[Amps] Svetlana 572B and FL-2100Z

[R.Measures]

On Aug 28, 2004, at 5:46 AM, Alek Petkovic wrote:

> A friend of mine Has recently bought a FL-2100Z and it is fitted with 
> Svetlana 572B tubes.
>
> He has had a couple of bangs so far on 20m resulting in the loss of 
> the 22 Ohm parasitic suppressor resistors.
>
This means that the tubes do not have low gain.  Unless the filament 
broke off during the osc., I would use the tubes.

> Also, a previous owner has put 33 Ohm wire wound resistors in the grid 
> circuit. The originals were of course non inductive resistors which 
> are very hard to source here in Australia.
>
> I am sending him some new 33 Ohm resistors and some nichrome wire to 
> make up some new suppressors plus a glitch resistor.

The new grid resistors should be no more than 0.5w, and the total grid 
bypass C should be c. 1500pF to protect the grid fuse resistors from 
10m RF.
>
> I am also sending him some new Cetron tubes and have advised him to 
> get rid of the Svetlanas and put some extra resistance in the filament 
> line to reduce the voltage to a safer value.
>
> Has anybody had any experience with Svetlana 572B tubes? I was under 
> the impression that they spelled trouble in hf amplifiers. Is this a 
> fact?
>
Alek -- Rumour has it that they have more gain than the old RCA or 
Cetron 572Bs, so naturally they are a tad harder to tame.

> ...
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org