An RCA 140 - Printable Version
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Re: An RCA 140 - exray - 11-24-2010
Ah, the beloved coil rack. Here's the 'other' side. Those caps had been replaced at least once already. The rubber stamps from the repair shop in the earlier photo were underneath the rack.
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Re: An RCA 140 - Jayce - 11-29-2010
Well, my 140 is now sitting silent at home. The cost to repair it right now is a bit high and still no luck on finding an input transformer for it. So, I think I will let it sit until next spring when I will feel like messing with it again.
Re: An RCA 140 - FStephenMasek - 12-01-2010
Doug Houston Wrote:...The 53 became 6A6 (both fat pin), then 6N7G (octal)...Is there any list of such tube history? I remember that somebody wrote that the 78 was superior to the 6D6 and a direct replacement, and some history on the tubes.
Re: An RCA 140 - Jayce - 12-02-2010
If I recall right, my radio buddy and paid repairman has said that the 78 and 6D6 are indeed interchangable. Not sure if one is better than the other or not. I think the 6D6 is just a more 'modern' replacement that happened in the time right before octals came into being. Now I am curious as well.
Re: An RCA 140 - exray - 12-02-2010
I might have this totally backwards but...78 is the older of the two but is preferred by some. Has to do with the internal shielding construction. Apparently the 6D6 is a bit more prone to self-oscillation in some circuits.
Re: An RCA 140 - Ron Ramirez - 12-02-2010
I tried using a 6D6 as a replacement for a 78 as an IF amplifier in a Philco once, and it didn't work. I don't remember which Philco model it was.
After that, I stocked up on 78 tubes.
YMMV.
Re: An RCA 140 - TA Forbes - 12-09-2010
I know this is an old subject, but WOW, NICE job on the cabinet!!!! I have an R 7a upstairs in my "someday I'll get to it" radio place. After looking at your nice work am now thinking about moving it up in the priority of things to restore next.
Re: An RCA 140 - Doug Houston - 01-01-2011
Well OK, but the output transformer is also a big offender. The whole set was so crammed into that chassis, that it appears that the output transformer was somewhat inadequate, especially sincw the operating conditions of the 53 were such that it could belch out 10 watts. In those few years, RCA was riding high, with their high power audio, but it was mostly, if not all, class B. If you opened the volume up all the way, you'd get lots of sound, but it was lousy (class B) sound.
The interstage transformer is a DRIVER transformer, so you'll notice on the schematic that the secondary DC resistance is lower than the primary resistance. The 56 is pushing a class B amplifier, and the grids do draw current.
Re: An RCA 140 - theboyzz - 01-28-2011
Hello.Was wondering if anyone has a 14o parts chassis?I have one of these and it is missing the tone control reactor(l35)..Tryed using a resistor in place of it but the radio breaks down at anything above 1/3 volume.