[Boatanchors] Revisiting: the R390A & 3TF7 substitutes

[Al Klase]

Hi Doug,

Schematic here: http://www.radiomuseum.org/tubes/tube_3tf7.html Looks 
like that's pretty much what the guy on E-bay is doing. Bridge rectifier 
and a three-terminal voltage regulator into a load resistor. 30 bucks 
ain't so bad for something that's ready to plug in.

Mish's solution is perfectly valid for most of us, unless you have 
wildly varying line voltage. I think the original spec was 90-130 VAC.

Another way is to short across the 3FT7 socket, and replace the two 
5749's (6BA6's) it regulates with 12BA6's.

My two cents,
Al

Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/

On 8/7/2015 8:10 PM, Doug Hensley wrote:
> Poking around for information on a solid state replacement schematic, I found some interesting comments on a fix.  People are reporting that Rick Mish puts a 40 ohm 10 watt Dale resistor where pins 2 & 7 had been and removes the socket.  A seller or two on the e-Place are marketing G-10 9 pin plugs with a current regulator and pair of resistors mounted on a small vertical board.  It, I guess, is a more professional solution but I have not found a circuit for it yet or parts list.
> I really don't want to go chasing after 3TF7 tubes so polling the list here for what seems to work best for them.
> Thanks,
> Doug
>
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