Speaking of 811A... What is the best source for unused tubes these days? Is
China the only alternative? I'm building a nostalgia project alongside with my
bigger amp build. Most of my junk box parts are rated below 2KV, so 811A would
probably be best for this glow-in-the-dark project.
73
Ulf
SM0NOR
Sent from my iPad
On 27 dec 2010, at 02:43, "Carl" <km1h@jeremy.mv.com> wrote:
> After all it IS just an 811A with a graphite plate and an elevated voltage
> and power spec.
>
> Run them at 1800-2000V tops and they last forever.
>
> Or swap them into a 30L1.
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "Shane Youhouse" <kd6vxi@gmail.com>
> To: <amps@contesting.com>; "Mike" <noddy1211@sbcglobal.net>
> Sent: Sunday, December 26, 2010 8:31 PM
> Subject: Re: [Amps] 572B AMP PLANS
>
>
> 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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