OK, so there is an open circuit in that side of the last IF transformer. Unfortunately that means you are going to have to get the can off of it to see what it going on. Sometimes this means completely removing the IF transformer, and sometimes not.

You will be the best judge of how to get in there. Obviously be careful because the wires of the coil are fragile. Chances are the break is right at the connection to the wires that exit the can.

Best of luck.

Curtis Eickerman

Good news and bad news. The good news is that the IF transformers on this radio are easier than most to get into than most. The bad news is that when I checked the resistance in T3 again it was fine. When checking the resistance I had attached one lead of my ohmmeter to the black lead of the other IF can ( they run close together) and this, of course threw off my reading...Back to stage one....

No problem. Let me confirm one thing. With your signal generator cranked up for as much output as it can produce, and hooked to pin 2 of the 6SF7 at 455 kHz, you still hear nothing at all?

If that is true and you back up to pin 4 of the 6SK7 you do hear something. If you do and you tweak the trimmers on T3 is there any peaking of the signal at all? Do both trimmers have an affect?

Curtis Eickerman

Injecting a signal at the max output of my generator at pin 2 of the 6SF7 produced no tone. Injecting at pin 4 of the 6SK7 did produce a faintly audible tone. Attempting to peek the trimmers in either IF can didn't seem to make any difference. If those trimmers had shorted out due to silver mica disease would that show on the ohmmeter ?

I believe the trimmers could be in real bad shape without being so low as to affect the resistance readings. They also could have become disconnected from the coils which would be just as bad.

The fact that there is no affect at all is disturbing, and probably merits opening things up and having a good look.

If you have any tube-radio-type 455 KHz IF transformers around that you could scavenge, you could temporarily patch one in place of the existing transformer without mounting it to the chassis and see what happens. Just unhook the 4 wires and hook up 4 new wires to the spare transformer. Lead lengths are not all that critical at that frequency.

Edit: Have you tried injecting the signal right at the detector plate, pin 5? Just trying to figure out if the transformer is so horribly mistuned that you never get the primary and seconday in agreement enough to get a signal through.

Curtis Eickerman

Pardon me for jumping in here, but in reading back through the posts, I don't see where it has been established that anything is passing through the radio/phono switch when in radio mode.

I read where you get good sound from an input in "phono," but a messed up switch might block anything in "radio" position.

Although you report a very weak sound when inputing a signal to the 1st IF, it very well might be just an accidental coupling somewhere.

What I'm getting at is that the IF stages and detector might be working fine, but the detected signal is not passing through the radio/phono switch into the audio section.

Won't it be nice if that's all it is?

Good point. I was assuming since something was being heard it is actually coming through the switch, but maybe not.

I need to remember my own advice when I tell people that switches and controls are generally the most unreliable parts of an electronic system.

Curtis Eickerman

Interestingly, while simply continuing to explore this radio I found that with the ground clip only from my signal generator attached to the chassis I was able to get some reception. It was faint and better at the top end of the dial. Performance didn't change when I switched off the signal generator. So it does appear that the thing isn't dead, I'm just not giving it what it needs to come back to life

By any chance have you done an ohm meter check on that phono switch to make sure it really connects to the detector circuit in the Radio position?

A short across R7 (2.2 M) would also generally kill things by shunting the audio to ground through C33 (0.05).

Curtis Eickerman

So I jumpered the switch...Lo and behold the signal comes through loud and clear. This still doesn't change the fact that I'm only picking up signals on the top end of the dial. I'm hoping I can clean the switch and make it operable as well, because this receiver has an oddball combination radio/phono/tone control all in one...At least I'm closer

Congratulations, and chalk on up for Oldbear (many thanks).

Sometimes switch issues go beyond just cleaning. With wafer switches, if that is what it is, the contacts can lose their spring pressue against the rotating contact. If that happens it can be fixed. It can be a delicate operation, but not all that difficult if you have access.

Losing operation at the lower end of the dial sounds suspiciously like variable capacitor plates touching at some point as they are closing together. A good visual inspection of the variable cap plates looking for anything bent is probably in order.

Curtis Eickerman

Here is a picture of the offending switch. If anyone has one of these I'd be interested in purchasing it. It's an interesting switch, twisted all the way left it selects "radio" all the way right "phono" and it also incorporates the radios tone control.

Looks like a slide switch.

For the record, I hate slide switches.

Having said that, this switch is repairable, but I won't say it's much fun. If squirting cleaner in there and working it back and forth a few times is not solving the problem it might have to come apart.

What you have, I think, is basically a slide switch with a rotating mechanical actuator.

The switch can be disassembled by bending out those metal tabs at the side. Don't bend them any more than you have to because you only get to bend them a few times before they just break off.

To make life easier if would be best to remove all the wires first after carefully documenting exactly what goes where.

Once you bend out the metal tabs the mechanism comes out the back. There will also usually be a loose piece that contains the sliding contacts that are getting pushed back and forth by the mechanism.

The sliding piece usually has springy contacts on it and they can get pretty tarnished. The fixed contacts are part of the terminals that come out of the back. They also get real tarnished. With slide switches I have taken apart I find that pencil erasers do a real good job of cleaning them up and getting them back in operation. You can also sometimes enhance the spring action by bending the sliding contacts slightly.

Putting the whole thing back together is real easy "if you have three hands". Otherwise it is a bit of a pain. So I guess that means it is pretty much always a pain. You are pushing everything back together and trying to rebend the tabs without breaking anything off. Yeah, three hands and maybe a foot.

If you want to attempt this, it might be best to take the whole thing completely out of the radio. Makes accessing with your foot easier.

Curtis Eickerman

But you've been doing a lot of fiddling and tweaking of the trimmers during your troubleshooting, haven't you?
You'll probably now need to do a full and formal alignment.
And you'll want to make sure you use the original loop antenna when doing that. Using a different one could definitely throw things off.

Yes, I have been messing around with all of the trimmers. Once I get reception across the dial I'll set about aligning the old beast ....Thanks again to all for the advice and instruction. It's very much appreciated