[Amps] 572B AMP PLANS

Mon Dec 27 01:13:17 PST 2010

To my thinking, a single GI35b beats 4x GI7b for about anything.  In fact, a single GI35b beats a pair of GI7b  - if a guy has the 
space.

The GI7b are nice because of the small size and sometimes, there just is no more space (e.g. SB200, etc).  But Jim has a very good 
point.  Building a 2KW unit is about as expensive as a 1KW unit especially when you factor in the value of your time...  And bigger 
stuff is a LOT LOT LOT easier to work on.

73, Jeff ACØC
www.ac0c.com

-----Original Message----- 
From: Roger (K8RI)
Sent: Monday, December 27, 2010 2:54 AM
To: amps at contesting.com
Subject: Re: [Amps] 572B AMP PLANS

On 12/26/2010 11:06 PM, Jeff Blaine wrote:
> Hsu,
>
> The 813 looks nice.
Wayyy back in another life, I beat the snot out of a pair of 813s for a
couple years, running the legal limit which back then was 1KW average or
2KW PEP. I probably ran about 60% CW and the other 40% SSB back then.
They were convection cooled with lots of space and a B&W 850A tank circuit.

>    But I am very impressed with the GI7B.  I really work that tube hard - both in the RTTY contesting and on the
> bench (one time, I ran the pair for 20 minutes key down at rated power) for simple endurance test on the amp.  Finally had to stop
> out of worry the DL was going to explode.  hi hi.
>
If you have the transformer, I think you could run 4 GI-7Bs well beyond
1500 out, so they should loaf along at the US legal limit.  You'd still
have less than the cost of one imported 3-500Z in tubes.
> If I am needing to use glass, I think I prefer the 3500Z if you have high enough plate voltage available.  I'm not sure what the
> 3-500z looks like at 2500V.
>
Although the 572b is basically an 811A on steroids, I believe the 811A
is far inferior to the 576b although if the power is kept down to the
*real* ratings of the 811's they will probably do fine.  OTOH IIRC 4 of
them only have 240 watts plate dissipation and they are not noted for
long life.

73

Roger (K8RI)

> Good luck!
>
> 73, Jeff ACØC
> www.ac0c.com
>
> -----Original Message-----
> From: Hsu
> Sent: Sunday, December 26, 2010 10:01 PM
> To:amps at contesting.com
> Subject: Re: [Amps] 572B AMP PLANS
>
> Jeff,
>     Thanks!IMO, I would like use GI-7B or 813 in GG.
> 811A/572B with very short life especially   811A.
>     My friends have some AL811/811H, the Chinese
> 811A only have few hundred hours tube life.the 813 is
> better than 811A and 572B.I guess 813 with higher
> filment power/transmitting capability?
> a problem, Chinese 572B with 125W Plate dissipation NOT 160W!
> This is the manufacturer's datasheet:http://www.tube.com.cn/en/product/productview.asp?id=65
>       73!Hsu
>
>
>
>
> ----- Original Message -----
> From: "Jeff Blaine"<keepwalking188 at yahoo.com>
> To: "Hsu"<hsu4qro at gmail.com>;<amps at contesting.com>
> Sent: Monday, December 27, 2010 9:13 AM
> Subject: Re: [Amps] 572B AMP PLANS
>
>
>> 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 at 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 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
>> 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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