From: "Dave Meitzen" <firstname.lastname@example.org>
> 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
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.
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