7S14 sampler bias mercury cell elimination


Ed Breya
 

I tried to use my 7S14 recently and found that the Hg cells had finally died. I had an idea years ago (planning for this eventuality) to generate the bias with optical power. So, I did some experiments, and found a very simple arrangement that seems to work quite well. If others are interested, I can write up a detailed description to post.

Ed


Jose V. Gavila <eb5agv@...>
 

Hi Ed,

Please, count me in as one interested party.

Thanks!

JOSE

--
73 EB5AGV - JOSE V. GAVILA - IM99sm La Canyada - Valencia(SPAIN)
Vintage Radio and Test Equipment........... http://jvgavila.com
RadioRepair BLOG............... http://radiorepair.blogspot.com

-----Mensaje original-----
De: TekScopes@... [mailto:TekScopes@...] En nombre de Ed
Breya
Enviado el: jueves, 04 de noviembre de 2010 18:02
Para: TekScopes@...
Asunto: [TekScopes] 7S14 sampler bias mercury cell elimination

I tried to use my 7S14 recently and found that the Hg cells had finally died. I
had an idea years ago (planning for this eventuality) to generate the bias with
optical power. So, I did some experiments, and found a very simple arrangement
that seems to work quite well. If others are interested, I can write up a
detailed description to post.

Ed


Dave Wise
 

Me too. While rehabilitating my HP 740B DC Standard/Differential Voltmeter,
I though of replacing the chopper amp with an op-amp, but it has to
be powered by a floating supply with 1000V insulation.

Dave Wise

-----Original Message-----
From: TekScopes@...
[mailto:TekScopes@...] On Behalf Of Jose V. Gavila
Sent: Thursday, November 04, 2010 10:03 AM
To: TekScopes@...
Subject: RE: [TekScopes] 7S14 sampler bias mercury cell elimination

Hi Ed,

Please, count me in as one interested party.

Thanks!

JOSE

--
73 EB5AGV - JOSE V. GAVILA - IM99sm La Canyada - Valencia(SPAIN)
Vintage Radio and Test Equipment........... http://jvgavila.com
RadioRepair BLOG............... http://radiorepair.blogspot.com

-----Mensaje original-----
De: TekScopes@...
[mailto:TekScopes@...] En nombre de Ed
Breya
Enviado el: jueves, 04 de noviembre de 2010 18:02
Para: TekScopes@...
Asunto: [TekScopes] 7S14 sampler bias mercury cell elimination

I tried to use my 7S14 recently and found that the Hg cells
had finally died. I
had an idea years ago (planning for this eventuality) to
generate the bias with
optical power. So, I did some experiments, and found a very
simple arrangement
that seems to work quite well. If others are interested, I can
write up a
detailed description to post.

Ed


 

I like to learn, too.
Helge

2010/11/4 David Wise <david_wise@...>

Me too.  While rehabilitating my HP 740B DC Standard/Differential Voltmeter,
I though of replacing the chopper amp with an op-amp, but it has to
be powered by a floating supply with 1000V insulation.

Dave Wise

>-----Original Message-----
>From: TekScopes@...
>[mailto:TekScopes@...] On Behalf Of Jose V. Gavila
>Sent: Thursday, November 04, 2010 10:03 AM
>To: TekScopes@...
>Subject: RE: [TekScopes] 7S14 sampler bias mercury cell elimination
>
>Hi Ed,
>
>Please, count me in as one interested party.
>
>Thanks!
>
>JOSE
>
>--
> 73 EB5AGV - JOSE V. GAVILA - IM99sm La Canyada - Valencia(SPAIN)
> Vintage Radio and Test Equipment........... http://jvgavila.com
> RadioRepair BLOG............... http://radiorepair.blogspot.com
>
>-----Mensaje original-----
>De: TekScopes@...
>[mailto:TekScopes@...] En nombre de Ed
>Breya
>Enviado el: jueves, 04 de noviembre de 2010 18:02
>Para: TekScopes@...
>Asunto: [TekScopes] 7S14 sampler bias mercury cell elimination
>
>I tried to use my 7S14 recently and found that the Hg cells
>had finally died. I
>had an idea years ago (planning for this eventuality) to
>generate the bias with
>optical power. So, I did some experiments, and found a very
>simple arrangement
>that seems to work quite well. If others are interested, I can
>write up a
>detailed description to post.
>
>Ed
>

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Clive Redfern <semiochemic@...>
 

I would be very interested.
Please write it up.
 
