Subject: GLOWBUGS digest 149

From: [email-masked]
Date: Wed, 3 Apr 1996 09:06:44 -0600 (CST)

GLOWBUGS Digest 149

Topics covered in this issue include:

  1) Sweep tube amp stories wanted
	by [email-masked] (David Feldman)
  2) The original all-bands transmitter
	by Jeff Duntemann <[email-masked]>
  3) Re: Sweep tube amp stories wanted
	by Jay Coward <[email-masked]>

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Date: Tue, 2 Apr 1996 13:29:12 -0800
From: [email-masked] (David Feldman)
To: [email-masked]
Subject: Sweep tube amp stories wanted
Message-ID: <[email-masked]>

I'm looking for people's experiences with sweep tube amps, designs, etc.

Thanx,

73 Dave WB0GAZ [email-masked]

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Date: Tue, 2 Apr 1996 15:28:04 -0700
From: Jeff Duntemann <[email-masked]>
To: [email-masked]
Subject: The original all-bands transmitter
Message-ID: <[email-masked]>

>I'm looking for people's experiences with sweep tube amps, designs, etc.

Back in 1975 I got my advanced and inherited a Central Electronics 10B SSB
exciter from a friend of mine.  It put out about 5W or so from its 6AG7
final, and nobody heard me.  So I scanned the magazine piles and hit on the
Shoebox II Linear, in an article in CQ Magazine from 1969, I think.  Don't
recall the author.  (W2EEZ?)  It was four 6HF5 sweep tubes with about 850V
on the plates.

It was the first linear I ever tried to build, and I'm sure I made some
mistakes, but I never really tamed it.  It was the original all-bands
transmitter...all bands at once.  Actually, I think the problem was
rampaging VHF parasitics, which seemed to ignore the little chokes by the
plate caps.

Sweep tubes have very high power gain, and a reputation for going wild at
the slightest provocation.  They weren't designed for continuous service
(they're pulse amplifiers, properly) and their envelopes are thin as those
of power tubes go.  Overheat them and the glass will deform under
atmospheric pressure.  Sometimes they "suck in" and die.

I've had better luck in lower power applications using older sweep tubes
like the 6BQ6. Lew McCoy published a couple of CW transmitters using that
tube, back in the 60s.  I built one and it put out a very clean 20W or so
without pushing. The late-era color TV sweep tubes like the 6HF5 and 6KD6
are supposedly hotter and much more cantankerous.  I've also heard it's
tougher to get a matched set.

My recommendation is, when possible, use 6146Bs.

--73--

--JD--

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Date: Tue, 2 Apr 96 15:15:35 PST
From: Jay Coward <[email-masked]>
To: [email-masked]
Cc: [email-masked]
Subject: Re: Sweep tube amp stories wanted
Message-ID: <[email-masked]>

*> *> I'm looking for people's experiences with sweep tube amps, designs, etc.
*> *> Thanx,
*> *> 73 Dave WB0GAZ [email-masked]
*>  Hi Dave,
*>   Do you remember the old marine band radios? I still have my Dad's 
*> Apelco xtal set.Used 4 or 5 6DQ6's in parallel for about 150 watts.
*> I also have a Hartman that uses only one sweep tube for around 20 w.
*>  Would it be a criminal act to modify an old boat radio for ham use
*> on 160m?
*>  73 Jay KE6PPF

--
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End of GLOWBUGS Digest 149
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