[Test-Equipment] HP 410C

[k4pf at juno.com]

Hi.
The 410B includes a probe tube heater a adjust procedure.  
There is only a fixed 6.0VDC heater voltage in the 410C, 
not good for the 2-01C tube life expectancy. 

The heater for the a.c. probe tube comes off the 6.0VDC
voltage regulated supply, pin 926 on the power supply board
(Fig 5-9 of 410C manual).

I use a 2-01C tube in the probe, after adding a series power diode
to knock the heater voltage down to 5.3V. That's "close enough"
to the 5.0V at 340mA heater power called for by the 2-01C specs.

I inserted a 1N5400 series diode in the wire between power supply
pin 926 and the a.c. probe jack to accomplish this.

I suppose you could just reduce the regulated supply output to 5.0
volts, by changing Zener diode A7CR8 on the power supply board.
However, that supply also feeds the Ohmmeter function,
and I didn't want to possibly disturb the calibration.

The 410C does put 6.3VAC on the probe heater in modes other than a.c.,
but you can unplug the 410C a.c. probe when not in use.

73,
Ed Knobloch

 
>bonddaleena at aol.com wrote
Hi. I have a pretty nice HP 410C. I bought it several years ago, and it 
works ok on DC and Ohms. It did not come with the 11036A AC / HF probe. 
I have since acquired one. Although I 'swear' I have several EA53 tubes 
here (somewhere) I also have several NOS 2-01C tubes, in my hot little 
hands. I was reading the instruction sheet that came with the 2-01C 
tube and they describe 'adjusting R50' (this sheet only talks about the 
410B), for 5.0 Vrms. They DO describe adjusting R50 for 6.3 V when 
using the EA53.
OK, I have a Manual for my 410C, and nowhere do I see how to adjust the 
voltage.
I DO understand that the 410C supplies 6.3 VAC to the probe filaments 
when in modes OTHER than AC. When AC is selected, the filiment voltage 
is changed from AC to DC. It 'looks' like the probe filiment voltage is 
6.3 V. Period. Is the 410C limited to using JUST the EA53, where the 
410B could use both???
Sooooo, it would 'appear' that the 2-01C cannot be used with the 410C. 
Is this correct? Man, I DO NOT want to buy a EA53!! Can I just 'drop 
the filiment voltage to 5 V? How long will a
2-01C last at 6.3 V??????