6BF6
For fun I bought a half a shoe box full of 6BF6 Tubes. These are little 7 pin single triodes with a pair of diodes. JAN, NOS, RCA all with the same 1980 date code.
http://www.mif.pg.gda.pl/homepages/frank/sheets/141/6/6BF6.pdf
I looked around for circuits that use the 6BF6, there are only a couple that I found and they just let pins 5 and 6 dangle, (the diodes) not connected to anything.
I made up a breadboard common cathode triode amplifier with the cathode resistor bypassed with an Os-Con capacitor. The noise voltage across 10hz to 22Khz is plain bad with the diode pins floating. With pins 5 and 6 connected to pin #2, the cathode, (remember the cathode is bypassed to ground) resulted in noise in the not bad range. The gm of this tube is ~ 2mA/V placing the shot noise contribution in the moderate range, which makes the flicker noise not so dominant. I recall that the noise above 2Khz, you know the noise that comes out of the tweeter, is not normally the noise that gets my attention anyway.
This test breadboard has gain of ~ 9 and an EIN of very near 4uV. At 2 volts output the THD+N is ~0.2%.
See the attached FFT plot.
Comments?
DT
For fun I bought a half a shoe box full of 6BF6 Tubes. These are little 7 pin single triodes with a pair of diodes. JAN, NOS, RCA all with the same 1980 date code.
http://www.mif.pg.gda.pl/homepages/frank/sheets/141/6/6BF6.pdf
I looked around for circuits that use the 6BF6, there are only a couple that I found and they just let pins 5 and 6 dangle, (the diodes) not connected to anything.
I made up a breadboard common cathode triode amplifier with the cathode resistor bypassed with an Os-Con capacitor. The noise voltage across 10hz to 22Khz is plain bad with the diode pins floating. With pins 5 and 6 connected to pin #2, the cathode, (remember the cathode is bypassed to ground) resulted in noise in the not bad range. The gm of this tube is ~ 2mA/V placing the shot noise contribution in the moderate range, which makes the flicker noise not so dominant. I recall that the noise above 2Khz, you know the noise that comes out of the tweeter, is not normally the noise that gets my attention anyway.
This test breadboard has gain of ~ 9 and an EIN of very near 4uV. At 2 volts output the THD+N is ~0.2%.
See the attached FFT plot.
Comments?
DT
Don't let the diodes "dangle". Ground them.
The triode seems pretty close to those found in the 7AF7 Loctal. Definitely a very nice voltage amplifier. However, the lowish gm suggests not using the type as a cathode follower or "concertina" phase splitter.
BTW, the 7N7 mentioned in the linked data sheet is electrically equivalent to the 6SN7.
The triode seems pretty close to those found in the 7AF7 Loctal. Definitely a very nice voltage amplifier. However, the lowish gm suggests not using the type as a cathode follower or "concertina" phase splitter.
BTW, the 7N7 mentioned in the linked data sheet is electrically equivalent to the 6SN7.
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