[Heathkit] SB-200 issues.

[Kenneth G. Gordon]

On 3 Jun 2007 at 21:58, Kenneth G. Gordon wrote:

> It appears that one tube, the one that wasn't lighting, is not drawing
> the proper current. All grid resistors seem to be OK. I am wondering
> if one of those little 200 pfd mica grid bypass caps is open.
> 
> And the difference in filament brightness still bothers me...one tube
> is considerably brighter than the other.

Well! It turns out that the tube that wasn't lighting, and obviously 
had not been lighting for quite some time, is the far better tube of 
the two. It is also the tube whose filament is not as bright as the 
other tube.

The tube with the brighter filament is just about shot, while the tube 
with the dimmer filament is carrying most of the load.

At key-down for any length of time, the dim tube's plate gets very 
red, while the bright tube doesn't get red at all.

I tried swapping sockets, and the differences follow the tube, not 
the socket, so it appears that the socket no longer has any 
problems.

Obviously, my friend who could not see the tubes, didn't know that 
only one was working, and therefore I have one practically new 
tube and one worn out one. :-)

It looks as though I am going to have to buy a pair of finals asap, 
however.

I have heard that the Cetron tubes are pretty decent. Anyone have 
a source they would share?