6AT6

[sunnydaze]

Hello everyone,

Back to Taiwan after a Christmas visit to the US. Usually, I bring some stuff back for myself and expat friends that I order from Antique Electronics and similar places. One of my friends recently acquired the Ivy league amp by Victoria. It's basically a dead nut copy of the Fender 5F10 Harvard. That amp uses an unusual (at least unusual for me) preamp tube the 6AT6. He asked me to bring back a few. That tube is 7 pin triode with a gain factor of 70 plus two diodes. NOS can be purchased from antique electronics for $3.55.

https://www.tubesandmore.com/search/node/6at6?cats[0]=1

That price got me thinking about maybe using in a build. Anyone have experience with this tube? Kind of wonder how the diodes might be used. Could the diodes be used as kind of regulated screen supply? From the data sheet, each diode can handle 1 amp of current. Might have to elevate the heaters - max heater to cathode voltage is 90 v.

Would appreciate any comments.

Thanks
Mike

[martin manning]

As I understand it, 6AV6 (equivalent to a 12AX7 triode) was also used in the Harvard for '50's high-gain tones. Re the unused diodes, they share a common cathode with the triode, and are rated at only 1mA continuous current. They were intended for small signal use.

[rp]

comes to life with the 6av6

[sunnydaze]

Thanks guys. My friend's Ivy League amp sounds pretty good with the lower gain 6at6. Will let him know about the higher gain 6av6.

The 6at6 is definitely priced right and the 6av6 is pretty good too at $5.35.

https://www.tubesandmore.com/search/node/6av6

Martin - could you expand on your small signal comment? The data sheets I checked didn't really give much on the diode sections. My experience with "diodes" has been limited to rectifiers.

Thanks
Mike

[martin manning]

Those two tubes were used in the front-end of AM radio receivers, and the two diodes were used as RF detector and for AGC (automatic gain control). They are rectifiers, just not designed to carry high current for power rectification.

[rp]

Martin, could they be used to bias a preamp tube, like a LED? Bias the tube itself?

[sunnydaze]

Martin, thanks for the prompt response. As always, I appreciate the information that you and other very knowledgeable members of this forum take the time to post.

RP - the data sheet advised not to use the diode section to bias the triode section.

Thanks again.
Mike

[martin manning]

They are the wrong way around to use as bias diodes, but if a positive voltage were applied at the anode of one or both diodes that would increase the current through the cathode resistor and shift the bias point.

[JMFahey]

Short answer, forget them for Audio or Power Supply purposes

They were meant , as mentioned above, as signal detectors in old style AM radios, you feed them a few millivolts of audio modulated RF (what AM transmitters transmit) and they "extract" the audio out of it, which later gets amplified by a simple but conventional audio amplifier.

The rectified DC they also output, is proportional to RF signal strength and is used to keep output level relatively stable, by varying RF gain.

Just ignore them, and use the triode section.

I also love to use surplus NOS "Radio and TV" tubes, which are ignored but still exist by the millions.

A Brazilian colleague, Max W. Fillies , makes amps *only* with them:

https://www.youtube.com/watch?v=SXSzlLYQY_M

https://www.youtube.com/watch?v=E39v8S-Xq8I

the first one uses "2 Válvulas Toshiba NOS 6EM5 de power e 2 válvulas 6BZ8 NOS GE, todas de televisão."

[sunnydaze]

Interesting, but too bad not much use in guitar amps for the diode sections. Leo was pretty frugal -probably would have found a use if any made sense.

Anyway, by buddy has a bunch he can roll through now.

Thanks
Mike