AW: [time-nuts] 5061 Cs frequency shift with long time constant?

Tom Van Baak tvb at
Wed Apr 6 14:26:22 EDT 2005

> My reprint of the manual has an asterisk by R6, but the note isn't there 
> (I suspect I have some missing pages).  The schematic around the mode 
> switch is a bit of a rat's nest to follow, but it looks like there's 
> 100k across the 12M R6 in normal mode, while in LTC mode R6 by itself 
> works against the 8uF C8.

Ah, interesting -- that note appears in the series
1248 manual (Feb 73) but not the series 1740
(June 1978). It shows up on the bottom of both
figure 8-2 (page 8-3) and figure/page 8-5.

That's why you won't find it in the online 5061A
manual (series 1740A).

PHK is also correct that what is C8 in some units
is C2/C3 in others.

Maybe it's time to put the manual aside and open
it up to have a look.

> The note seems only to apply to the high performance tube option.  I 
> wonder if it's not called out for standard unit because there's 
> something different in the circuit, or just because the shift is within 
> spec for the normal tube?  The 2E-12 is pretty similar to what I saw 
> when I made the switch.

That was my guess too; the standard unit isn't
good enough for this to matter much. I think the
option 004 tubes are also the only ones with the
degauss option. Note also that older 5061A didn't
have a LTC position on the mode switch.


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