[dconant]

No I'm not sure where you are going other than check my work which I have been doing. Did you notice I said there is a 60 volt drop across the field coil? Is this normal? I disconnected 14X and still at 235 volts on the B+ side of that resistor. Also when I did my initial IF alignment I could not get 1XC to peak. It did get louder as I screwed it in but it never dropped off and it is almost all the way in now. Does this mean anything?

[dconant]

I got my signal generator out to check the audio section and found the plate of the phase inverter volume was somewhat lower than the grid. Is this normal?

[RodB]

Yes, 60v drop on the fc is normal. 660 ohm field coil with about 110-120 ma is 60-70 volts. What we should look for is a reason B+ is below what it should be. It may be a normal thing for this radio but it should be looked at.

Check the grid cap voltage of the 6K7 IF tube, should get a few volts negative and a few more when a station is tuned in. This would be the AVC working. It's also possible that if it is very negative then it will cut off the tube gain and result in low volume.

[RodB]

Now you're getting into theory. Phase inverters typically have a gain of one. This is to make the signal at the plate equal to the signal at the cathode, but 180 degrees out of phase. You'll notice the plate signal is fed to one output tube and the cathode signal (thus called cathode follower) is fed to the other output tube. This is the push and pull, one tube is conducting the other is cut off, then vice versa. Now, that said, the signal amplitude at the plate should be pretty close to the grid signal and cathode signal amplitude.

[dconant]

The grid of the 6K7 is -2.5 with antenna disconnected and connected tuned to a station. No change tuned or not. I understand the AVC cuts off strong signal and lets more through for weaker signals. But I don't understand electrically how the AVC circuit works.

BTW thank you for sticking with me.

[RodB]

We'll check the AVC later. It seems to be inactive. What is the B+ voltage at the first two filter caps 96 and 97?

[dconant]

97 is 310 and 96 is 290. I used 8.2 e caps.

[RodB]

The B+ voltage is low right from the transformer, so I have to ask are you using a dim bulb to limit the power? Second question: Can you verify that neither filter cap negative lead is grounded to the chassis? Have you noticed if the power transformer is very warm or hot? Is there a 5X4 rectifier tube in the power supply or is it a substitute? Try replacing the 5X4 if possible.

[morzh]

Also, even if using 110V (from a Variac), i/o 115V, that alone would result in 15V or so reduction.
In fact the readings should be even a bit higher, if accounted for using a modern DMM vs the old type meter.

[dconant]

No dim bulb just a isolation transformer. Input voltage was 113 now set to 118. Neither cap is grounded but connected to center tap of HV. Transformer does not get hot. I have seen most 120 degrees. Running with 5X4. I don't have another. With 118 volts in caps are at 325 and 295. Didn't notice any volume change. All DC voltages I report are from VTVM (RCA WV77E). Should I get another 5X4?

[morzh]

How accurate your VTVM?
Have you tested the 5X4 (simple Good/Bad, they also call it "English")?

[RodB]

The purpose of this exercise is to eliminate the B+ as a cause for the low volume. At this point here's what I would do: I have several bad octal tubes in my "bad tube" box specifically for this purpose. I remove all the glass from the base of a tube then solder in two 1N4007 diodes in place of the rectifier diodes. Now I have a substitute 5X4. It's quick and simple. But, I m thinking the volume trouble may be elsewhere.

[morzh]

I agree with Rod, that the volume trouble is probably elsewhere.

One has to be careful with diode sub: you will have two processes that increase the voltage: 1) diodes have almost no voltage loss, so your rectified voltage will rise (and quickly so, so you might have quite a bit of inrush current, if turned on at the peak), 2) also due to the fast rise, your other tubes do not come on-line as loads, and so the voltage for a few seconds will not create any load current and stay at its peak.
If your capacitors are not 500V WV, you will be over-stressing them.

[dconant]

I don't know the accuracy of the VTVM. I tested the 5X4 again and it reads well into the good section. Digital meter reads 345 and 325. I am not convinced the low voltage is the problem but it is possible. Please tell me how to wire diodes and I will make one.

[morzh]

Well, digital meter reading is pretty close to where it should be.
I suggest you use it for consistency.
This kind of confirms, you should look elsewhere.

I suggest an experiment:

Put the volume pot to the max, while tuned at a known station that will not ruin your speaker or your ears. It should be loud enough but to the point where you can tell for it to become less loud, or more loud.
Also, have your tone control switch to the "Middle" position (where it does not affect the sound). This is the one in the middle, where nothing is connected to the the contact.

Then disconnect both C61 and C62 from the pot, and connect them together.
See if the volume has increased.
This will tell us if your volume ct is involved at all in the situation.

While at it, measure your pot to conform to what the sch says it should be.