[Amps] SB-220 diode failure

[Will Matney]

John,

The first thing that comes to my mind is a bad zener diode. It controls the bias on the tube on transmit. On idle, there's a 120 Vdc source connected to it. If the plate current is ok on receive, and off and transmit, I about be the zener is bad.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 8/9/05 at 10:05 AM John Adkins wrote:

>My sb220 cooked one of the diodes on the pc board a couple of days ago. 
>I replaced the faulty one
>with a 1kv piv 2.5 amp substitute that was in my junk box.  Resoldered the
>wires back to the pc
>board, reassembled it, and fired it up.  When I went to tune the amp up,
>with no exciter power, I
>get a plate current of 200 ma instead of the 120 ma the manual indicates
>should be seen.
>
>HV is 2.2 kv on low power, 2.8 kv on ssb.
>
>The manual suggests that the zener may be blown.
>
>What do you think?  Should I just get the Harbach rectifier/metering board
>substitute for the
>original pc board and eliminate the zener altogether?  Other suggestions
>for troubleshooting this?
>
>Thanks
>
>John
>w4kv
>
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