6AS7 at low voltages

OTL Asylum

OTL, Output Transformerless Amplifier User Group.

0

FYI,
From the Joe list,
just thought the 6AS7 gurus here might be interested
in something like this.
Has anyone tried 6AS7G's as preamps at low voltages?
Yves
> last night i was testing various 9-pin-twin triodes for a
> balanced line
> stage with transformer input and output.
>
> very simple topology; sowter 8920 input x-former > 2x10k stepped
> attenuator (dact) across the input x.former secondaries > twin triode
> with common cathode resistor (unbypassed) > sowter 8650 (9:1
> ct) or 9041
> (5:1 ct) output transformer. power supply was a huge old
> fluke lab supply.
>
> 5687s looked and sounded nice, so did e182cc. 2 x 12b4 was
> not as good,
> 6bx7 was lousy. out of sheer curiosity i tried the same thing with a
> 6080/6as7g. of course cathode current was waay to high for
> the max 2 x
> 30 mA the sowter 8650 could handle. hmm. i turned the voltage all the
> way down. incredible, but at 25 volts b+ (!!) and 12 ma (6 ma per
> triode) i ended up with -6 volts bias and *perfect* 1khz and
> 10khz sqare
> waves with the output transformer's secondaries loaded with
> 600 ohms. i
> hooked up my distortion meter and measured a thd of 0.03% - i
> was unable
> to determine how much of this was 2nd and 3rd harmonics with
> my siemens
> frequency analyzer because the signal was just too weak...
>
> so i inserted the 6080 low voltage line amp to my system and
> gave it a
> listen. just about as clean, neutral and extended as can be!
>
> gain of the "line stage" with the attenuator fully open was a little
> over unity which is ok with me since my sources have enough
> output and
> my amps low input sensitivity.
>
> (of course i tried even lower plate voltages, but then the
> bias got too
> small. also thd started to rise again below 15 volts b+..... )
>
>
> http://www.rintelen.ch/6080_2.jpg : pix of the square wave test
>
> http://www.rintelen.ch/6080_1.jpg : pix of the setup with the
> thd-meter
>
>
> i then tried the same set up with a 5998 (same as 6080 but
> higher mu),
> but the results were lousy. next came a 6336a - on the scope it looks
> just as good as the 6080, gain is a little higher.
>
> of - so now i wound up with a line stage that draws 5 amps
> heater power
> and runs at 25 volts b+. i suppose next thing would be a 25 v battery
> supply... and of course constant current sources.

This post is made possible by the generous support of people like you and our sponsors:

Schiit Audio

Topic - 6AS7 at low voltages - Yves 22:44:49 06/25/02 (3)

Re: 6AS7 at low voltages - mark 07:20:45 06/26/02 (2)

Re: 6AS7 at low voltages - Yves 18:17:36 06/27/02 (1)

Re: 6AS7 at low voltages - mark 20:12:44 06/27/02 (0)

You can not post to an archived thread.