[R-390] 26Z5W Tubes - Other Devices?

Fri Apr 17 16:57:02 EDT 2026

Jim...the diagram on that page shows the Diode mod and the subsequent 
dropping resistor just inside the outline of the audio deck...I believe the 
diode sub was a Navy mod, and they would even pinch the tube socket metal 
closed to show the mod had been performed...
Why...?  you got me...!

Jordan...

----- Original Message ----- 
From: "Jim Whartenby via R-390" <r-390 at mailman.qth.net>
To: "R-390 Mailing List" <r-390 at mailman.qth.net>
Sent: Friday, April 17, 2026 1:51 PM
Subject: Re: [R-390] 26Z5W Tubes - Other Devices?

> Jordan
>
> Thanks for the quick reply.
>
> I checked page 5-50 of the Y2K manual and found no mention of adding 
> voltage dropping resistors when replacing the 26Z5 rectifiers with solid 
> state rectifiers. I then checked "NAVSHIPS-0967-063-2110-FC6-1966 R-390A 
> Internal Heat Reduction" and it too has no mention of adding voltage 
> dropping resistors. AFAIK, there is no military sanctioned modification 
> that adds these resistors to any military receiver.
>
> If the purpose of FC6 is to reduce the heat in the R-390/URR by 
> eliminating the heat generated by the 26Z5 rectifiers, then just over 10 
> watts of heater power is saved by eliminating the tube rectifiers. Not 
> mentioned is the worst case heat caused by the 26Z5 "internal resistance" 
> of 2.2 watts per tube plate when the B+ current is 100 mA per rectifier 
> plate. So for the R-390, as a whole, it is just about 19 watts of heat 
> that is eliminated by using solid state rectifiers.
>
> Eliminating the voltage regulator would save three times the above in 
> waste heat. In fact, the voltage regulator and the rectifiers account for 
> some 40% of the power used by the R-390/URR, not including the oscillator 
> heaters. Since the B+ transformer winding specification for both the 
> R-390/URR and the R-390A/URR are the same and both receivers have the same 
> B+ current requirements, then eliminating the voltage regulator and using 
> the power supply designed for the R-390A/URR will greatly reduce the 
> operating temperature of the R-390/URR.
>
> Regards,
> Jim
>
> fLogic: Method used to arrive at the wrong conclusion, with confidence. 
> Murphy
>
>    On Friday, April 17, 2026 at 12:34:20 PM CDT, Jordan Arndt 
> <outposter30 at shaw.ca> wrote:
>
> Jim and the group...you can find the info in the Power Supply diagram on
> page 5-50 of the Y2K manual....
>
> I also added ceramic caps shunting the 1N5408 diodes to kill any rectifier
> "hash". don't recall offhand the value, but they're either .1 or .01uF 1kV
> ceramics.
>
> 73...Jordan VE6ZT
>
>
> ----- Original Message ----- 
> From: "Jim Whartenby via R-390" <r-390 at mailman.qth.net>
> To: "R-390 Mailing List" <r-390 at mailman.qth.net>
> Sent: Friday, April 17, 2026 10:57 AM
> Subject: Re: [R-390] 26Z5W Tubes - Other Devices?
>
>
>> JordanWhich manual are you referring to?JimLogic: Method used to arrive 
>> at
>> the wrong conclusion, with confidence. Murphy
>>
>> On Friday, April 17, 2026 at 11:00:00 AM CDT, Jordan Arndt via R-390
>> <r-390 at mailman.qth.net> wrote:
>>
>> While I do have a couple of spares, I found that a 1N5408 will simply 
>> plug
>> in to the tube socket very very tightly, so I added the dropping resistor
>> in
>> the Audio deck as per the manual...I have one 390A with the diodes and 2
>> with the required tubes...
>>
>> 73...Jordan VE6ZT
>>
>> ----- Original Message ----- 
>> From: "Alex Hopper via R-390" <r-390 at mailman.qth.net>
>> To: "R-390 Mailing List" <r-390 at mailman.qth.net>
>> Sent: Friday, April 17, 2026 9:16 AM
>> Subject: [R-390] 26Z5W Tubes - Other Devices?
>>
>>
>>> Hi All,
>>>
>>> I am going through an R-390/URR at the moment, and recently experienced 
>>> a
>>> shorted (filament to cathode) 26Z5W rectifier tube in the power supply.
>>> Thankfully I had a spare on hand, and was able to find a few more online
>>> to
>>> keep in my 'stock'.
>>>
>>> But this led me to wonder - were there any other devices that used the
>>> 26Z5W? I know they are a fairly rare/uncommon tube these days (hence the
>>> outrageous prices for them), but I have never seen another piece of
>>> equipment use the 26Z5W.
>>>
>>> Just curious.
>>>
>>> -Alex
>>> ______________________________________________________________
>>> R-390 mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:R-390 at mailman.qth.net
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>
>> ______________________________________________________________
>> R-390 mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:R-390 at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>> ______________________________________________________________
>> R-390 mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:R-390 at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>
>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html 