[Hammarlund] HQ-129-X filament current requirements

[Frank Barnes]

Thanks for the advice and sorry to hear you must part with two
Hammarlunds.  I've always liked them - I had an SP-600 that I pulled out of
a Navy dump, for years.  I also had an SX-28A for about thirty years.  Good
set.  But I sure like this HQ-129-X - great dial readouts.   Smooth tuning.

On Wed, May 29, 2019 at 3:29 PM Joel Hallas <jrhallas at optonline.net> wrote:

> Frank,
>
> Yes, that was a rather remarkable design decision by the folks at
> Hammarlund, and I have always respected it. While a different tube could
> provide improved noise figure, I submit that in a high noise (or most any)
> environment, the external atmospheric plus local noise will surely dominate
> the receive S/N and any improvement will only be noticeable at the high end
> of the 129's coverage range -- say above 20 meters (where it doesn't work
> well in any case).
>
> My recommendation would be to stick with the 6SS7s in all designed
> locations. The cost and difficulty of finding a replacement power
> transformer would be way more than any benefit of a quieter receiver --
> especially since it would just be noticeable with the antenna disconnected.
>
> I doubt that it would hurt to try it for a few minutes while listening to a
> weak station -- my guess is that there will be no noticeable improvement.
>
> Enjoy the HQ-129X -- imho it is one of the best two-dial receivers of the
> period. Spreading the range over more bands makes such an improvement in
> usability that I'm amazed others didn't do the same -- well I guess Halli
> did in the SX-28 and later the SX-88, and try to find one!
>
> BTW, due to declining health, both my HQ-129X and a nice HQ-110A-VHF
> (double
> conversion, ham bands only 160-2 meters, with internal 2 meter nuvistor
> converter) are available for inspection and purchase 50 miles NE NYC,
> e-mail
> direct for more details.
>
> Regards, Joel Hallas, W1ZR
> Westport, CT
>
>
> -----Original Message-----
> From: hammarlund-bounces at mailman.qth.net
> [mailto:hammarlund-bounces at mailman.qth.net] On Behalf Of Frank Barnes
> Sent: Wednesday, May 29, 2019 14:50
> To: Glowbugs; hammarlund at mailman.qth.net
> Subject: [Hammarlund] HQ-129-X filament current requirements
>
> I've restored an old and now very enjoyable HQ-129-X and now it is time to
> do some upgrades.  The first is to replace the 6SS7 RF tube with a 6AC7.
>  The 6SS7 has a Gm of about 1850 and an Equivalent Noise Resistance of
> 10,800.  So it does not hear as well as some other tubes and it is noisy.
>
> The 6AC7 is much "hotter" with a Gm of 9,000 and an ENR of less than
> 1,000.  So it hears much better, is very quiet and is a plug-in swap.  I
> have one so that's what I plan to use; I know there are others (e.g., 6GM6
> with Gm=13,000)..maybe later.   I have a very high noise level here so any
> signal to noise ratio improvement I can achieve will help.
>
> BUT, the 6AC7 filament current draw is 300ma MORE than the 6SS7.   The
> total 6.3V filament requirement of a stock rcvr is 2,400ma.   An additional
> 300ma increases the filament requirement by 12.5%.
>
> My question to those knowing much more than I do, is will a 12.5% increase
> be a harmful thing for the power transformer?   Hammarlund built
> conservatively but who knows?
>
> I'm thinking of adding a small fan to relieve the internal heat...that
> might help the xfmr a bit...or not.   I could replace the 5V rectifier tube
> with solid state to help the xfmr a little more, heat-wise.   Or add
> another small filament xmfr.
>
> Or maybe a 12.5% increase is not worth worrying about.  I know that many
> have changed tubes and increased the filament draw and have heard of no
> failures.
>
> Comments?
>
> The mixer tube will be next; after the RF tube is changed, measured and
> stable.
>
> Frank
> W4NPN
>
>
>
> --
> Frank Barnes
> W4NPN
> Chapel Hill, NC
> Grid Square FM05
> Cell 919.260.7955
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-- 
Frank Barnes
W4NPN
Chapel Hill, NC
Grid Square FM05
Cell 919.260.7955