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Re: [Amps] SB-230 question

To: "Dave Meitzen" <>,"'Amps Reflector'" <>
Subject: Re: [Amps] SB-230 question
From: (Jim Kearman)
Date: Mon, 12 Jun 2006 17:44:14 +0000
List-post: <>
From: "Dave Meitzen" <>
> My brother picked up a SB-230. It has a couple of mods. At .1 ohm resister
> in the cathode and the TR relay has been removed so you have a input and a
> output. Why would someone make these mods?
> I guess is the .1 ohm resistor protects the tube but the other?

Is there anything connected across the .1-ohm resistor? Sounds more like a 
meter shunt.

The relay probably failed and the owner wasn't up to replacing it. The stock 
relay is no speed demon, so replacing it with a combination such as suggested 
on Rich Measures' site would be a good  improvement. 

While he's about it, your brother should consider ways to blow some air around 
the tube. The heatsink is inadequate, IMO and others'. I use a 4" fan resting 
on the top cover, straddling the PA and power supply areas. A glitch resistor 
would be a good idea. I also installed a fuse holder with 7-amp fast-blow fuse, 
as I learned the hard way that the internal circuit breaker is useless when the 
amp is wired for 240 V. The new $Peter $Dahl transformer works quite nicely, 
however. If the original electrolytics are still in place, they have to go. I 
made a Lucite plate to mount over the holes for the old caps, and cemented the 
new caps onto it. The 150-uF electrolytic for the relay power supply should be 
replaced, too, if it's still there. 


Jim, KR1S 
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