[Alex Pogossov]

"Patrick Turner" wrote in message
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In most old radios with DC flow across the volume control pot track
the adjustment of the volume is often very noisy after the pot has
aged a few years.

So instead of the conventional arrangements put forward by RDH and
most others to avoid parts costs I will have the last IFT coil biased
at say +50V at one end, and the live end goes to a triode grid of 1/2
12AU7 CF buffer to remove any loading effect of diode detection on the
last IFT LC. Then I use Ge diode feeding RC circuit, and this can
directly feed second 1/2 12AU7 CF buffer and then usual CR coupling to
any a volume control and while employing time passive poles to give
say -3dB at 30Hz before any power amp which has NFB. I often add in
another 12AU7 gain stage for tone control to boost/cut treble; bass in
AM is usually OK.

Alex:
Is adding two extra tubes a reasonable "mod"? It is the radio redesign. If
one wants to go that far, op-amps would be far better. Take TLE2074. With
10MHz bandwidth and 45V/us slew rate it can work as IF amplifier to increase
sensitivity, tone control, buffer, AGC integrator, etc.

And after that why do you need to retain a lousy tube amp? Why not to use an
IC? All the radio can be powered from a 6.3V winding with a bipolar voltage
doubler (four caps, four 1N4004 diodes)

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I like to use paralleled 12AX7 as V1 and EL34 in triode as V2 for the
audio amp and with 12dB global NFB.
This works far better than anything with 6V6 or EL84 etc.

Alex:
Works better in which respect? EL34 takes as many amps for its heater as the
whole original radio circuit. What about the poor lousy power transformer?