Thread: 6CA7 in AB2.
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john stewart
 
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Patrick Turner wrote:

Anyone have any experience in driving 6CA7
in either tetrode, triode, or UL, into class AB2?
The 6CA7 is supposed to be equal to EL34.
EL34 don't much like AB2; but since the
6CA7 is a tetrode, not a pentode, perhaps, like the 6L6,
AB2 operation is perhaps fine.

What sayest thou, and they of years challenged,
and who accompanied history's beginning, and who must
have memory of a bygone age?
What noble efforts at AB2 were sustained,
leading to much music well listened to?

Patrick Turner.


See ABPR for the attachments referenced in the following.

Hi Pat- Never ran a 6CA7 / EL34 in AB2 but last year built an
experimental 6V6GT rig running AB2. It managed 26 watts in burst
mode & 19 watts continuous after the PS sagged to steady state.
The 6V6 grids are driven by a PP 6BQ7 CF. That helps to minimize
distortion as a result of G1 current.

IMO should be OK for a music amp since the grids will be driven
+ve only on peaks which are but a small percentage of the time.
See the attachment for test results. This all part of an article on
Amplifier Burst Testing to appear in the November issue of
AudioXpress magazine.

Also built an AB2 amp using a PP pair of 33 two volt pentodes.
It runs triode or UL. The driver is a triode connected 33, which
in turn is transformer coupled to the following grids.
That one is published in the "Glass Audio Projects" book from
AudioXpress.com.

The attached graph is a composite
shewing the drive signal to the grids (LHS with X10 Probe) &
the resulting G1 current (RHS) measured across a 10R sampling
resistor in the grid circuit. This one manages 4.85 W in UL &
2.5 W in Triode mode.

Cheers, John Stewart