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Subject: glowbugs V1 #66
glowbugs            Saturday, June 28 1997            Volume 01 : Number 066


Date: Fri, 27 Jun 1997 20:47:36 +0000
From: Sandy W5TVW <ebjr@worldnet.att.net>
Subject: RER: SX-71 oscillation!

        OK gang, I FINALLY found the cause of my intermittant RF stage/mixer
oscillation problem with the SX-71.  This one drove me nuts!  I soldered/
resoldered ground lugs to the chassis in the RF box.  Also the grounds on the
tuning gang that went to the riveted lugs.  Everything I did seemed to make the
problem get worse! 
        The cure?  I should have known ahead of time!  The spring brass shim
grounding strips between the capacitor gang sections that are grounded to the
tuning capacitor shield partitions were making very poor contact.  They
LOOKED OK and I lubed them up with de-ox-it.  I had to defeat the "staking"
with a hammer
and a 1/8" pin punch, them remove the brass contacts.  Cleaned them up, rebent
them to make good contact with the gang shields and PRESTO!  No more problemo!
I shoulda known!!!  Hallicrafters tuning gangs are notorious for bad grounding
contact problems, but usually once you get them cleaned up with de-ox-it the
problems disappear.
        Watch out for this.  No matter how many years I have fooling with
this gear,
as a hobby and as an every day job, this stuff is always throwing NEW curve
balls to you!  I hope this saves someone else from this kinda grief.  Old dogs
can learn new tricks, I guess.

73,
E. V. Sandy Blaize, W5TVW
"Boat Anchors collected, restored, repaired, traded and used!"
417 Ridgewood Drive,
Metairie, LA., 70001
ebjr@worldnet.att.net
**Looking for:  860 tubes, WL-460 tubes**
**Butternut HF2V antenna, G-R test gear.....................***



Date: Fri, 27 Jun 1997 23:02:20 -0700 (PDT)
From: Ken Gordon <keng@uidaho.edu>
Subject: 1L6 substitutes...(long)

I inadvertantly mentioned here the other day that I had substituted
another tube for the 1L6 in my R-1004 and the said substitution had made a
great difference in the performance of the two receivers I was working on.

This substitution was suggested to me by Bob Rolfness, W7VZX, which he had
learned from an article he had found on the internet.

The tube(s) are either the 1AC6/DK92 or the 1AB6/DK96 pentagrid
converters.  They are available for considerably less money than the 1L6.

The reason I said "inadvertantly" above is that I have not yet finished a
thorough test of how the tube operates in a circuit originally designed
for the 1L6 and did not really want to get users' of the 1L6 hopes up
without reason.

Before I plugged the 1AC6 into the socket, I compared the base diagrams of
both tubes. The only important difference was that (essentially) pins 5
and 6 were reversed.

My first inclination was to swap the connections to pins 5 and 6, but upon
a suggestion from Bob, I just plugged the 1AC6 in his receiver and
let 'er rip. Although the receiver DID work, it oscillated fiercely on any
frequency higher than the bottom 1/3 of any tuning range. I.e., it worked
fine on 40 meters but broke into oscillation at 8 mHz. and above.

After talking with Bob, we decided that a) swapping the wiring to pins 5
and 6 was completely reversible, and b) neither of us ever intend to use a
1L6 again.  So I swapped the connections on his receiver and aligned it.

Although oscillator alignment on bands 1 and 2 (3 to 6, and 6 to 12 mHz)
was fairly easily accomplished, band 3 was not. The oscillator padder cap
could not be adjusted so that the upper band edge (24 mHz) could be
brought into alignment.  The cap was adjusted to minimum capacitance but
needed to go lower yet. So I did the best I could with it and left it
there.

This simple mod made a MAJOR difference in how the receiver operates! The
oscillator no longer pulls off frequency when I key the transmitter, the
overall noise level is MUCH lower, and the sensitivity is MUCH greater,
although it still drops as the operator tunes higher in frequency. The
evening I finished this mod, I worked K7EW on 40.  He was running one watt
to a dipole and I couldn't even HEAR him on the SB-301 which was connected
to the same antenna as the GRC-109.

To do the alignment, I used a simple Beckman signal generator, a Heath
frequency counter, and a Heath scope.  Until I get the URM-25D set up I
cannot give you a true value for receiver sensitivity and/or
signal-to-noise ratio.

As soon as I am able to do some more experimentation and testing, I will
post the results here.  This information should be of interest to Zenith
TransOceanic owners also.

1AC6s are fairly easily available in Europe where they were made by the
millions and its filament voltage/current requirements are identical to
the 1L6's.

After this project, and the 15 watt 12AX7 push-pull class B transmitter
project is finished, I intend to dig into the SB-301 to see why it is not
up to par.

BTW, anyone have a schematic diagram for a push-pull single tube
oscillator transmitter, crystal or otherwise?

