DuMont RA-103 Doghouse Horizontal Problems

[M3-SRT8]

Doing resistance checks on the 6K6GT Horizontal Oscillator (V21, per Sam's) and came up with open readings on Pins 3,4, and 6. They should read 6Kohms, 11Kohms, and 800 ohms, respectively. It is measured from Pin 8 of V27, the 5U4 LV Rectifier.

Also did resistance checks on 6AC7 Horizontal AFC (V20) and came up with open readings on pins 6 and 8. They should read 20Kohms and 23Kohms, respectively, and are also measured from Pin 8 of V27, 5U4 LV Rectifier.

The symptoms on the CRT is a bad smearing of the horizontal picture, and a stretching and cutting off of the left end of the picture. Unable to use L30, the Horizontal Output Trans, to restore the left side of the picture.

I replaced the Horizontal Sweep Coupling (C90, 1000pF, 500V), Horizontal Discharge (C89, 680pF, 500V), Phase Shifter (C84, 10000pF, 500V), and Horizontal Synch Coupling (C78, 47pF, 500V) (along with all new Tubulars and Lytics) because I've read how these Caps are frequently toast. I used new Silver Micas, all rated 500V.

What's amiss?

Thanks

[Phil Nelson]

Is your set an "original recipe" RA-103? I used the Riders manual when restoring mine. I thought the Sams (93, anyhow) was for a later flavor, RA-103D.

Either way, have you done any voltage checks on those tubes? Might be informative.

Phil Nelson

[M3-SRT8]

Originally Posted by Phil Nelson

Is your set an "original recipe" RA-103? I used the Riders manual when restoring mine. I thought the Sams (93, anyhow) was for a later flavor, RA-103D.

Either way, have you done any voltage checks on those tubes? Might be informative.

Phil Nelson

It's really a DuMont Clone, a Stromberg-Carlson TS-10, with a 10BP4A, but, the circuitry is virtually the same. I'm using Sam's Set 90 Folder 3. It's a DuMont Doghouse RA-103 in a different cabinet. Cool cabinet, BTW.

I'll do Voltage Checks today. I stopped for the night when those circuits showed open. I thought that was obvious enough...

[Tom Albrecht]

Hi Lee,

Your function selector switch needs to be in the "TV" position for this measurement to work. If it is on FM or Phono, you'll measure open. Can you check that?

[M3-SRT8]

Originally Posted by Tom Albrecht

Hi Lee,

Your function selector switch needs to be in the "TV" position for this measurement to work. If it is on FM or Phono, you'll measure open. Can you check that?

Confirmed. Open circuits on TV1 and TV2.

I checked T5A, the Horizontal Deflection Coil, it reads 12.7 ohms, specs call for 14 ohms.

[Tom Albrecht]

Well, something is not right here. If there actually were an open circuit from the points you mention to the B+ supply on the 5U4, the horizontal oscillator would not function, and you would have no picture. Somehow the measurement you are making doesn't seem correct. Not sure what to suggest other than to turn the set on and measure those pins for voltage, where I'm sure you will find that B+ is present.

[M3-SRT8]

Originally Posted by Tom Albrecht

Well, something is not right here. If there actually were an open circuit from the points you mention to the B+ supply on the 5U4, the horizontal oscillator would not function, and you would have no picture. Somehow the measurement you are making doesn't seem correct. Not sure what to suggest other than to turn the set on and measure those pins for voltage, where I'm sure you will find that B+ is present.

I know. I'm getting a full raster.

I checked T3, the Horizontal Output Transformer, just for kicks. It read the following:

Pole 1 to 3: 407 Ohms, Spec 405
Pole 1 to 2: 168 Ohms, Spec 165
Pole 4 to 6: 7.3 Ohms
Pole 4 to 5: 7.1 Ohms
Pole 5 to 6: 0.5 ohms (this is the Width Adjustment)

So, that looks ok to me.

I'll do voltage checks, and get back to you...

[M3-SRT8]

Originally Posted by Tom Albrecht

Well, something is not right here. If there actually were an open circuit from the points you mention to the B+ supply on the 5U4, the horizontal oscillator would not function, and you would have no picture. Somehow the measurement you are making doesn't seem correct. Not sure what to suggest other than to turn the set on and measure those pins for voltage, where I'm sure you will find that B+ is present.

...and, make sure to bridge the M7 Relay to close.

Gad, what a twit I am sometimes.

The readings (resistance) are as follows:

V20 (6AC7) Hor. AFC: Pin 4, 696K vs 1.8Meg (spec)
Pin 6, 11.88K vs 20K (spec)
Pin 8, 24.9K vs 23K (spec)

V21 (6K6GT) Hor. Osc: Pin 3, 5.38K vs 6K (spec)
Pin 4, 8.7K vs 11K (spec)
Pin 6, 466 ohms vs 800 ohms (spec)

I'll get back to you with Voltage Readings. Pin 4 measurement on the 6AC7 seems odd...