[Milsurplus] Ben Hall's Tube Adaptors: Get You Some'o These!

[David Stinson]

We've been working on substituting affordable trasmitting tubes 
for those that have been abducted by the audiophile crowd 
and thus, priced out of reach for we mere mortals.
Been concentrating on substituting for two VT-25s 
and two VT-52s in the BC-230 transmitter. 
So far have worked with 6AQ5 (7 pin) and 5763 (9 pin).
Ben Hall, KB5BYB rose to the challenge and created
adaptors for this task and kindly sent me two sets.

Folks- I am impressed!  These are very high-quality and
obviously a "labor of love."  Outstanding work, Ben.
The bases can be assemble for either 7-or-9 pin sockets.
Assembled them with no trouble and they work a treat.

http://home.netcom.com/~arc5/SCR-183/7pinsubs.jpg
http://home.netcom.com/~arc5/SCR-183/7pinBC230.jpg
(Note to Hue:  That's the transmitter you sent.)

I installed a capacitor across the filament pins
so both heater and cathode connections would be at 
the same RF and audio potentials.
http://home.netcom.com/~arc5/SCR-183/9pins.jpg

IMPORTANT:  Whatever your application, the Cathode
of the miniture tube needs to be connected to the Heater pin
on the 4-pin base that is electrically nearest to ground.
In the BC-230, connect the MO and PA cathodes to 
Pin 4.  If you don't, the tube cathodes will be filament 
voltage above ground and it will mess-up stage bias.
Once these are installed tuning and neutralization will 
need to be tweeked, of course.
They lowered the stage losses as well.
With the transmitter running on the original dynamotor 
in the complete SCR-183 set, he 6AQ5s are doing
 between 6-7 watts out on 40*
(one "hot" tube is giving me between 8-9)
and the 5763s are making 5 watts out on 30 meters.*
The 6AQ5s work best when running 80 and 40 meters
"normally."  The 5763s don't do so well there for some 
reason but work fine when doubling in the final.  
Maybe it's because 5763 was designed as a VHF tube?
I'm making contacts on 30 meters using the 5763s.**
I think there's a better 9-pinner out there.  Still looking.

The $40 price tag for a set of four of these is a good deal.
If you try to buy ONE VT-25, you're certainly going
to pay a lot more than that.  Might get an empty tube 
base for that.  And try to get all these parts together for
your project; your time is worth more than that.

Ben- I think you should offer these to the Audiophiles.
I'm betting for say, $60 a set, they'd buy them like hotcakes.
Just need to convince one of the Audio "Gurus" to try them.

If you ever intend to get that -230 or -223 or any other
such rig running, get some of these.   Excellent investment.

GL ES 73 OM DE Dave AB5S

* The 40 rig has a non-destructive change to make it 
   xtal control.  The 30 rig has a 5 MC coil pack with
  a broken PA/Antenna coil wound to double in the final
  and feed an antenna tuner.  
  Chirps a little but works well.

** (NOTE for those working on these transmitters:
I'm back to fiddling with the bias on the modulators again.
"Stock" bias runs the 6AQ5 modulators too hot. 
Still investigating. For the 30- and 40-meter rigs which 
are only used for CW, I disconnected the MOD plates 
and the two tubes are there just for filament string ballast.)