Interesting. Just so you know that you are not alone
- I had exactly the same problem (exact same tube
position and the exact same failure!) with an AL-811H
that I had some time ago - and - it happened 3 times,
twice after replacing the "older style" parasitic
supressors with the "new style." New style has circuit
mounted on a PC board while the "old style" (read that
to mean the original run of 811H amps) had the
resistors simply coming off the top of the rf choke
with the inductiors wound around them - very
traditional setup.
Frankly, something in my gut tells me that it has
something to do with the "neutralization" circuit that
is used in that amp. I know that a couple of
manufactures tried the neutralization route in grouded
grid 811 amps in the distant past and abandoned them.
Just a hunch - but then again, maybe the supressor is
just not low q enough - never the less, it's very
strange that it should be in that particular tube
placement position 3 out of 3 times for me and for you
as well. New tubes with higher gain seemed to make it
worse and I went back to some with nominal gain.
As an experiment, I took out (completely removed the
toroid, coupling cap and aluminum plate, etc) that
neutralization circuit in the 811H and it performed
extremely well (even easier to drive and delivered
more power on the higher bands) with no gasps, burps,
etc! Tuning was very docile. In fact, if my memory
serves me, the AL-811 (3 tube model) does not use it
and is quite docile as well.
Sorry I can't suggest the exact reason or a sure fire
fix. GL es 73 -- Don N4HH
--- D Pipes <dpipes@earthlink.net> wrote:
> Dave,
> Thanks for the reply. I do have an added question.
> Would I be seeing
> parasitic conditions before and without any RF ye?
> This has happened only
> when i switch the amp on (power switch) still in
> standby and no RF load
> applied as yet just at start up on the power switch?
> thanks
>
> > Date: 08/15/2005 9:01:37 AM
> > Subject: RE: [Amps] 2nd grid resistor blow
> Ameritron AMP 811H
> >
> > You are getting a parasitic sometimes in that
> tube. Replace the tubes
> > parasitic suppressor. Get a kit from R. Measures
> on this list.
> > Dave aa9tt
> >
> > -----Original Message-----
> > From: amps-bounces@contesting.com
> [mailto:amps-bounces@contesting.com]On
> > Behalf Of D Pipes
> > Sent: Monday, August 15, 2005 9:47 AM
> > To: Amps@contesting.com
> > Subject: [Amps] 2nd grid resistor blow Ameritron
> AMP 811H
> >
> >
> > late last year I purchased a Ameritron 811-H amp.
> First amp I have had in
> > years. Back in January i posted on this list my
> problem that I had blown a
> > grid resistor on the back right side tube. With
> the help of this list i
> > learn much and replaced the resistor after i also
> found what I had assumed
> > to be the total reason for the blown resistor. The
> tube in that socket
> had a
> > visible defect where the top spring like wires
> actually had blown loose
> and
> > cold be shook up and down with light shaking.
> Anyway replaced the tube
> with
> > a set of Taylor select (4 matched) from RF Parts.
> That was in January and
> > all has been perfect.. not an arc not a pop and
> tuned fine. I kept the 3
> > "good" tubes and tossed the obvious bad tube.
> >
> > Well now to the point of this email. Last week I
> came in to do a little
> ham
> > radio.. switched on the radio and then as always
> switched on the amp. POW!
> > arc and glow. Same resistor same tube. I pulled
> cover replaced the
> resistor
> > and replaced the tube with one of the original
> "good" tubes I had. Amp is
> > back to working perfect.
> >
> > Any ideas? The last fix lasted 7 months.. all
> perfect. Both times the
> > problem occurred at switch on. opr mode in standby
> no RF load just when
> the
> > switch power was turned on. I did re-check the
> tube that appeared bad (no
> > physical defects seen) and proved that the tube
> has an internal short.
> (blew
> > the replaced resistor) .. anyway re-replaced the
> resistor and put the
> older
> > "good" tube back in and all is just fine... right
> now...
> >
> > Question is.. does this sound like a tube problem
> an amp problem or
> both??
> >
> > I do have a 3rd party soft start nit that my amp
> is plugged into and the
> amp
> > is wired for 240 v
> >
> > Any suggestions?
> > Thanks for nay and all help...
> >
> >
> > D Pipes
> > dpipes@earthlink.net
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
>
>
>
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