[Amps] 572B AMP PLANS

Mike noddy1211 at sbcglobal.net
Sun Dec 26 17:25:32 PST 2010

Interesting you say that about key down with 572b's, I noticed that a new
set of four that I had did not work for very long on RTTY in the Dentron
amp, where as the 3-500 amp and the 8877 are still plugging along nicely
using RTTY.


-----Original Message-----


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

-----Original Message----- 
From: Hsu
Sent: Sunday, December 26, 2010 6:02 PM
To: amps at contesting.com
Subject: Re: [Amps] 572B AMP PLANS

In  your experience, how long tube life of GI-7B?
----- Original Message ----- 
From: "Jeff Blaine" <keepwalking188 at yahoo.com>
To: "Roger (K8RI)" <sub1 at rogerhalstead.com>; <amps at 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

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

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

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