# [time-nuts] HP 5061A/B Cesium tube conundrum

paul swed paulswedb at gmail.com
Mon Jan 16 17:07:19 EST 2017

```Corby thats a heck of a puzzle. I am trying to think about how you could
prove it. I have some thoughts that are not at all well formed. It comes
from my experiments on Frankenstein temp control.

If you could please tell me what you might expect the alternate bridge
resistors to be overall I will look through my various bits to see if there
is anything.

Regards
Paul
WB8TSL

On Mon, Jan 16, 2017 at 3:58 PM, <cdelect at juno.com> wrote:

> I've been doing some work on testing some HP 5061A/B tubes
> and came across something that's not making any sense!
> The R11 and R12 values marked on the tubes for use with the
> new style A11 are supposed to reflect a parallel value
> that is 10X larger than the thermistor reading.
> This to agree with the ratio of the bridge resistors in the
> A11 module.
> For instance a 3112A prefix tube shows values of 3.83K
> and 42.2K. This gives a parallel value of 3.511K which when
> divided by 10 gives 351.1 Ohm. The value marked on the tube
> was 352 Ohm. That all makes sense!
> Now I have three 3232A prefix tubes and they all do not
> reflect this ratio.
> For instance one has values of 51.1K and 5.11K which gives
> 4.65K. This divided by ten gives 465 Ohms. However the
> Thermistor value marked on the tube is 915 Ohms!
> I tested all three tubes and they come up to the proper
> temperature with the thermistor value marked on the tube.
> Did HP make a change to the A11 bridge resistor ratio, and
> if so where did they document it!
> If not and you used the R11 and R12 values you would
> seriously overheat the tube!
>
> Cheers,
>
> Corby
>
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```