Late 1920s Eveready Model 1 TRF Set need info

[vortalexfan]

OK so I took and hooked up my radio's original speaker up to the radio (I had to use an aligator clip lead with a mini banana plug on the end to hook one of the leads from the speaker up to the radio as the original pin plug was missing on one of the speaker leads and I powered on the radio and it actually worked (albeit with a loud hum) which I assumed was because the set needed neutralizing so I got my signal generator out and set it to 1400 KC and I was able to get the hum to partially clear up, but it still had some hum to it.

So I went to turn the radio off and check something out underneath the power supply to see if maybe a ground wire was loose or something, and there wasn't and so I went to turn the set back on again and now the output tubes aren't glowing anymore and there is absolutely no audio coming out of the speaker except for a little crackling noise when I wiggle the output tubes in their sockets.

I checked the heaters on the output tubes for continuity and they still have continuity but they for some reason just refuse to light and I checked the filiment winding for those tubes on the power transformer and its still has continuity (its not open or shorted).

I'm not sure what's wrong with this radio right now and I'm so close to getting this radio going I'm just not sure what's going on with this thing right now and why the audio section suddenly decided to take a dump on me.

Any ideas?

Also can a tube die and still have continuity on the heater pins? Just wondering because it seems weird that both of my output tubes would of died at the same time but I guess its not completely unheard of just really uncommon.

[Kevin Kuehn]

Originally Posted by vortalexfan

OK so I took and hooked up my radio's original speaker up to the radio (I had to use an aligator clip lead with a mini banana plug on the end to hook one of the leads from the speaker up to the radio as the original pin plug was missing on one of the speaker leads and I powered on the radio and it actually worked (albeit with a loud hum) which I assumed was because the set needed neutralizing so I got my signal generator out and set it to 1400 KC and I was able to get the hum to partially clear up, but it still had some hum to it.

So I went to turn the radio off and check something out underneath the power supply to see if maybe a ground wire was loose or something, and there wasn't and so I went to turn the set back on again and now the output tubes aren't glowing anymore and there is absolutely no audio coming out of the speaker except for a little crackling noise when I wiggle the output tubes in their sockets.

I checked the heaters on the output tubes for continuity and they still have continuity but they for some reason just refuse to light and I checked the filiment winding for those tubes on the power transformer and its still has continuity (its not open or shorted).

I'm not sure what's wrong with this radio right now and I'm so close to getting this radio going I'm just not sure what's going on with this thing right now and why the audio section suddenly decided to take a dump on me.

Any ideas?

Also can a tube die and still have continuity on the heater pins? Just wondering because it seems weird that both of my output tubes would of died at the same time but I guess its not completely unheard of just really uncommon.

If the 71 filaments aren't open they should still light. Did you measure the 71's filament voltage, both at the 71 sockets and wherever it exits the power supply?

Edit - Also, neutralizing a Neutrodyne has nothing to do with eliminating hum in the audio. It's purpose is to neutralize capacitance in the RF tubes. Hum is an entirely different problem. Did you replace the power supply filter caps like you planned?

[vortalexfan]

Originally Posted by Kevin Kuehn

If the 71 filaments aren't open they should still light. Did you measure the 71's filament voltage, both at the 71 sockets and wherever it exits the power supply?

The filiment pins on the tubes had continuity on them, which is the strange part.

Also I measured the filiment voltage on both 71A tube sockets and they both had 5 VAC on them, the filiment winding for the output tubes on the power transformer has continuity, between the transformer and the tube sockets, so its not an open winding either.

Edit - Also, neutralizing a Neutrodyne has nothing to do with eliminating hum in the audio. It's purpose is to neutralize capacitance in the RF tubes.
Hum is an entirely different problem.

I had just read in a Rider's tube substitution buidebook that I have that the 71A tubes need to be replaced as a matched set or else they will hum which these 71A tubes were NOT a matched pair, one was the original RCA Radiotron branded 71A tube and the other was a Tung-Sol branded tube, which I think might of been where the hum was coming from the fact that the tubes weren't matched.

Did you replace the power supply filter caps like you planned?

Yes I replaced the filter caps like I said I would, I replaced them both with 4 MFD 450 VDC Electrolytics wired in the exact same spots as the originals were.

[vortalexfan]

I just rechecked the filiment voltage for the 71A tubes and they were only measuring about 300 mV and I rechecked the continuity between the wire going from the terminal strip for the output tube winding to the tube sockets and I'm getting intermittent continuity and I looked at the wire and there was spots where the wire was bare and was shorting against the output transformer and the chassis of the radio so I think if I replace the wire going from the terminal strip to the tube sockets I think it might fix the problem.

[Kevin Kuehn]

Originally Posted by vortalexfan

I just rechecked the filiment voltage for the 71A tubes and they were only measuring about 300 mV and I rechecked the continuity between the wire going from the terminal strip for the output tube winding to the tube sockets and I'm getting intermittent continuity and I looked at the wire and there was spots where the wire was bare and was shorting against the output transformer and the chassis of the radio so I think if I replace the wire going from the terminal strip to the tube sockets I think it might fix the problem.

Sounds like you found your problem, hopefully before you damaged the winding. Partial grounding of one side of the filament could have something to do with the hum too. For such reasons it's a good idea to keep the set plugged into a dim bulb tester until you're very confident everything is working reliably.

[vortalexfan]

Originally Posted by Kevin Kuehn

Sounds like you found your problem, hopefully before you damaged the winding. Partial grounding of one side of the filament could have something to do with the hum too. For such reasons it's a good idea to keep the set plugged into a dim bulb tester until you're very confident everything is working reliably.

The problem with this thing is that the wiring is so hard to get to in this portion of the chassis and trying to clean the solder off the holes where the wires go into on the tube sockets is a pain in the butt because the ouptut and the interstage transformer are in the way and I can't move them very easily.

[vortalexfan]

OK, so I got the wiring replaced for the 71A tubes and that fixed the issue, now I just need to figure out how to properly neutralize this set and get the tuning dial to track correctly because several of the known local (and distant) stations are not showing up at the correct positions on the dial and one of the local high powered Mexican stations on the AM Dial is showing up on two spots on the dial.