:From: Lee Roberts <ki7rw@arrl.net>
:I have heard of a rumor about a mod for this amp that involves
:changing the tube to an 572 and changing a tap on the
:transformer. Is it true? If so, anyone have any details on this
:and/or experience with this?
An 811a to 572b conversion requires some of the following
considerations:
The 572b is often larger in size.
The zsac bias voltage will have to be reset. If it's a zener
diode, you'll have to replace it. Often the "string of diodes"
method becomes unwieldy when higher bias voltages
are required. 24 volts is much more practical to obtain with
one hefty zener diode.
There have been reports of stability problems with
"higher gain 572b's." The conversions I've done gave no
indications of parasitics because Nichrome Suppressors
were installed during the retrofit.
I used NOS Jan tubes...
cheers
skipp
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