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Ron's RCA 6T2 Restoration - Printable Version

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RE: Ron's RCA 6T2 Restoration - Ron Ramirez - 12-08-2018

So this morning I aligned the set. The IF was off significantly, but not now. On band C, I was not able to bring the 15 MC signal down to 15 on the dial as I ran out of thread on the screw - as it is, the oscillator screw is just about all the way out and 15 MC is still coming in at about 15.5 on the dial. I guess that will have to do. AM (band A) aligned up nicely. No adjustments for band B.

I made a slight mod, temporarily, to the tone control circuit. I disconnected the end of C33 from the tone control. The radio no longer squeals as a result.

Once I find an apporpriate tone control and install it, this radio will be finished.

Oh, and I forgot to mention - the power transformer is not overheating, even though it had obviously leaked out a lot of wax when I acquired the set. Someone must have kept playing it on failing electrolytic capacitors. Fortunately it seems to be OK. The Solen film caps it now has in place of the electrolytics should last a long time.

RE: Ron's RCA 6T2 Restoration - Steve Davis - 12-08-2018

Ron, could you add a capacitor in series with the trimmer or possibly remove a turn or two from the coil?

Steve

RE: Ron's RCA 6T2 Restoration - Ron Ramirez - 12-09-2018

The trimmer is on the tuning condenser so no way to add a cap there.

Hmmm...remove a turn or two from the oscillator coil... Icon_think

RE: Ron's RCA 6T2 Restoration - Steve Davis - 12-09-2018

The trimmer is on the tuning capacitor, of course. You might snip a little bit of the corner off of the movable plate of the trimmer.


Steve

RE: Ron's RCA 6T2 Restoration - Steve Davis - 12-09-2018

The trimmer is on the tuning capacitor, of course. You might snip a little bit of the corner off of the movable plate.


Steve

RE: Ron's RCA 6T2 Restoration - Ron Ramirez - 12-09-2018

Thanks, I'll try that. Maybe tomorrow evening.

RE: Ron's RCA 6T2 Restoration - mikethedruid - 12-09-2018

If you can do it, you might try adding another dielectric layer to what is already between the plates of the trimmer. You might try cutting a piece of the clear plastic they use to make a bubble for the items and seal in items to the packaging cards. Worth a try before you go snipping anything off the plate itself.

RE: Ron's RCA 6T2 Restoration - Ron Ramirez - 12-09-2018

Oh, the movable plate is already far above the fixed plate, large gap between and the 15 mc oscillator trimmer screw is almost all of the way out.

RE: Ron's RCA 6T2 Restoration - Arran - 12-10-2018

I don't think that snipping the movable plate will help much since it's all the way out. It may be worth checking some of the fixed mica caps in the oscillator circuit, one may have increased in value if the black plastic case is giving out.
Regards
Arran

RE: Ron's RCA 6T2 Restoration - EdHolland - 12-11-2018

I seem to remember having issues with the RCA 110K2 that made alignment tricky, particularly on the 30m Spread Band, which uses fixed caps to modify the range of the tuning cap. I seem to remember replacing some micas to get it to follow properly.

The capacitance meter I bought definitely helped to trace drifted values, even in the pF range, when used with care.

RE: Ron's RCA 6T2 Restoration - Ron Ramirez - 12-11-2018

I'll revisit this, but it will have to wait until after the first of the year. Back into the wilderness (chemo) tomorrow, and my next "good" weekend is Dec. 22-23 during which there will be a lot of visitors. I might be able to look at it on 12/23. We shall see. I guess I'll consider the 6T2 to be my Christmas radio this year. For those of you not in the know, every year I restore a radio around Christmastime and then call that my Christmas radio. Icon_smile Last year it was a Fisher tuner.

RE: Ron's RCA 6T2 Restoration - Ron Ramirez - 12-22-2018

This evening I revisited the 6T2.

I pulled the oscillator coil after unsoldering and removing what seemed like a million wires.

Hmmm...maybe I didn't have to remove the oscillator coil. Take a look at C14, 4500 pF;

[Image: http://philcoradio.com/images/phorum/6T2/6T2_060.jpg]

Notice how it is cracked?

I also pulled C9, 50 pF. Its case isn't cracked but it does look a little swollen.

Guess I'll have to see if I can find a 4500 pF mica cap...

Question for youse guys. Once again I refer you to the service manual for this radio, previously posted in this thread but HERE it is again (WARNING - LARGE FILE - 32.1 MB).

If I still need to remove turns on this coil, do I remove them from L7 or L6? I would assume L7 since the cracked 4500 pF cap was connected to one end of it but want to make sure that is correct.

OR

Since I have to replace C14 anyway, should I just make it a lower value and leave the coil alone?

While I was looking under the chassis, I noticed that I failed to replace R1, 220 ohms. Trimmer C3, the 1400 kc antenna trimmer, is turned out at the end of its travel also, just like the 15 mc oscillator trimmer on the tuning condenser. I'm starting to think that I really should just replace all of the mica caps under there since C14 is clearly bad and C9 is questionable.

It's funny that I didn't run into this issue on the RCA T7-5. It is the radio that had obviously been in a damp environment rather than this one.

RE: Ron's RCA 6T2 Restoration - EdHolland - 12-23-2018

Hi Ron,

I'm trying to figure out the answer to your coil question. If you can replace the micas, it is quite possible the issue will be solved.

The fact that the 1400 kc trimmer is trimmed all the way out is telling us something. Might be a common factor, might be suggestive that more mica caps are suspect.

If I have any more thoughts, I'll follow up later.

Cheers

Ed

RE: Ron's RCA 6T2 Restoration - Ron Ramirez - 12-23-2018

Ed

Thanks. I'm thinking the same thing.

I believe I will reinstall the (otherwise untouched) oscillator coil today and concentrate on micas instead. It really doesn't bother me if I can't get the oscillator to track perfectly.

I can get a 4300 pF mica from Mouser but boy, are they pricey...only $8.91 EACH for a 5%, $10.26 EACH for a 1%. Since 4500 is no longer a standard value, I thought I would start at 4300. I could always add 100 pF or so in parallel if needed.

I have replacements for the 50 pF. (I think.)

*****

The more I look at the schematic, the more I think I should reduce the value of C9 (50 pF). It is connected directly to the trimmer that is all the way out...and to C band oscillator coil section L6. I think I should get a 4300 pF and a 200 pF, connecting in parallel to achieve 4500 pF. (Or maybe a 2000 and 2500 pF).

I'll see what I have on hand before ordering anything, although I'm pretty sure I don't have any such large value micas.

RE: Ron's RCA 6T2 Restoration - Nathan Slingerland - 12-23-2018

This might be a bit cheaper off of eBay:

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F252504872268