On Tue, 19 May 1998 07:24:49 +0000 Tom Rauch
>
>There is a simple reason they used a "shotgun approach" where they
>wanted to have lower Q even at the operating frequency.
>
>Back then, tubes were pretty crummy. Even the best state of the
>art tubes had VERY long thin leads.
The 811 is a 30's era design and the 572B is a takeoff on it. Several
other popular ham tubes go back to the early 40's and are still produced
today.
External circuits weren't much
>better, well shielded enclosures with excellent ground plane
>characteristics were virtually unheard of,
Not in most home brew equipment but the quality commercial gear made
effective use of shielding, etc. Military transmitters were very stable,
the old TBK, TBM and TBL series that I used aboard ship were mid-30's
designs; failures were almost unheard of and they were still operational
30+ years later.
and some amateur equipment
>was simply built on insulated boards.
Ah yes, the grand old ARRL inspired designs of old!
>
>With circuit layout and components of that era the system needed
>high ESR at, and even near, the operating frequency to insure
>stability.
>
>It would be my recommendation that anyone using push-pull 304TL's on
>a wooden chassis use resistance wire for all element leads, or better
>yet insert regular resistors with adequate power dissipation in
>series with every lead.
Why would anyone want to use the 304TL for an amp? The 304TH was the
popular tube for early day SSB amps, the TL was used mostly as
modulators.
I've used home brew 100TH, 250TH, 450TH and 750TH amps; they all worked
fine, never did nasty things in linear or Class C.
>
>Not only that, the suppressor Rich alludes to was NOT the suppressor
>he describes in the kit he sells. It was a clone of an AL-80
>suppressor, multi-turn inductor and all. It was not a short hairpin.
>
>I'll certainly be the first to agree that adding series resistance in
>the coil path lowers Q and can increase ESR through ALL
>frequencies (especially the operating frequency down through dc), but
>the bottom line is at VHF it does nothing a small resistance and
>turns adjustment doesn't accomplish without all the HF losses.
>
>It isn't the nichrome suppressor won't work, it's just that:
>
>1.) The suppressor tested was NOT the one Rich sells.
>
>2.) Lower Rp is not always a good idea.
But those suppressors appear to help in amps that were marginal to start
with, either by design or aging of the original suppressor. Not everyone
has the knowledge, time, patience, parts or test equipment to develop a
one-off design for their amp.
If Rich can make a few $$ by selling an aftermarket replacement so what?
In most cases the original manufacturer is out of business and/or the amp
owner cant find new 2W carbons without a $25 minimum order.
73 Carl KM1H
>
>73, Tom W8JI
>w8ji.tom@MCIONE.com
>
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>
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