[Heathkit] SB-401/HW 101 Final Questions

[Kenneth G. Gordon]

On 25 May 2008 at 7:16, Michael Waldrop wrote:

> 
> The SB-400 and SB-401 both have the 10 ohm resistors. However, the
> HW-100 and HW-101 do not. The only bypass resistor in the HW-100 and
> HW-101 is the 2.2 ohm 1 watt resistor from pin 6 to ground. This
> single resistor serves both tubes.

Yes. That is correct. I was thinking of the SB-102 I just rebuilt and got it 
mixed up in my mind with a couple of HW-101s I worked on.

 In fact, there are 6 ea 10 ohm resistors in the cathode circuit of the SB 
rigs: 2 connected to each cathode, and one connected to the each 
"screen" grid connection, which is connected internally to the cathode, for 
a total of 6. That works out to 1.666666666667 ohms between the 
cathode and ground.

However, I DID have to replace the 2.2 ohm 1 watt resistor in at least two 
HW-101s I recently rebuilt. Both were cooked to a fare-thee-well: the 
cathode current indication was WAY off. When I thought I had set the 
idling current to 50 mA, it was actually sitting at 150 mA.

Also, both 470 ohm metering resistors were cooked: one was open.

After I replaced all three of those resistors, everything started to work 
correctly.