[Amps] SB-230 question

[Jim Kearman]

From: "Dave Meitzen" <dmeitzen at comcast.net>
> 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. 

73,

Jim, KR1S
http://kr1s.kearman.com/