Zenith 6S254 Intermitten Reception
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You could possibly do this (be careful with it).
Power down.
For the #4 1st IF XFMR, disconnect the B+ (the wire shown to connect to C6 and the lower coil terminal in teh sch). Make sure it is disconnected and maybe insulated so it does not touch anything.
Turn the radio and make sure the B+ is not present at the 6A8 plate.
Connect the generator (you can do it via 0.1 - 0.5uF cap or even directlyacross the #4 1st IF transformer ). Connect the GND to, say, the lower pin and the signal to the 68A plate.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Hi DConant,
Stert by trying the grid cap of the 1st IF (with the grid wire in place; ground the ground lead of the generator; set the generator to the IF frequency). This does not check the 1st IF transformer secondary coil but may check the trimmer capacitor. You could connect to the 6A8 plate terminal through a capacitor (I'm guessing 0.001uF; remove the tube). That would validate the transformer. If the intermittent occurs, then the issue is in the IF, Detector or Audio stages. However, if you played an external input for a long time with no issues, the AF stage and most of the power supplt is good.
Next step would be to connect to the grid cap of the 6A8 directly (Disconnect the grid wire and connect the ground terminal of the test lead to the chassis). Set the tuning cap full open, set the generator to whatever frequency near 1630KHZ that is received.
Next, same connections but connect the grid wire also. If the first 2 steps are successful but the 3rd step causes issues, then the antenna coil may be at issue.
Finally connect across the antenna and ground terminals.
One other possibility:
Check the screen grid voltages on the 6A8 and 6K7 when this happens If too low, this will greatly lower the gain of these tubes. In fact, in very early "Screen Grid" radios (radios containing tetrode RF amps), varying screen grid voltage was a method of controlling volume, but adjusting cathode bias and shunting the antenna coil with the same pot was more popular.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
Best Regards,
MrFixr55
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Its a nice day today and I have outside work to do. Hopefully tomorrow.
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I have the sig gen connected across the primary of the first IF as Mike described. Sig gen is set to 456kc at 600mVpp. Tone is playing with AVC at -5 volts. My sig gen goes to sleep after a while but I don't know if it just the screen or the whole thing.
MrFixr I will do your suggestion after this test.
Dan
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Do you have some cheap old one lying around? It sounds the one you are using is the newer type with some microprocessor inside.
Or a real old-fashioned digital like my HP. They are digital synthesizers but are old school at heart.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Yes I have an Eico 330. My new one is a UNI-T UTG962E. Signal is still playing and the screen is sleeping. AVC is still -5 volts. Gonna step out for an hour and leave radio and gen running.
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Gotta get that outside work done!
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If it never fails with this one, then the gen goes to the outside antenna connector
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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If you do not see problems within the same more or less time when they would normally occur, then move the sig gen to 6A8's grid cap with the lead wire removed.
Then if it is still good, you could connect the grid cap back and connect the gen to the Antenna input.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Quote:Yes, Candohm was and still is my suspect also, but I think it was measured for the voltages (well, for the one that biases the Cathodes, 2V or something, which is the one that matters) and the voltage stayed put.
Yes, I recall reading that, but with only 3 resistors it is such an easy mod, I figured it was worth a try. Plus, it's a good idea to pull that candohm to prevent issues down the road.
John KK4ZLF
Lexington, KY
"illegitimis non carborundum"
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Exactly.
Good things are not called Candohms.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Hello Dan,
I know with beautiful weather outside and lots yard work restoring one my radios is hard to do I am only working on stuff for other's right now mine will wait till winter.
Sincerely Richard
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I don't have anyone to do work for.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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The tone from the sig gen played for 12 hours yesterday. I turned it off everything and went to bed. Turned back on this morning with tone still going and AVC at -5 volts. B+ is now connected back to the 6A8, gen is connected to ground and grid cap with wire off. Gen set to 1600kh at 100mv (lowest it will go) showing AVC of -8.5 volts. Now we wait.
I will order up some resistors and replace the candohm.
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