Heathkit SB-200 audio distortion

[Tom Chesek]

I wasn't following the posts but Harbach has a soft key and a soft start 
module. Soft key for keying old amps with new radios and soft start to 
slowly power up old amps.

Tom K3TVC

----- Original Message ----- 
From: "Jeff Goldman" <k3dua at EROLS.COM>
To: <HEATH at LISTS.TEMPE.GOV>
Sent: Sunday, March 01, 2009 12:15 PM
Subject: Re: [HEATH-TEMPE] Heathkit SB-200 audio distortion


> Tom,
> 
> After reading a few of the related posts, I want to clarify some  
> wording.  In your last paragraph below, you refer mention installing  
> the "soft key to connect it to the FT-840".   The Harbach soft start  
> option is used to slowly start up the AC power to the power supply  
> when the main power switch is first turned on.  It has nothing to do  
> with keying the amp from the exciter.  I am not sure exactly how you  
> have things hooked up, or if you may need some sort of keying  
> interface between the amp and your radio, but whatever it requires,  
> this interface is definitely not the "soft start" option.
> 
> I agree with one of the other commenters that it sounds like you amp  
> is locked in the keyed position as soon as you turn it on.  Disconnect  
> the cable going to the amps relay control connector on the back panel  
> and measure the voltage at the connector (ground to the center  
> conductor) - - it should be about negative 130-175 volts DC, which is  
> the standby cutoff bias being applied to the tubes, which in turn  
> causes the plate current to go to zero ma.  If the bias is not there,  
> its time to open up the amp and find out why there is no cutoff bias.
> 
> Good luck with the fix.
> 
> 73,
> Jeff, K3DUA

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