a tube primer for guitar and bass players - Guitar Amplifier Blueprinting

12AU7-Y – Ei
Expected Gain 16-18 Expected Output 10-11 milliamps
These are commonly used as phase inverters in McIntosh Hi-Fi amps, some Ampeg amps, and will yield the most clean headroom in many
amps. In the latest Fender Pro Series amps such as the Pro Reverb, Concert, and Twin, this tube in V2 (or a 12AY7), will drop the gain of
the gain channel where some feel the tone is of a less intense or “buzzy” character. This will then allow a much wider range in the sweep
of the volume and gain controls of this channel.
http://www.groovetubes.com/product.cfm?Product_ID=1592
To the left is a GT EF86 adapter. This was developed as new production EF86 tubes are very inconsistent, and
can be noisy, or hard to find at times. For a group on tour using an older Vox amp, a Matchless, Victoria
Sovereign, Bad Cat, or Dr. Z amp, these can be a life saver. These allow a 12AX7 to be used in the place of the
EF86 / 6267 pentode tube.
This adapter can be seen at http://www.groovetubes.com/product.cfm?Product_ID=2044
EF86 – 6267
Expected Gain 400-2000 and higher Expected Output 3.0 milliamps QA: 50% +
A 9 pin pentode, used in the first gain stage of some newer amps such as the Matchless, Bad Cat, Dr. Z, and others. The current versions
of this tube from the Russian factory, are very inconsistent. Their output is way above spec, sometimes as high as 50% over what is to be
expected. They have transconductance that is not close to the original tubes 80% of the time in factory sample tests. These factors make
finding a low noise version of this tube very difficult. These need to be closely screened and tested by a tube supplier that has very
sophisticated test gear that is generally out of reach for most Internet tube vendors or smaller vendors.
http://www.groovetubes.com/product.cfm?Product_ID=1593
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