I was looking for a push pull 6V6 schematic to build and came across this one:
http://diyaudioprojects.com/Schemat...ier/6SL7-6V6-Push-Pull-Tube-Amp-Schematic.png
The 6SL7 phase inverter doesn't look right to me. I looks like the 100R resistor connects the cathodes together, but doesn't go to ground. Shouldn't the cathodes connect together and then the 100R resistor connects from them to ground (in parallel with the 100uF, 16v cap)? Or am I missing something?
thanks.
http://diyaudioprojects.com/Schemat...ier/6SL7-6V6-Push-Pull-Tube-Amp-Schematic.png
The 6SL7 phase inverter doesn't look right to me. I looks like the 100R resistor connects the cathodes together, but doesn't go to ground. Shouldn't the cathodes connect together and then the 100R resistor connects from them to ground (in parallel with the 100uF, 16v cap)? Or am I missing something?
thanks.
See the original here: Dynaco Push-Pull EL84/6BQ5 or 6V6/6AQ5 Tube Amp Schematic
This is correct as drawn, but no question it is a slightly odd implementation of a paraphase inverter/driver.. (Not a floating paraphase since the cathodes are independent of each other for AC signals - more similar in terms of AC performance to the implementation that HH Scott used in their amps prior to going to a cathodyne inverter) David Hafler and company was noted for the economy of his designs and that is what has been done here, quite clever.. Study it a bit more and it should be obvious as to what is going on.. I will hint that the feedback resistor provides cathode bias to both halves of the 6SL7, and the 100uF capacitor forces the cathode of the inverter section of the paraphase to be at AC ground, the 100 ohm resistor is also part of the feedback network and prevents the decoupling cap from seeing the other cathode which is the actual feedback node. (And as a side effect provides a small amount of additional bias to that stage) Every part here performs multiple functions, a very studied and economical design at a time when parts and tubes were relatively expensive.
This is correct as drawn, but no question it is a slightly odd implementation of a paraphase inverter/driver.. (Not a floating paraphase since the cathodes are independent of each other for AC signals - more similar in terms of AC performance to the implementation that HH Scott used in their amps prior to going to a cathodyne inverter) David Hafler and company was noted for the economy of his designs and that is what has been done here, quite clever.. Study it a bit more and it should be obvious as to what is going on.. I will hint that the feedback resistor provides cathode bias to both halves of the 6SL7, and the 100uF capacitor forces the cathode of the inverter section of the paraphase to be at AC ground, the 100 ohm resistor is also part of the feedback network and prevents the decoupling cap from seeing the other cathode which is the actual feedback node. (And as a side effect provides a small amount of additional bias to that stage) Every part here performs multiple functions, a very studied and economical design at a time when parts and tubes were relatively expensive.
Kevin,
I have reservations about the 470 KOhm grid to ground resistance at the circuit's I/P. That will combine with the large CMiller of the triode to roll HF info. off.
I have reservations about the 470 KOhm grid to ground resistance at the circuit's I/P. That will combine with the large CMiller of the triode to roll HF info. off.
Hi Eli,
That resistor could be replaced by a lower value - I generally use 100K, but bear in mind it appears in parallel with the source impedance of whatever is driving it which in most cases should be pretty low.
That resistor could be replaced by a lower value - I generally use 100K, but bear in mind it appears in parallel with the source impedance of whatever is driving it which in most cases should be pretty low.
Thanks to all who replied.
I've mostly build guitar amps, so that particular PI looked odd to me. Thanks for the clarification.
I've mostly build guitar amps, so that particular PI looked odd to me. Thanks for the clarification.
I have built this amp and it sounds quite nice. I used Hammond organ opt iron which really surprised me at how good it sounded.
It's just a basic floating paraphase splitter slightly modded to accept a gNFB connection. The cathodes of the 6SL7 do go to ground, through the secondary of the OPT with Rf doing double duty: a gNFB voltage divider + cathode bias resistor.
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