In my experience, the 572 is a superb tube for keydown modes....
IF YOU OPERATE IT AS AN 811A!!!!!
IE, about 20 watts carrier each.
--Shane
KD6VXI
On Sun, 26 Dec 2010 17:25:32 -0800, Mike <noddy1211@sbcglobal.net> wrote:
> 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.
>
> Mike
>
> -----Original Message-----
>
>
> 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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--
It's a sad state of affairs when your tubes don't have handles but your
dummy load does.
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