• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6112 and 6111 Mini-preamp

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SY

SY

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Joined 2002
SYclotron.com
Constant current is the opposite of constant voltage. Let's assume that the swing here is low compared to B+ (for a line stage, it's about 2V swing versus 90V B+). We keep the current constant, so for a (roughly) constant plate voltage, Vgk has to be constant. So any voltage impressed on the grid will cause the cathode voltage to track it in order to maintain the current at its fixed level. That can be measured versus the (constant) -12V or versus ground- the output is generally ground referenced.

Keep in mind that the signal is AC, all you're doing is shifting it by a constant amount when you change the reference point.
 
TV7

TV7

Member
Joined 2011
Thanks SY, so with a constant current flowing through the tube, and a voltage swing across the CCS, does this mean good linearity? as compared to a resistor where the voltage increases, so does the current flow.....phew my head is hurtin. Time for bed. :yawn:
 
SY

SY

Ex-Moderator
Joined 2002
SYclotron.com
Yes, a triode always has maximum linearity with a constant current load. Now once you connect it to the next stage, the load is no longer a CCS, so the linearity is degraded- but with an ECC88 or paralleled 6111, the degradation when paralleling the CCS with a 10k load at AC is not terribly bothersome.

Get some sleep! When you wake up, read through the cathode follower explanations in "Valve Amplifiers." You DO have a copy of that, right? :D
 
J

Jones20992

Member
Joined 2021
TV7 said:
Had a go at designing a basic line level preamp to give me a taste of 'tube' sound with one 6112 front stage and a 6111 as a twin cathode follower, SY will love this.

Could have gotten away with using only one 6111 but decided on two, making the total complement 4 tubes for stereo operation, and seeing as I would like this portable, a 12V gel battery will power the heaters nicely.

Going by the data sheets I think I have everything close to right, although they could be totally wrong, anyone have any suggestions? Open for opinions on the HV supply from 12VDC.... I'm trying to follow the KISS principle on this one, no SS, single end. Nice and simple with reasonable sound......

Sorry about the photo, no scanner at the moment so used my camera...

Cheers :)
Click to expand...

I hate to wake the dead with a 10 year old thread but......

Did this ever get built?
 
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