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Philco 38-2 Low Volume - Printable Version

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RE: Philco 38-2 Low Volume - dconant - 11-13-2024

It has but not RF as I don't have the dial yet.

RE: Philco 38-2 Low Volume - morzh - 11-13-2024

RF does not matter: IF does. This RF transformer is RF; if not aligned, it will attenuate the signal.
Make sure it is peaked, both sections.
And, then try to remove the tube 6H6 and see if it affects the loudness in the tracer.
You could also try to increase C45 to 1uF, see if it makes things better. The time constant of this filter is in audio frequency. Not sure why.

RE: Philco 38-2 Low Volume - dconant - 11-13-2024

Using the tracer, when I pull the 6H6 it gets a little louder on the 6R7. Didn't seem to change at all on the 6K7 tube.

RE: Philco 38-2 Low Volume - MrFixr55 - 11-13-2024

Did you have a cap in series with the signal tracer probe? Is there a diode in series with the probe? If yes to both then you may have to turn down the gain of the tracer. If no cap, then you may have been overdriving the tracer with B+

Ohm the secondary. It should be quite low, about 8 Ohm. There is a good possibility that it is open. If you connect the tracer to either diode plate of the detector / 1st AF Amp Tube (6R7), i suspect that the sound level will be low. Isolating the ground on the probe with a large cap (like 0.1uF, connect ground side of the probe to the green wire on the IF Out trans and probe the brown wire with a diode in the circuit. The signal should be quite loud.

Note that there are 2 100pF caps, 39A and 39B, each between ground and either side of R43. These are likely mica and, although rare for them to fail, it may still be possible. Excessive leakage of either cap will definitely lower the volume and AVC signal.

Hope this helps.

RE: Philco 38-2 Low Volume - MrFixr55 - 11-13-2024

C45 serves as a decoupling cap for the B+ for the IF Stage. If all components test good, revisit the IF and Local Osc alignment. Remember that the oscillator must be 470KHz above the desired station. If this cannot be adjusted to be within spec, you may have to align the IF not to 470 KHz but to the difference that you actually get between the local oscillator frequency and the station frequency.

RE: Philco 38-2 Low Volume - dconant - 11-13-2024

MrFixr55 I am using the second schematic, the one with the X parts as that is my radio. The 39A and B are 16X, containing 110pf caps that are in a bakelite block. I had already changed them with silver micas. Having to use two different schematics sure makes this harder. Some sections are on one and some the other.

The coils in both IFs are all good. I had checked them a while ago.

No caps in series with probes. I will try again with caps. I was told a while ago there were blocking caps in the tracer. Not sure about the ground though.

I don't know how to measure the difference frequency. I don't have a scope so the best I might do is a frequency counter but I would not know how to do that either.

As for the non peaking compensator I'm wondering if the internal cap might be bad. The schematic does not list the value for them except for 2XD (110pf) which I changed.

If RF alignment is off could that render the AVC inactive? I'm wondering if I should put the radio aside until I get my dial and then I can do the RF alignment.

RE: Philco 38-2 Low Volume - morzh - 11-13-2024

BTW, when you do all that, is your magnetic tuning ON or OFF?
Should be OFF.

RE: Philco 38-2 Low Volume - dconant - 11-14-2024

Yes it is off.

RE: Philco 38-2 Low Volume - dconant - 11-14-2024

I watched a video on IF transformers. The guy said at one point if the peak is still increasing while turning in you need less capacitance. For that compensator I have that won't peak I was thinking of adding a couple of PFs in series with what is there. What do we think of that?

RE: Philco 38-2 Low Volume - morzh - 11-14-2024

I do not know what compensator you mean, as the Rider's references are different from yours.
But when you add capacitance in series, the result is, you total capacitance is always less than the smallest of the two. Not larger.

Also, coming back to my question about the IF alignment: if you could not peak an IF part, you have not aligned it yet.

RE: Philco 38-2 Low Volume - dconant - 11-14-2024

So if I can't peak a trimmer/compensator (2XA) how would I fix that. Please see the last page of https://philcoradio.com/library/download/service%20info/wiring%20diagrams/vol2/split/Part34-Philco%20Wiring%20Diagrams%20Vol.%202.pdf The parts of that schematic all end in X. That schematic is my chassis.

RE: Philco 38-2 Low Volume - dconant - 11-14-2024

I added a 500pf in series with the internal cap, no change then I noticed number on the side of the block holding 2XA and 2XB. It said 110 so I though maybe this is the value of the internal cap so I disconnected the internal and put in a 110. Now the trimmer peaks and the volume is what it should be. I'm going to change the 2XB cap. The 2XC cap has a 160 number which I assume will be 160pf. Finally getting somewhere.

Now to figure out why the AVC voltage is not changing. Is the 6R7 grid the proper place to measure that. if I measure the grid of the 6A8 tube the voltage varies when going off and on stations.

RE: Philco 38-2 Low Volume - morzh - 11-14-2024

So you have Run 2? Are you sure?

So, it has variable slug instead of the padder. Is this what you have? You move the slug and not trimming the variable cap?

If this is the case, you simply do not know, whether you cannot get the inductance low enough or high enough to peak. So you need to see, whether the slug goes in the coil, or out of it. If it goes in, while the signal is increasing, then you need to increase the cap. In this case you PARALLEL the small cap (5-10% of the existing cap value) across the cap that is there (again, the cap is not variable if you have that Run 2).
If however your slug is going out of he coil when you are peaking, while the signal is increasing, you need to DECREASE your cap. This is achieved serializing another cap with the existing one. The cap has to be about 10x larger than existing one: this way you will reduce the capacitance by about 10% or so.

RE: Philco 38-2 Low Volume - dconant - 11-15-2024

As for having run 2, I am 99 3/4 percent sure as the run 2 schematic matches my chassis part for part. I have found no differences.

I have variable slugs not padders.

RE: Philco 38-2 Low Volume - morzh - 11-15-2024

Well then, if you could not peak on the way in, then use a 4-5 pF cap in parallel.
Try to align IF before proceeding.