[Milsurplus] R-390 hints

[Steven Gajkowski]

Modules are different in the 390, but close to same methods to remove them.  The manuals are excellent, so read through and familiarize yourself before proceeding and follow Pete's advice as well.

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Peter Gottlieb
Sent: Sunday, October 6, 2019 1:23 PM
To: milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] R-390 hints

I am not too familiar with the differences between the 390 and 390A.  I have a 390A which I made a few repairs to in order to return to life.  You will need to read the manual to learn the procedure for removing these subassemblies.  In my unit it was absolutely essential to do this in order to apply de-oxit to all the rotary switch contacts.  You will need a set of Bristol spline keys to remove knobs and couplings; these are available on ebay.  Once you understand the procedures the job is not nearly as complicated as it appears.

Peter


On 10/6/2019 12:53 PM, David Olean wrote:
> Hi surplus gurus,
>
> I am overhauling a Collins R-390, a fairly low serial numbered unit, (#870) 
> from the 1951 production order.  (NOT AN R-390A) When I got it, it was dead 
> and a tag said it had a bad 6082 voltage regulator.  I noted all sorts of 
> crispy surge resistors in the power supply as well as in the regulator circuit 
> in the audio amplifier.  I replaced all the fried parts and tried operating 
> the audio/ regulator unit all by itself on the bench. I was greeted by no 
> regulation at all. I traced the problem to a 0.22 ufd Sprague Vitamin Q cap 
> that had long un-insulated leads. Someone had pushed it aside and the bare 
> wire was touching another circuit. This caused the regulator to malfunction. 
> When I fixed that, I saw that the regulator was stuck on 220 volts rather than 
> 180 volts.   A bit more sleuthing produced some out of tolerance parts, no 
> doubt caused by the excessive voltages that burned up all the 47 ohm surge 
> resistors! Incidentally, the 0.22 ufd cap tested perfect with zero leakage 
> after 68 years.  I am running the receiver on 115 vac with solid state 
> replacements for the tube rectifiers. At 185 volts regulated, the 6082s are 
> not all that hot. I can touch the tops, but not the sides near the plates.
>
> So I got the rig running with 185 volts regulated, and things started to work, 
> but many of the lower 8 bands were inop.  I noted that fiddling with the 
> Megacycle band knob would sometimes cause a band to start working.  After 
> fixing a stuck tuning rack and broken slug, I narrowed the problem down to a 
> bad crystal oscillator sub assy. The 1st crystal oscillator was not working 
> properly.  It would show up as poor sensitivity on a band and the crystal 
> output was low and at twice the frequency that it was supposed to be on! A 
> look at the schematic showed that Collins switched in trimmers and fixed caps 
> for each band. If the switch was messed up or dirty, the trimmers were not 
> connected and the output tuned circuit was at a much higher resonant freq as a 
> result. This explains the crystal output at double the correct frequency.  The 
> second crystal oscillator for 8 MHz and above seems OK.
>
> The previous owner had attempted to remove the crystal oscillator sub 
> assembly. It was missing a screw or two on the back panel, and the internal 
> green phillips head screws on the oscillator were rather loose.  So my 
> question is. How difficult is it to open up the crystal oscillator and get at 
> the band switch? It looks like a bear to work on, but possibly someone has 
> done it and has a few ideas on how to proceed.  I suspect that the switch 
> inside is not clean or maybe is not exactly indexed.  Things are packed so 
> tightly, that you cannot really see the switch or get at it. Dis assembly 
> looks difficult and I am sure there are many pitfalls to watch out for.
>
> Any helpers?
>
> Dave K1WHS
>
>
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