Dumont RA-103D "Rumson" restoration

[John Marinello]

Is it just the photo, or is that 12LP4 aluminized? 12KP4??

[bandersen]

No, it's not aluminized.

[M3-SRT8]

Originally Posted by bandersen

At least the ceramic inductuner shaft is unbroken.


A 100 q-tips later

How did you get that tuner cover off? It has small phillips head screws behind the RF towers and I can't get to them.

Lee

[bandersen]

Needle nose pliers and patience

[M3-SRT8]

Originally Posted by bandersen

Needle nose pliers and patience

Ah. No easy way. Just like when I cleaned up an RA-105B tuner 20 years ago.

Lee

[bandersen]

Who's up for a challenge? Speaker cone is trashed and output transformer primary is open.

New cone has been ordered and I dug up a transformer I think will work. At least it's the same size and has continuity.

[bandersen]

Meanwhile, I patched the set up enough to try a full power up. Relay is still bypassed and power resistor just tacked in place.
Need to dig up a new eye tube too.

Also, discovered the flyback is a replacement and not secured very well.

Replaced HV cable with more convention HV cup and rigged up a 5AXP4.



After a few pops and cracks that made me jump, we have a raster!


A lot of control fiddling later, we have an image. Tuner seems to be off by a couple channels.
I'm both surprised and relieved this set actually produces an image after all it's been through.


Some tube swapping and more control twiddling and we have a decent image.
Mind you I have no shields installed and am feeding a signal in with alligator clips.

[Electronic M]

Originally Posted by M3-SRT8

Ah. No easy way. Just like when I cleaned up an RA-105B tuner 20 years ago.

Lee

One thing you can do is remove the IIRC 4 Philips screws under chassis that hold the tuner to the chassis and with the tuner loose you can get to those screws....I will add the caveat that Ive never owned a square dial 103 (only both versions of the round dial) so I don't know if the square dial tuners allow you to do this as easily. I've had at least 3 RA-103 tuners off in the something like half dozen RA-103s I've benched. Two were to swap when I was making a good chassis out of 2 mouse eaten ones, and the other was to deal with a snowy picture issue...That one it turned out that a mica in the lower compartment of the tuner that coupled the antenna to the RF amp had a snapped off lead at the cap body.

[bandersen]

Just about done, but have one annoying issue.
The dial scale is off and I can't tune below channel 4!
Now the cam kicks in at the right spot where it spreads out the FM radio portion but LO is off.

Closer examination revealed that when I am tuned as low as it will go, there are still a couple turns left on the coil.
When I'm at the top of the dial, the coil is nearly at the opposite end.

It seems like I need to bump all three coils over one turn.

Is that even possible and, if so, how? Short of taking it apart that is.
Is there a way to adjust the mechanical stop?

[bandersen]

It sure looks like one could tweak C23 to shift the LO. Not sure if I can get at it easily or if that would also require tweaking C16 and C17 to track properly.

[Electronic M]

Bob, if you have full shaft rotational travel stop to stop, just pop out all 3 sliding contact fingers (one under each coil) and reinstall them on the end winding. Just push them out from the side with a small screwdriver. I always pop them out to clean them. One coil is reverse spiral so one contact goes in on the opposite end from the other 3.

[bandersen]

Yikes. Do they really come out that easily? That big IF can will make one section extra tricky.
Before I attempt, I want to double check reception at the upper end of the dial.

[bandersen]

Yes, upper end also off by about two channels. Ok I'll give it a try

[bandersen]

Well, down the rabbit hole we go...

I removed the stop and turned one more rotation towards the low end and it's now cleaned and lubed.

[bandersen]

So, the rollers are all shifted over one rotation now. Did it solve the problem? Sort of.
Yes, I can receive 3 and 4 now, but 3 is smeared over a big range. I think I need to adjust the cam behind the dial that alters the action through the FM band. Upper VHF reception seems a bit degraded but the goal to get clean 3 & 4 has been achieved.