[ARC5] Ben Hall's Tube Adaptors: Get You Some'o These!

[Ben Hall]

Good morning Dave and all,

On 1/24/2015 6:18 PM, David Stinson wrote:
> 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.

Thank you much for a nice review of them, the photos, and your continued 
work on using the 7/9-pin tubes to replace the very expensive VT-25's 
and VT-52's.

For those wishing further information, I put together a little webpage 
summarizing all the details:

<http://www.kd5byb.net/tubeadapt/tubeadapt.html>

There is one change I've not made to the website.  After dropping one of 
the tiny nuts and it rolling off into oblivion...I now include some 
extra hardware.  ;)

> 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.

Very interesting!  I had my 6AQ5's wired cathodes to Pin 1.  Everything 
seemed to be okay, but I'll admit, my work on the set got interrupted by 
a couple of repairs on my test equipment (one of my power supplies died) 
and on stuff around the house (broken toys, mostly).  I had not gotten 
to more than a few power ups into my dummy load.  I did get around to 
wiring an un-un for it so I could use standard 50 ohm dummy loads and 
power measuring equipment.  (I can remember if it was 4 to 1, or 9 to 1. 
  I looked at both.)

I've now got them rewired to pin 4 and will try them today once I get a 
few other things taken care of.

> "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.

I've done a little poking around myself.  I've not found anything that 
seems radically better.  The 6BQ5/EL84 looked interesting, but seemed 
like the specifications were so close to the 6AQ5 that making the change 
wasn't worth it.

The 6CM6 may be worth a look.

> 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.

I'll have to investigate this.  I know the VT-25 and VT-52 tubes are in 
demand in the audio circles, not so sure if the "lesser" tubes like the 
6AQ5 are as highly regarded.  On the flip side, it does allow 
experimentation in amps originally taking the 4-pin tubes.

Thanks much and 73,
ben, kd5byb