[Amps] more sb220 questions

[Will Matney]

John,

There's several thing that could cause no power output from the amp. That zener diode being one which I'd check first. It sets the tubes bias on transmit. No heater voltage. No high voltage would also do it, but I assume you checked that. You could still show plate voltage on the meter in the amp and not have it on the tubes because of an open plate choke. Another thing to cause it would be a bad relay. The amp supposed to use a 3PDT relay with 10 amp contacts and was an open frame type. You can use an enclosed one here also. Bad tubes would be the last.

I'd check the bias voltages first. On receive you should have around +120 Vdc on the C.T. of the heater transformer. On transmit it should be around 7 volts (zener voltage). The antenna relay switches this voltage through the 3rd contact. Next, check the plate choke for continuity.

Best,

Will


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

On 8/31/05 at 2:02 PM John wrote:

>I  never got any power out at all.  No noise, either, except for the fan 
>increasing rpm.  I'm already moving toward restoration of the amp to a 
>condition closer to the original kit.  Any other suggestions appreciated.
>I have posted another page of pictures.  These include views of a 
>relatively unmodified SB-220 for comparison.  
>http://www.geocities.com/w4kv/sb220-2
>
>73
>John
>w4kv
>
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