[R-390] A better rectifier tube for many B/A receivers. The 5AR4

[Jacques Fortin]

Hello Perry,

The 5AR4 "ancestor" is the GZ34 (G=5V filament, Z= rectifier, type 34).
Real NOS Mullard GZ34 reach stratospheric prices by now.
Many US and Japanese equivalents were made under the 5AR4 number, the Sylvania's being especially good.
Beware however that the voltage drop across a GZ34/5AR4 is smaller than the one in rectifiers using a filamentary cathode.
So the supply voltage will increase but the regulation will be better...
YMMV again...
To replace the 26Z5 in the R-390 or R-390A, I prefer the 12BW4 solution.

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 Perry Sandeen via R-390
Envoyé : 18 octobre 2024 16:18
À : r-390 at mailman.qth.net
Objet : [R-390] A better rectifier tube for many B/A receivers. The 5AR4

List,
It is easy to miss the detail that was put into the 26Z5 rectifier. It was designed with indirect heated cathodes.  This makes for an easier startup on the PS.
In most of the old B/A's they were equipped with 5V4's and similar large tubes having a cathode filament  cons5ruction.
Besides being big the y caused major problems with early R388's where the rectifier tube was  next to the power transformer causing the insulating tar to melt out and ruin the transformer.  Later Collins put a "Z" shaped shield or on some an added straight plate for heat protection.
Circa mid-50's or so Mullard in England developed what I believe they called IIRC the GZ53, It is and indirectly heated cathode tube about the size of a 5Y3 and capable of powering all B/A's using the old 5XX series.  I've had one in my 18W per channel stereo amp for years and years and it works like a champ.
Now the audiophools have repro's from a bunch of venders for astronomical prices.
The good news is a ham tube seller on line sells soviet reproductions 5AR4 for $10. The Russians make GOOD and inexpensive tubes.  The problem with the 6BA6 sized tubes is the pin configuration doesn't match what we have.
The smaller size allows for much better cooling as well as space saving.
Perry KM6FQV


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