[Heathkit] SB-200 issues.

[Kenneth G. Gordon]

On 18 Jan 2008 at 9:27, Glen Zook wrote:

> Mixing an original Cetron with a Chinese 572B is about
> as bad as mixing a 6146A with a 6146B!

Well, the Cetrons were gifts and pulls. A pair of Chinese tubes 
were in it when I got it.

The SB-200 ran fine for about 6 months with the two different kinds 
of tubes.

When I got the SB-200, the filament connection to one of the tube 
sockets had never been soldered and the ham I bought it from (she 
is blind) had been running it for quite some time with only one tube
working. Her husband isn't a ham, and she couldn't see that one 
was not lighting.

The tube that HAD been carrying the load had a grid to filament 
short.

When I fixed the filament connections, the one good tube would 
get a red plate. So I swapped one of the gifted Cetrons with the 
dead tube and the amp ran fine for several months.

Recently (about a month ago) the AC power switch contacts welded 
shut, so I had to pull the plug in order to turn it off.

I let the amp run for about 2 weeks 24/7 to see what might crop up. 
I think that stressing a piece of gear a little bit can make problems 
show up eariler.

I think at least one of the tubes has gone flat.

In any case, running the two different tubes didn't seem to cause 
any problems.

Everything was very stable and power input/output was good, and 
was always steady...until recently.

I think a big part of the problem is that the fan failed some time 
ago, and I didn't notice it until recently. I know the first inkling I had
that the fan was probably not rotating was when I accidentally put 
my hand on top of the case and got burned. The entire case was 
REALLY hot!

Since I put the muffin fan on top of the cage with the lid open, the 
amp is now almost as cold as the room, which is freezing most of 
the time. :-)

Thanks for the hints, but in this case (only) I don't really think the 
two different types of tubes had anything to do with it, although they 
MAY have made the problems show up a bit earlier.

Ken W7EKB