6146'S

[Steve Harrison]

At 06:12 PM 1/7/99 -0500, Russ Hines wrote:
>Hi Edward:
[snip]
>I thought the commercial rigs you mentioned used something else, like
>6850's.  No?  A pair of 6146's at 170 Mhz generates what... 40 watts
>maybe?  Very efficient.<grin>

Once upon a time, long, long ago, a neighboring ham loaned me his old Heath
Seneca so I could generate some powah on two meters at long last. To make a
long story short... it wasn't too many hours before I'd melted down the
old, original 6146s in his radio. I replaced them with some unmatched
spares lying around and couldn't get the thing to stop taking off (the
tubes would gradually run away). I couldn't get the neutralization to work
properly on both 6 and 2 meters; one or the other but not both. In
desperation, I pulled the 6146As out of my SB400, expecting no improvement
anyway as that transmitter hardly generated any power, either... maybe 60
watts on 80, as I recall. They sure drew a whole lot more plate current in
the Seneca, though! And they went sore even faster than the original tubes
did, too. And again, I could not get the neutralization to work on both
bands. The Seneca had seperate wire stubs for each band; every time I got
one band trimmed nicely, the other band would be way off.

Eventually, I splurged and bought a whole carton (10 tubes, I think) of
6146Bs from a local surplus outlet in LA for $5 each. Got the SB400 working
great again, got my T-599A (which came with the Japanese S2001 equivalents)
finally running once again, and then tackled the Seneca. But it was the
same old story; the neutralization just wouldn't handle both 6 and 2
simultaneously. Finally, since I was most interested in 2 meters, I peaked
every last electron outta that poor Seneca on that band alone. It would
just barely make 90 watts output, which was just peachy compared to my 10
watts Comm IV (also a loaner from still another neighbor). But I had to
keep it down to 60 or 75 to keep it from running away. Boy, did that plate
transformer sound ominous when those tubes lost it! Came within an inch of
scaring the dickens outta me the first time that happened since the Seneca
had been outta production for over a decade by then.

After a few years came the time to return the Seneca to my neighbor. I
hadn't had it on the air for a year or more so fired it up to be sure it
still worked. Yup, same old 90 watts on 2 meters and infinite plate current
after a few seconds on 6 meters. So I took it back, telling him what I'd
done to it. He had some spare time and was, at that moment, retubing a few
KWM-2s that he'd picked up somewhere; so he happened to have a stock of
brand new 6146As right there on the bench. Pop the covers, pull the Bs out,
shove the As in place. After a quick check for neutralization, he pulled it
outta the cabinet so he could redo the neutralization wires which I'd
trimmed and replaced countless times during my own trials and tribulations.

20 minutes later, the Seneca was happily perking along, making over 130
watts output on 6 meters and almost 110 watts output on 2 meters... mike
button down, clean and stable, plate current dip producing maximum output
power just like it was supposed to do! "Incredible!!", I thought. Moral:
after blowing the tubes the first time, I should have asked for his help
since he had much more experience, having built and operated the Seneca for
over 10 years. I dunno if he reads these reflectors: if you do, Emmett,
thanks again for teaching a young squirt a soft lesson!

Since then, I've had a hard time thinking positive thoughts about using
6146Bs on VHF frequencies. Not that it can't be done; after all, I had the
Seneca running fine with a pair, but only on one band. But I think
cautiously now when I see so many megacycles trying to escape out the plate
cap of a pair of those jugs now. (A caveat: the Seneca also had the tubes
connected in a bandswitched push-pull circuit, something that has probably
only been done since in old-timer ham workshops).

73, Steve Ko0U/1

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