75A2 Main Tuning Question

[Carl WA1KPD]

I just got my 75A2 of eBay and have a question. The main tuning knob is a bit wobbly as if it is on a flexible shaft. The PTO tracks nicely with no jumps or anything. It is as if the knob is floating.

Never having owned one of these before is this normal, and if not any ideas on what might be remiss?

Thanks and 73s

Carl KPD

[KL7OF]

Carl,   Take the knob off and check out the bushing in the panel...It could be worn or missing......Gud Luk    Steve

[Carl WA1KPD]

Thanks Steve,

You nailed it!!!!. I took the knob off and both screws holding the bushing oin place were very looks. Oiled it up, snuggged them down and it feels great. Never thought it would be that simple.

First time I have owned a Collins so I  had no idea of what I would find.

Best 73 OM

Carl, KPD

[w3jn]

Carl - were you the guy who bought the "parts" 75A2 from a guy in Kansas or somewhere? 

I just got 2 from the same guy.  Both have loose shafts.  One has a product detector mod using a 6SN7 plugged into the FM adapter socket and a mechanical filter mod.  That one had a seriously bad static problem which turned out to be a bad 56 pF capacitor on the plate of the 12AT7 oscillator, but other than a seriously out of cal PTO and a funky RF gain pot it works well.

THe second one is completely different.  It appears that this one is a factory unit that has been updated in accordance with the QST article by Collins engiineers circa 1956.  It has 6BA7 mixers (vice 6BE6s) and a 6CB6 RF tube.  The tubes are labelled on the chassis with factory silkscreening.  It is much more neatly wired under the chassis also.  Haven't powered it up yet.  It's missing the meter, a bunch of tubes, and some knobs, but is otherwise complete.

[Carl WA1KPD]

Hi John,

This one came from NV. The seller has a rather morbid id:  ”dead-peoples-things ” I am not aware of other ones he has sold. Radio is in pretty good shape. Very clean inside and could use both some outside cosmetics and is a little deaf. Going to keep my eyes out for a better front panel. Also need to find a source for pint for the cabinet

Never liked the A4 series on AM and have played with a J4 and got tired of cranking the mc knob so I wanted to try a A2 and it seems to be what I have been looking for. Time will tell as I can be fickle!

How is the Meissner coming along? I was the guy set up across from you at Hosstraders who kept coming over and drooling on it. Still envious!

73
Carl- KPD

[w3jn]

Carl - not the same guy then.

The Meissner is sitting waiting patiently for some time to attend to it.  I took it out of the cabinet and it's pretty much a mess underneath.  It's going to require a complete rebuild, and it appears the RF section will have to come out as I see no other way to get to the bypass capacitors entombed within.

BTW that product detector mod that was done to one of my 75A-2s works very well.  It's a typical dual triode product detector that can be found in any 60's Handbook.  All the audio switching and filament wiring is done already at the FM socket.  I did a mod to the AVC circuit so as to have some fast attack/slow decay.  Works better on fluttering AM signals also.

This 75A-2 has typical crummy Collins audio.  I'm thinking that the other one, as it's in much filthier condition, might benefit from a push pull audio stage