Ken W7EKB



Date: Sat, 28 Jun 1997 09:04:53 -0400
From: Ray LaRue <raylarue@gte.net>
Subject: Re: 1L6 substitutes...(long)

Ken Gordon wrote:
> 
> I inadvertantly mentioned here the other day that I had substituted
> another tube for the 1L6 in my R-1004 and the said substitution had made a
> great difference in the performance of the two receivers I was working on.
> 
> This substitution was suggested to me by Bob Rolfness, W7VZX, which he had
> learned from an article he had found on the internet.
> 
> The tube(s) are either the 1AC6/DK92 or the 1AB6/DK96 pentagrid
> converters.  They are available for considerably less money than the 1L6.
> 
> The reason I said "inadvertantly" above is that I have not yet finished a
> thorough test of how the tube operates in a circuit originally designed
> for the 1L6 and did not really want to get users' of the 1L6 hopes up
> without reason.
> 
> Before I plugged the 1AC6 into the socket, I compared the base diagrams of
> both tubes. The only important difference was that (essentially) pins 5
> and 6 were reversed.
> 
> My first inclination was to swap the connections to pins 5 and 6, but upon
> a suggestion from Bob, I just plugged the 1AC6 in his receiver and
> let 'er rip. Although the receiver DID work, it oscillated fiercely on any
> frequency higher than the bottom 1/3 of any tuning range. I.e., it worked
> fine on 40 meters but broke into oscillation at 8 mHz. and above.
> 
> After talking with Bob, we decided that a) swapping the wiring to pins 5
> and 6 was completely reversible, and b) neither of us ever intend to use a
> 1L6 again.  So I swapped the connections on his receiver and aligned it.
> 
> Although oscillator alignment on bands 1 and 2 (3 to 6, and 6 to 12 mHz)
> was fairly easily accomplished, band 3 was not. The oscillator padder cap
> could not be adjusted so that the upper band edge (24 mHz) could be
> brought into alignment.  The cap was adjusted to minimum capacitance but
> needed to go lower yet. So I did the best I could with it and left it
> there.
> 
> This simple mod made a MAJOR difference in how the receiver operates! The
> oscillator no longer pulls off frequency when I key the transmitter, the
> overall noise level is MUCH lower, and the sensitivity is MUCH greater,
> although it still drops as the operator tunes higher in frequency. The
> evening I finished this mod, I worked K7EW on 40.  He was running one watt
> to a dipole and I couldn't even HEAR him on the SB-301 which was connected
> to the same antenna as the GRC-109.
> 
> To do the alignment, I used a simple Beckman signal generator, a Heath
> frequency counter, and a Heath scope.  Until I get the URM-25D set up I
> cannot give you a true value for receiver sensitivity and/or
> signal-to-noise ratio.
> 
> As soon as I am able to do some more experimentation and testing, I will
> post the results here.  This information should be of interest to Zenith
> TransOceanic owners also.
> 
> 1AC6s are fairly easily available in Europe where they were made by the
> millions and its filament voltage/current requirements are identical to
> the 1L6's.
> 
> After this project, and the 15 watt 12AX7 push-pull class B transmitter
> project is finished, I intend to dig into the SB-301 to see why it is not
> up to par.
> 
> BTW, anyone have a schematic diagram for a push-pull single tube
> oscillator transmitter, crystal or otherwise?
> 
> Ken W7EKB

Ken,
There is a short section on push-pull oscillators in "Practical Radio
Communications", Arthur R. Nilson, McGraw Hill, c1935, p150.
73, 
Ray, W4BYG



Date: Sat, 28 Jun 1997 10:46:35 -0400
From: "Brian Carling" <bry@mnsinc.com>
Subject: Re: T20 Substitute

On 25 Jun 97 at 10:48, EWoodman@aol.com wrote:

> I have a transmitter circuit that uses a 6L6 oscillator driving a T20 final
> at about 50 watts input. The description says an 801A or similar will sub for
> the T20. I don't happen to have data on the T20 or 801A. Can anyone give me
> the basic data on it or maybe any other tubes that would be similar?  

Eric - an 809 might do -that was a popular final back then.
Heavier power level than the 807 but I think you could drive it with 
the 6L6

That's IF you can find one!

I got a couple of 828 pentodes the other day at ahamfest. They look 
promising for a QRO final!
****************************************************
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**  E-mail to:  bry@mnsinc.com                     *
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Date: Sat, 28 Jun 1997 17:15:33 -0600 (MDT)
From: Art Winterbauer <art@comet.ucar.edu>
Subject: John Ruskin Special...problem

In the March 1990 issue of CQ magazine (p. 76) Dave Ingram wrote up
the John Ruskin Special, a 6L6 transmitter.  Having wired it up as
shown (I think), there is zilch output.

I'm not sure why there is shown a tap from the heater filament on pin
2 going off to the ground side of the HV supply (and hence to the
key).  If anyone has that article, could they check this out to see if
that connection dot on the schematic is in the wrong place--that
instead of showing a connection to the negative high-voltage DC
supply, the dot should be moved up to the .01uF paper capacitor?

If the schematic makes sense to everyone, then I'll start
troubleshooting my connections, whether the 6L6 metal tube I'm using
is good, etc.  I've been stung before on an incorrectly printed
schematic in CQ before and don't  want to chase me tail.

Thanks! & 73 de Art, WA5OES



End of glowbugs V1 #66
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