[Amps] 572b

[Jeff Blaine]

Jim,

I don't know why either.  Maybe I don't understand the spec or the 
application or some other error.  Or it could be a faster roll off in 
emission at higher sustained currents.  No idea.  I gave up on the tube as 
my goal was to build a RTTY contesting amp out of the SB200.  Eventually 
went with the GI7b which has been a work-horse.  However, in retrospect, I 
could have paid for a LOT of 572b had I not done what ultimately turned out 
to be an extensive and costly conversion.

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie

-----Original Message----- 
From: MU 4CX250B
Sent: Thursday, May 02, 2013 5:32 PM
To: Jeff Blaine
Cc: L L bahr ; amps at contesting.com
Subject: Re: [Amps] 572b

I'm afraid I don't understand why the plate dissipation would affect
longevity, provided the tubes have adequate cooling. Exceeding rated
grid current or plate current, or using the wrong filament voltage
could kill the tubes, as could  inadequate cooling, but I don't see
why running the tubes at their rated dissipation with plenty of air
would shorten tube life, if all other tube parameters were within
specs,
73,
Jim w8zr
Sent from my iPhone

On May 2, 2013, at 4:22 PM, Jeff Blaine <keepwalking188 at yahoo.com> wrote:

> I have used about 8 of the Chinese 572 specifically for torture testing in 
> RTTY service and I can say without qualification that the plate 
> dissipation limit (IIRC 160w) is not something which will keep the tube in 
> long service. But whipping the hell out of these tubes in AM/FM/RTTY 
> service with all the guns blazing is not the common application.
>
> I would expect the current breed to give long SSB service as long as 
> tuning is done properly and kept to a minimum.  For CW, almost as well. 
> From there, it goes down hill fast.
>
> Comparing them with prior generations makes no sense because there are 
> virtually zero NOS old tubes remaining.  You either buy the Chinese 
> (through some direct or distribution method) - and that is the only source 
> available and take what service life you can get.  Or you can flip to 
> another tube type at some considerable amount of work and expense.
>
> 73/jeff/ac0c
> www.ac0c.com
> alpha-charlie-zero-charlie
>
> -----Original Message----- From: L L bahr
> Sent: Thursday, May 02, 2013 5:00 PM
> To: amps at contesting.com
> Subject: Re: [Amps] 572b
>
> If quality control is so poor, how do you test for longevity or 
> robustness? Just checking the emission when new may have nothing to do 
> with longevity. I'd like to know how well a Chinese 572B will hold up 
> compared to a Cetron 572B.  I wonder what short cuts the manufacturer has 
> taken in production when many new ones go out the door with poor emission. 
> What else is wrong with them?   Maybe it's time for these amplifiers to be 
> retrofitted with other type tubes.
>
> Lee, w0vt
>
> ----- Original Message -----
> There's no doubt that the manufacturer is the problem, but since they are 
> the only one making them  and most Ham's just need a few, a reputable 
> distributer is very important in the supply chain.  He tests them before 
> selling them to be confident that they worked when they left his facility, 
> that is one of the reasons he is considered reputable.  It costs more, but 
> he must becompensated for his time.  A reputable dealer is paramount in 
> buying a tube you know has a decent chance of being good, andis the one 
> thing you can do anything about-choose who you buy from !! Cheers,  Matt 
> 73AD7XN
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