Topband: Neutralizing your 833As
mikewate at gmail.com
Sun Jan 17 20:42:10 EST 2016
Thanks for the note. I agree that they might add more unwanted G-P
capacitance. And I forget just how many hours I stared at those tubes
wondering about that. :-)
Wide anode leads are used on many amps, and the purpose is to reduce the
inductance of the leads, which in turn reduces the chances for VHF
parasitic oscillations to occur. I think W8JI talks about that somewhere on
his web site.
Whether those wide copper strips helped or not, in the end I did not need a
parasitic suppressor. And if you look at the photos, I took care to make
each plate strap a different length, so as not to create a balanced
push-pull circuit at VHF frequencies. Perhaps that was more important than
the wide low-inductance anode conductors.
They WERE made with the goal of removing heat and keeping the
glass-to-metal seals cool, yes. As for heat sinks on the 833C anodes, I did
extensive research on that. I found no commercial transmitter using one,
nor any manufacturers' tube data sheet recommending a specific anode
connector heat sink design than was any more elaborate than what I made.
The 833 only needs forced-air cooling when run near its maximum ratings.
There's a link to an old data sheet at the top of
www.w0btu.com/833C_linear_amplifier.html and there are others on that web
I have no doubt that I could have done some things different. But it works
great, and was a fun and inexpensive project. And I've ran it hard many
times on 160 at the legal limit in CW contests.
> I was browsing your 833 amp pictures as a couple of those bottles sit on
> my shelf.
> Could you explain the wide Cu straps on the plate? I don't know much
> about tube amps, but would think with more area, they would make
> neutralizing more difficult than the usual machined heat sink.
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