HW-101 Tube Subsititution

[Fred Olsen]

Lew28 at AOL.COM wrote:
> ... adverse effects if I substituted any of
> the 6AU6 tubes with 6AU6A's?

Lewis, the short answer is no.  Many A-suffix receiving tubes simply
have a controlled heater warm-up time, for use in series strings.  The
6AU6A also has perhaps 10% higher maximum ratings of several
characteristics, the major difference being more than doubling the peak
heater-cathode voltage to 200.  The running characteristics of
amplification factor and so forth are essentially the same.

I would NOT suggest subbing a 6AU6 for a 6AU6A in a late tube era
circuit without checking that the operating conditions are within the
older tube's limits, especially heater-cathode voltage.

I'm curious about one thing though.  I would have thought that the
HW-101, introduced in 1970(?), was 'late' enough that it would have been
designed around the 6AU6A.  I should think that the original 6AU6 would
have been out of production perhaps 10 years prior.  Anyone else have an
opinion on that?

Best of luck,
Fred
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