?
I’m interested in getting Edcor to make an opt for 6P1P/-EV and 6AQ5. I expect this may also be suitable for 6V6 and other derivatives. The smallest transformer they currently offer is a 25W one and a bit big for these tubes (at least the smaller output ones). One possibility would be to make it compatible with the 6BQ5, but there are more compromises to be made in this case.
If the compromises become to great I’d leave out the 6BQ5, but I think setting it as the top end would make for a nice transformer with good versatility although it would add a slight cost compared to leaving this out.
I figure with the 6BQ5 I would need to specify 17W, and without it 10W, presuming response at rated output from 20Hz to 20KHz, UL 40%taps, 4, 8, 16 ohm output taps.
Another fly in the ointment would be the impedance. 6BQ5 looks like it is best at 8K p-p, and the 6AQ5, 12AB5, 6P1P/-EV are normally specified at 10K and it appears to me that 12K would be even better if one were pushing lower distortion with a slight trade off in lower output power.
I considered a separate UL tap like the A-440 as the 6P1P/-EV is specified for 250V max screen, but expect this would really make the transformer more difficult as it would effectively add an additional 40% secondary winding and it’s associated complexity in interleave and therefore really drive the cost up.
Comments?
Is anyone else interested in 10-15W transformers? Or is this just the “rework an old console” level?
I’ve got Hammond 1608s/1609s but I’m not completely satisfied with them. Too much base extension.
The CXPP10-8-10K transformers are nice and greatly exceeded my expectations, but I’d like to get something at the next level.
So what am I asking?
I've been reading a bit on UL and Schade feedback and in particular “An Ultra Linear Amplifier feedback Including UL” by Hafler and Keros,
And “ULTRA-LINEAR DISTRIBUTED LOAD AUDIO AMPLIFIERS”
ultra-linear
I'm also interested in trying transformer cathode feedback
In looking at this transformer, last page bottom right :
http://www.the-planet.org/pdf/transformer.pdf
… it seems to me that the use of the separate winding for Screen taps is great for tubes that have much lower screen voltages wrt plate voltage. However, I’m confused by the alternate use for cathode feedback.
Wouldn’t that provide an awfully lot of cathode feedback (40% of plate voltage) ?
Most of the commercial schematics I’ve seen with cathode feedback use the output windings with the 4 ohm tap tied to ground and one cathode to the common terminal, and the other cathode to the 16 ohm tap?
I’m interested in getting Edcor to make an opt for 6P1P/-EV and 6AQ5. I expect this may also be suitable for 6V6 and other derivatives. The smallest transformer they currently offer is a 25W one and a bit big for these tubes (at least the smaller output ones). One possibility would be to make it compatible with the 6BQ5, but there are more compromises to be made in this case.
If the compromises become to great I’d leave out the 6BQ5, but I think setting it as the top end would make for a nice transformer with good versatility although it would add a slight cost compared to leaving this out.
I figure with the 6BQ5 I would need to specify 17W, and without it 10W, presuming response at rated output from 20Hz to 20KHz, UL 40%taps, 4, 8, 16 ohm output taps.
Another fly in the ointment would be the impedance. 6BQ5 looks like it is best at 8K p-p, and the 6AQ5, 12AB5, 6P1P/-EV are normally specified at 10K and it appears to me that 12K would be even better if one were pushing lower distortion with a slight trade off in lower output power.
I considered a separate UL tap like the A-440 as the 6P1P/-EV is specified for 250V max screen, but expect this would really make the transformer more difficult as it would effectively add an additional 40% secondary winding and it’s associated complexity in interleave and therefore really drive the cost up.
Comments?
Is anyone else interested in 10-15W transformers? Or is this just the “rework an old console” level?
I’ve got Hammond 1608s/1609s but I’m not completely satisfied with them. Too much base extension.
The CXPP10-8-10K transformers are nice and greatly exceeded my expectations, but I’d like to get something at the next level.
