[R-390] Removing RF Deck -R390

[Jacques Fortin]

Hi Robert,

 

The “1958” manual version is in fact the issue date of the Change #4 (C-4) and the complete manual (including the changes) is here:

https://www.jamminpower.org/PDF/R-390%20R-390A/TM%2011-856.pdf

 

T207 have to be resonant, especially if you disconnect P225 and P226.

Unless C324 is defective… Ah… maybe you find your “noise” problem also…

Could it be that C324 test open, or intermittent, as a consequence of silver migration disease ?

 

73, Jacques, VE2JFE in Montreal

 

De : Robert Nickels <ranickels at gmail.com> 
Envoyé : 29 novembre 2025 18:57
À : Jacques Fortin <jacques.f at videotron.ca>; 'R-390 Mailing List' <r-390 at mailman.qth.net>
Objet : Re: [R-390] Removing RF Deck -R390

 

On 11/29/2025 3:48 PM, Jacques Fortin wrote:

Once you will be in the RF deck, change the C231 (bathtub 50µF/50V RF gain line decoupling cap) which will give you problems sooner or later.
Read the removal and re-installations carefully !

Thanks Jacques - I've been reading and re-reading and following the procedure in the TM 11-856 manual.  I also have the Field and Depot manual dated 1962, but haven't found those corrections (so far haven't found a 1958 manual).

Just finished removing the RF deck and am puzzling over why sweeping the primary of the output transformer to the IF module T207 with NanoVNA in S21 mode,   I can't see a hint of a resonant peak at 455 kHz.  The manual says it should have a broad peak but there's just nothing.  So that'll probably be coming out.

Thanks for that tip on C231,  I'd rather not have to do this more than once!   

73, Bob W9RAN