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Simple cathode CCS

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Klimon

Klimon

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Joined 2005
#1
Hi,

Any suggestions for a component for ultra-cheap and simple cathode CCS? Current draw is 25mA, ca. 15V per tube.

LM317 is easy obtainable here (my local electronics store can supply all Farnell-parts), stuff like 10M45 or DN2540 unfortunately not...

Diyaudio / Gary Pimm / Machmat CCS are probably better but I'ld like to start cheap and easy... If Farnell has alternatives for Lm317 I'ld be interested to know 🙂

Simon
 
#11
Unfortunately any cathode CCS needs bypassing. Otherwise the effect would be to block all of the AC signal and so produce no useful output.
I took the opportunity to configure my CCS's as a differential pair. This has a PP pair with the cathode bypass caps tide together and their cathode's lifted from earth with a 1meg resistor. The implementation of the differential pair goes some considerable way to overcome the limitations of the cathode bypass caps.

If your valves are well matched and likely to stay that way, you can use a single CCS in a power LTP (differential again) without the need for any cathode bypassing at all.

Shoog
 
#13
Unfortunately any cathode CCS needs bypassing. Otherwise the effect would be to block all of the AC signal and so produce no useful output.
Click to expand...

Strangely enough Yeo uses cathode CCS without any bypass and it seems to work a treat: http://www.diyparadise.com/buildel84b.html

I plan to start with a lm317 for each tube, unbypassed, then experiment a little with caps. The solution you use on your 6080 is probably the better one (any idea; better bass, more gain?); I'll report here with my findings (within a few months time ofcourse)

Simon 🙂
 
#14
Strangely enough Yeo uses cathode CCS without any bypass and it seems to work a treat: http://www.diyparadise.com/buildel84b.html
Click to expand...

The reason this works is because the cathodes are tide together and so the AC signal can "communicate" cathode to cathode. No signal needs to go through the CCS. This is exactly like a driver LTP.
If you have seperate CCS for each cathode, the AC signal cannot talk cathode to cathode (because there is no connection) and must go through the CCS and its bypass cap. The method I use allows the cathodes to talk through the bypass caps whilst fixing the DC current.

Shoog
 
#15
The reason this works is because the cathodes are tide together and so the AC signal can "communicate" cathode to cathode. No signal needs to go through the CCS. This is exactly like a driver LTP.
Click to expand...

Okay, thanks.

How do you determine the bypass cap value in this kind of cathode circuit (ccs + 1 meg to ground)? When I see the very high values you're using I presume the formula for calculating a simple cathode resistor bypass isn't valid here.

Simon
 
#16
I would say that it is the same formula as the normal bypass cap. However if you are going to tie the caps cathodes together, the two caps are connected in series and so their effective bypassing value is halved. So in my case its down to 1000uf. I chose such a large value because of the extremely low output impedance of the 6080. I did this by ear when I found that 500uf (1000uf series 1000uf) produced poor bass.

So go with the standard formula and double the calculated value.

Away on holiday now so thats all I can add for a fortnight.

Shoog
 
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