> On 4/12/2010 3:35 AM, Jim Thomson wrote:
>> Somebody asked a while back abt the need for parasitic suppressors' on
>> a GG- 813 amp. A buddy
>> had one blow up on his 2 x 813 amp last yr.. across town. he tossed
>> both the blown one.. and also
>> the remaining one. Amp runs just fine with NO suppressors. Another
>> fellow runs a 4 x 813 amp,
>> again with no suppressors. The tubes all balance out too..equal glow.
>> I'd try it with it with no suppressors
>> 1st.... then if you do have stability problems.. then add them.
>>
>> If the screen and control grids are well grnded [via strap] to chassis...
>> you won't have stability problems.
>> I have had 813's with as high as 3 kv on em, no load... yrs ago, with
>> no stability problems, but that amp
>> did have suppressors in it [2 x 813's in GG] [80-10m]. That was back
>> in 1975. It's a pretty stable tube.
>
> I was the one that asked. I have to admit that I haven't made a decision
> as to whether to
> use GG or grounded cathode. Since I'm planning to run it class C, I will
> have to lift the
> grids from DC ground to bias them even if it is GG. However I'm planning
> to bypass the RF
> grounded elements with paralleled 0.001 and 0.01 uf capacitors with leads
> as close to zero
> length as possible, grounded at a spot common to the pi input capacitor
> frame connection.
>
> Also I'm going to use a method of feeding DC to the plates suggested by
> WC6W in which part
> of the coil is wound from rigid coax or tubing with a hv-insulated wire
> running through
> it. The outside of the tubing is connected through the usual blocking
> capacitor but the
> wire goes directly to the plate. At the cold end I'll use a simple
> pi-wound RF choke of 1
> or 2 mh. This takes the stress off of the choke on the high bands,
> provides better choking
> on 160, and reduces the stray capacity across the tubes. Whether it will
> be better or
> worse from the point of view of VHF parasitics remains to be seen.
>
> One of my goals is to have an amplifier for CW which is efficient from 160
> through 10
> meters (another goal is to spend as little money as possible on it).
> Getting rid of the
> suppressors will improve 10 meter efficiency.
** Say what? All that tells me is you are not designing the suppressor for
the tube.
I'm also going to have a small inductance
> before the input capacitor to transform the tube's Rl to a lower value to
> keep the Q of
> the pi network reasonable on the higher bands. Who says 813's don't work
> on 10 meters!
** Nobody says that on here. Ive been running 4 of them that way for several
years Class C AM 160-10M
>
> For the other end of the frequency range I think the plate feed system
> described above
> will keep a lossy choke out of the tank circuit on 160. And -- I intend to
> avoid the
> mistake made by Heath in the SB-1000 and keep the tank coil away from the
> cabinet. I
> improved output on 160 in the SB-1000 by moving the coil as much as I
> could away from the
> steel cover. In my HB amp I plan to mount the coils well clear of anything
> metal (and
> there won't be any ferrous metals around!).
** Thats why they make aluminum, it is less sensitive to the RF field.
Ive had aluminum covers bent for Amp Supply (especially No Tunes),
Clipperton L, MLA-2500, and others. 1200W out on 10M in a Clipperton with
100W is now easy and with no tube color.
Carl
KM1H
> --
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco/
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