[MrFixr55]

Hi Lead Fingers,

First off a beautiful job on what looks to have been a clean radio to begin with.

This is essentially cathode biased, but a little strange. For 2 42s or 6F6s in push pull class A or AB1, the cathode resistor is 340 Ohms. This may explain the 136 Ohms and the 205 Ohms in total. The strange part of this is that the difference between cathodes and grids is still only 205 ohms. If you add the 130 ohms between the HV secondary center tap and the 205 ohms, you get the required 340 ohms. Problem is that the extra 130 ohms is in the wrong place to add to the cathode resistor. I think that the important thing would be to measure between the cathodes and the driver transformer secondary center tap, and you have only -4.7V. It should be a lot more negative. Is the radio working? Is the speaker connected? Are the transformers good? You may be drawing too small a current. I would expect a grid bias between -16V and -24V depending on plate voltage. The more current, the more the voltage drop across the 205 Ohm resistor.

It is very important to not run a pentode with power connected to the screen but not the plate. Doing so will cause the screen to glow incandescent, then burn up, shorting the tube. This is visible as a bright light from the top of the tube that is not coming from the heater.

One possibility for where the r136 ohm resistor is placed is create a voltage difference that would prevent current flow from the cathode to the heater. This is a practice done with the introduction of the RCA 27 triode, the first indirectly heated cathode outside of the Western Electric / Bell System.

When 6V tubes were first introduced, around the time that this radio was introduced, the tubes were designed for car radios and rated for DC. Maybe this is an early set and they eliminated it in later models as they found that these tubes work just fine on AC without this scheme. Just my guess.