[TMC] GPR-90 6BE6

[Richard Knoppow]

    ICM probably has all the crystal parameters.  They will tell you 
over the phone or via e-mail. Unless its something very exotic I would 
guess the price at around $25. I've gotten a number of crystals for 
Collins and Drake from ICM, all were perfect and came in a couple of days.

On 8/28/2016 1:31 PM, John Poulton wrote:
> 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