[R-390] TR: R-390 Woes

[Jim Whartenby]

Jacques
I find your comment about trying different tube types in a socket interesting.  No two tubes of any designation have all of the very same characteristics.  This is do to the tube's bogie number which is just a statical average, a bell curve if you will.  It is quite easy to match two tubes to a single bogie number, more difficult to match two bogie numbers and very difficult to match four.  I have been told that swapping tubes of the same type found in the same radio chassis could improve overall performance for final acceptance testing.  

For a radio initially designed during WW2 and first advertised in 1946, I would think that the tubes initially used in the 51J could be easily replaced with tubes of improved characteristics which should make for a better radio.  The 6BA6 and 6BE6 were released for production by RCA in October, 1945.  Tubes with higher gain and lower noise, like the 6BY6 and 6CS6 were both released in 1953.  They were designed for the demanding TV market.  The four digit tubes mentioned were made for the burgeoning computer industry and were released in 1965 and 1985 respectively.  I find it interesting that new computer tubes were developed in 1985!  All of these have the same 7CH basing diagram.

Perhaps all of this is similar to the improvement made in the performance of the WW2 Spitfire?  All that was changed was to put 100 Octane gas into the fuel tank!  <grin>

Regards,
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy 

    On Wednesday, October 8, 2025 at 02:45:13 PM CDT, Jacques Fortin <jacques.f at videotron.ca> wrote:   

 Hi Jim,
Yes, this should have been the Bill Orr PD mod.
As we are there, VE3TOU (Treetops Circuits) made a plug-in PD for it (well, kind of) see attached.
About trying different tube types on a R-388 PD, I never do it, despite I have one Collins R-388 but it is still to be restored.

73, Jacques, VE2JFE in Montreal

Jacques
Good catch.
I have a 51J-3 aka R-388 that also had the 6BE6 Product Detector mod installed.  It must have been inspired by the Bill Orr Ham Radio magazine article.  I agree that it doesn't work very well.  I removed the mod but haven't decided on what to do.  Either make it work better in SSB or return it to original condition.  I think that there are several pentagrid tubes that have the same pinout as the 6BE6 but are less noisy with higher gain.  Has anyone tried the 6BY6, 6CS6, 5915 or 7036 in place of the 6BE6?
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy