Help - Can anybody steer me in the right direction? I've repaired many of my old radios but I have five of them that sound like there under water ( Gurgled sound). New E caps of the proper mfd. new paper Caps, clean vari condensers. Tried other speakers, cleaned volume controls, swapped tubes,checked resistors and wiring. An Emerson db 301, Admiral, Motorola,Zenith, GE all are doing the same thing. Plenty of Vol., Picks up stationsthough out the dail. Some sound that way all the time, others after playing for about 15 min. Any ideas? Thanks Don
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An improperly connected loop antenna will do that.
-Bill
Thanks Bill, I did check that also. I did get the Zenith going, Two resistors were almost at the 20% limit so I replaced them and its been fine now for hours. So maybe I'll go after the others at 10% limit ? Maybe I'll get Lucky Thank You, Don
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Old carbon resistors can be really cantankerous. Even out of circuit they test OK, but once they warm up, they can go way up in resistance. Best defense it to replace all the hard working ones, you know the cathode resistors in the output, all of 'em in the voltage dividers, and if it's not drifting that is happening, just about all of 'em after the detector stage.
About the only other thing to be on the lookout is micas with mica disease. In the early stages, they usually cause no signal or weak signal. In the later stages, they can produce distortion. Wait until the condition occurs, and insert a clean audio signal to rule this stage out, then an IF signal, and see if it holds. It is a process of elimination.
It's a rare tube that craps out after 15 minutes, unless there is a problem with the connection with the socket or an arc trace on the base.
This is an interesting one, keep us posted.
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Most of the "gurgly" underwater type sounds Ive experienced in the past,in a fully restored set, were a improperly grounded loop-antenna back to chassis. Some loop antennas were the "balanced" types,some 3 or 4 wires type "coil-tapped type"antenna, that the orig mica caps & resistors were previously removed that connected center of the loop antenna back to chassis ground by a previous hacker. Try adding a 250 pf cap, or similar, in series with about a 150k resistor ( if I remember correctly?) from center of loop antenna back to chassis. Play around subbing in/out different values mica caps/resistors combinations from the center antenna loop lead back to chassis in series. If you know your resistors/& tubes are all within spec, this antenna solution idea may help. Ive been lucky before finding antenna probs by looking closely over the schematics, and finding some orig antenna loop parts/components missing in many restorations of the past. If we are all discussing overall audio "distortion"?.. try subbing other known-good output tubes as subs also. Sometimes,.. the IFs trans can be tweeked abit to "hot" also when aligning by ear. If so, back'em off abit and detune volume down slightly.Ive also ran across orig cold-solder joints at the IF cans wiring-points. Add abit of new solder just in case. Just submitting a few other ideas to check.
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Many times the loop antenna is the D.C. path to the first grid of the converter/mixer tube for the AVC voltage.
With no gain "throttle" on the front end of the set, it's running "wide open" and stations will be overloading the front-end, and then the IF stage
and the detector causing the audio distortion you hear.
The Admiral is alive again. I took the IF transformers 1st and 2nd from a admiral 615-F (the cabinet all broken up) and installed them in the other. After a little drilling, fitting and going back and forth between both wiring dia. its fine. Playing for two days now. Good sound and volume, picks up across the dial. The org. have a wafer in them, the others I installed don't they are adjusted by screws. I hope this makes sense, I've been collecting radios for some time now but only tried repairing some of them recently. Still very new to this but very careful. Don't want to kill one of them beyond repair. Also the only things I have is an old 260 and a tube tester. Well Thanks for some of the ideas. Don
