[Heathkit] sb200

[jeremy-ca]

Jim, substitute the word bias for screen which I assume is what you were 
measuring.

Standby bias is ~ -125VDC. In transmit, this bias depends upon where it is 
measured. Altho the 572B is referred to as a zero bias triode it does in 
fact operate with a slight bias to determine class of operation and add a 
bit of stability.

In the SB200 the Operating (AND Standby) bias measuring point (easiest 
accessibility without removing the cabinet) would be at the terminal strip 
on the rear wall of the RF compartment. Looking from the front it is the 
right most terminal and it shouldbe about -2V and idle current of 90 ma.

The usual cause of a low reading would be a leaky filter cap C3 and possibly 
C19.
Hope this helps.

Carl
KM1H
----- Original Message ----- 
From: "Jim Brannigan" <jbrannig at optonline.net>
To: "Glen Zook" <gzook at yahoo.com>; "ted orant" <ted1970 at sbcglobal.net>; 
<heathkit at mailman.qth.net>
Sent: Tuesday, August 15, 2006 10:37 PM
Subject: Re: [Heathkit] sb200


> Thanks Glen, I thot I was having a "senior moment"
> I ran a HB 572B amp for years and started to say to myself, "what was the 
> screen supply voltage"?
>
> Jim
>
>
>> There is no screen voltage in the SB-200.  It uses a
>> pair of 572B triodes which have a filament, grid, and
>> plate.  To have a screen the tubes would have to be at
>> least tetrodes, not triodes.
>>
>> Glen, K9STH
>>
>>
>> --- ted orant <ted1970 at sbcglobal.net> wrote:
>>
>> Have sb200  and wondering if screen voltage should
>> drop to -50 volts on key down.
>
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