I
>
> The circuit:
> 1) 1-3cx3000a7
> 2) plate voltage=4200 vdc (choke input)(4 uf capacitance)
> 3) plate choke=123 turns of #21 mag wire on 1" dia. form 5" long
> 4) c1= 5-250pf 15kv vac. var.
> 5) c2= 50-1200pf 7.5kv vac. var.
> 6) blocking cap= 1200pf @ 30kv
> 7) L1= B & W COIL 10 Thru 80m
> 8) High Voltage is bypassed at the entrance to the plate choke by 3 caps in
> Parallel values: doorknob type 500 @ 20kv, doorknob type 500 @20kv and
> ceramic disc type 4700 @10kv.
> 9) no Parasitic Suppressor
>
> The amp works pretty good on 40 but not as good on 75. When I remove the
> 4700pf bypass cap the amp becomes a monster on 75 and will hardly work on 40
> at all. I have yet to be able to tune thru the peak on c2 on any band. C2
> likes to be at full capacitance. When I add fixed capacitance to c2 it
> doesn't change the way it wants to be set.(fully meshed)c1 tunes fine. I
> have noticed some welding type arcs down around the bottom of c2. There
> isn't anything down there. Could I have a bad c2? I don't fully understand
> what effect the plate choke and bypass caps have on the tank circuit and why
> the removal of that one little cap would have such a dramatic effect.
> Any Help would be appreciated.
>
> Tnx,
> Jay
>
Hello Jay,
What L is the B&W coil on 80m and what
DC anode current are you drawing?
I guess c1 and c2 are a bit low in capacity for
a Q of 10-12 on 80m unless you are using Pi-L.
Probably you need more capacity on c1 and
a 1000pf padder parallel to c2.
73
Peter
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