Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on July 28, 2015, 02:38:51 am

Title: Mystery Cap
Post by: TIMBO on July 28, 2015, 02:38:51 am

Hi guys, this may not be a mystery to some of you but it a new one for me.
My recent buys have had a small value cap across the plate and screen supply on the power tubes.

Can anyone enlighten me on their purpose. Thanks

Title: Re: Mystery Cap
Post by: kagliostro on July 28, 2015, 03:47:51 am

Ciao TIMBO

this is your schematic

(http://i.imgur.com/FaHeh0o.jpg)

and this is the Selmer Stadium TV19/T schematic

(http://i.imgur.com/UFl6F5v.jpg)

I think they are the same concerning those caps

explanation of the function of the caps here

http://el34world.com/Forum/index.php?topic=18467.msg188642#msg188642 (http://el34world.com/Forum/index.php?topic=18467.msg188642#msg188642)

Ciao

Franco

Title: Re: Mystery Cap
Post by: trobbins on July 28, 2015, 05:02:56 am

It can also function as anode over-voltage protection - that position needs a lower voltage rating cap, than if it was placed from plate to ground, or plate-plate.

The Selmer TV19 has anode stoppers, so the anode caps would further tame any high frequency instability that may have occurred.