[Heathkit] SB-200 issues.

[Peter Markavage]

I would suspect one of the tubes has gone soft. Tubes don't have to be
matched; they're not in push-pull. I would check those resistors just to
make sure they haven't changed value. I'll assume you checked to make
sure both tubes are lit. If you're going to replace the fan, watch the
clearance to the tubes. The spacing between the bottom plate and the
tubes is not that great. Check and/or resolder the filament choke
connections to the pins of the tube sockets. One of mine became
intermittent after 20 years of operation.

Pete, wa2cwa

On Thu, 17 Jan 2008 22:22:22 -0800 "Kenneth G. Gordon"
<kgordon2006 at verizon.net> writes:
> On 17 Jan 2008 at 23:45, James M. Walker wrote:
> 
> > Ken,
> > Ola, I know you are familiar with the unit, but I have to ask, is 
> the
> > AC line to the amplifier stiff enough?
> 
> Yup. It is a dedicated line, using #10 wire, and goes directly 
> back to a new 200 amp panel with nothing else connected to 
> that line. The line voltage is nominally nearer 130 VAC than 
> 125 some of the time, but mostly hangs around 126 VAC, even 
> at key-down.
> 
> > Reason I ask is if it sags
> > going in that effects the filament voltage as well as the high
> > voltage.
> 
> Yup, thanks. I was aware of that.
> 
> > 
> > Also I may have a left-over fan motor with the blades that goes 
> on
> > that I would have to check. It is the same fan used on the TX-1
> > Apache. which is also in my Johnson thunderbolts.
> 
> I think that all I have to do to mine is take it out and lube it 
> properly. Actually, I think what I am going to do is to replace it 
> with a "muffin" fan which has a lot more air-flow. One can't 
> really have too much cooling for an amp, IMHO.
> 
> > 
> > First place I would look is the AC line, then check the resistors
> > cold, and again after warm-up.
> 
> Thanks. I'll do that. SOMEthing is changing drastically with 
> heat...all I have to do is figure out which "thing" it is.
> 
> > 
> > Also is this the rig with the 572Bs in it?
> 
> Yup. The two that I have in it are NOT a matched pair either. 
> One is a lightly-used Cetron and the other is an almost new 
> Chinese one...at least they were about 6 months ago. :-)
> 
> When everything is working as it should, I can easily get 500 
> mA at 2100 VDC, which is a little over a KW input.
> 
>