[Heathkit] Amp question

[Bill Cromwell]

On Wed, 2012-05-09 at 09:08 -0400, Walt dabell wrote:

> 
> It looks to me like it has too much capacitance in the output pi.
> I tried to verify this by scabbing in a 100pF doorknob of suitable
> RF quality to the 80m cap and it made things worse. took it back
> out and things improved to where they were.
> 
> Assuming my assumption is correct, that it looks like the amp,
> on low bands, has too much capacitance, why? Could this be a sign
> of a softening tubes? Or perhaps the padding caps for 80 and 160
> being cooked off of (over) value? I would think they would
> decrease in capacitance if cooked, not increase.
> 
> Thoughts or ideas?
> 
> Thanks!
> 
>     Walt Dabell - W3WMD
> 

Hi Walt,

I don't have an amp like yours but one thing that can put the range of a
variable cap off is warped plates or a change in spacing or both. Are
the rotor plates centered between the stator plates? Wear or a
mechanical shock may have shifted the tuning shaft a little. Are the
rotor and stator plates all parallel all the way through their tuning
range? I have found a lot of caps out of mechanical alignment. Some of
them don't come back. Maybe some of them were never aligned right.

73,

Bill  KU8H