[Heathkit] RE: Heathkit SB-200 - no output

[Tom Buchanan]

I pulled the relay after noticing it had evidence of clipped leads and
solder.  I think it must have been a used relay when it was installed by a
previous owner.  The relay tested bad so I will be replacing it.

The amp had a soft start mod that was damaged most likely from too hot of a
soldering iron then covered in RTV silicone and adhesive foam. It was a mess
so I took it out completely and put a brand new soft start mod in which is
wired correctly.  

Thanks for the help & 73,

Tom
KG4KGY

-----Original Message-----
From: Kenneth G. Gordon [mailto:kgordon2006 at verizon.net] 
Sent: Sunday, January 20, 2008 6:17 PM
To: Tom Buchanan
Cc: Heathkit at mailman.qth.net
Subject: Re: Heathkit SB-200 - no output

On 20 Jan 2008 at 14:19, Tom Buchanan wrote:

> There is
> no idling, grid or plate current and adjustment of the load and tune
> controls has no effect on output.  Increasing the drive from either
> rig doesn't affect the amplifier either.

No idle current indicates that either the amplifier's antenna 
relay is not switching properly, or you have completely flat, 
dead tubes.

The hot side of the jack labeled "Antenna Relay" on the rear 
of the amp MUST be shorted to ground in order for the amp 
to show idle current.

Shorting the center conductor of that jack to ground 
accomplishes at least three things: 1) it switches the 
antenna from the exciter to the amp, 2) it switches the 
exciter OUTPUT to the amp's INPUT, and 3) it connects the 
grid bias resistor network to ground, reducing the bias on 
the amp tubes to that required to provide the proper idle 
current.

I am betting that your soft-start module is not wired 
correctly, and is preventing both the antenna relay from 
activating and the bias from being dropped to the proper 
value.

You say that the amp HAD a "soft-start" module in it, and 
you added a second one? Am I reading this correctly? If so, 
I would 1) remove ONE of the soft-start modules, and 2) 
THOROUGHLY recheck the wiring and operation of the 
remaining one.

Your problem lies there.

Ken Gordon W7EKB