Question about VTV 6SN7 Schematic

[mf2]

A friend and I are building line stages based on VTV's 6SN7 schematic. One question we both have is what is the purpose of R6, the 100K resistor in the power supply?

We have split the power supply after C1, into two chokes, ect. Is the R6 to R7 connection necessary, if yes, where does it go when the power supply is split into left and right channels? What value would be required?

Thanks!

[dsavitsk]

It, in conjunction with R7, creates a voltage divider to bias the heaters up a few volts. Probably not necessary here -- try it and see.

[P.Lacombe]

This arrangement is preferable if any of the tubes are used in cathode-follower configuration, in order to limit cathode-heater voltage, which can cause noise (at very low level, but...)

PL.

[dsavitsk]

Oh, and if there are limits of heater to cathode voltage that might be exceeded, you'll need a similar arrangement -- a likely scenario given the high B+. So maybe you should post the rest of the schematic.

[nerdorama]

R6 & R7 form a voltage divider which elevates the heaters to a DC offset above the cathode voltage. The purpose is to reverse bias the cathode to heater in order to minimize hum induced from the heater to the cathode. You can read RDH4 section 12.10(G).

Regards,
John

[mf2]

Thank you for the responses! I should have noted there is an error in the voltage specified in the schematic - it is 330V, not 370V as indicated.

I have posted the rest of the schematic - courtesy of northbirdten's website.

[ArtG]

The designers primary purpose is noted in the posts above, however the resistor could also could serve a more subtle function. In the event that R3 would fail open, it would serve as a backup "bleeder" to discharge the power supply, when powering off. A good safety design, in a supply with considerable energy storage!