Clive F5VHS


From: Ed Breya
To: TekScopes@...
Sent: Thu, November 4, 2010 6:01:57 PM
Subject: [TekScopes] 7S14 sampler bias mercury cell elimination

 

I tried to use my 7S14 recently and found that the Hg cells had finally died. I had an idea years ago (planning for this eventuality) to generate the bias with optical power. So, I did some experiments, and found a very simple arrangement that seems to work quite well. If others are interested, I can write up a detailed description to post.

Ed



stefan_trethan
 

me too.

Not because of a 7S14 but optical power interests me.
I used a halogen spotlight and solar cells to power meters for EMC
measurement that had to be earth free.

PMM in Italy makes an EMC measuring receiver head that is powered with
a laser through a fiberoptic cable.

ST

On Thu, Nov 4, 2010 at 6:01 PM, Ed Breya <edbreya@...> wrote:
I tried to use my 7S14 recently and found that the Hg cells had finally died. I had an idea years ago (planning for this eventuality) to generate the bias with optical power. So, I did some experiments, and found a very simple arrangement that seems to work quite well. If others are interested, I can write up a detailed description to post.

Ed



------------------------------------

Yahoo! Groups Links




santa0123456
 

--- In TekScopes@..., "Ed Breya" <edbreya@...> wrote:

I tried to use my 7S14 recently and found that the Hg cells had finally died. I had an idea years ago (planning for this eventuality) to generate the bias with optical power. So, I did some experiments, and found a very simple arrangement that seems to work quite well. If others are interested, I can write up a detailed description to post.

Ed
I am interested by this improvement. Count me in.


Jochen Feldhaar <jochen_feldhaar@...>
 

Hi Ed,

I am also interested in the workaround/repair. Please count me in.

Greets, Jochen

Ed Breya schrieb:

I tried to use my 7S14 recently and found that the Hg cells had finally died. I had an idea years ago (planning for this eventuality) to generate the bias with optical power. So, I did some experiments, and found a very simple arrangement that seems to work quite well. If others are interested, I can write up a detailed description to post.

Ed


Ed Breya
 

It looks like there is some interest in this, but it really breaks into two categories - the 7S14, and photonic power, a subject that I also have a lot to say about, so I will start another thread on that later. Anyone interested in photonic power may find this discussion somewhat dissapointing - it only involves a few microwatts. Also, this could get to be a long story, so it may need to be a multi-part saga. In responding, please remember the posting rules, and truncate redundant previous material so the message sizes don't get out of hand.

Part 1. Background:
In the 7S14 design, the sampling diode pair is reverse biased by two 1.35 V Hg cells that float along with the sampled signal at the input to the high-z input amplifier, in a megohm impedance environment. Mercury batteries have not been available for quite some time, so a good substitute is needed. The main problem is that Hg cells are very stable, more than any other type, and they have a voltage different from other types, so without knowing the design requirements of the circuitry from about 40 years ago, it's hard to know how precise they actually need to be, and what other voltages may work.

My initial thought was to just use 1.5 V alkaline or silver oxide cells, and increase the strobe drive level to maintain sampling efficiency, but I figured that they would tend to drift around a lot, and still need regular changing - perhaps annually - and eventually leak and make a mess if forgotten for a few years. This still may be a good enough solution, but I didn't pursue it further.

The only other options I could see were to redesign the input amplifier so the biasing didn't need floating sources (not very appealing), or to make the sources with optical power. Since the circuit is high impedance after the sampling gate, it turns out that not much current is needed, so small optical devices seemed possible. The objective was to first get enough power, then regulate it to +/- 1.35 V, all in a space no larger than the original cells.

Optocouplers seemed like a good start, but you need two (or more) Si junctions in series to get into the 1.35 V neighborhood. Using conventional LED/transistor types, you're stuck with six-pin packages (to access the base), with at least four for each channel, plus any additional circuitry.

It seemed like a few uA was fairly easy to attain, so next I looked for regulation parts. I found some shunt regulators from Maxim that can run on 1 uA (!) but of course only at a few standard voltages, including 1.2, 2.5 and 3, so it would still be necessary to use resistive dividers or more complex circuitry to produce the exact voltages needed, but it is possible.

