[murf]

Ok,
Will check this stuff out tomorrow night.
Thanks again

[murf]

Hello again fella's,
Got my meter out and got a few readings again in response to Morzh's questions.
First I checked the voltage of the output of the field coil with the speaker unplugged and powered up.
Read 457 volts.
Plugged it back in to the speaker and waited a while before checking caps.
Could not find anything with the caps ohmming them out to chassis ground.
Check primary of the output tranny to ground and looked ok.
Any idea's?
murf

[Arran]

I think that Mike meant the filter cap at the input of the field coil not output, since if the speaker was unplugged you would not get anything at the output. Again you have to be careful what you use as a ground reference point, this set has a floating negative side, true B- is the center tap of the power transformer with a chain of resistors in series with it. You will want to check the resistance across each capacitor from one side to the next, not from one side to the chassis ground unless the other side is connected to the chassis. But if you get a resistance reading check to make sure the cap is not connected in parallel with something like a coil or a resistor, if it is clip one lead on the suspected cap and check again.
Regards
Arran

[murf]

Did get the high voltage reading off the speaker plug on the input side. Coming off the E cap, because your right, there is nothing on the output side with plug disconnected.
On checking the caps as you say, one side to the other, are you testing for a shorted cap?
I do have a cheap little cap tester that will test the value of the cap too.
When the speaker is plugged in the voltage checked on the input side of the voice coil from that first e cap is 250 approx.
SO it's ok from the power transformer,to the voice coil, but then gets lost somewhere between the voice coil and the output transformer.
Puzzling thing to me is not only the low voltage on both 42 tubes, but the fact that the voltage is so much different between the 2 tubes.
Oh well, I only paid $30 for the radio, but have logged lot's of hours on it which has only made it worth $30.
It is a good way to learn a little about trouble shooting though.
I need the experience.
murf

[morzh]

Mrf

by chance your #32 resistor is not hot when powered? And #33 cap, have you changed it?


In a nutshell, you need to take your meter and with the radio unplugged and discharged, unplug the speaker and measure the centertap of the ouput transformer to Chassis resistance.

You are looking for a short or a low resistance between the B+ and chassis.

[murf]

Will check resistor tonight if I can find it on the blurry schematics.
Have changed 33 cap. That is an 8mfd electrolytic. I used a 10 MFD.
I have checked from centertap to chassis, but not with speaker unplugged.
Thanks,
murf

[morzh]

Murf

>>SO it's ok from the power transformer,to the voice coil, but then gets lost somewhere between the voice coil and the output transformer.

You meant the field coil, right?

In addition to the above: simply check the panel of the 42 tube (without the tube installed and un-powered), which had the lowest voltage on the pin 2, buzzing pins 2 and 3 to GND. Especially 2.
Note the resistance.

if nothing conspicuous, repeat for the other 42 tube.

[murf]

Did that last night on both tubes. checked ok.
I stand corrected on the coil.

[morzh]

Murf

I forgot if I asked that already - does your field coil produce resistance of 860 Ohm (or whatever that is shown on the sch)?

Also - how good is the contact between the coil and the socket? When you measure resistance between the 80's filament pins (the fat ones) and the #3 pins of either 42 tube when the speaker is plugged (the radio is powered down and unplugged) - is it the same 860 Ohm? You have to measure at actual points I asked - electrically it is not the same as just measuring across the field coil.

Shot in the dark....that Candohm, or whatever it is that connect the Power Transformer Centertap to the Chassis (three resistors shown under the field coil in the sch) - when you buzz between these two points do you get roughly 200 Ohms (208 to be exact) ?




PS. Now let's summarize: we are dealing with a low B+ voltage.
It can be explained by:

1. Bad field coil (excessive resistance).
2. A large drain on the B+. Either short or a bad leakage.
3. Bad connection between the Field coil and the socket down the B+ line.

The B+ has very few direct loads:

1. Output 25uF el. cap. Check for leakage / polarity.
2. Output transformer. Will load if the 42 tubes are bad OR if the caps at their plates are bad.
3. Both 7B7 tubes. Check tubes and sockets for short/low resistance between the plate and cathode (chassis).
4. #32 resistor of the #33 cap (8uF) is bad. But - probably won't bring the voltage down to 50V and the resistor would smoke.
5. Simply check the B+ wire going across for insulation damage and touching things it should not be touching.


How I would start:

1. Ohm out the B+ wire to Chassis. There is no DC path so the only thing you should see is the capacitive leakage which could result in MegaOhms readings or open. If there is any finite resistance, it should be investigated.
2. If it seems OK, I would then remove EVERY SINGLE TUBE, plug in the speaker and briefly measure the B+ voltage. It should be practically the same as the rectifier output. Meaning both ends of the field coil should read the same voltage. If the output is much lower then input like you are having it now, there is a leakage.
BE VERY CAREFUL - UNLOADED B+ COULD BE CLOSE TO 500V. AFTER YOU DONE MAKE SURE THE CAPS ARE DISCHARGED. You can do it by plugging the output tubes in and turning the radio on for a minute, and then turning it off. Check the voltage to make sure it is down to safe low levels.

[murf]

Printed out all your suggestions and will let you know what I find.
Still think it is a bad connection somewhere versus a short.

If it were a short, you would think something would get hot.
Might be the field coil output not getting back to the chassis due to a bad plug?
I don't know We'll see.
murf

[morzh]

Murf

I suggested a bad connection in #3 of the above differential diagnosis.

The further actions are all pointed to find short as finding a bad connection is as simple as m
traing the wire.

[murf]

Well fella's,
I took it over to a friends shop to look at, and he says the output tranny is shorted.
P.N. 32-7981m.
Where should I get a replacement?
I have a 40-180 chassis which has twin 41's.
Would the output tranny from the 40-180 work in the 41-300x?
murf,
Still don't understand how the outtranny could cause that kind of voltage drop in the B+ as it is downstream from the 42's?
But then I am totally confused on this stuff anyway.
murf

[morzh]

Murf

Post #45, item #4.

This was checking the transformer shrt (input to output).

Any transformer driving similar speaker from the same tubes will do.

[murf]

Talked to my buddy today who did the diagnosis, and he said the B+ returned after he isolated the transformer.
Shorted out on frame of tranny.
Go figure.
murf

[murf]

Ok,
I am so close,
Hate to keep bugging you guy's.
Mike has been really a good sport about helping a newbie like myself.
Onto the Philco, 41-300x problems.
If you have been reading this thread, you will see that the B+ problem was solved with an out put transformer that was shorting out.
Brought it home and hooked up the loop and had no reception on broadcast band.
I did find that I had reception on 2 of the shortwave bands as well as AM stations ,but only on the pushbutton mode.
Did a quick alignment adjustment on the pushbutton mode and could get stations with good volome.
Go to broadcast band and I get nothing.
Is there a seperate coil for the broadcast band?
I have checked things out as far as the coils go, and have cleaned the bandswitch.
Any suggestions without getting to technical?
If I don't understand what your talking about, I have not gained anything.
Keep it simple for newbies like me if possible.
Thanks and have a great weekend,
murf