Taking the "heat" off printed circuits
 

We've all had those tubes we try to pull out and end up taking out half of a circuit board with it. As soon as it happens, you just want to hollar "F*** it!" and chunk it out to the curb. Other times you end up with a tube socket that makes a bad connection, and you're afraid to try changing the socket because the board looks too brittle. Usually it is only the really hot ones that give this nightmare. CTC-15's use 6AQ5's for sound as do many other chassis. My Curtis Mathes is basically a CTC15, and the sound tube socket makes a poor connection. Luckily, I have the option of listening to the sound thru the stereo system, so I have removed the 6AQ5 altogether. I've noticed that this CTC9 uses two 6AQ5's, and the Predicta Princess uses the 6BQ5 for sound (and mine has a bad connection there as well).

At least RCA got wise with the CTC16 and placed the 6AQ5 on the metal part of the chassis.

Has anyone here ever thought up a way to try preventing this from happening? I was thinking about attempting to make a socket to place in the exhisting TV socket, and then place the tube on top of both. This would raise the tube about an inch higher away from the circuit board. Of course, most of the heat is going up anyway, but evidently the some of that heat is reaching the board below it.

Comments? Ideas anyone? Gimme your thoughts!

Charlie,

That elevated tube socket adapter is a darned good idea. Some circuits where inter-element and lead capacitance changes would detune the circuit wouldn't like it but in an audio output stage, vertical oscillator and output, etc. this would work fine. You could also ad a polished aluminum disc heat deflector around the new socket to stop radiated IR from illuminating the circuit and components below the tube.

Rob

Rob,

Yes, that is a good point about detuning some of the sensitive circuits. Sound output circuits is what got me going on this because I have two sets that are suffering in that department. I have thought a few times about attempting to fix my Predicta's sound socket, but usually I end up deciding not to because that PC board looks weak and brittle due to the heat, and also the fact that taking apart a Predicta Princess is such a pain in the butt!

In addition to the heat emanating from the tube itself, there is also the fact that some of that heat is traveling from the heater though the tube pins. I would think that adding the socket would cut down on the heat at the solder joints at the original socket and PC board.

What I do, when there is an intermittant connection or the board/tube socket is burned, is to desolder and remove the old socket, then take a good quality chassis mount socket, and solder about 6" of bare wire to each pin. Then, I run the bare wires through the corresponding holes in the circuit board and solder them to a good connection point further back each PC trace that went to the original socket. The new socket then sits on top of the board, making the tube a little higher. This is not esthetically elegant, but it really works. It will work even when the board is totally burned under the tube socket. The method makes sure that there is a positive connection to each pin rather that relying on the burned-up PC board solder pad at the old socket. Yes, heat travels back down through the pins and can cause micro-cracks in the solder connection and therefore open circuits---also heat can destroy cheap plastic PC mount tube sockets.

Using several small computer box fans to help push air through back boards should help keep temperatures down. I'm thinking about even using AC ducted air for some of my rarer sets eventually.

That's my suggestion!
 

I have a CTC-15 ans I think I will put one fan on that 6AQ5 or use the set with the back off.
I want the chassis to look original. I wonder if a fan underneath could do well enough by blowing through the screen underneath where that tube is. My socket and board look great so I hope to keep them that way.
How about one of those little home fans right underneath the set blowing up through the screen? I think that's what I'll do unless someone here thinks it would cause some problem.

I considered doing this just for the hell of it. I think I'd want to close off the rest of that screen so that the air wouldn't blow back out the bottom. Also, it would be wise to put a filter screen on the outside of the fan so not to be blowing fresh dust into the set... which of course would be just as bad as heat.

I thought of doing this during the winter... kinda like a forced-air heater for the room! :D

I recovered several small GE portable TVs from the TV shop that I cleaned out. They have nice styling. However as all tubes are on vertically mounted PC boards (including HO, Damper, and Verical output), I only found two that had PC boards that were not charcoal.

Another reason that it is so much easier to restore Zeniths. Until about 1970, all tubes in Zenith TVs were on a metal chassis. The quality did go in before the name went on(in Zenith TVs) in those days.

To my knowledge Zenith never used tubes mounted on PC boards...on the ones with modules and tubes the tubes are still hard-wired. Even on the portables, I haven't seen a Zenith B/W tube portable that wasn't a hand wired chassis.

I also have never seen tubes mounted on a PC board in a Zenith set, including a 12" portable B&W set that I have. The set was made around 1970.

I've never seen a Zenith with tubes and PC boards either. They don't mix in my eyes. :no:

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