[Pepperoni]

I finished the overhaul of this Philco 90 with the single 47 output and it plays but I have no control over the volume. It's just stuck at one volume level and operating the volume control in either direction doesn't change it. VC bench tests good after cleaning. I've gone over all my circuitry and can't find a problem. The only voltage anomally I see is on the plate of the Det. Amp. Paperwork calls out 140 volts and I have 54 volts. But this copy of the paperwork is a little fuzzy. It looks like 140 volts.

I don't know where to look next and could sure use some help.

Thanks,
Pepper

[rghines1]

1) Break inside control on ground side of wiper or lacking a good ground connection of same?

2) Cap 18 is connected to wiper terminal of control?

[Pepperoni]

Even slaved in a brand new VC and the problem remains.

Cap 18 is NOT connected to wiper terminal of VC. It's connected as shown on the schematic.

Pepper

[morzh]

Is your volume control GND terminal connected to the Chassis?

Use Ohm-meter, make sure it is connected, not to the rivet, but to the chassis.

[Pepperoni]

Yeah morzh I drilled that rivet out during the resto because it looked a little corroded. I reused the ground strap, it's good but I replaced the rivet with a small screw, lockwasher and nut. My lead resistance is .1 ohms and the volume ground reads .1 ohms.

It's late here so I enlarged two more copies of the schematic to 11X17 and in the morning I'm gonna go through the whole circuit and highlight each section as I go. This will be the third time. If I'm missing something I must be blind. I can ground the grid on the Det. Amp. and I still have volume. So I still have an audio signal going into the 1st AF from somewhere.

Appreciate the help from all of you! Let you know what I do or don't find.

Pepper

[rghines1]

Amazed that this is proving so hard. See this topic on NA and ARF forums with similar ideas mentioned.

Need hard data. A well equipped test bench with signal generator and scope would be nice. Without that, try measuring the AC voltage of the audio signal on a strong station. Start at the 2nd detector, through the volume control all the way to the audio output to see where you are not getting any level control of the audio signal.

A logical approach will get to the solution sooner rather than later.

[TA Forbes]

Pepper, have you checked to make sure that the volume control is connected properly? It sounds like the leads going to the wiper and the top of the volume control have been reversed......

[Pepperoni]

I've seen the other talk about a similar problem. The google world. My CT/Wiper of the VC goes directly to the grid of the Det. Amp. #27. The ungrounded leg goes directly to 18 & 19 which are new parts and verified good.

I took two new 11X17 schematics and started highlighting each section of the radio as it pertains to each circuit. So Far all connections and components around the Det. Rect., VC and Det. Amp are good. Something is looping around and putting an audio signal directly to the grid of the 1st AF without going thru the Det. Amp.

I ground the grid of the Det. Amp. and I still have the same volume and that says that some signal is getting to the 1st AF via something else besides the Det. Amp.

I'm proceeding with my troubleshooting while paying close to the other forums to see what they come up with. I know that Terry D. guy and he's pretty sharp. I'm gonna follow some of his steps too to see what I come up with.

Headlines at 11!

Pepper

[Pepperoni]

So I've gone over the complete schematic (for the 3rd time now) and highlighted every circuit. I find nothing that's out of place, open, shorted etc. I still have about 50% volume with no control over it. I checked the AVC at the junction of #46 & #48 reading to chassis ground and I do see a substantial change in the negative voltage at this point when I go on and off of station.

I ground the grid of the Det. Amp. and I still have the same volume. I remove the Det. Amp. tube and my volume goes away completely. This is about all I can tell you. I'M STUMPED!

EDIT: There is one thing that I have in question. The #55 choke. It is obviously an aftermarket product. I read about 150 ohms across it's leads. I have no reference on this so I don't even know if it matters.

Pepper

[morzh]

No it should not matter. You have 1-47 model of 90?

#55 is a filter choke for the rectifier; it smooths the ripple of the rectified voltage, forming a Pi-filter with C56 and 57 caps.
It would not result in your volume not being regulated.

[morzh]

Here's some other thoughts:

1. Often times if a tube goes bad a radio still receives station(s). If this tube is the 27, 1st det-amp, you may still hear station(s) but you won't have volume regulation. Check the tube (better yet - all ov'em).

2. Turn off your power, put one end of your Ohmmeter to the wiper of the pot (It has no active resistance in parallel, so you don't have to desolder nothing), and another and to the Chassis. Rotate the shaft and see the resistance going from 500K to 0. Repeat the same with the other Ohmmeter end at where the pot connects to the 18 and 19 caps together. Same thing only in the opposite direction.

[Pepperoni]

Hello morzh, I've looked at those VC readings and it does do what it's supposed to do. But before I put this set back together I bench tested that volume control. From outer leg to outer leg it reads 250K. Part # on it matches the parts list and a 500K pot is what belongs there. But when I measured from the CT to each outer leg it was an audio taper so not linear and I did see 500K. Kind of confusing I know. Why does it read 250K across it. Don't know. So for sh$#^ts and giggles I slaved in a new 1 meg pot. All I had but it was new. It didn't change what the radio is doing. About 40% or so volume but no control via the VC at all.

So I did start swapping out tubes. No change with the 27's. I didn't have any 24's but I had 3 very good 35/51's. Swapped each tube out (with that gleam in my eye that one of them would cure the problem) and got the same results. Volume with no control over it.

