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Possible Oscilator Problem? - Printable Version

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Possible Oscilator Problem? - Kahuna59 - 10-10-2023

Hi all. I struggling a bit with the 41-610P set that I have been restoring. I recapped and replaced at least 95% of the old decomposed rubber insulated wire. The presets work great but I get nothing when using the tuner on any band. I removed the tuning condenser, cleaned and test it and it's fine. I assume that since the presets work , then the tubes shouldn't be the issue.  I removed the Oscillator transformer and measured the resistance. You can see the results in the attached pictures. The coil between terminals 5-6 measure 3.7 Ohms. The schematic lists a spec value of 0.4. Would this be enough to cause the problem I'm seeing? Any suggestions of path forward? Thank you!

RE: Possible Oscilator Problem? - Chas - 10-10-2023

Quote:Would this be enough to cause the problem I'm seeing? Any suggestions of path forward?
-Yes.

-Look for breaks at the solder tabs, reconnect, solder.

-Remove replace with another coil.

-Remove from chassis, remove wax, determine wire size and turns of errant coil, rewind, wax over, re-install.

GL

Chas

RE: Possible Oscilator Problem? - Kahuna59 - 10-11-2023

OK, thanks and appreciation for the reply. I guess that's the problem then. Good to know, I'll start start chipping away at it.
I hate dealing with thin wire - it always leads to new swear words.

RE: Possible Oscilator Problem? - Chas - 10-11-2023

Quote:I'll start start chipping away at it.
Do not "chip away", there is risk of mechanical damage that could obscure how it was made. Do look for poor connections to the errant coil winding, usually at the terminations. Besides, if it is an easy fix, the heat will drive off 90 years of moisture. A solvent such as mineral spirits will dissolve bees wax too.
Warm with a heat gun, bees wax only needs 140F or so... Look for poor connections at terminals, green spots are corrosion. Keep heat away if mineral spirits are used, fire danger. Spirit fumes will be carburized by heat gun, toxic, as well as dangerous

If intent is rewind, number of turns, wire size (type) is important. If there is a insulating layer between coils, that is celluloid and decays then corrodes the wire...

GL

Chas

RE: Possible Oscilator Problem? - Kahuna59 - 10-12-2023

Yeah, poor choice of words. By chip I meant start working. The heat gun worked really well, thanks for the tip. Took about 170F to soften it up. Used Q-tips to gently remove the wax. I still have an insulation layer on it to deal with. I'm going to take it real slow and make sure I have everything I need before I start unwinding. I didn't see any obvious failure areas but there's clearly an issue in the coil between the #5 and #6 terminals. I need to determine the AWG and get some wire, determine what kind of insulating tape to use and how to keep the wires in place while winding. I could also use some new eyeballs and a pair of smaller hands as well. Thank you for the advice.

RE: Possible Oscilator Problem? - Chas - 10-12-2023

Try to keep the insulating plastic layer the same thickness. I have found plastic bottle is O.K. (PETE or PEET). But Kapton tape in layers probably better because adhesive will keep it in place.

Avoid using coil dope, if there is a mistake any dope will make it difficult to undue.

Plain bees is useful, no paraffin as that is slippery and melts at a lower temperature.

Bees wax for encaustic painting is hardened with Damar resin, that, also raises the temperature. IMHO the mix ratio is likely less than for encaustic as encaustic is rather hard... But is is a tough painting wax in use since the 5th century Icon_eek

Dipping the clean form into cup of melted bees wax will drive out moisture, leave long enough to thoroughly heat the form then remove, "drip-dry" a thin film of bees wax will leave the form "sticky" and wire will wind nicely and stay in place. Don't let wax get under Kapton tape as it won't stick.

If your unsure of connections...

Pick a terminal preferably #1 bend a terminal to ID., using a sheet of paper, put #1 in upper left, draw a large rectangle near the edges of the paper and translate (un-roll) all the data on the coil to the paper as a diagram. The wind direction, turns, wire size, access holes, positions of windings. Then, if you get tired or forget details, work can be set aside finished later, bees wax will hold the windings for a week or so... it is extra work but a complex coil, like an oscillator for a multi-band set, is a memory nightmare...

You can dip the completed coil in the hot wax. Bees wax with Damar would be better but I have used just plain pure bees wax. Dip and let sit heating to drive off moisture. Then remove and let cool to room temp.. Then, dip quick again, like dipping for a candle, dip twice and the wax will build but QUICK so not to heat the coil and loose the wax build.

GL

Chas

RE: Possible Oscilator Problem? - Kahuna59 - 10-12-2023

Thank you Chas. I appreciate the good advice. Have ordered the wire, Kapton tape and I have a supply of Bee's wax. I'll get my plan together. Good idea about mapping the coil specifics. I don't want to screw this up - I've already put many hours in the restoration. While I'm waiting for the order I'll have time to work on the Beam of Light tonearm. The photocell should arrive today. Thanks again.

RE: Possible Oscilator Problem? - Kahuna59 - 10-23-2023

May latest progress on the 41-610P was rewiring the oscillator. Many thanks to Chas for the advice on how to go about it. It helped al lot. I took my time and it all seemed to go pretty well. 

I installed it and turned on the set. At first everything seemed as before. The presets worked fine but nothing out of the tuner. Also, the volume was less than before. I probed around to check the connections and also tweaked the BC trimmer a bit. Didn't do anything very significant. At one point I switched from the presets back to the broadcast band and started picking up all local stations, that's progress, but the volume was low and the signal quality wasn't the best. Tried other bands and probed around some more looking for what could have changed. Then I lost the variable tuning reception and, on the presets the voices were sounding  like the chipmunks. I think the oscillator is ok because I was able to tune on stations, at least for a while. 

I'm curious about what caused the volume drop and why the problems seem to come and go. Any ideas on where to start looking?
Thanks,
-E