Hsu,
No idea. I tried to kill one pair. But there were other weakness of the amp
(or rather, the age of the amp), which caused the last
failure and pushed the amp to backup role (the ancient bandswitch). The tubes
kept producing about the same power as when I started
working on the amp until the day I sidelined it.
I built in hour-meters for both fil hours and key-down hours but never having
finished the amp, I never did mount a set of "virgin"
tubes and reset the hour counters to do a proper study.
I can say that I have a box of 572b - operated specifically within the
recommend plate disipation, which died a slow death over
about the first 30-100 hours of key down performance. The 572b is fine for SSB
work. But it's fickle for more demanding duty
cycles. If a guy is going to build an amp, why buy the 572b, when for the same
$$, he can have a pair of much tougher 572b.
73, Jeff ACØC
www.ac0c.com
-----Original Message-----
From: Hsu
Sent: Sunday, December 26, 2010 6:02 PM
To: amps@contesting.com
Subject: Re: [Amps] 572B AMP PLANS
Jeff,
In your experience, how long tube life of GI-7B?
Hsu
----- Original Message -----
From: "Jeff Blaine" <keepwalking188@yahoo.com>
To: "Roger (K8RI)" <sub1@rogerhalstead.com>; <amps@contesting.com>
Sent: Monday, December 27, 2010 7:19 AM
Subject: Re: [Amps] 572B AMP PLANS
I cannot think of a single reason, that means zero reasons, to build with a
572b. The GI7B is a far far far far far superior tube
(did I say far superior? hi hi) than the 572b. And all the rest of the amp is
essentially the same. 1 GI7B = 2 572b from a power
standpoint.
You can buy GI7BT at a reasonable price from QRO-STUFF.COM. They will ship
from a TX warehouse but the freight term is a bit odd.
The way it works is you get the delivery from TX, but you pay for a partial
shipment cost for the original transit from Russia -
which is why the freight cost seems so high.
2500V is the sweet-spot for B+ on that tube as well. A pair of them well
ventilated will run about 1KW out on the lower bands and
remain under the 700W plate dissipation limit for a pair. Match that with the
G3SEK triode control board and you will have a modern
amp.
Having said that, one thing to consider - it's often more expensive to build
unless you have a lot of time to hunt around for parts
on the cheap or unless you have a well stocked junkbox (most guys don't). And
to an extent, the same caviet applies to doing mods
on something like an SB200 - I beleive I must have the only $3000 SB200
upgraded amp on the planet! So if you are thinking you can
build for less than buying, you can get pretty far toward your goals with an
AL80 which is a much superior amp to an AL572 and uses
a much more rugged tube.
Good luck.
73, Jeff ACØC
www.ac0c.com
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