Re: tektronix 7S14 batteries and time base question


Bruce Griffiths
 

The 7S14 uses a 2K resistor in series with each battery.
20uA photocurrent implies a slope resistance of around 2.5K for a photodiode with n =2.
This more than doubles the series resistance and adds some nonlinearity as well.
Simulating the sampler and preamp (including blowby compensation) will be helpful in establishing the effects of using photodiodes instead of batteries. Start with batteries to give a baseline for comparison.
Then substitute photodiodes (diode driven by current source should suffice) to see the effect of varying the photodiode current and the effect of shunt capacitors across the diodes.

Bruce

On 27 December 2019 at 08:58 Dave Wise <david_wise@phoenix.com> wrote:


Oh, LH1262, not LC1262. Short-circuit current is a few uA, I wonder what it puts out at a couple volts. There are lots of PV-output SSR's, many of which put out more, but still only 10-20uA max. IIRC, an expert told us we need at least 50uA.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Dave Wise via Groups.Io <david_wise=phoenix.com@groups.io>
Sent: Thursday, December 26, 2019 11:54 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] tektronix 7S14 batteries and time base question

Can you confirm that part number, Tom? Mouser returns zero hits on "LC1262".
And what's the output current? This is probably one of those photovoltaic-output SSR's like I mentioned a moment ago.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Tom Bowers via Groups.Io <pvhengineering=gmail.com@groups.io>
Sent: Thursday, December 26, 2019 9:30 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] tektronix 7S14 batteries and time base question

I haven't been following too closely, but just remembered some old Western Electric parts that Vishay still makes. These may be of value to consider for this mercury battery replacement. Take a look at the Vishay LC1262, an LED coupled to a diode stack, dual. I see Mouser has stock.

Tom Bowers












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