Bogan DB-110

[J M Fahey]

Since the resistor goes to the CT of the tube heaters, and 4,5 are wired to X that resistor is in series with the two tube heaters. I figure it drops a volt and a half. Now sure why.

There may be a rationale for that in this as a PA amplifier, but as a guitar amplifier, there is no reason you can't simply shunt that resistor and have all 12AX7s running on straight 6.3vAC.

And we really should check it for open before we do that just for science.


R39 is part of the hum control in the same sense the tube heaters are part of it. I don't see how it would abate any hum, other than to lower the emissions of the cathodes.

Quite close.
300mA through 2.7 ohms will drop 0.81V .

**Maybe** they found that a colder cathode leads to less hiss, of some importance in Microphone preamps which have high sensitivity to cope with low signal levels.

"Shouldn´t" affect Hum, but I might be wrong.

Probably differences are measurable on a bench but not too noticeable by ear.

In any case, using filaments with straight 6.3V is the way God intended (ok, ok, RCA )

[Chuck H]

In any case, using filaments with straight 6.3V is the way God intended (ok, ok, RCA )

It's understandable. They kind of look the same.