The AM Forum

Hi Folks,

In the Viking II, is C7 the .001 uF across the secondary of interstage transformer T3 needed? If it is, I have some 1kV ceramics 360, 390, 470, 560 pF, one of those should be fine right?

Thanks
Kevin

Is this the original Interstage Transformer?

Phil - AC0OB

Hi Phil,

Yes, it's the original

Thanks
Kevin

Kevin, that cap is meant to bypass RF off of the audio going to the 807s. It does roll off audio highs. I replaced it with a .0005 cap giving a higher roll off start frequency. Been working fine for 40 years on my Viking 1.

Kevin,

I did the same thing as Bud except I use a 560 pF ceramic at 1kV.

On every Viking I have worked on that paper Aerovox cap has shown leakage around 50k, which reduces drive to the 807's.

Most people replace the original T3 as it is failure prone and has narrow frequency response. My preference for the replacement transformer is the Hammond P-124B, which has a 1:3 primary to secondary turns ratio and wide frequency response. Others prefer the Hammond P-124D, or the lower cost P-T156 available from Antique Electronic Supply, https://www.tubesandmore.com/products/P-T156 .

Phil - AC0OB

Thanks Phil and Bud, I really appreciate your help and the tip on the transformer upgrade too.
Bud, thanks for explaining the function of that cap too. I wasn't really sure if it was for RF, AF or both.

73
Kevin - KD1NW