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Author Topic: RME 4350A questions  (Read 2277 times)
W7VO
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« on: June 04, 2012, 05:01:27 PM »

Well, at the SeaPac ham swap this weekend I picked up a new treasure, a clean 1958 vintage RME 4350A ham band receiver for a really good deal. It is 99.9 % complete, and I was listening to some 20 CW on it this afternoon. Not exactly a FT-2000, it has lots of background noise, (and not very good ears with a 2uV sensitivity rating), but hey, it was receiving CW signals! (No SSB adapter, so this is AM or CW only). I bought it because the dial reminded me a LOT of the dash in my old 1955 Chevy.... ;-) .

A couple of questions though:

1. It is missing the 100kc calibrator crystal. Will any generic HC6/U cased 100kc crystal work here? (ie: Drake, Heath etc)
2. The vernier drive needs some help. The fine tuning control (the outer knob) moves the dial, but does not move the variable cap. Anybody rebuilt one of these, or is this why the radio was at the swap in the first place?
3. It is apparently missing the shield on the OA2 regulator tube. (Has a tabbed socket that implies that one is used.) That said, every 4350 that I've seen on Google images is missing it too. Does that mean that it does not use one, or that the tube fails so often that everybody loses the shield?
4. Is this a keeper, or should I go back to restoring my HQ-120X?

Thanks and 73;

Mike, W7VO

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AD4U
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« Reply #1 on: June 04, 2012, 06:33:14 PM »

I can only comment on #3.  I have never seen an OA2 tube that used a shield nor do I know why one would be needed.

Dick  AD4U
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K8AC
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« Reply #2 on: June 04, 2012, 08:43:48 PM »

I believe every 4350A I've ever seen (excluding new ones around 1960) had bad vernier drives.  About 25 years back I took a 4350A dial apart and decided that there was no way to restore it as the design didn't allow for wearing of the race, which is what happens.  Most of them you see have had the original vernier knobs replaced by something else.  You might want to look at Jackson Bros. ball drives, still available and sold new on eBay.  If you're creative mechanically, you might be able to use the original knobs.

73, K8AC
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W4OP
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« Reply #3 on: June 11, 2012, 06:12:58 AM »

You might find my article on updating the RME4350 in the March 2012 issue of Electric Radio of help.
The OA2 does not require a shield.
I have repaired several of the  ball drives and the article addresses this along with a backlash issue.

GL- a very nice receiver,

Dale W4OP
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W7VO
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« Reply #4 on: June 15, 2012, 11:00:49 AM »

Dale;

Even though I do not subscribe to ER, I actually have the March 2012 issue due to a trip to HRO in March where I picked one up! I read it last night in great detail. Very nice article. Right now, the drives are my main concern as they work fine sometimes, and other times the rear vernier drive does nothing. I also can see how there is quite a bit of backlash, as your article suggests. It is very hard to actually tune in a signal since the 1:1 drive is WAY too fast. This 4350A is currently absolutely bone stock, which is a great starting point.

Any caveats on getting the drives apart?

Since you seem to be an expert on these, can you answer the question about the 100kc crystal (which mine is missing)?

Thanks again;

Mike, W&VO
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W4OP
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« Reply #5 on: June 15, 2012, 11:29:53 AM »

Hi Mike,
Any 100KHz rock will work fine.
I would lay out a towel (light colored) on a smooth surface and disassemble the drive.
There are number of drawings of the exploded drive on the internet. Completely clean the races and ball bearings. I used lithium grease when reassembling. The trick is clean parts and properly adjusting the three tensioning screws w/o overtightening. The end result is a beautifully smooth drive. I still don't have a clue about that weird spring loaded coupling piece.

Dale W4OP
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