[Boatanchors] R-390A crystal oven question

[Jacques Fortin]

Hello Brian,
If this is not the 5654 filament that gone south, it can be C357 that gone
short.
This capacitor was reported going faulty in a few instances (silver
migration within).
When it fails, it can be replaced by a 100pF, NPO Ceramic.
It can also be R210 gone open (have to use a 56k ohms there, BTW) or R211,
eventually.
If P221 is disconnected from J221, the center pin can be probed to see if
there is any 17MHz present there.
If nothing can be seen using a new 5654/6AK5W, you are due for a RF Deck
maintenance, I fear.
The Crystal Oven that contains both the 17MHz and 200kHz Xtals should feel
hot to the touch when the set is on and not be harder to remove from it's
socket than an octal based tube.
If it resists, maybe some previous owner glued it in place, or worse,
soldered the pins below the chassis....

I do not believe that the 17MHz Xtal became bad, but... who knows ??
If ever a new T207 is needed, I still have some spares.

73, Jacques, VE2JFE

-----Message d'origine-----
De : boatanchors-bounces at mailman.qth.net
<boatanchors-bounces at mailman.qth.net> De la part de brianpepperdine
brianpepperdine
Envoyé : 8 novembre 2021 14:42
À : Boatanchors-qth <boatanchors at mailman.qth.net>
Objet : [Boatanchors] R-390A crystal oven question

My R-390A lost reception below 8 mhz. This is the triple-conversion
operation of the receiver, thus I have turned my attention to the first
mixer area etc., which includes the 17 mhz injection via the crystal oven.

I swapped out the 6C4 and another 6C4 in the mixer chain (interchanged) and
it runs still OK above 8 mhz in Double Conversion mode, so the 6C4 is fine I
think.
V207 (5654) tube is bit hard to get at... so the other issue to be looked at
is the 17 mhz crystal in the HR202 crystal oven. If I take out the oven in
theory I can swap in (temporary) a 17 mhz xtal from elsewhere in the
receiver xtal bank.
However, the xtal oven seems a bit resistant to being pulled out... the Y2K
390A manual talks about a spring retainer on top of HR202 (I have none). It
seems to me that HR202 is sort of in a tube socket kind of thing (as per
diagram) but with any gentle tube removing kind of movement (gentle rocking
and pulling) it does not seem to budge. I don't want to really 'wrench' on
it. It IS in a socket arrangement, right? Not hard wired....?

In any case, having the xtal swapped would help diagnosis or fix.. but even
so its lack of presence would also help me in getting my fingers into the
tight space to remove V207 out to test it (it does glow, but what does that
really mean in the Grand scheme sometimes).

Anyhow any opinions on the xtal oven removal would be appreciated... 
or ideas on loss below 8 mhz reception.
I hope its not a transformer (one other possibility)  because then we are
getting way beyond my level of competence ( and obvious lack of spare
parts). 

Tnx
Brian VE3HI