Sun May 13 10:46:53 EDT 2007
parameters except for the plate dissipation.
The 4-125 IS different...lower filament power, different spacing,
lower maximum voltage rating....
I think the best way to modulate these tubes is with the separate
mod transformer winding.
You can do fine with the choke in the screen circuit, but
the peak power seemed to be lower than with other tubes.
The 813 seems to love the choke setup...lots of peak
power without even trying hard.
The original 30k-1 design had a separate mod transformer
winding...worked great till I blew it up running
on the air frequency tests!
(this was a long time ago, before I knew better)
The thordarson mod transformer with the choke did not
modulate quite as well.
> Just slightly orange, Jay? Mine used to get *quite* orange
> and pulsate with the
> voice peaks. In fact, when I first got the rig and powered it
> up, they got just
> plain orange and tossed fuses left and right, due to a lack
> of bias from an open
> 4-pie choke just behind the front panel. Luckily the wire was
> broken just at the
> point where it was soldered to the terminal on the choke, so
> I didn't even have
> to look for a new one. Thanks to Mr. Bill Wheeler, K0DEW for
> the help on that
> one. I called him, we both got our schematics out and went
> through until
> we(okay, he) found a likely suspect.
> What the old timers told me was that using 4-400s in place of
> the 4-250s
> wouldn't give me more power, it would just allow the
> transmitter to loaf along
> with perhaps a 'mild' glow of the plates and less strain on
> the rig overall. As
> explained, the 4-400C was the best choice, and the 4-400
> series in general was
> just a more stout or 'rugged' version of the 4-250, lending
> itself better to the
> higher power requirements that came along after the 4-250.
> *shrug* I haven't a clue. I had the assitance of a former
> broadcast engineer in
> getting the rig online, so I figured he knew his stuff(he's a
> ham as well). And
> of course, some really good suggestions from Uncle Ed WA3PUN
> and the gang down
> his way the first night I dared to transmit. Hey, these
> 'suggestions' didn't
> require drilling any holes, and are reversible, so...
> After moving to my new home, the old girl was back to
> spitting out 15 amp fuses.
> I need to set some time aside and dig into it a bit more.
> Something either got
> jostled in the move (only about 15 slow, careful miles)or
> decided to go south in
> the time it sat unused.
> I do recall that the 4-250s seemed prone to shorts, though.
> Just reach in with a
> broom handle and rap 'em a bit and they were fine....
> 73 de Todd/'Boomer' KA1KAQ
> Jay Bromley wrote:
> > Hi John and all,
> > I had some 4-250s in the final of my old KW-1, then later
> switched them out
> > to 4-400s. While I liked the looks of the slightly orange
> plates of the
> > 4-250s and under modulation the 4-250s getting brighter in
> color, the 4-400
> > seemed to work better with the 810s modulators. I can't
> show any proof, but
> > it just seem to modulate and have more headroom. Was this
> in my head?? All
> > I had to go by was my monitor scope.
> > 73 de jay/w5jay..
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