[lasurveyor]

    Hi all,
Maybe someone will give me some insight into what's going on with my 90. It's the chassis with one 47 tube. I've re-capped it and replaced most or all resistors. About half way thru re-capping I powered it up and had reception at a low volume. When complete I again had reception at a low volume for a couple of minutes then some crackles, then some more crackles, then dead. First I looked at the last thing I did which was restuff the two tobacco cans, #24 & #30. I didn't take them back apart, but proper capacitance was there on all. I checked and rechecked my wiring and the tubes. The primary in the first detector transformer #7 checked open, so I rewound that. Still dead. One day I went to pull the 47 output tube to listen for the click and at one point of the pin contact all of a sudden the sound came blasting through beautifully loud. Great! I think that I merely have a pin contact problem. Playing with the 47 pin contacts worked for a short while then it went dead again. Now, can't get anything again. At one point about the time it went dead again I accidently shorted across a compensating condenser, possibly #9 across the 1st IF primary.  Something that I don't understand is why when I check across the coils of both IF transformers they come up open. They can't all four be open, I'm misunderstanding something. Does it have to do with the compensating condensers?

Thanks for any insight, I have the cabinet looking quite good so I'm looking forward to figuring out my chassis problem.

Alan

[morzh]

The #9 shorting should not do anything to the coils unless instead what you think you did you shorted the top (as shown in the sch) part of the cap to the GND; then that could burn the primary.
The secondary could've been open on its own.

I advise you to inspect all the coils, every single one, for oxidation, green spots etc. Even if they do not test open, that warrants rewinding them.

As for the tube contact, there could also be intermittent contact inside the tube's pin. Not necessarily in the panel.

[lasurveyor]

Thanks, don't relish more re-winding, but the one I did was pretty rotten to the touch. I have good plate voltages through all stages, does that say anything about the coils? I can send an RF in the early stages and AF in the later ones and get at least a low volume signal through the set. An odd thing to me, I have no cathode voltage. Should be around 20 volts. Is this telling me something? or am I measuring it wrong. Tubes should be good. They're tested on my Hikok and swapped in and out to be sure.
Thanks Phorum.
Alan

[morzh]

You don't have K voltage where? On all three tubes, RF, IF and OSC?
Check the 58 big wirewound resistor.

But, even if you do have plate Vs and continuity, if your windings are oxidized, you have to take care of them, as continuity is not what matters: the inductance is. And oxidized wire might have turn shorts and what have you.

[lasurveyor]

Yeah, no K voltage leads to the power resistor, but what voltage comes into the resistor? taps 4 & 12 off the transformer have nothing seem to be grounded, at least leads to the antenna ground.

[morzh]

The voltage comes nto the tap 4 from the Field Coil of the speaker.

[lasurveyor]

Thanks for pointing me to the field coil. I did have a pin problem with the 47 complicating things with intermittent function, and now I'm convinced that the field coil is open. The radio is dead until I short the field coil, then it comes alive. Of course I then have over a hundred volts on the screen grids. I have a 1930 Dayfan speaker that I am able to fire up including the field coil, while I can't get any magnification out of the Philco speaker. I do get a small amount of sound out of the Philco without the field coil. I see speakers for sale often emphasize "working field coil". Is it common for these to open?

Looks like an expensive fix but I'm into this so deep I have to do something. Either a loner radio or a salvaged speaker? Does anyone repair these?

Alan

[morzh]

Yes, it is quite a common problem and is harder to perform than the re-coning, especially in the 70/90 speakers that have pressed-in magnetic rod.
In a 20's speaker which is pretty much the same, the rod is held by a nut, and so it is in model H or G speakers.
Still, a field coil, even if easier to extract, uses lots of wire and many-many turns.

[Brad Winder]

There was a 70/90 speaker for sale, on eBay, last time I looked.