[Heath] SB-200 problems...solved...

[Kenneth G. Gordon]

On 20 Sep 2011 at 13:08, Jerry Haigwood wrote:

> Ken,
> I use a "soft" key made by Jackson Harbor Press.  It is basically
> a solid state relay.  It requires +3 to +12V to operate it. I half wave
> rectify the 6.3VAC and use it to supply the required voltage.  Jackson
> Harbor Press calls this device the "keyall."  It sells for $17
> including shipping. Jerry W5JH

OK. I ordered one.

However, checking the characteristics of the IRF-820, I see that the 
Rds, i.e. the drain-to-source "on" resistance, is typically 2.5 ohms, 
with a maximum of 3.0 ohms. For the two in series, that is 5 - 6 
ohms.

I suspect that, given the method that is used to determine grid-bias 
voltage in the SB-200, that is going to result in that voltage being 
raised above (below?) -2.0 VDC, and I will experience the same effect 
as that caused by the Harbach unit.

I must confess to never liking the method that Heathkit uses in the 
SB-200 to control grid bias, considering it to be a complete 
"kludge".

Well...we'll see...

I suspect now that in order to have a "soft-key" unit that will NOT 
effect resting plate current, I will need to use a REAL mechanical 
relay, which exhibits as near to zero ohms resistance at the contacts 
as possible when closed.

Poop. :-(

At this point, I am going to leave this particular SB-200 alone, and 
will concentrate on making the modifications to my other one which I 
have wanted to do for a couple of years.

These are: 

1) modifying it for high-speed switching/full-QSK using a slight 
modification of that HSS method of Rich Measures.

2) Adding 160 meter capability to it.

3) Making other mods to improve the efficiency of the amp.

4) Incorporating Carl KM1H's neutralization method.

Ken W7EKB