Trying to restore a 40-180 for a friend. Recapped and checked resistors and replaced a few. Speaker was missing so I found a comparable Philco speaker same size but different part number. Checked it on another Philco 46-480 and it sounds great so I know it's good. Output trans was bad so replaced with another within 10 ohms of the original on the primary. So when powered up all tubes light and pin voltages are close so all seems to be well, but all I get is a low hum from the speaker and a very weak signal which appears to be coming out of the output trans which is strange to me. I did the 2nd radio oscillator test and got a loud squeal so I believe the oscillator is good.So at a loss right now on where to look. Any suggestions?
You have to :
1. Check all tubes. The fact they light up is not enough to deem them good.
2. Check all your RF coils. At least for continuity.
3. Attempt alignment. See if all signals go through.
Welcome to the Phorum!
Welcome, Bill! I recently had a radio that I couldn't get any stations on. Turned out to be way out of alignment; so, I would move morzh's #3 to #1.
Larry
Larry
I only have it as #3 because I think without knowing all the tubes are good it makes no sense to do alignment.
But I agree to make it #2
because the alignment will show if you should start taking a look at the coils.
Thanks for the welcomes and suggestions. I have checked the tubes and all checked good with no shorts but I have not subbed any in. I will try that as I have learned that tubes tested good may not be good in circuit. The only change I made on the tubes is I substituted a 7G7 for the 1232. I figure my replacement output transformer should be good since it ohmed out close and I have plate voltage on the two push pull 41's. I should have checked the other coils but didn't. So I will get into alignment and and see what happens. Thanks all.
I agree Mike about the tubes. I always check mine before powering up after a recap. I didn't know if he had a tester. Since he mentioned presence of a weak station, I wondered about alignment (since that was a problem I recently experienced). I'm certainly no expert at this.
I just powered up my Zenith, but right after the tube check. (Works).
I just don't want an extra variable. If it doesn't work, at least I know it's likely not them.
I'm sure you probably know this but the farthest right button must be pushed for Broadcast mode. Sometimes it's the simplest thing we forgot that is the problem. Just sayin!!
Good reminder.
Myself had to figure it out when restoring my 41-280
Thanks for the reminder on the button. Sometimes it is something very simple like a band switch on phono instead of broadcast which I have done. Not so lucky this time. I had the dial tuning button in. And yes I have learned to have all good tubes in before that first power up. I'm using a Jackson 648 tester and I try to have doubles that test good.
So I tried a signal generator hooked up to the antenna just to see if any sound came thru and got a slight buzz thru the output trans same as the weak reception I got before which was coming out of the output trans and not the speaker.First time I've ever experienced that. So I started checking continuity and ohms of the two I.F. transformers and did find one side open. Should have checked that while recapping since its under the button coil assembly so now I have to pull that out again. I've been doing this for about 9 years now and learn something on every one that I do. Thanks for leading me in the right direction and I'll pull out both I.F.'s and check them. Hopefully that is the only problem. I'll post my results.
One more thing: buzz out of your output transformer.....is this mounted on the speaker? When you checked the speaker on that other radio, was the transformer on it?
If yes - good, if not - see if the OT has a turn short (not so easily detected on the secondary as it is low resistance, and on primary is also not necessarily easily detected). One way of doing it - feeding it an AC 60Hz (if you do not have an audio generator) and measuring the output: the input/output should ratio should be your turns ratio. If not (little or no output), you have some short.
The Output is not mounted on the speaker. It is on the underside of the chassis. Don't have any way to measure the output as you suggested. Even though I have plate voltage with this OT I have felt that it is suspect of not being correct. I need to find another that will match and try that. I pulled out the IF that I thought was open but it is OK. There was a resistor between the two wires on one side that gave me a false reading of no continuity.
OK, so the output xfmr is not on the speaker; this makes it a suspect.
I suggest then another way:
Do as you would during the alignment, putting the modulated signal through with your speaker connected.
First measure across the primary winding when supplying a good level of signal. Put the meter (use a DMM) om "AC Volts", so only to measure AC component and make sure you do have a good few (few tens maybe) of AC Volts of audio across the primary (Plate-to-Plate).
Then if you do (if you don't - you have other problems), move your meter to the secondary and see if you have the output. If you don't - you have a problem with the xfmr.
To confirm that, see if you have any good output transformer (you need a push-pull of course) and try to sub it.
PS: do you mean you have no Variac?
Sorry, yes I do have a variac. Bear with me as I have not had to do this before and was thinking the wrong way on your suggestion. I understand now what you are saying to do. Right now I have the 2nd IF out and things moved out of the way. Once I get it back together I will try that.