[dconant]

Morzh I didn't see your post before I replied to RodB's post. My caps are 500V. Will bringing up on variac slowly help?

[MrFixr55]

If you sub diodes for the 5X4, then yes, the variac will allow a controlled buildup of B+. There is a whole theory of cathode stripping when B+ comes on strong immediately, but most rectifiers like 5X4s, 5Y3s etc. come up before the heaters of tubes like 6K7, 6F6, etc. come up so I would not worry about it.

However, you raise 2 points that tell me that your issue is not B+ or audio:
1. That in peaking, you had too totally crank down on a trimmer cap and volume increased but did not pass through a peak.
2. That the AVC at the IF tube grid was only -2.5V. This tells me that the issue is in the "radio" section and not the Amp or PS section.

Sorry, I have not posted detailed instructions for the "aux jack" I will when I get a chance. Do perform this mod as the amp section of
this radio makes a great tube amp, guitar amp, etc. Even without doing the mod, you can inject a signal into the pot at the ungrounded end. Tune the radio to an "dead spot" where no signal is received and connect an audio source such as an mp3 player to the ungrounded leg of the pot (C61 connects to this point) and ground. This will put the Audio and Power supply issues to bed permanently.

When you aligned the IF, what was your sig gen set to? is it accurate? IF for this set is 470, so if you set for 455, this may be an issue. Set the IF for 470, then ensure that the oscillator is 470KHz above the signal.

AVC works by taking a voltage from the detector stage and filtering it to a pure negative DC. The stronger the signal, the more negative the voltage is generated. This is applied as grid bias to the IF tube and possibly the convertor and RF tube. The more negative the grid bias, the less the gain from the stage. This AVC voltage is also used on tuning eyes, shadow meters, etc. So the AVC of only -2.5V indicates a weak gain in the radio section. Work this area first.

Hope this helps.

[morzh]

And, I assume, all other tubes have been checked? The 6R7G (2nd det) especially?

[dconant]

All tubes have been tested and are good. The 6F6s are not into the good very much but another set that tests better did not make any difference. I retested the 6R7 tube and all three elements are 70 percent or better where 50 percent is questionable. The diodes are 80 percent and the triode is 70 percent. Signal generator is not accurate so I use a frequency counter to set it to 470. "then ensure that the oscillator is 470KHz above the signal" how do I do that? I do not have an MP3 player. I can try one channel of my tape deck output. Will I need a capacitor between the two for that? The picture is a shot of one of my IF cans.

[morzh]

Well,

your IF is your RF Input signal minus the Local Oscillator.

So, your IF = |RF - LO|

(that is the absolute value, depending on whether it is hi side or lo side injection).
That is, if your signal 470, then your LO is 940KHz.
How you do that...not sure what they used the procedure for. Using a scope?
usually it is not required.
Once you trim your IF, then the procedure involves setting the oscillator and RF trimmers/padders.

[dconant]

I connected my tape deck to the pot as stated with a .01 cap between. Volume is still low. Maybe I am expecting too much out of the radio. Full volume is way louder than I would want to listen too. It is not distorted at full volume. Other Philco radios I have worked on normal volume is about one third or less. The AVC and non peaking IF concerns me.

[MrFixr55]

HI DConat,

It wouldn't hurt to put a 0.01 uF cap between the deck and volume control.  However, there is a 0.01uF cap between the wiper of the volume pot and the grid and another between the high end of the pot and the signal from the radio.

Attached below is a section of the schematic showing where to break the audio connection to add the Radio-Aux switch and aux jack, and a schematic of the switch connections:
   
   
Switch shown in radio position.

You could connect the jack to the switch through a 0.1uF cap if desired.  If the device that you wish to connect is stereo, a stereo to mono "Y" adaptor is required to hear both channels.

Hope this helps.

[MrFixr55]

Sorry, I did not see your post as I was writing mine. I would think that with a consumer electronics level Aux input of about 300mV, the output of the radio should be quite loud. The schematic rates this radio at 7W. However, if the amp sounds good and can be made much louder than you desire, the amp is good.

This radio requires a long wire antenna. If you have other radios of a similar vintage that also require an external antenna, this radio should be as sensitive as your other radios. By this, I don't necessarily mean how far the volume control needs to be turned; this radio should receive as many stations as the others and, unless the station is extremely weak, the stations should be te same volume.

This is a longshot but check out the muting switch, #71 and ensure that nothing has carbonized, causing a leak to ground.

[dconant]

Hi MrFixr55, Thank you for the drawing. I can handle that. I disconnected the muting switch from the center pin of the pot so that rules that out. While I was there I measured the pot and found it is 2.7 meg vs the 2 meg the schematic says. I had a junk 2 meg pot with the 1 meg tap that I swapped in but it made no difference.

[MrFixr55]

Hi DConant,

I don't think that the extra 0.7 MOhm would make much difference. If the pot was supposed to be a 500KOhm, that may be an issue.

The only other thing I could think of is the tone switch. See if there is a major difference when stepped through the various positions. Is the sound good when an aux signal is injected? Is the aux signal stronger than the radio? Can it be made "too loud". If so, consider the amp to be working.

[dconant]

Hi MrFixr55, The aux sound was good and yes it can be made too loud. The tone has no real effect on volume just tone, gets more base or less treble, depending on how you look at it. Any idea what can be up with the AVC not active or the non peaking compensator. Any chance any of those mica caps causing trouble that are in the tuner section?

Dan

[dconant]

If you guys are still with me I might have found something. Using my signal tracer the signal coming out of the 6K7 plate is very loud and not very clear but that maybe just overloading the tracer. This would be the white wire of the 2nd IF coil 2XB. The signal coming out of 2XB, red wire, is very low with some buzzing and maybe distortion. The signal going into the ungrounded diode (green wire of 2XA) is weaker than what was on the plate of the 6K7 but clearer than what was on the red wire (no buzz). Is this normal?

[morzh]

Out of the red wire you should have barely anything at all: this is the filtered Plate Power, and the coil is the load. Red wire is Positive power, and the signal transfers through the transformer to the 1st audio.

[dconant]

Should the ungrounded diode of 6R7 signal be lower than the 6K7 plate?

[morzh]

Has your IF been aligned?