Question on a Philco 95 capacitor....

[Kamakiri]

Working on this for a friend, he's coming home for Christmas, and I'd like to finish it up for him to have for the holidays

This radio's got a few screwy tube caps that have resistors built into them, Philco part number 3787-A, which is a combined resistor and cap. I was able to easily figure out which terminals represented the resistor, I know the chassis ground is for the cap, but I can't figure out which terminal is the other side of the capacitor.

My capacitor tester shows that there's capacitance on both sides of the resistor terminals, which of course it would, since I can't take the resistor out of circuit in this case. Anyone have experience with these?

[Reece]

Can't you tell by where the wires go on the schematic compared to the actual chassis? Nostalgiaair shows the 95 and I "guess" this device is indicated as no. 10 on that drawing? One end of that cap goes to the screen on the first '24 tube. Maybe that's not the one you mean?

[Kamakiri]

This one's confusing to me....partly because I'm not used to hunting for components that don't have a familiar look to them, and partly because the set uses 3 #27s and 2 #24s.

A Sams for any TV or radio I can follow. I can't make heads or tails of this one.

http://www.philcoradio.com/tech/images/95.jpg

[wa2ise]

See which side of that resistor shows 0 ohms between the screen grid of the 1st RF amp tube. That would be the cap's. And that same side should show 250 ohms when you go to the 2nd and 3rd RF amps' screen grid.

[bob91343]

Any impedance bridge will show you which. Or measure ESR; it will be lowest without the resistor.

[Kamakiri]

Originally Posted by wa2ise

See which side of that resistor shows 0 ohms between the screen grid of the 1st RF amp tube. That would be the cap's. And that same side should show 250 ohms when you go to the 2nd and 3rd RF amps' screen grid.

You're going to have to dumb that down just a tad

And unfortunately, I have neither an impedance bridge nor an ESR meter....

[philcophan]

An easy solution would be to lose the ground, leave the rest in place since you need the 250 ohm resistor, and bypass the screen with the appropriate cap... looks like a .05. Otherwise you could lose the whole shibang and put in the resisitor and cap separately.

[Kamakiri]

Well, that's the ultimate plan, but the trick here is figuring out which terminal is what, for the cap. I have two choices here. One side of the cap goes to ground, as it shows in the schematic.

[old_coot88]

Gadzooks. Just as a point of interest, it looks like the first '27 is being used as a AGC diode*, with the plate and grid strapped together.
Wunner how well the AGC (or AVC) actually works, considering that the '24s are sharp-cutoff type.

*as well as audio detector diode.

[Reece]

Yes, one lug is one side of the cap and goes to ground. Another lug is the other side of the cap and goes to the screen of the first 24 tube, and this same lug connects to the resistor, i.e. this end of the resistor also goes to the screen of the first 24 tube. Then the final lug on the device is the free end of the resistor and goes to the screens of the other 24 tubes etc. All three lugs are accounted for. Should be able to trace this out.

[wa2ise]

Originally Posted by Reece

Yes, one lug is one side of the cap and goes to ground. Another lug is the other side of the cap and goes to the screen of the first 24 tube, ... Should be able to trace this out.

That's essentially what I was trying to say (being a EE I may forget what it was like before I learned this stuff). And he should set his DVM to the low ohms range, say below 200 ohms. So it reads as an open if he gets on the wrong side of the resistor. Or he should look for either a 0 ohm reading, or a reading of 250 ohms.

[bandersen]

You might find this ARF thread useful: http://www.antiqueradios.com/forums/...ic.php?t=36022

[Winky Dink]

I hope I'm not embarrassing myself with this reply, because I really can't follow everything you've said, but it looks the same as a Philco 87 I did a few months ago.



Sorry I didn't post sooner, but here it is for future searchers. If it's not the same thing, then, well...never mind.

[teevee]

From your picture, the side away from the mount looks to be the cap side. The clipped lead there appears like it was connected to the adjacent tube socket screen grid pin.