Thanks for the reply, Lou. The first thing I suspected was the padding
capacitor for 80m, or the additional portion of the loading cap that is
switched in on 80m. I checked all the capacitors, as well as the wiring to the
band switch, and all looks fine.
The symptoms began after he put the new tubes in and changed the grid resistors
and chokes. That's not to say something else failed when one of the 500ZG tubes
failed, but so far I see nothing that looks out of spec.
Eric
K2CB
> On Sep 17, 2016, at 9:46 AM, Louis Parascondola <gudguyham@aol.com> wrote:
>
> No, it is just the opposite. Grounded grids require LESS drive. It sounds
> like your padding capacitor is wrong, missing, or bad. It can also be the
> switching that kicks it in.
> I recall reading in the past that directly grounding the grids requires
> increased drive. Thus my suspicion that the new inductors may be the culprit.
>
> Could the lower drive condition be related to the lack of sufficient loading
> capacitance?
>
> Eric
> K2CB
>
>
>
> -----Original Message-----
> From: K2CB <k2cb@comcast.net>
> To: Amps <Amps@contesting.com>
> Sent: Sat, Sep 17, 2016 9:25 am
> Subject: [Amps] TL-922 80m load issue
>
> Helping a friend with a TL-922.
>
> On 80m, it is suffering from not enough loading capacitance. The peak at low
> drive levels is at 1. If driven to 1kw the peak it not attainable, as it
> appears to be past the lower limit.
>
> I suspected that maybe the padding capacitor for 80m, or its associated band
> switch wiring failed Also the second portion of the load variable cap which
> is switched in for 80m. All tested good, including the band switch.
>
> The issue seemed to begin when both tubes were replaced with new RFP 3-500ZG
> tubes. At that time the 4.7k resistors and 470uh inductors on the grids were
> replaced. The original external wire wound style inductors were NLA, so
> standard sealed resistor-like style 470uh inductors were used.
>
> On the upside, the amp now does 1000w with only 50w drive now. So with that
> in mind, I wonder if the lower drive requirement is related to the "lack of
> sufficient loading" ?
>
> I recall reading in the past that directly grounding the grids requires
> increased drive. Thus my suspicion that the new inductors may be the culprit.
>
> Could the lower drive condition be related to the lack of sufficient loading
> capacitance?
>
> Eric
> K2CB
>
>
>
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