[HBR] 1929-Style "QST SUPER 12" Receiver: UPDATE

[Dan Merz]

Hi Eddy,  thanks for the info on ST vs. globe 24's.  I have a number of  sets from
the late 20's/early 30's that use 24's but never made a systematic study of
comparing the two types of tubes.  I always liked the ST's when trying to get the
most out of a set and found that 01A's seemed to do a better job when the ST's were
used despite having "good" tubes,  (from a tube tester) in both cases.  But most of
this comparison was on much lower frequency broadcast band.   I would like to see
your set - did the pic's get posted somewhere - or are you sending to individuals?
best regards,  Dan

Diane Swynar wrote:

> Well, to anyone complating the construction of a receiver like this
> utilizing ancient tubes---or ANY tubes, probably, for that matter---do not
> always suspect the worst when trouble-shooting...!
>
> Two cases in point: the CW & SSB signals on my newly-minted retro-receiver
> sounded harsh, rough, & just plain AWFUL...I re-built the BFO with a new IF
> transformer---same thing. I was considering yet ANOTHER re-build of the
> BFO, when it dawned on me that the signals sounded an awful lot like those
> CW/SSB sigs through my old Hallicrafters S-77A on 10-meters.
>
> Well, the local oscillator on the S-77A is just terrible above anything
> much higher that 14-MHz, or so---sure enough, I monitored my BFO signal on
> a nearby Yaesu FT-980: sounded clean...perfect! Next, I monitored the local
> oscillator frequency on the '980: shades of the old S-77A!
>
> Now, what to do..? I added RF chokes to the plate lead of the 224 balloon
> oscillator tube: no difference. Next, I make-shifted a shield for the same
> tube: nil. Finally, I swapped in a newer shoulder-type envelope 224A and---
> PRESTO!---the oscillator was as stable as the BFO.
>
> Next problem: a very high, scratchy, ambient noise level coming out of
> the 'phones. I started to pull out tubes from the audio driver on up, to
> localize it. PRESTO! ANOTHER 224A balloon tube in the detector was the
> culprit! I replaced it with another ST 224A---PROBLEM GONE.
>
> The moral of the story is simply this: even if your tubes pass muster on a
> dynamic tube tester, it is NOT an accurate indication of how they'll
> perform "...in the field". Both of these old 224A's were NOISEY in their
> specific applications, for whatever reason(s)---and yet both had
> transconductance levels just in excess of 800 umhos.
>
> I don't particularly like using the more modern "ST" tubes in a 1929
> design, but then again, I *DO* want to use the dog gone thing! Guess I'll
> just kepp my eyes peeled for MORE globe/balloon 224A's in the future, & use
> the process of elimination as to which will be "keepers"...
>
> So far it's been a real blast with this behemoth on the bench...before
> setting it up alonside my 3x227 MOPA, though, I want to run experiments
> with regenerative feedback on both IF stages---looks EXTREMELY promising!
>
> Stay tuned...
>
> ~73!~ Eddy VE3CUI - VE3XZ (that's "c3CUI" & "c3XZ" to anyone REALLY old
> enough to remember! Hi Hi)
>
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