[Heathkit] SB-200 Help

[Kenneth G. Gordon]

On 9 Aug 2007 at 23:48, KBØNLY wrote:

> It says to switch it on and put the meter switch on Plate and i should
> see 90ma of idling plate current with no drive from the exciter, i got
> ZERO.

OK. That is your FIRST problem. WHY do you have no idle current? Is 
that reading accurate? You say you got the amp from another fellow 
and it worked fine for him. Ask him about the idle current. If the meter 
shunts have gotten flakey, that COULD be the reason. Or something 
could have gotten jarred when the amp was moved...like a grid to 
filament short in one of the tubes for instance.

A grid to filament short in one of the tubes could also effect the input 
SWR.
 
> Than it says i should advance the drive level of the exciter for 200ma
> of plate current.  Can't, why?  Because the amp is presenting a 3:1
> SWR to the radio and the FT-847 backs down the power output because of
> the HI SWR condition it's seeing.

That is your SECOND problem. It may be related to the first one. In 
fact, it sounds to me as though they are related, since idle current 
almost demands that everything in the grid side be good.

> 
> If i flip the meter switch to the Rel Pwr position i can see the power
> output of the 847 but thats about it.  I can adjust the tune and load
> controls until i'm blue in the face and get nowhere.

What does your HV read? 

BTW, the RelPwr position of the switch only reads RELATIVE power. It 
does NOT read power output in watts, and is dependent on where you 
set the REL PWR pot. It will change on each band, reading higher on 
the higher bands if you don't reset it for each band.

> This amp was working perfectly before i bought it, and yes i am sure
> of that, but now i can't get it to do diddly.

Then I would talk with the guy you bought it from and ask him a lot of 
questions.

Often, the input circuits of the SB-200 have to be "tweaked" in order to 
get the best INPUT SWR.

Also, are you CERTAIN that the cable between your 847 and the amp is 
good? I had a bad cable to start with and had many of the same 
symptoms you are having. You might experiment with the different 
cable LENGTH too.

Is it plugged into the correct jack? Remember, there is an ALC OUT 
jack on the back that is right next to the INPUT jack.

Connect an external SWR meter between the 847 and the amp. It will 
generally read differently due to differences in cable lengths.

To adjust the input circuits, you have to connect an SWR meter 
between the 847 and the amp, remove the cover from the amp, and 
adjust the slugs of the coils in the back, one for each band, in the 
center of the band you are using. BE CAREFUL!

Ken Gordon W7EKB