[Heathkit] SB-200 and 572B to GI7b conversion or new 572B's ??

[wb4mnf]

This would be a one for two swap or a 2 for 2 and dispense with the
anode blower???
-bob


John Peters wrote:

> Hi All,
> 
> Just got a SB-200, in working order but tubes are lazy, only 300W out with
> 100W drive. So I need new tubes, there are a few options, buy a pair of new
> 572B's
> 
> Which ones are preferable ??  Taylor or Svetlana ??
> 
> Or should I convert the PA to a pair of GI7b's it seems others has done this
> before.. I have a bunch of these tubes laying arround, they are much cheaper
> than the 572B's and more solid too, but need more air so the PA will get
> noisier. More gain, and a pair will last for ever in this configuration. 
> 
> Is this done before ??? And how should I make bias ?? Real GG design or like
> with the 572B's with 200pf to Gnd and make a DC ground via some resistors (33
> Ohms with the 572B's) to get the right Bias current.. 
> 
> any info is very much appreciated,
> 
> 73! de John PA5MS
> 
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