On Jul 21, 2006, at 8:59 PM, Joe Subich, W4TV wrote:
>
> Rich writes:
>
>>>> K-202 looks like it's a grid shutoff.
>>>
>>> There is no K-202 on the schematic or parts list of the PA-374,
>>> PA-76
>>> or PA-78 amplifiers on the BAMA site. Those are the only amplifiers
>>> produced by Alpha to use the 8874. In all three cases the grids of
>>> the 8874 are connected directly to the chassis.
>>>
>>> Which amplifier/schematic are you looking at?
>
> Rich, where is K-202?
On the 374 Plug In Board CB2 Schematic, to the right of Q203, D213
and Q204. K202 is labeled "Grid" so I assume it has something to do
with protecting the grid.
>
>
>>>> I was looking at Alpha's diagram.
>>>
>>> Apparently not the diagrams provided to BAMA by Alpha (W0UN
>>> and AE0Q).
>
> Which diagram from Alpha?
"Plug In Board CB2 Schematic"
>
>> Thanks. Since grid-current meters typically connect from the
>> cathode / neg-HV to gnd I missed this.
>>
>> Does this circuit stop the flow of grid-current or just open the PTT
>> line?.
>
> Rich, the manual clearly states if the grid-current overload occurs
> by itself the PTT is opened (which applies cutoff bias) since the
> likely cause is overdrive or mistuning.
Could there possibly be a third reason?
> If grid current overload
> occurs at the same time as a plate overload the HV is removed. This
> would deal with both an arc and parasitic oscillation.
>
> In both cases the action is appropriate and will stop the flow of
> grid current by addressing the root cause. Pretty clear, well written
> and easily understood.
>
> Now, what amplifier is it that uses a transistor to open a 50 A
> grid circuit?
There aren't any, which was my point.
> Specifics please - including URL to the schematic.
>
> 73,
>
> ... Joe, W4TV
>
>
>
>
R L MEASURES, AG6K. 805-386-3734
r@somis.org
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|