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@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@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@yahoo.com>
> To: "Hsu"<hsu4qro@gmail.com>;<amps@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@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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