Date: Sun, 28 Oct 2012 13:49:57 +1030
From: "Leigh Turner" <invertech@frontierisp.net.au>
To: <amps@contesting.com>
Cc: gdaught6@stanford.edu
Subject: Re: [Amps] The GU84B and GU78B tubes / some brief history
George, comparing Tx triodes with tetrodes is akin to comparing apples with
oranges, so things must be put into proper context.
## actually, they are not apples and oranges. One has an extra grid in it,
requires a regulated screen supply, neutralization, and some method to cancel
out
the Xc between the cathode and control grid, so u just cant slap a 50/200 ohm.
passive grid resistor in there. Bottom line is, hams want a tube that has good
gain, simple,
stable, and has good tube life and superb imd. In that regard, the russian
tetrodes
just don’t cut it imo. The only reason OM power et all is using em, is cuz at
one point
they were dirt cheap. Cheap enough that even with the added cost and
complexity of a
regulated screen supply, etc, they could enhance profits.
The 3CX1500A7/8877 and 3CX800 are indeed fine / best of breed SSB linear
triodes, but tetrodes have their own following with RF amplifier designers
and users.
## agreed. Look no further than “ ssb systems and circuits”, written by a
slew of collins engineers. They just love grid driven amps..and just hate
GG triode amps, the rational being that the xcvr has to be as clean as the
GG amp, or imd results from the xcvr.
Now with proper attention to *very important* screen supply design and
voltage regulation, and the application of judicious RF negative feedback
with cathode degeneration, a savvy amp designer can extract IMD performance
from tetrode amplifiers in AB1 mode that's nearly on par with these triodes.
After the Iron Curtain came down, a group of creative American entrepreneurs
got together with the esteemed St Petersburg tube factory managers and had
re-branded certain Tx tubes from that plant as "Svetlana".
The "4CX" number designations for these tubes are a pure invention by the
American marketeers, strictly for Western consumption. The Russians never
used that scheme of numbering - they had always used a GS/GU/GI-digit format
- and the attempt to paste the Eimac style of numbering onto these tubes has
created a lot of confusion.
## IE: “ 4CX-800” ? That must be the russian version of the infamous
Eimac tetrode. Eimac made such a tube, and the hams all got sucked in.
The US-Svetlana venture initially looked very promising because the tubes
from the St Petersburg factory were of very adequate quality, and prices
were so much lower than Eimac, which were arguably inflated through Eimac's
exclusive distributor agreement with Richardson Electronics. Many also
believe that Eimac had lost their way technically, after the retirement of
the golden generation of vacuum tube engineers who grew up with Bill Eitel
and Jack McCulloch (and all of whom were upfront and proud to be hams). They
also lost one of their best technical marketing men, the late George Badger
who left Eimac to help found Svetlana US...so Eimac then had every cause to
be worried.
Unfortunately for radio hams the US-Svetlana venture failed, mainly because
of erratic delivery problems, and competition from the very same tubes being
available even more cheaply through surplus channels! And I do mean exactly
the same tubes - some of the problems with getting shipments out to the USA
were almost certainly due to tubes going out the back gate to the surplus
dealers and a parallel channel market supply chain.
## svetlana is still in business, and RF parts etc, still sells their tubes.
I know of one FM and also one AM broadcaster who literally have
worn out Svetlana tubes stacked to the ceiling. They were pissed cuz they
can’t get the tubes rebuilt anywhere. They saved them cuz they were sure
that one day they would be able to get em all rebuilt. A lot of tube rebuilders
have tried rebuilding svetlana tubes but with no success and /or poor success.
In the end that have saved .....nothing.
Svetlana USA tried hard to get the St Petersburg factory to develop totally
new products that would be genuine plug-in replacements - and competitors -
for Eimac tubes. They were particularly keen on developing a 3CX800 clone,
to be followed of course by an 8877 clone; but as far as I know, these never
progressed beyond engineering samples and promises.
## They were going to build a 3-600Z as well... never happened.
Anyhow, it all resulted in Svetlana USA being unable to meet their delivery
commitments, and the whole venture collapsed. The 4CX1600B would have been
an absolute killer in the market, and could have easily completely displaced
Eimac's then aging 4CX1500 in new designs. Svetlana USA wanted the factory
to ramp up production...but that's just another thing that failed to happen.
Because the GU91B/4CX1600B was over-sold and over-ordered, it became very
scarce, and amplifier manufacturers and their customers left in a hole in
respect of being able to source a modern high performance low-cost linear
SSB tube. All this against the backdrop of a relatively small global market
for ham tubes had doomed the venture right from the start.
Nevertheless the inimitable GU74B, and the bigger GU84B and GU78B tetrodes
did prevail and were eagerly adopted by European OEM amplifier manufacturers
who'd recognised their fine technical qualities and designed for them.
## Leigh, do you still have your hammer + sickle stashed away some where ?
You may well need it someday.
later.......... Jim VE7RF
Cheers,
Leigh
VK5KLT
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