>Anyone have any comments about this amp?
>
Before the Ameritron 811 amplifier began to be sold, I received a
telephone call from an amateur radio operator in Simi Valley who writes
product reviews for an amateur radio periodical. He told me that he had
a prototype on loan from the factory for evaluation. He said that during
evaluation, the amplifier made a popping sound and stopped making RF. He
asked me if he could bring the amplifier over for a look. I said yes.
It did not take long to figure out why there was no RF output. The
filaments of the 811As were broken in pieces, laying in the bottom of the
glass envelopes. I checked the anode resonant circuit with a dipmeter.
The VHF dip was sharp and deep.
IMO, VHF parasites subject the filament to lateral stress. [photo in
"Parasitics Revisited", 9/90, 10/90 QST]. . In a 3-500Z, such stress
can bend the filament until it shorts against the grid. In an 811A or
572B, such stress can shatter the filament.
During the recent VHF parasitics debate on the
rec.radio.amateur.homebrew Newsgroup, myself and the AL-811H's designer
(Tom Rauch) submitted competing designs of VHF suppressors for evaluation
by Wes, N7WS, using a Hewlett-Packard Model 4191A RF Impedance Analyzer.
The VHF Rp of the Ameritron suppressor was about 60% higher than a
similar suppressor that was made from resistance-wire. Since VHF
voltage amplification is basically VHF-Mu multiplied by VHF-Rp, more
VHF-Rp equals more VHF gain. .
There is nothing new or revolutionary about making VHF suppressors from
resistance-wire. Mr. F. E. Handy wrote about it in the 1926 Edition of
*The Radio Amateur's Handbook*. However, "recognized experts" Dick
Erhorn and Tom Rauch ridiculed the idea.
Rich---
R. L. Measures, 805-386-3734, AG6K
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