[TMC] GPR-90 6BE6

[Richard Knoppow]

    Intermittent _could_ be the crystal but also could be a lot of other 
things including bad solder joints or dirty contacts somewhere. Have you 
treated the tube socket with Deoxit, apply some and wiggle the tube 
around.
    For some reason I have always been intrigued with the GPR-90 since I 
saw the first one at Henry Radio when they came out. Was never able to 
find one I could afford. I think TMC made a mistake when they advertised 
them because the ads suggested the dial calibration was not very good. I 
think Collins specs made it difficult for anyone else, I remember 
hearing those who could not afford Collins saying "if I had wanted a 
frequency meter I would have bought one".  I understand the calibration 
of the GPR-90 is actually very good.  It is certainly one of the sexiest 
looking receivers ever made.

On 8/29/2016 1:33 PM, Dave McDonald wrote:
> John, Richard and Jim,
>
> While I agree that the crystal could be the culprit, I don't see how it could "come and go".  Like PG!  Now, it has been playing for a few hours.  I pulled the V4 again and re-plugged it.  I tweaked L19 again, tight range to oscillate.  Earlier today, it would quit oscillating and come back on.  Hasn't done that again.
>
> I'll let it play and see what goes on.  Digging out the crystal is major effort!
>
> Thanks for the lead.  I'll get back with any permanent fix.  Still love the receiver.  Quite stable on 20M after it gets warmed up.  I don't even use the GSB-1 since it sounds so good with the BFO.  I have all this Collins gear around , '380. 'A4 and 'SB-3 but I migrate back to the GPR-90. Shows what us TMC folks like! Barcelona IY was coming in earlier.
>
> tnx agn,
>
> Dave
>
>
>
>
> From: John Poulton
> Sent: Sunday, August 28, 2016 4:31 PM
> To: Dave McDonald
> Cc: tmc collector's group
> Subject: Re: GPR-90 6BE6
>
>
> Dave,
>
>
> We're talking about the 2nd mixer, V4, right?  I have actually encountered a variation on this problem on multiple GPR-90's, but in all cases found that it was the 3.5 MHz xtal, Y2, not the 6BE6, that was causing the problem.  I wonder if it's the xtal cooling down that's causing the behavior you're seeing?
>
>
> If you do need to replace the crystal, International can make them for you.  This xtal is used in a series-tuned arrangement..   I'm sorry that I don't know the fixture capacitance in this circuit, but perhaps you can find a way to measure it.  Again... always assuming it's the crystal, and not something else!  The xtal frequency isn't terribly critical, in any case--you can "align around it" if it's a few Kc off.
>
>
> The crystal is "conveniently" located in the subchassis that sits on top of the main chassis on the left side of the radio, viewed from the front.  You can (barely!) get at the crystal by removing the mounting screws for this chassis, and gently prizing it up to expose the underside of the chassis.  Not really the most fun thing you could be doing, but easier than the dreaded RF-compartment repair on an SX-28!
>
>
> I'd be very interested to hear what you find out once you bottom out on this problem.
>
>
> 73, John K4OZY
>
>
>
>
>
> On Sun, Aug 28, 2016 at 4:13 PM, Dave McDonald <jdmcd at ij.net> wrote:
>
>   John and TMC Net
>
>   Has anyone experienced the converter tube, 6BE6, quitting after about an hour from being turned on?  Swapping tubes doesn't help.  The pentagrid converter works properly but after about an hour quits oscillating and receiver goes dead.  OK when switch to lower bands where dual conversion turns off doesn't help.  I tried with IERC heat dissipating shield but no help.  I leave the shield off so can swap tubes to see if helps.  Tube cools off and starts oscillating again.  I haven't tried swapping the 220 pf cap, C33, yet and don't really want to.
>
>   Any help?
>
>   Tnx,
>
>   Dave K4EWC
>
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL