OT Primary Doubt

[sluckey]

About the Footswitch, the DP uses a relay, but if going for a traditional Fender style I was checking for reference the 6G15 reverb unit which places it right after the reverb pan return. Now my question is where would be the best placement for the Ftswtch, before or after the 6.8K to ground (illustration below)

The two points you have indicated are the same point electrically. Absolutely no difference.

[Bombacaototal]

About the Footswitch, the DP uses a relay, but if going for a traditional Fender style I was checking for reference the 6G15 reverb unit which places it right after the reverb pan return. Now my question is where would be the best placement for the Ftswtch, before or after the 6.8K to ground (illustration below)

The two points you have indicated are the same point electrically. Absolutely no difference.

Thanks Sluckey, ah yes of course

[Bombacaototal]

One more thing I am scratching my head over is the reverb screen and the bias adjust. I think Zinky is using the transformer wires usually (fender blackface) used for a tube rectifier as the bias adjustment and the ones usually used for C- as the reverb screen?

If keeping the standard blackface C- circuit would there be an alternative way for the reverb screen, like maybe tapping it off the screens (Y) with maybe adding a resistor to ground, a dropping resistor and the 100uF/350V cap to try to get the VDC down to 232 (somewhat similar to how he did with the supply caps for the rest of the reverb circuit)?

[sluckey]

One more thing I am scratching my head over is the reverb screen and the bias adjust. I think Zinky is using the transformer wires usually (fender blackface) used for a tube rectifier as the bias adjustment and the ones usually used for C- as the reverb screen?

The reverb screen and bias circuits have nothing to do with each other. They both come from totally separate circuits. The brown wires on the OT are a separate low voltage winding, probably in the range of 24VAC. Fender blackface tube rectifier requires 5VAC. This separate winding is used to develop the low voltage relay power and the low voltage negative bias. The reverb screen voltage is derived from the centertap of the HV PT winding. Notice that the voltage is exactly half the voltage seen at point "Z"?

If keeping the standard blackface C- circuit would there be an alternative way for the reverb screen, like maybe tapping it off the screens (Y) with maybe adding a resistor to ground, a dropping resistor and the 100uF/350V cap to try to get the VDC down to 232 (somewhat similar to how he did with the supply caps for the rest of the reverb circuit)?

There are plenty of alternative ways to develop the screen voltage for the reverb driver. You could even just do it exactly like the 6G15, ie, screen and plate voltages come from the same B+ node. But Zinky designed this reverb driver to operate with a lower screen supply. This is consider a superior design as compared to the 6G15 circuit. This justifies the price tag.

[Bombacaototal]

One more thing I am scratching my head over is the reverb screen and the bias adjust. I think Zinky is using the transformer wires usually (fender blackface) used for a tube rectifier as the bias adjustment and the ones usually used for C- as the reverb screen?

The reverb screen and bias circuits have nothing to do with each other. They both come from totally separate circuits. The brown wires on the OT are a separate low voltage winding, probably in the range of 24VAC. Fender blackface tube rectifier requires 5VAC. This separate winding is used to develop the low voltage relay power and the low voltage negative bias. The reverb screen voltage is derived from the centertap of the HV PT winding. Notice that the voltage is exactly half the voltage seen at point "Z"?

If keeping the standard blackface C- circuit would there be an alternative way for the reverb screen, like maybe tapping it off the screens (Y) with maybe adding a resistor to ground, a dropping resistor and the 100uF/350V cap to try to get the VDC down to 232 (somewhat similar to how he did with the supply caps for the rest of the reverb circuit)?

There are plenty of alternative ways to develop the screen voltage for the reverb driver. You could even just do it exactly like the 6G15, ie, screen and plate voltages come from the same B+ node. But Zinky designed this reverb driver to operate with a lower screen supply. This is consider a superior design as compared to the 6G15 circuit. This justifies the price tag.

Thanks a bunch Sluckey! It indeed makes sense now. So instead of grounding the center tap HV PT winding (Red/Yellow) he used it for the reverb screen supply! I will follow the same approach but instead of using the borwn wires on the OT I can still use the PT Red/Blue for C- like a Fender Blackface

Would the 8200pF caps from both red PT cables be necessary in this application?

[sluckey]

The Dual Pro PT requires a FWB rectifier. You cannot use a typical blackface era PT with this power supply circuit! You will have to build the power supply exactly as shown or totally redesign the entire power supply to fit the PT you have. If you decide to redesign you will need a separate low voltage PT for the relay circuits.

[Bombacaototal]

The Dual Pro PT requires a FWB rectifier. You cannot use a typical blackface era PT with this power supply circuit! You will have to build the power supply exactly as shown or totally redesign the entire power supply to fit the PT you have. If you decide to redesign you will need a separate low voltage PT for the relay circuits.

Got it! Thanks again for helping out. I was thinking of replacing the blackface reverb by this one on a build with solid state rectifier. Might be easier to reconstruct the power supply to get the required voltage!

[Bombacaototal]

Sluckey, I was thinking of something like the attached for the reverb screen and I will not need the relay. Given the reverb needs 195VDC and the Verb Screen 232VDC and the anode before is 392VDC is there any reason why the attached would not work?

The original Zinky design has a 470K to fround before the "V" (reverb anode) but maybe this ground would need to be moved right before the verb screen on this new configuration

[Bombacaototal]

*double*

[sluckey]

Should work. You don't need the "red resistor ?" to ground though.

[Bombacaototal]

Should work. You don't need the "red resistor ?" to ground though.

Perfect, many thanks for the help! I really appreciate it

Just curious if is there any benefits in doing like Zinky did on the DP versus the drawing I did. It looks so much more complicated his approach in my opinion

[Bombacaototal]

Just one more question on this specific amp. I am wondering what is the low impedance side of the circuit relating to the .1uF and .68uF caps highlighted below.

I would assume the .1uF will be the tube PIN2 side and the .68uF will be MIX pot side?

I am particularly interested in these are for the placement of the outside foil of the capacitors

[sluckey]

I would say the left side of both of those caps is the low z side.

[Bombacaototal]

I would say the left side of both of those caps is the low z side.

Many thanks for the feedback!

[Bombacaototal]

Just one question about grounding. Should the power supply cap (100uF/350V) of the Reverb Screens (470R off the 6V6 PIN4) be grounded together with the amp power tubes supply cap ground or have a separate ground of its own or yet (pobably not a good idea) grounded with the pre-amp ground?

My original idea was to ground it along with the power tubes supply cap ground...but I am concerned with ground loops as the original Fender amp has a fair bit...