[Amps] 572B - News?

[Carl]

The FL-2100's with 572B's did not have sufficient bias for Svetlana and even 
some Chinese tubes, the fix was easy.

OTOH those amps have a wacky neutralizaion circuit that is far from stable 
on all bands and can take out the bandswitch. Modifying for the old Heath 
Chippewa or Gonset GSB-201 circuit took care of that.

The SB-201 is not fully neutralized on 10/12 M with any brand of tube and a 
similar rework saves a lot of "smoke" issues.

Carl
KM1H



> Plus, if I recall, there was a service bulletin on the 2100 (not sure it 
> it applied to the Z variant) regarding the use of the Svetlana tubes.  The 
> amp needed a modification (probably to the parasitic suppression?) to use 
> that tube.
>
> Al
> AB2ZY
> ________________________________________
> From: Amps <amps-bounces at contesting.com> on behalf of Carl 
> <km1h at jeremy.qozzy.com>
> Sent: Friday, November 7, 2014 1:03 PM
> To: David Harmon; 'Marcelo Cabral'; amps at contesting.com
> Subject: Re: [Amps] 572B - News?
>
> The Svetlana works OK but has a smaller anode and less dissipation. They
> havent been made in several years now.
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "David Harmon" <k6xyz at sbcglobal.net>
> To: "'Marcelo Cabral'" <py1kr.marcelo at gmail.com>; <amps at contesting.com>
> Sent: Friday, November 07, 2014 12:25 PM
> Subject: Re: [Amps] 572B - News?
>
>
>> Marcelo.....
>> Try to find some 572-B made by Svetlana.......they are much better
>> quality.
>> I have had several sets of them and I prefer them over the Chinese mfgd
>> tubes.
>>
>>
>> 73
>>
>> David Harmon
>> K6XYZ
>> Sperry, OK
>>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Marcelo
>> Cabral
>> Sent: Friday, November 7, 2014 11:18 AM
>> To: amps at contesting.com
>> Subject: Re: [Amps] 572B - News?
>>
>> Hi, Carl!
>>
>> Good news at the end!
>> Sincerely, I will try a MP pair of these new tubes after January, but I
>> haven't big expectations about their reliability.
>> But, if them survive at least one year, I must be finished the others
>> projects and be able for start this mod for GI7B. For today, I'll buy 
>> some
>> GI7B's from UR4LL, must be useful in a near future.
>> Thanks everyone, hope to meet everybody in CQWW CW soon.
>>
>> Marcelo - PY1KR
>>
>> -----Original Message-----
>> From: Carl [mailto:km1h at jeremy.qozzy.com]
>> Sent: sexta-feira, 7 de novembro de 2014 14:52
>> To: Marcelo Cabral; amps at contesting.com
>> Subject: Re: [Amps] 572B - News?
>>
>> RF Parts will be taking new 572B orders in Jan 2015, Id rather wait than
>> hack up a perfectly good amp for an inferior tube.
>> http://www.rfparts.com/tubes/tubes-572b.html
>>
>> Carl
>> KM1H
>>
>>
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