{Collins} Re: Help! Newbie restoring a pair of gold dust twins



Paul,
If none of the major components are missing, you got a fantastic deal on 
your twins.

For the 75A-4, a good place to start would be to pick up a copy of the 
75A-4 published modifications compendium from Electric Radio (www.ermag.com)
This has most of the good (and bad) modifications for the 75A-4 that 
have been published in amateur radio magazines over the years, plus a 
fairly extensive discussion on which of these are effective and which 
are not.

There are several articles on the web about the "seven deadly caps" (or 
more) in the 75A-4.  I replaced all the paper and electrolytic 
capacitors in mine, and all the interstage coupling silver mica caps 
that had high dc voltage across them before ever turning it on.  Antique 
Electronic Supply has a direct replacement for the triple 40 uF 
electrolytic in the power supply.

The V3 mod is probably a change to the first mixer, originally a 6BA7 
converter tube.  Done correctly, along with a change to the RF amplifier 
tube, a mixer mod can improve the overall receiver noise figure, dynamic 
range, and intermod distortion. There is a good low noise dual triode 
"Pullen Mixer" mod for this mixer in the ER compendium. However, if 
you're a purist, the original circuitry has performance that's nothing 
to sniff at.

The pots mounted near V22 are for S-meter adjustment.  I don't know why 
these would be dangling loose unless yours has something extra added here.

I would recommend a new three wire AC power cord for safety reasons - 
very cheap insurance.

I'm getting ready to work on resurrecting a KWS-1 myself.  I haven't 
researched this much, but we can compare notes during the process.

 From my experience with other systems, the solid state replacements for 
the 866A mercury vapor rectifiers, that is, the type that are made 
specifically for this purpose and plug into the existing tube sockets, 
are a good thing.  I would keep this mod.

Bob
WB4TGG

W4QG wrote:

>Hello All,
>Excuse the long post. This is my first attempt at restoring 
>any vintage equipment and I could use some advice. 
>
>I just purchased a pair of gold dust twins. 
>I think I got a pretty good deal, $1000 for both.
>That's the good news....
>
>Here is the rest of the story:
>I bought these from a another ham who purchased
>them from the wife of a SK who was the original owner.
>(who knows what he paid for them from the SK's wife but I'd bet 
>it was next to nothing)  He didn't do anything with them except run 
>a damp cloth over them.
>
>The 75A-4 is missing a couple of tubes (5Y3GT and 6AL5) and according to
>the fellow I bought them from the receiver was believed to be not working 
>by the wife of the SK. It appears to have had a modification around V22,
>There is a pot hanging out from the chassis. There is also a mod on V3, 
>a socket adaptor has been cut in and a cap is hanging off of it.  
>The paint is fair at best. Lots of small chips all over the enclosure - none
>or very few on the face. Has CW and SSB filters. It still has the original power cord.
>
>The KWS-1 is supposed to be working or at least it was the last time the
>SK used it - about 10 years ago. The KWS-1's RF deck appears to be in good 
>shape besides for the paint. The paint is pretty rough, front 
>face is nice except for around the lid - many many small chips on the enclosure. 
>There is a large cap from V102 to ground. It is just hanging there. Pretty sloppy...
>The audio gain knob is not original. No blower hose. The power supply seems 
>to have several mods. Paint is rough. Missing F501 and F502 fuses. 
>Also missing V506 (OB2) and V505 (12AX7). V509 (6A57-G) has been pulled and
>has a jumper wire attached between two receptacles on the socket. V503 (5Y3GT)
>has been pulled and two wires are running to some resistors (also just hanging there)
>Looks like another wire is just hanging there not attached to anything. Apparently the 
>power supply has been converted to a solid state rectifier V501 and V502 (886A's)
>have been pulled and replaced with diode rectifiers by Solitron Devices Corp. 
>Looks like the door has the original key. There are many holes along the front sides
>of the enclosure. Is there supposed to be trim there or something??? Is anyone familiar 
>with these modifications? If so are they preferred to the original design? 
>The modification around V503 looks highly suspect.....
>
>What are my options on the hose?
>
>I have read about the cap replacements in the KWS-1, any similar issues with the
>75A-4? ( I am planning on tackling the 75A-4 first....) Any advice on bringing up the 75A-4
>after being dead for 10+ years??? I wish I had a big variac... I would assume it would be a 
>good idea to replace the 2 prong power cord with a three before doing anything???
>I am planning on pulling the chassis and giving it a through cleaning. Then scrubbing
>the enclosure with some mild detergent and water.  In have checked the reflector archives 
>on the painting issue. Anyone have any recommendations?
>
>I also bought a ITT R-390A ($150), I've done some checking around on that one, I can't
>find any mention of it anywhere. Any ideas?
>
>Thanks to all.
>
>73,
>
>Paul W4QG
>
>
>Sponsored by the Collins Collectors Association http://www.collinsradio.org
>Nets: Tues: 3.805 Mc-2000 Central / Thur: 3.875 Mc-2000 Central
>Fri: 3.895 Mc-2000 Pacific / Sun: 14.263 Mc-2000 UTC
>1st Wed (of the month) AM Net 3.880 Mc-2000 local (ET, CT, MT, PT)
>Sun AM Net: 29.050 Mc-1200 Central
>
>
>  
>

Sponsored by the Collins Collectors Association http://www.collinsradio.org
Nets: Tues: 3.805 Mc-2000 Central / Thur: 3.875 Mc-2000 Central
Fri: 3.895 Mc-2000 Pacific / Sun: 14.263 Mc-2000 UTC
1st Wed (of the month) AM Net 3.880 Mc-2000 local (ET, CT, MT, PT)
Sun AM Net: 29.050 Mc-1200 Central






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