Better current source than LM317 on a 12B4 line amp

[sparkle]

Hi guys,
I have been using for few weeks LM317 in cathode arranged as current source in my 12B4 grounded cathode line amplifier. Plate current is arround 25mA and voltage on LM317 current source is arround 10-11V depending on a tube caracteristics.

I would like to use something that is better than LM317 that will give me arround 25mA and that will work better on that voltage across ccs. A friend of mine suggested TL431 - I would like to hear some other options that might be even better ....
Maybe something discrete .....
best regards

[sparkle]

i was thinking about something that is better than this tl431 and LM317 ccs.....
Vi=10V
R1= 1K
Rs=100R
Io=25mA
hfe=the bigger the better

[SY]

Could you explain further? You say that this is a grounded cathode circuit but you have a current source on the cathode?

[sparkle]

oups..... made mistake... picture of the current arrangement (almost current-but You will get the idea)...
((100uF is 220uF in fact and it is bypassed with 1uF MCap; also voltaage on anode of the tube is not 65V but 130V and high voltage on plate res. is arround 260V))

[poobah]

Why do you not like the 317 circuit? What are you wishing to improve or change?

[ilimzn]

In this circuit, it is the cathode capacitor that is the most critical component in the cathode circuit. It's whole point is to efficiently bypass the CCS anyway, so the CCS only sets DC condition. Last I checked, humans can't hear DC so if something is wrong, your cap is not doing it's job.

[Mark A. Gulbrandsen]

I have to agree.... whats wrong with the 317.... they can be had for 50 cents? Any noise that it might introduce would be bypassed with the caps anyway. There are other regulators one could use by IXYS and others however the 317 is pretty cost effective and you'll still need the boutique capacitors in the cathode with the others as well..... I doubt there would be any major audible difference between cathode based current sources due to the major effect the bypass caps have on overall sound.

Mark

[Onra]

The datasheet says the tube needs about -15 to -20V gate voltage to deal with 130V plate voltage and 25mA anode current.
Your 10V-Cap will not withstand this voltage for a long time.
Onra

[tubelab.com]

I am partial to the IXYS 10M45 chip myself, but I have not tried it in this circuit........yet.

In this circuit the cap would eliminate all artifacts caused by the CCS, IF THE CAP IS PERFECT. We all know that caps are far from perfect.

I want to build this circuit soon, I have all of the parts, a lab grade power supply to run it (Fluke 407D) and both kinds of CCS chips. I am just short on time right now.

[mach1]

I'm just putting the finishing touches to a new 12B4 linestage, the details of which I will post shortly.

I tried a 317 on the cathode with a couple of good quality bypasses (silmic II, cerafine) plus a generic for good measure. However, I preferred a 10M45S cascode CCS on the anode with no bypass cap on the cathode resistor.

The sound with the 317 CCS changes markedly depending on the cap used: I think tubelab hit the nail on the head - this type of circuit is great, assuming you have the perfect cap. Otherwise you are listening to capacitor artefacts, which to my ears are worse than those of the 10M45S.

Doubtless there will be those who contend that their latest iridium / boron laminate caps with powdered unicorn horn dielectric can achieve sonic nirvana in this application. Me - I'd rather not have a cap there in the first place...