The suppressor seems too small to me!
I would expect to see about 2 to 4 turns of that copper strap, about 1 inch
in diameter. As for the oscillation frequency, an educated guess would be
80-90 MHz, typical of those tubes.
BTW the mere fact that it breaks into oscillation at 3kV, is indicative of
the cross coupled oscillator mechanism being in effect. Cross neutralization
and/or a baffle shield between the tubes might be of help too.
Alex 4Z5KS
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Robert Perdue
Sent: Friday, September 04, 2009 5:53 PM
To: 'Mike K4EAR'; Amps@contesting.com
Subject: Re: [Amps] 4-1000A neutralization
Thanks to all for the replies. I have not measured the frequency of the
oscillation as of yet. The sockets I am using are the plastic Eimac and the
grid/screen pins are tied to ground using one piece of copper strap on each
socket tied to ground at a single point each socket independent of the
other. No drive applied the oscillation starts when the plate voltage climbs
just over 3000v both filament and HV are variac controlled. no tuned input
may have to add later. For suppressors I am using a single 3 inch copper
strap 1/8 inch wide bent in a U shape with two 100 ohm resistors in parallel
across the open end of the strap. I am leaning to the input divider I made
up using the two .o1 caps with a single .01 across the divider the two caps
are in series RF fed into the center each end goes to a filament pin on each
tube with the third cap paralleling the divider. I used my capacitance meter
and closely matched the values and plan to pull and recheck. More to follow
this weekend again thanks for the suggestions so far.
Bob
-----Original Message-----
From: Mike K4EAR [mailto:hinrgdj1@comcast.net]
Sent: Friday, September 04, 2009 7:58 AM
To: kc0hfl@cox.net
Subject: Re: [Amps] 4-1000A neutralization
Bob,
Does each tube have it's own grid/screen straps to ground at each socket
pin? IOW, your not tying
across from socket to socket with the strap? Are the sockets the black
plastic ones? They have a
slot that the strap is routed thru for a shorter ground. Do not use the
grid/screen tube solder pins
made for a wire connection.
Can you drop the plate voltage and get it stable? At 6kv squirrely things
might happen ;-)
Is it oscillating without drive? Are you using a tuned pi input? suppressors
at each plate cap?
A picture would help.
I fought this battle 30+ years ago!
Mike
----- Original Message -----
From: kc0hfl@cox.net
To: "Mike Schelly" <hinrgdj1@comcast.net>
Sent: Thursday, September 3, 2009 8:28:50 PM GMT -06:00 US/Canada Central
Subject: RE: [Amps] 4-1000A neutralization
I am using a 75Amp center tapped transformer using a 50K resistor to
hold the tubes in cutoff I have adjustable bias 5-30V 6K for plate
voltage using B&w 850 bandswitch the one with the isolated shaft. Vacume
variable tune,Load 350, 1500pf 500pf plate bypass cap. Each tube has
it's own filament transformer. The grids are tied together with a 1/4
copper strap tied to ground one location.
Bob
On Thu, Sep 3, 2009 at 8:05 PM , Mike Schelly wrote:
> Hi Bob,
>
> Are you using a 15 vac center tapped transformer for the filaments in
> series
> or one 7.5vac transformer for each tube or a high current center
> tapped
> 7.5vac for both in parallel???
> Single band or ?, bias voltage?, plate voltage??
>
> Mike, K4EAR
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On
> Behalf Of kc0hfl@cox.net
> Sent: Thursday, September 03, 2009 7:30 PM
> To: Amps@contesting.com
> Subject: [Amps] 4-1000A neutralization
>
> I have completed my 2 tube 4-1000A amp but am experiencing self
> oscillation
> when I apply plate voltage. My question is do I need to add a
> neutralization
> capacitor in the plate line? I reviewed all the schematics and
> artical's I
> used for research and found none to be used with the 4-1000 I did
> notice
> there use in the 3-500/3-400 amps. I am running the tubes grounded
> grid
> feeding the input thru .01 caps to each socket with a .01 across my
> input
> divider. The entire cathode end of the tube is in a metal enclosure
> below
> the RF deck. I also bypassed the filament leads going in the
> enclosure with
> .01 caps. Any ideas?
>
> Bob, kc0hfl
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
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