[Hammarlund] HQ-129 and 717A mod.

[Kenneth G. Gordon]

On 7 Nov 2007 at 14:01, jeremy-ca wrote:

> Ah yes, your long love affair with those subminiatures. I dont have
> any listings on those little beasts.

Yes. The "wee beasties" as the Scots called them. I have 
found considerable good information on them from various 
on-line sources, some not so easily found.

> I wonder how they would hold up under strong signals?

The first versions were originally developed for hearing aids. 
Then they were substantially improved for use in proximity 
fuses for anti-aircraft shells. Being fired out of a gun, they 
had to be tough.

If transistors had been even a few years later, the subminis 
would have taken over for a long time.

They are TOUGHER than heck, are extremely carefully 
built, and have an MTBF that beats any other tube all 
hollow. They are precision built.

They are electrically tough little beggers when operated 
within a reasonable distance of their specifications too.

The only iffy thing about most of them is that they are limited 
to not much more than about 120 VDC since the element 
spacing is so close.

> For that matter why not a pair of 6CW4's or 7586's ? The latter
> especially are rather available.

Excellent tubes, but not high enough gm for my tastes. 

> Heathkit certainly had superb results with the 6HS8 but I appreciate
> your comment on individual triodes. Isolation between sections is
> important.

Yup. I use 6AH6s in the RF and mixer stages of my HW-
101s and SB transceivers since they are not running so 
close to "red-line" as the 6HS6s, and they provide 
comparable results. Besides, there are a HECK of a lot 
more 6AH6s than 6HS6s around! :-)

> 
> I think I already mentioned the 7F8 as used by Hallicrafters in the
> SX-42/SX-62 as a nice dual triode performer well into the VHF range.
> At least a loctal socket fits in an octal hole so no metalwork
> required.

You did, and I am investigating that one too. Thanks for the 
info.
 
> All I need is a few 36 hour days to get some evaluations started much
> less completed!

Ha! Tell me about it! :-)

Ken Gordon W7EKB