Hi All,
I have a very nice Model 80 where I replaced all caps and rewound the oscillator coil (was open). I made the changes listed on the Phorum re: the 2 meg resistor and the other changes recommended. The radio only plays one channel (570am), a strong NY station. It is very clear and loud enough, even w/o the antenna hooked up. It does not play across the dial. I have to be tuned in to get it.
I switched the oscillator connections in case it was wrong and have the same symptom. I would it very carefully with about 18 turns of number 40 wire. I am not sure what to do, as I have checked everythng several times with no change or problem noted. I adjusted the regen and other trimmers with no change as well. Not sure what to do. Could I have amde a mistake on the coil (its the second I have done, the first was a Model 60 and plays great)?
Any help is appreciated.
Thanks,
Steve
Have you confirmed that the oscillator is actually operating?
You can do that by listening on a separate nearby radio tuned to the dial reading + IF frequency. Should be easy to hear.
-Bill
I just tuned in 1010 on a radio that the Model 80 is sitting on. As I turn the dial I dont hear anything different. What should I hear?
Hi Steve & Welcome!
If your Philco is tuned to 1010kc take a working set and tune it to 1010kc + the IF frequency 450kc equaling 1460kc.With the working set tuned to 1460kc. If the working set is a small transistor job hold it near the Philco's osc coil. If it is a tube set hook the antenna leads together. Now if the Philco's osc is running you will hear a swish as you gently tune the Philco around 1460kc.
Or
Another thing to check is to see if there is any - voltage on the grid of the mixer tube. Use a high impedance meter( like a vacuum tube job No vom) If it is running measure grid cap + to the chaiss ground - and you should see a small - voltage like a 1/2volt or so.If there is any + voltage there it ant' working. Just for laughs you may have wound the osc tickler in the wrong direction. If so just switch the connection where the wires are soldered the the components in the set.
Also
Check ALL of the resistors. They are CRITICAL to the performance. Have worked on a bunch of these superhet/regens and have found that the resistors have been WAY out of spec. Particularly the ones around the mixer and if amp/regen det.
I've got a little model 600 it''s very similar to your 80 that I did a crap load work to it.It plays great but has an intermittent it that is going to drive me nutz!!! If you care to read about my woes do a search on model 600
Terry
Thanks. I tried the oscillator test and no sound at all comes out.
I did a voltage check and noted the following (what it should be is in parentheses):
36 Det-Osc: 253 (245) P to K, 80 (80) SG to K, 6.4 (6.4) CG to K, 5.2 (8.4) K to F
36 2 Det: 45 (40) P to K, 24 (15) SG to K, .4 (.7) CG to K, 0 (0) K to F
42: 248 (240) P to K, 257 (255) SG to K, 4 (15) CG to K, 0 (0) K to F
80: 328 (340) P to K,
I am not sure how to interpret these. Does it mean anything to you?
Thanks,
Steve
Well lemme scratch my head a bit hummmm
Check #26 grid bias seems a bit low on the 42 tube.
Check #19 screen voltage seems to low on the det tube. That's a little tricky to measure as they don't tell if the det is oscillating or not. That will affect the readings.
Check #6 That will affect the control grid voltage on the mixer.
How much voltage do you have across #36?
Have you tried the align the if trimmer (#17) to 450kc? (frequency not regeneration)
Check #7 and #12 by making sure there not short to the chaiss and loosen the adj nut and retighten it to about where it was set before.
Check the the two windings on the osc coil for resistance should very low a few ohms if good
I think I would start at the speaker side of things and work towards the ant. Get bias up a bit on the 42 tube and align the 450kc if and get the if to regenerate. (I'll bet the #19,20,22,and 11 are bad)
Terry
Most of the resistors are replaced with new ones except #20 and #6. I didn't have any 10ks. #20 reads a little low at 8k, and #6 is spot on. I'll have to check later in the week as I have to leave town.
Thanks
Those should be OK. there within 20% of rating
Terry
Steve, you might try trading places with the two 36 tubes. Sometimes a perfectly good type 36 tube won't oscillate in this circuit.
Steve
I hate to state the obvious, but are you sure you don't have a problem with the rotor-stator short on the variable tuning capacitor? After all 570 is just about fully open. Ususally it's on one of the ends where the bend occurs. Disconnet and measure with a VTVM for each section to rule this out
Of Course I meant closed.
ps. 570kc would just about all the way closed.
Terry
When you rewound the oscillator coil, did you wind that outer (tickler) winding clockwise, or counterclockwise in relation to the pins at the bottom?
The winding should be wound counterclockwise in relation to the bottom pins. Although, if you would it clockwise by accident, switching the connections to pins 1 and 2 might have brought it back to life? (You said you had already tried that.)
The size of the original wire was 36 gauge; using 40 gauge should not have upset the circuit that much as these coils have a fair amount of leeway.
I just looked up my notes, and I see the outer winding should have 34 to 35 turns, not 18. You may have to try that again and then see what happens.
Funny you should mention that. Years ago (like 40) when I rewound my first tickler winding I only put 13t of #30 on it. At that time nobody had written down the specs for it. It did oscillate but only over about half of the dial. If memory serves me I think it would conk out as the frequency got higher. I would think with smaller gauge wire you would want to add a few turns to increase the coupling. The tickler or feedback winding isn't all that critical but should be close the original spec. What I do now is I take a guess at the gauge of the wire, find some in the junk box and fill the empty space where the old winding was. If it works I jot down the gauge and turns. If it doesn't just work I keep working on it till it does and jot down the gauge and the turns.
Terry
w/am 740 in the background
waiting for the shows to start
on Pete's old 37-675
I've since bought a micrometer, so I can now determine the exact gauge of wire needed for a particular application. That having been said, I have found that most Philco coils have primaries using 36 gauge wire (sometimes 37 or 38), and secondaries using either 31 or 32 gauge (occasionally 34 gauge).