[Amps] SB-220 question

[w8hw at comcast.net]

Hello Cathy,

I repair amplifiers and have seen this before.

I can only guess that the Door Knob cap went bad and someone replaced it 
with the orange cap just to its left. Doorknob cap are often replaced with 
Mica caps that have proper voltage ratings.

Hope this helps

73, Bruce, W8HW, Port Saint Lucie, Florida.
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-----Original Message----- 
From: Catherine James
Sent: Saturday, October 15, 2016 11:41
To: amps at contesting.com
Subject: [Amps] SB-220 question


I've just bought a Heathkit SB-200.  Superficial inspections looks good; no 
sign of burned contacts, corrosion, etc.  Transformers appear fine.

There do not appear to be any Harbach board modifications made.  I will need 
to install the softkey before I can use the amp, and I am planning to put in 
the soft-start at the same time.

There is one connection that I cannot reconcile with the manual, but I am no 
expert on this amp.  See the photo below:

https://s3.amazonaws.com/files.qrz.com/r/n5wvr/SB_200_plate_wiring.jpg

The plate connections of the two tubes run through a capacitor/inductor 
circuit to a green RF choke.  There is a short uninsulated wire that runs 
from this choke to a lug, and it appears that it once connected to a screw 
terminal on the capacitor bank wall.  However, it is hanging loose.

There is also a capacitor of about 5800 pf running from the end of the green 
RF choke to a grounded lug on the sheet metal panel above the capacitor 
bank.  I am not seeing this in the manual at all.

Is there a known SB-220 mod where this direct connection is replaced by a 
capacitor?  What purpose does it serve?

73,
Cathy
N5WVR
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