G'Day Jim,
In answer to your question my amplifier running the Russian GU-74B tetrode /
so-called 4CX800 tube is now in its 12th year of faultless service and still
makes full rated power.
Similarly the amp using its big brother 2500W plate dissipation GU-84B tube
still makes rated 2+ kW key-down / 3 kW PEP output in its now 10th year of
faultless service in my shack. Photos can be seen on my qrz.com page.
At this rate and anecdotal experience the Russian tubes in regular ham radio
duty SSB service are likely to see out and outlive its owner; thus seem like
they're on a trajectory path for ultimately yielding your mentioned 20 year
service life :-) Now this is entirely consistent with expectations in the
context they were originally designed as rugged mil-spec Tx tubes for the
Russian military service.
As I previously mentioned the key to Tx tube longevity in my experience is
to not abuse them and to always conservatively use tubes within their
manufacturer's published Data Sheet ratings. The peripheral electronics
placed around the tube also play an important role in ensuring the tube is
well cared for and protected under all conceivable adverse conditions.
You're right about rebuilding the bigger broadcast service Eimac tubes and
repurposing them virtually endlessly; but my Russian AB1 tetrodes were also
cheap to purchase and have yielded outstandingly good bang for the buck.
Sadly all good things come to an end as supply of these NOS surplus tubes
eventually dry up :-(
However the capable and affordable FU-728F Chinese counterpart military Tx
tube is still in current day production and has become the new benchmark for
today's high-end ham amplifiers. I commend folk to study it closely.
Cheers,
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Jim Thomson
Sent: Sunday, 25 January 2015 12:39 AM
To: amps@contesting.com
Subject: [Amps] ceramic vs glass
Date: Sat, 24 Jan 2015 12:53:21 +1030
From: "Leigh Turner" <invertech@frontierisp.net.au>
To: "'Bill Turner'" <dezrat@outlook.com>, <amps@contesting.com>
Subject: Re: [Amps] 5 Minutes for Ameritron 811H to warm up?
Personally I wholeheartedly concur with your sentiments here Bill; most of
my shack amps are of the ceramic tube variety and indeed do seem to last
forever.
My only exception amp is the venerable Kenwood TL-922 with its nostalgic
pair of Eimac 3-500Z glass bottles...they too have proven very reliable
workhorses! The proviso rider with any tube is absence of abuse.
73
Leigh
VK5KLT
## What's the most anybody has gotten out of these russian ceramic wonder
tubes like GU-74B etc ?? Can you get 20 years out of them, beating on em
7 days a week, like an Eimac 3-500Z ?
## What is longest anybody has gotten out of an Eimac 8877 ??
## at least with the bigger eimac ceramic tubes, like 3x3, 3x6, 3x10, 4x5,
4x10, they can be re-built till hell freezes over, unlike their throw away,
smaller ceramic siblings. IMO, you get a bigger bang for the $ with the
bigger ceramic tubes, esp since being thoriated tungsten fil, you can reduce
the fil V way down, like 12% or more, further extending tube life. Take a
3x3... rated for 2.5 A CCS plate current...then run it at 1.5 to 1.7 A plate
current..along with reduced fil V. It will last forever.
The typ 2 x 3-500Z amp is rated at 800ma max plate current.... and my L4B
runs at 800ma...just to get 1290W po.
Jim VE7RF
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