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Old 10th May 2008, 09:45 PM   #21
SY is offline SY  United States
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Quote:
Originally posted by Koifarm
If you like to try, below the schematic.

That does not look terribly linear. The tube will not be happy at near-zero bias and with a load of 150 ohms.
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Old 10th May 2008, 11:27 PM   #22
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Quote:
Originally posted by ionomolo
I'm going the opposite direction, do you know of any good tube and layout to work at high voltages and low currents (200V 1.1 mA) ? It would be intended to give some color to a solid state amplifier so it has to operate at low gain.

I need such a low current since i plan to operate it from a flash camera inverter.

Look at the 12AY7 data sheet. It appears that 3 V. Lithium battery bias and 1 mA. CCS loading will achieve the objective. A cathode follower has a small insertion loss, which should be fine between a CDP and a SS power amp.

While a 12AY7 cathode follower has an acceptably low O/P impedance, operating at Ib =1 mA. strongly suggests you use low capacitance interconnects between the line stage and the power amp.
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Old 11th May 2008, 12:25 PM   #23
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I havn't done any ccs-loaded cathode followers, but I assume that the ccs should be placed at the cathode and not at the anode as in standard mu-followers (otherwise if there is no grid current and constant anode current the voltage drop at the cathode resistor would keep constant.).

I will give a try to this tube.
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Old 11th May 2008, 01:20 PM   #24
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Quote:
Originally posted by ionomolo
I havn't done any ccs-loaded cathode followers, but I assume that the ccs should be placed at the cathode and not at the anode as in standard mu-followers (otherwise if there is no grid current and constant anode current the voltage drop at the cathode resistor would keep constant.).

I will give a try to this tube.

In the case of a cathode follower, CCS = constant current sink. Yes, the CCS replaces the load resistor. AAMOF, sink or source, the constant current stuff always replaces the load resistor.

Assuming your source(s) don't have a DC offset, the following should work out well. Use a 50 KOhm log. taper pot. at the preamp's I/P. Connect the control's wiper, via a 68 nF. PIO cap., to a 150 Ohm Carbon composition grid stopper. A 510 KOhm metal film grid leak resistor connects the cap./stopper junction to the negative side of a 3 V. Lithium "coin" cell. The positive side of the bias cell connects to the cathode of the triode. At least 3.3 muF. is required in the O/P coupling position, when working into the IFH "standard" 10 KOhm load.
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Old 11th May 2008, 05:57 PM   #25
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I will try it tomorrow. Now i've just finished a PCC88 cathode follower loaded with a 6KOhm resistor and it sounds wonderful (If you look at the plate current it should be very linear at arround 0.5 mA).

It lies at 10 cm from the LM4702B noninverting input so capacitive losses aren't a problem even with such a high impedance.
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