>
>On Fri, 25 Jul 97 21:42:03 -0700 Rich Measures <measures@vc.net> writes:
>>>
>>>On Wed, 23 Jul 97 19:15:00 -0700 Rich Measures <measures@vc.net>
>>writes:
>>...snip...
>>
>>>I built quite a few one and two 4-1000A amps in AB2 that were quite
>>>clean. The key was regulated bias and screen supplies.
>
>>How much screen V?
>500V when the Ep was down in the 4500V range. Up to 750 at 6KV.
>
6kV to 7kV is good for SSB operation. 750V on the screen would result in
an anode current of about 460 mA without paying an IMD penalty of driving
the grid positive and drawing grid current. Raise the screen V to
c.1000V and you could draw 700mA of anode current without the grid
current penalty. However, a paltry 500V on the screen means that one
would need to draw much grid current to obtain much output power.
...snip...
>> How did you regulate the
>>grid
>>bias V?
>
>The standard 6080 or 6AS7 regulator circuit that was common then.
Was the 6080 used a pass regulator?
>
>> - Did you measure the IMD yourself, or did you accept on the air
>>reports?
>
>Heck no. Back then on the air reports were sufficient. The majority of
>the exciters were extremely clean and anyone with a dirty signal was
>told VERY quick.
I have heard many bogus reports given to friends. When Roy Neal, K4DUE,
was NBC's science advisor he used to run a solid-state bipolar amplifier
that required a lot less drive than Roy was reportedly driving it with.
The IMD products from Roy's signal were about -22db one morning near
3875KHz. I asked Roy if he wanted a IMD report. He said yes. I
provided it. However, Roy's pal told him that he could not even hear
Roy's signal when he tuned his receiver up 500 Hertz. Yeah, right.
...snip...
>>Eimac does not list the 8166 for Class AB2 linear service.
>
>So What!
In grid-driven service, the 8166, and most other tetrodes, generate much
on-the-air feculence when the grid is driven substantively into the grid
current region. The fix is simple: Raise the screen and anode voltages,
increase the grid bias voltage and RF drive voltages. Do this and there
is no need to run grid current in order to obtain maximal suds from the
tetrode.
>They dont list it in GG either in any official spec sheet. It was only an
>after the fact newsletter.
>
The Class AB2 cathode-driven (grounded-grid) configuration produces
linear results with virtually any tetrode. Class AB2 grid-driven
produces linear results with tubes that are designed for very low
grid-interception (4cx600J and 4cx1500B), running grid currents that are
typically in the 0.5mA region.
Rich---
R. L. Measures, 805-386-3734, AG6K
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