Posts: 1,107
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Joined: Jun 2011
City: Tacoma
State, Province, Country: Washington
I might try an outboard bias resistor. As for the output transformer, it's fine. I've even tried another transformer in there that closely matches p-p 45's.
The interstage transformer seems to be quite well matched. I get nice clean audio out of the secondary. In fact, I can drive a high impedence speaker directly from the interstage transformer at a good volume.
Posts: 1,107
Threads: 88
Joined: Jun 2011
City: Tacoma
State, Province, Country: Washington
Well.... color me stoopid....
I've solved the entire problem with the output on this radio. It sounds quite nice now, as long as I keep the volume level below the level the signal itself distorts going through the RF/IF chain. I get at least a good 2 volt signal across the voice coil before clipping. I'm not familiar with the voice coil impedence on this speaker, so can't compute the RMS power, but it's quite loud.
Now, wouldn't you like to know what the problem was? Wouldn't ya?
Well, let me tell you.. some idiot who shall remain ME connected the interstage transformer to the plates and the output transformer to the grids of the 45's. It's a wonder that a) any audio made it through to the speaker at all and b) the grids didn't melt down with B+ on them. I might have caught my error sooner if the grids had ANY DC bias on them at all (or maybe I should have taken better notes when I disconnected all the leads from the bottom plate..)
I'm sure that the 45's are probably pretty damaged at this point, so it's a good thing I have some more coming in. At least the radio is working and I can honestly say that I've tackled one of the biggest PITA radios in existance, and come out the winner.
What makes it even more amazing is that when I got the radio, it was in the form of a 3-D jigsaw puzzle. The cabinet was totally disassembled, the speaker lying on top of the chassis, the knobs broken off (not the shafts), the tuning mechanism broken, the power transformer extra crispy and literally everything in the filter can needed to be replaced (except the RF choke, but rather than re-use that and have it go out later, I just bought a new 50uH RF choke and replaced everything in the can.
I wish to thank everyone here that helped me with this set. All help is greatly appreciated.
Take care, and stay well.
Posts: 4,639
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Joined: Sep 2008
City: Sandwick, BC, CA
I don't know if the #45s would be damaged or not from hooking them up that way, at least not for the short period of time that they were hooked up wrong. I think if you test the #45s, and they come up good, that will be the end of it, there just isn't a lot to them since they have a directly heated cathode.
Don't feel bad about it, with a Canadian Westinghouse 801 I was working on last summer I got a similar level of performance to that Majestic model 20. At first I though maybe the audio interstage was stuffed, it wasn't, nor was the output transformer, the voltages were all there. Then my uncle figured it could be an alignment problem since I had to replace one of the IF cans, it did not make a difference. Then we had a look at the tube layout diagram, when I replaced the tubes I got the lead for the IF amp tube and the second detector mixed up. You see in the Westinghouse 801 just because the grid lead is near a tube did not mean that it connected to that tube. So we swapped them around and the set nearly blew my eardrums out.
I think that every one of us has caused a self inflicted snag at one time or another, wrong lead connected to wrong tube pin, wrong tube in wrong socket, etc. I still do this from time to time which is why if I really go at a radio I check my work two or three times comparing it to the diagram, it's easy to do on something like an octal socket.
Regards
Arran
Arran
Posts: 4,639
Threads: 51
Joined: Sep 2008
City: Sandwick, BC, CA
Speaking of the Majestic model 20, look what I found while looking for details about a G.E model 140:
http://www.mcclellans.com/Majestic20restore.htm
Right at the top it says, "A Radio To Avoid", oh brother! It looks like Brenda Ann wasn't the only one who had trouble with one of these old pigs.
Regards
Arran