Bottlehead Forum

Bottlehead Kits => S.E.X. Kit => Topic started by: wwmhf on April 25, 2010, 02:05:27 PM

Title: Bias capacitor voltage rating
Post by: wwmhf on April 25, 2010, 02:05:27 PM

I have several nice capacitors rated 25V and I am considering to use them to replace the Cbias 1000uf capacitors. However, the official plan states their voltage rating as 35V.

I know that it is always a good idea to use electrolytic capacitors with a specified or higher voltage rate. The consequence of exploding an electrolytic capacitor is usually dramatic. On the other hand, I really do not any alternatives at this moment and those 35V capacitors were leftover from previous projects. Hence I would be grateful if you can let me know if swapping those 1000uf/35V capacitors by the 25V ones will be dangerously wrong.

   

Title: Re: Bias capacitor voltage rating
Post by: Dyna Saur on April 25, 2010, 03:36:56 PM

Going by my somewhat  less-than-perfect memory, the SEX  6DN7 power stage's  bias runs around  16 to 17VDC (27 mA thru 620 ohms) .  A 25V cap rating  would be cutting it  kinda close, but not dangerously so. , 35V has a better safety margin.

I do not know if the 17VDC "bias"  rises to a higher voltage during start-up / warmup, or power-off,  I would presume not, as the "cold" tubes are not conducting fully..

HTH

/ed B in NC

Title: Re: Bias capacitor voltage rating
Post by: wwmhf on April 25, 2010, 06:13:12 PM

Dyna,

Thanks for sharing your opinion. I am trying to push to the limit based on a similar thinking like yours.

Title: Re: Bias capacitor voltage rating
Post by: Paul Joppa on April 25, 2010, 06:47:09 PM

There should be no problem with 6DN7s using a 25v part.

Title: Re: Bias capacitor voltage rating
Post by: wwmhf on April 26, 2010, 03:36:05 AM

Glad to get the confirmation from Paul. I feel good that my spare ELNA capacitors can be put into a good application.