[Heathkit] SB-220

[Duane Fischer, W8DBF]

Tnx Ed - 	


----------
From: ma.locksmith at juno.com
To: w4ych at earthlink.net
Cc: heathkit at mailman.qth.net
Subject: Re: [Heathkit] SB-220
Date: Thursday, November 25, 2004 11:58 AM

Your description of the symptoms indicates it's not a measurement
problem, you actually don't have any plate current.

The high voltage meter reads the voltage in the power supply and not at
the plates of the tubes....  so, there might be an open between the
supply and the tubes.....  check the RF chokes for an open.

Then, the return from the tubes is through the filament transformer
center-tap.  This line, which does go through the zener diode, also goes
through a very low value resistor to ground.  Open resistor, no current.

However, you are not actually reading the current there....  you are
reading it between the negative terminal on the power supply and
ground......  so that the meter does not have high voltage on it.  Yet
this point is also returned to actual ground through the same low value
resistor as above.

While you are on the circuit board, check each of the resistors for
change in value, generally up.  Replace any out of tolerance....  it will
save you from trying to find a problem that comes up after it's working.

Ed
K1ZOK

.


On Thu, 25 Nov 2004 11:06:31 -0500 "Don Flenner" <w4ych at earthlink.net>
writes:
> Greetings All and Happy Thanksgiving,
> 
> I recently acquired a SB-220 in a non working condition...The 
> problem is:
> 
> When the antenna change over relay is energized I get no idling 
> plate 
> current...
> 
> The 3-500Z's light up, I have checked them in another amp and get 
> the proper 
> idling plate current, the plate voltage reads 2500 in tune and 3200 
> in SSB. 
> I have changed the 5.1 volt zener, checked the wiring of the antenna 
> relay. 
> The plate current meter deflects when a put an ohm meter across it, 
> so I 
> amuse the meter is OK.  Also, as a further test to make sure it was 
> not a 
> meter problem. I hooked the amp to a transceiver. With the amp off I 
> get 100 
> watts out. When I turn the amp on and press the PTT, the relay 
> energizes in 
> the amp but no output.
> 
> Sure could use some guidance from the knowledgeable on this 
> reflector.
> 
> Thanks in advance.
> 
> 
> 73,
> Don, W4YCH
> http://www.home.earthlink.net/~w4ych
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
> 
> 
> 
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