[Heath] More info on 572Bs in SB-200

[Kenneth G. Gordon]

On 8 Aug 2012 at 11:21, van wd8aam wrote:

> Very interesting data you have gleaned, you make a grand case for not
> trusting Chinese tubes.  I have an original pair (new cetrons) and a
> new pair of svetlana tubes.  I guess I'll hang on to them for a while.
> Van Lincoln wd8aam

I certainly would if I were you, Van.

The Svetlana's are very good tubes, although even those are not exact 
copies of the original Cetron types either. 

In fact, I would say that the Svetlana's are really excellent tubes, despite their 
looking like they are smaller. Trouble is, Svetlana has not made any of those 
for the past several years. I have a pair of those, NIB, here and may use 
those in one of my SB-200s.

In the SB-200, however, the Svetlana's require neutralization, which, for a 
GG amp is not difficult but the proper procedure is a bit different than for a 
grid-driven amp.

In the SB-200, your Cetrons should last you at least 10 years of normal use.

So should the Svetlana's, if the amp is neutralized.

With the Cetrons, keep your grid current as low as you can keep it and still 
get the power output you want. What I do here with mine (although mine are 
most certainly NOT new either) is to lower the grid current, by reducing the 
drive, after I have loaded the amp up, until I see the power output drop about 
50 watts.

Grid current under those conditions is usually under 40 mA per tube.

Power output is usually at least 500 watts, depending on the band.

I get around 700 watts output on 80 and 40 meters, dropping to around 550 
watts on 20 and 17 and 15 meters.

With the bandswitch set on 15 meters, the amp loads very easily on 17 
meters. Even input SWR is reasonable. I drive it on that band with either my 
TS-820S or one of my TS-940SATs.

Ken W7EKB