[MRCA] R390A dropping resistor value

[Ray Fantini]

I used to do a lot of replacement of rectifier tubes but not so much anymore. The advantages of SS Diodes are obvious, no heat load and higher B+ but the thing that sticks out most in my mind is that when you turn the radio on with solid state diodes the B+ supply goes to stupid levels until the rest of the tubes light up and that can cause stress on the components in the radio. Also, somehow at first the idea was to replace tubes that may not be easy to obtain but have to say I have enough 5Y3 and 6X4 tubes around here to last a lifetime and then some. With the R-390 think you have a better argument being the two rectifier tubes they are using are not that common, and heat load in the R-390 and A version has always been an issue.
Least thats me, your results may be different.

Ray F/KA3EKH

________________________________
From: mrca-bounces at mailman.qth.net <mrca-bounces at mailman.qth.net> on behalf of Mike Feher <n4fs at eozinc.com>
Sent: Friday, January 23, 2026 9:46 PM
To: 'Bill Mellema' <n3wm at yahoo.com>; 'Jeep Platt' <jeepcomms at outlook.com>; 'Military Radio Collectors Association' <mrca at mailman.qth.net>
Subject: Re: [MRCA] R390A dropping resistor value


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On a similar subject, I always change out the 3TF7 and put in a dale chassis mount 50 ohm resistor. Works great. 73 – Mike



Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

908-902-3831



From: mrca-bounces at mailman.qth.net <mrca-bounces at mailman.qth.net> On Behalf Of Bill Mellema via MRCA
Sent: Friday, January 23, 2026 9:11 PM
To: Jeep Platt <jeepcomms at outlook.com>; Military Radio Collectors Association <mrca at mailman.qth.net>
Subject: Re: [MRCA] R390A dropping resistor value



Great….thanks Jeep



Bill N3WM


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On Friday, January 23, 2026, 7:30 PM, Jeep Platt <jeepcomms at outlook.com<mailto:jeepcomms at outlook.com>> wrote:

Bill, I have the Navy book that shows solid-state rectifiers.  I will look it up in the morning...

Jeep K3HVG



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From: mrca-bounces at mailman.qth.net<mailto:mrca-bounces at mailman.qth.net> <mrca-bounces at mailman.qth.net<mailto:mrca-bounces at mailman.qth.net>> on behalf of Bill Mellema via MRCA <mrca at mailman.qth.net<mailto:mrca at mailman.qth.net>>
Sent: Thursday, January 22, 2026 8:23:33 PM
To: Military Radio Collectors Association <mrca at mailman.qth.net<mailto:mrca at mailman.qth.net>>
Subject: [MRCA] R390A dropping resistor value



Guys,



I'm in the process of solid stating the power supply on a R390A. I need the value of the series resistor listed in the field change.



If anyone can help, I would appreciate it.



Best 73's



Bill N3WM



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