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Hi,

there is a 6CZ5 and a 2AS-15 in the regulation loop of the
Tek 555 heater supply voltage. The 2AS-15 is probably the one
you mean.
Quoting from the 555 manual:
'The circuit operates by regulating the voltage applied to
the primary winding of the [heater supply] transformer [T750].
Any variation in the amplitude of the ac output from T750
appears across the secondary winding between terminals 11
and 12 of the transformer and is applied to the heater of
the special diode tube, V799 [2AS-15]. The amplitude variation
causes the diode to conduct more or less current, depending on
the direction of the change, and produces a voltage change in
the plate circuit of V799.'

I hope this helps.

Laurent Lamesch

John Rehwinkel wrote:

I need someone to refresh my memory. The old Tek scopes with
the separate power supplies (555 and similar) had an unusual
filament voltage regulator that operated with a saturable core
reactor. Part of the feedback circuit involved a tube that (I
think) was very sensitive to its filament voltage. I have a
clear mental image of the tube, it was a glass octal type with
a horizontal filament and a cylindrical plate around it. I'm
looking for the type number of this tube. Anybody know offhand
or have a manual with this info? Otherwise, I'll probably have
to wait 'til the next hamfest and see if one of the Tek manual
vendors will let me have a peek.

-- Thanks,
John Rehwinkel KG4L
spam@...

Hi,

there is a 6CZ5 and a 2AS-15 in the regulation loop of the Tek 555
heater supply voltage. The 2AS-15 is probably the one you mean.
Quoting from the 555 manual:

I hope this helps.

Laurent Lamesch

Yep. That's just what I needed. Thanks much!

-- John Rehwinkel