resistor in series with cap

[andrew]

Hi,I saw this in a TopHat schematic and I'd like to know why it is: 12ax7 cathode>10uf cap>10k resistor( bypassable)> ground. Thanks.

[xtian]

Can see why you're wondering. Usually it's the cap that's bypassed. Can you show the schem?

[andrew]

http://www.freeinfosociety.com/electron ... deluxe.pdf Thanks.

[Firestorm]

It's a fat switch or a deep switch. Shorting the 10K kicks in the 10uF bypass cap. Otherwise the cathode resistor is bypassed by only a .1.

[xtian]

I love how the schematic looks thrown down on a cocktail napkin.

[andrew]

Hey Firestorm thanks for the reply.Why not just short the negative end of the cap? I don't see a need for the 10k resistor. Thanks.

[FunkyE9th]

If you don't have the 10K resistor, you will hear pops when you switch the negative end of the cap to ground. The cap wants to instantaneously charge from no charge to some voltage and that comes out as a pop.

The 10K resistor is there to allow for the cap to charge so that when you short out the 10K resistor, the cap is already fully charge, so no pops. The resistor value is usually chosen so that it's large enough so that it does not affect Rk (i.e. the 820ohm resistor). In this case 820 || 10K = 757, still approximately 820.

[andrew]

Thanks, I got it now.