Old Sony SE OPT's /w 600r tap... cathode feedback maybe?

[aletheian]

I have a couple of OPT's from an old Sony reel to reel that drove 6AQ5's in SE config. They have the standard 8r secondaries, but also 600r windings that drove a line out (presumably).

Anyway, they look like good quality trannys, so I was considering a pair of SE monoblocs for listening at my computer, but didn't know if I could make use of the 600r taps. I perhaps cathode feedback?

[rdf]

I'm on the watch for something similar to pop up again on E-bay. Snoozed through the last one. The experiment will be to try the extra secondary winding - - in series with the output tube grid.

[Yvesm]

Hi !

Assuming primary is 6K, Z ratio would be 10 and turns ratio 3.16.

Says 30%. Good for use in Ultra Linear configuration.

Yves.

[aletheian]

Originally posted by rdf
I'm on the watch for something similar to pop up again on E-bay. Snoozed through the last one. The experiment will be to try the extra secondary winding - - in series with the output tube grid.

Huh?! What kind of evil plan are you scheming there?

[rdf]

Evil or daft , you decide after reading my reasoning.

Feedback's effectiveness partially depends on the linearity of the return path. The best way for me to visualize this is with an extreme or limiting example. Imagine the general case of returning the feedback to the inverting node through a diode. The gain will be reduced but the feedback circuit will also generate new distortion on the output. Returning to reality, I think it's correct to say all feedback loops do this to some extent because no matter where you return the correction it's never in a perfectly linear relationship to the output. In the case of cathode feedback the cathode to plate transfer function is slightly different than that from grid to plate so the 'correction' won't perfectly follow theory. On balance it still reduces distortion on the output but at the expense of that well known mechanism whereby low order harmonic components are supressed at the expense of generating lower levels of higher harmonics not originally present.

A separate secondary winding provides an opportunity to apply the corrective signal directly to the grid, the same terminal accepting the input signal. Use a 600 ohm grid stopper and strap the winding across it. If I understand the voltage phases correctly, doing so also applies an opposing voltage to that of the driver plate. This should mean the driver sees a higher impedance and though you wouldn't measure lower distortion interstage - because it's now the sum of driver signal and feedback signal - the driver should actually be operating more linearly. Finally, 600 ohms is nothing in a grid circuit. There should be plenty of latitude to adjust the feedback winding's termination to optimize the correction and flatten frequency response above the audio band.

One last thought, while it's true that the signal on the the 600 ohm winding won't be identical to that on the 8 ohm tap, that's a constant no matter where you tie it anyway. That 'feedback loop distortion' can't be corrected. And now you see why I want to try it with cheap trannies too.

[Ciscokid]

Hi,
Here is a picture of my 6aq5 se stereo amp using the same opt's as you have. I did not use the 600r windings, though I have thought about using them to drive a subwoofer. Currently, I am using this amp at the office with a MAC as the source.



Check out my web site if you want more details of this amp.
Regards,
Danny

Here is a link to a post by member Planet10 concerning these OPTs.

Planet10 Post

dg

[aletheian]

Originally posted by rdf
Evil or daft , you decide after reading my reasoning.

Feedback's effectiveness partially depends on the linearity of the return path. The best way for me to visualize this is with an extreme or limiting example. Imagine the general case of returning the feedback to the inverting node through a diode. The gain will be reduced but the feedback circuit will also generate new distortion on the output. Returning to reality, I think it's correct to say all feedback loops do this to some extent because no matter where you return the correction it's never in a perfectly linear relationship to the output. In the case of cathode feedback the cathode to plate transfer function is slightly different than that from grid to plate so the 'correction' won't perfectly follow theory. On balance it still reduces distortion on the output but at the expense of that well known mechanism whereby low order harmonic components are supressed at the expense of generating lower levels of higher harmonics not originally present.

A separate secondary winding provides an opportunity to apply the corrective signal directly to the grid, the same terminal accepting the input signal. Use a 600 ohm grid stopper and strap the winding across it. If I understand the voltage phases correctly, doing so also applies an opposing voltage to that of the driver plate. This should mean the driver sees a higher impedance and though you wouldn't measure lower distortion interstage - because it's now the sum of driver signal and feedback signal - the driver should actually be operating more linearly. Finally, 600 ohms is nothing in a grid circuit. There should be plenty of latitude to adjust the feedback winding's termination to optimize the correction and flatten frequency response above the audio band.

One last thought, while it's true that the signal on the the 600 ohm winding won't be identical to that on the 8 ohm tap, that's a constant no matter where you tie it anyway. That 'feedback loop distortion' can't be corrected. And now you see why I want to try it with cheap trannies too.

Wow... you lost me three times in there, but i think I see what you are shooting for. I'd be very interested to read about the results.

[aletheian]

Originally posted by Ciscokid
Hi,
Here is a picture of my 6aq5 se stereo amp using the same opt's as you have. I did not use the 600r windings, though I have thought about using them to drive a subwoofer. Currently, I am using this amp at the office with a MAC as the source.

Check out my web site if you want more details of this amp.
Regards,
Danny

AMAZING! That is incredibly helpful. I hunted down the link to the auction for those trannys and there wer VERY detailed specs, and the diagrams on your site will be invaluable. I even have that same power transformer (the whole power board actually), but i have been too lazy trace out the circuit.

If i may ask you one more question... what is the purpose of the 12BH7 in the power supply?

[Dave Cigna]

I sure does beg to be tried as cathode feedback, doesn't it? The 340 ohm DCR of the 600 winding might turn out to be about right to bias a 6V6/6AQ5. Expect the DCR to drop a little as the copper wire warms up.

-- Dave

[Zen Mod]

Originally posted by aletheian





If i may ask you one more question... what is the purpose of the 12BH7 in the power supply?

if memory serves me....maybe I even have original schematic for that RtR...12BH7 is in oscillator circuit......