[R-390] Conversion of R-390 IF Deck

[Tom M.]

 When I did my conversion I used the stock tubes in the R-390 deck and rewired the deck for 6V filaments according to the schematic for the series 500 deck in the R-725.
Tom

    On Monday, January 27, 2025 at 02:03:46 PM CST, Jacques Fortin <jacques.f at videotron.ca> wrote:  
 
 Hi Byron,
All depends from which R-390A transformer winding you plan to power the filaments.
The R-390 IF deck (and all the other decks, btw) are powered from the 25.2V winding in the R-390.
But in the R-390A, almost all filaments, except the PTO-BFO sting and the 26Z5 rectifiers, are powered from the 6.3V winding.
Maybe it will be preferable but more job to do,- unless you want the R-390 IF deck being able to go back in a R-390 frame again -, to modify it for the 6.3V.

For sure the 5814A should not be used in a R-390 because of their different filament current requirement (175mA @ 12,6V instead of 150mA for the 12AU7).
But they are the original tube type used in the R-390A.
They will be OK to use only if your R-390 IF deck is converted to 6.3V filaments power as a whole.

On another note, the 12AU7 and 5814A can be replaced by 5963s, which is a "computer" version of the 12AU7 made to better resist cathode poisoning than the standard 12AU7.
The more rare 7316 can be used also.

73, Jacques, VE2JFE in Montreal

-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la part de Byron Tatum
Envoyé : 27 janvier 2025 14:08
À : R-390 Mailing List <r-390 at mailman.qth.net>
Objet : [R-390] Conversion of R-390 IF Deck

A quick question regarding the filament string re-wiring in R-390 IF deck to allow use in an R-390A. I am assuming 12AU7A tubes should be used (as marked on IF deck chassis) due to their slightly lower filament current draw. Are 5814A tubes to be avoided in regards to this string re-wiring?Byron W5FH ______________________________________________________________
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