[AMPS] SB-220 TUNE Cap Arcing

[Norell Bennett W.]

> >>I was under the impression that some of the mods he did on the input 

side 
> >>might have been adding nichrome suppressors to the grid leads like 

you 
> >>suggest.  
> >
> >The resistance-wire grid-grounding suppressors I recommend for the 
> >4-1000A/8166 do not increase or decrease the inductance in series with 
> >the grid.  Such suppressors decrease the Q of the unavoidable VHF grid 
> >resonance. 
> 
> I am confused.  First we were on the 3-500Z of these guys amp, now on 

the 
> 4-1000A.  Anyhow, Rich adding any kind of thin wire to a grid to ground 
> path vs. having the grid directly grounded with a very short piece of 
> braid does add more inductance.  However, sometimes adding the 

inductance 
> is necessary for moving the resonance point.
> 
> 73,
> 
> Jon
> KE9NA
> 
> 
> 
Hi Jon,
Just a followup and maybe the epilogue....
I checked the resistors in the (resistor-nichrome wire) plate
suppressors and they each read about 100 ohms as indicated.
I cleaned the TUNE-C, which had a couple of specs (I mean real
small specs) of solder sticking to a couple of fins. Also had
slightly sanded a couple of TUNE C fins that had black or rough-
ness where there had been some of the arc spitting.
The TUNE-C was quite rough to turn, so I retensioned the nuts 
for smooth but not loose condition.
Here is the present condition:
Into a dummy load, using a Bird wattmeter and on amp meters:
No apparent arcs on any band, at any power.  Temporary key-down:

band    Grid(ma)   Plate(A)   HV(SSB pos.)   POut
10m     300        .88        2300           900w
15m     250        .75        2400           1000w
20m     240        .70        2500           1100w
40m     225        .68        2450           1100w
80m     235        .725       2450           1159w

Of course the meter readings on the amp are not precise, but
is the Plate Amps or Grid amps too high on 10m? I may have read on the
reflector that max Plate current is 400ma on a single 3-500.
Do these average readings look average for this amp, given that
the tubes may or may not be showing their age?
Other than a little foreign material on the TUNE C, I cannot 
explain the original arcing.  
After doing the above tests, I did the same connected to my
outside antenna (SWR was below 1.7:1 on all bands). No arcing
here either.
Any comments before we close the subject?
I have appreciated everyone's observations given to my problem.
Thanks,
Bennett ko2ok.

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