[Amps] AMPS

[R L Measures]

On Jul 21, 2006, at 5:24 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?
>
>>> However, since W0UN, AAA0RS and W0ID no longer contribute regularly
>>> to this forum - schematics for the 76 and 86 amplifiers are on BAMA
>>> if you care to check the facts before you make wild (wrong)
>>> statements.
>>
>> I was looking at Alpha's diagram.
>
> Apparently not the diagrams provided to BAMA by Alpha (W0UN and AE0Q).
>
>
>>> The manual includes an extensive, well written
>>> discussion of tube protection, how it works and how to configure
>>> it.  However, since it does not agree with your pseudo science you
>>> don't acknowledge it - as usual.
>>
>> The Q1 is a TIP-147 and is rated at 5A.  Q1 appears to carry grid
>> current. Is this true?
>
> If you read the explanation, Q1 and U1 are an "adjustable zener" that
> provide bias.  Looking at the schematic they are in the cathode  
> circuit.
> The only transistor in the grid circuit is Q6 (page 31, lower left
> corner) used in the grid current sensing circuit.

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?.
>
> If you bother to read the rest of the manual, you will find the G3SEK
> board is designed for use with the grids bolted directly to the  
> chassis.
>
> 73,
>
>    ... Joe, W4TV
>
>
>

R L MEASURES, AG6K. 805-386-3734
r at somis.org