I've taken the schematic and blown it up to 11X17 (4 Copies) for clarity and space and went through the set from the front end to the speaker. No wiring errors, no bad caps or resistors, no solder splash or unwanted shorts etc. etc. When I had it all apart I checked every coil in it for continuity. No real reference to what the resistance should be but all coils were consistent on the primary and secondary sides.

I went over my notes of every wire and part that came out of it along with comparing my 75 pictures I took before I disassembled it. Just nothing wrong.

But something is and it seems as if my problem lies somewhere between the Det. Rect. and Det. Amp. But everything is correct. One thing I didn't get a picture of until I disconnected the wires was the tuning condenser wiring on top of the chassis. Where each wire attaches to the TC from their respective locations inside the chassis. My notes and pictures tell me where they all connected inside the chassis but not on the TC itself. The grounds were simple but they do connect to specific points in the radio. Looking from the front of the radio I have the 1st and 2nd gang "HOT" wires if you will, connected to the front screws on the TC 1st and 2nd gang. The 3rd and 4th gang hot wires are connected to the rear screws on the TC. I believe this is correct because those four screws were backed out from when I disconnected them. But if someone could clarify these connections this would be one more thing that I could eliminate as being the problem.

Also something that doesn't seem right to me but it may be normal... When the radio is playing and I short the fins on any of the gangs the radio goes silent except for one gang. May be normal, I don't know.

Pepper

[morzh]

Here's an idea, pepper,

Short the wiper of the regulator to the chassis. If then the volume is still the same.....you know what I mean?

Idea #2: In Det. Amplifier (the tube that has the pot connected to its grid), with the power off, measure the resistance from the Cathode to the Chassis. Should be about 60 Ohms.

Hello morzh, I've looked at those VC readings and it does do what it's supposed to do. But before I put this set back together I bench tested that volume control. From outer leg to outer leg it reads 250K. Part # on it matches the parts list and a 500K pot is what belongs there. But when I measured from the CT to each outer leg it was an audio taper so not linear and I did see 500K. Kind of confusing I know. Why does it read 250K across it. Don't know. So for sh$#^ts and giggles I slaved in a new 1 meg pot. All I had but it was new. It didn't change what the radio is doing. About 40% or so volume but no control via the VC at all.

So I did start swapping out tubes. No change with the 27's. I didn't have any 24's but I had 3 very good 35/51's. Swapped each tube out (with that gleam in my eye that one of them would cure the problem) and got the same results. Volume with no control over it.

I've taken the schematic and blown it up to 11X17 (4 Copies) for clarity and space and went through the set from the front end to the speaker. No wiring errors, no bad caps or resistors, no solder splash or unwanted shorts etc. etc. When I had it all apart I checked every coil in it for continuity. No real reference to what the resistance should be but all coils were consistent on the primary and secondary sides.

I went over my notes of every wire and part that came out of it along with comparing my 75 pictures I took before I disassembled it. Just nothing wrong.

But something is and it seems as if my problem lies somewhere between the Det. Rect. and Det. Amp. But everything is correct. One thing I didn't get a picture of until I disconnected the wires was the tuning condenser wiring on top of the chassis. Where each wire attaches to the TC from their respective locations inside the chassis. My notes and pictures tell me where they all connected inside the chassis but not on the TC itself. The grounds were simple but they do connect to specific points in the radio. Looking from the front of the radio I have the 1st and 2nd gang "HOT" wires if you will, connected to the front screws on the TC 1st and 2nd gang. The 3rd and 4th gang hot wires are connected to the rear screws on the TC. I believe this is correct because those four screws were backed out from when I disconnected them. But if someone could clarify these connections this would be one more thing that I could eliminate as being the problem.

Also something that doesn't seem right to me but it may be normal... When the radio is playing and I short the fins on any of the gangs the radio goes silent except for one gang. May be normal, I don't know.

Pepper

[Pepperoni]

Shorted the wiper to chassis...Still have music and I also ran the VC thru it's full range just to see if anything happened. Nothing.

56.0 ohms from that cathode to chassis.

Bought the parts to put a new thermostat and housing gasket on the Ranchero. Decided to do it tomorrow. It was already 2pm. Sat on my butt the rest of the day. I don't usually do that. I'm not a TV person and I always need to be doing something. But I'm taking 5 days off from everything on the 20th and heading north to sit on my butt some more with my best friend. Haven't had a day off since the new year weekend.

Pepper

[morzh]

Shorted the wiper to chassis...Still have music and I also ran the VC thru it's full range just to see if anything happened. Nothing.

56.0 ohms from that cathode to chassis.

Bought the parts to put a new thermostat and housing gasket on the Ranchero. Decided to do it tomorrow. It was already 2pm. Sat on my butt the rest of the day. I don't usually do that. I'm not a TV person and I always need to be doing something. But I'm taking 5 days off from everything on the 20th and heading north to sit on my butt some more with my best friend. Haven't had a day off since the new year weekend.

Pepper

But you can tune? Or you cannot? If you cannot this pretty much means your Audio stage is your detector, and the RF amp, detectors etc don't do anything.

If you shorted the wiper to GND and it's still there - you can safely assume everything prior to this tube, and including this tube, is not doing much.

Do this: just yank the tube of that detector-amplifier.
Does it still play?
If it does, then yank the 1st AF 27.
And (hard to imagine, but) if it still does...there is nothing more to yank.
If it stops, there is no signal going from your Det. Amp to the 1st AF.

If you yank the det. and it stops playing - keep yanking in the opposite direction (towards the Antenna) until it stops playing.

Let's do that whole exercise first.