Late 1920s Eveready Model 1 TRF Set need info

[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.

[vortalexfan]

OK well she's good to go now, all I need is a period correct cloth cord (a reprodution one of course), and this radio will be ready to go back together!

This thing is super sensitive for a TRF set because most of the time these TRF sets get a bad rap for being very lousy at getting anything in (radiotvphononut for example says these things are horrible as DX'ing) but I was receiving stations from Cincinatti, Chicago, Waterloo, Iowa, Fort Wayne, Indiana, etc on this radio earlier this morning with no problems and all I had hooked up to it was a 6' length of wire.

[Kevin Kuehn]

Sounds like a fun radio. With 4 tuning stages and push-pull audio I'm sure it was a pretty impressive performer back in it's day.