[Amps] Problems with 3cx3000 amp

[2]

>
>Hey Guys
>Hope you can help me.
>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? 

**  The only way to check a vacuum cap is with a high-pot tester. 

>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.
>
**  1000pF is not much of a bypass below about 10MHz.

If you are interested in building a resistor-less vhf suppressor that 
other 3cx3000A7 users have had success with, in the interest of 
amplifier-science, I will send you the materials gratis.  

>Tnx,
>Jay
>
>
>
>
>_______________________________________________
>Amps mailing list
>Amps at contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>


-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K, 
www.vcnet.com/measures.  
end