[Heathkit] SB-200 issues.

[Kenneth G. Gordon]

On 18 Jan 2008 at 9:11, jeremy-ca wrote:

> Ken, if it happens on all bands it could be tubes,

The way it is acting, I think you're right. I have one Cetron 
and one Chinese knock-off in there. I think the Chinese tube 
has had it.

> the output blocking
> cap or the grid caps if they are the rectangular style and not the
> later dipped mica. Ive had many SB-200's come thru here with both cap
> problems.

I'll check those. I think mine are the dipped.

> 
> The grid resistors usually drift up over time but not short term as in
> a key down test. They are there to both act as an aide to parasitic
> supression as well as providing a bit of drive balance. If one tube
> has gone bad it may have opened its resistor and you have one tube
> taking the full load hastening its demise.

I'll check those too. 

> 
> Try using one tube at a time after checking the resistors and caps.
> Drive with 40-50W on 40M. The input VSWR will change but ignore that.

OK. Good idea. 

> 
> Replacement fans are available from Harbach but you can probably fix
> yours by taking apart, cleaning the shaft and oiling the bushings.
> When they lose torque and slow down and then stop they dont burn out.

Yes, I knew that part of it. The reason I think the fan isn't 
turning is because when it DOES turn, it rattles, and I 
haven't been hearing any rattles.

So, I guess I'll take it apart and lube it. I like that bicycle 
lube, TriFlow. It seems to last longer than some lubes.

I use TriFlow to lube computer fans that have seized up too.

I use TriFlow to lube the fan in our air purifier too, but since 
the fan is placed in the air-stream AFTER the filtering, the 
oil oxidizes fast.

Thanks for the hints. I think the problem is tubes.

It is very interesting to me how tuning changes so drastically 
as the a tube or both tubes get flat.

Ken W7EKB