After pondering trying to cram all this stuff in there, I decided to experiment with discrete LEDs, to see if I could get enough voltage using fewer devices with bigger band gaps. I found that high intensity blue and "white" ones can make 1.5 to 1.6 V open circuit, so that looked promising, but none would produce even 1 uA at 1.35 V, so they couldn't even run the shunt regulator alone.

After much experimenting, I settled on a design using one high intensity red LED, driven by one high intensity "white" LED, to substitute for each Hg cell, making 1.35 V, using the intrinsic diode characteristic as the shunt regulator. The only other parts are a bypass capacitor across each red LED, and the resistors etc. to set the driving LED currents.

This is getting a bit long, so I will break here. In Part 2 to follow, I will explain the part selection process, the details of construction, and some experiments on circuit performance.


rensetel
 

My 7S14 is still functioning but the problem will occur.
I am interested
Rens


From: Ed Breya
To: TekScopes@...
Sent: Thu, November 4, 2010 6:01:57 PM
Subject: [TekScopes] 7S14 sampler bias mercury cell elimination

 

I tried to use my 7S14 recently and found that the Hg cells had finally died. I had an idea years ago (planning for this eventuality) to generate the bias with optical power. So, I did some experiments, and found a very simple arrangement that seems to work quite well. If others are interested, I can write up a detailed description to post.

Ed



Michael Dunn
 

   At 1:16 AM +0000 11/5/10, Ed Breya wrote:
Optocouplers seemed like a good start, but you need two (or more) Si junctions in series to get into the 1.35 V neighborhood.

  Someone (maybe IR?) makes (or used to make) "opto-couplers" that had a photovoltaic stack on the receiving side, enabling many volts of output (one use was MOSFET drive).

  It's been a while since I looked at the xS14 schematic, but if the power floats with the signal, then the capacitance of this may be too high. I'm surprised batteries were workable!


Michael


p.s., very tempted to take the list back to reply-to-sender mode after seeing all those "me too" posts.




Ed Breya
 

Yes, Michael, there are indeed MOSFET-level PV couplers. I even have a sample of one I got many years ago, but I was trying to use conventional types that I already had in sufficient stock. You have anticipated one of the options I was going to mention in Part 2.

Ed


David DiGiacomo
 

Alkaline cells do work fine, but the problem is needing to find or
make tabbed cells, or find or make a battery holder. The LED approach
seems easier since they already have leads.

You could also use a Clare FDA215 and a shunt regulator, to save the
trouble of coupling the LEDs, but they are expensive if you don't find
them surplus.


Ed Breya
 

Part 2. Design and construction:
The forward voltage of red LEDs happens to be in the right range, at low current, at room temperature. I looked at a number of them on a curve tracer and figured the knee region was reasonably flat enough past about 1 uA. The trick was then to get enough optical power into them, and land at the right voltage range. The only ones that seemed to have enough output were high intensity types. The plan was to have the generating LED be nose to nose with the driving LED for maximum power transfer. I found that although using the same type of LED for the driver was potentially more efficient, it was very difficult to align. The best drivers seemed to be "white" LEDs - the type that are actually blue, with a phosphor to generate the whitish spectrum. I think the phosphor causes the light to be more diffuse, yet still very bright, so alignment is not as critical.

The easiest way to pick the generators is to measure them with a DVM that has at least 10 megohm input resistance, while illuminated with one of those LED flashlights - the kind with a cluster of LEDs. It should be possible to find some that will run at about 1.35 to 1.4 V into a 10 M load. I used one of my good old Fluke 8400As, which has virtually infinite input R in the 10 V range, and 10 M in the 100 V range, to easily see the loading effect.

Now for the construction. This may not be suitable for some, since surgery is involved. Before attempting this, it would be best to wait until Part 3 (to be added since this part is getting too long already) which describes my findings and recommendations.

On the sampler board there are (approx 1/4 inch diameter) holes at the centers of the Hg cell locations. I removed the sampler assembly and drilled 4 holes through the aluminum box for the drivers - one exactly aligned with each board hole, 2 per channel. The LEDs are standard size type about 3/16 inch diameter, so the holes should match, and be a snug fit. I made a small one-sided vector board piece to attach to the bottom of the sampler, with the LEDs passing through it and the box. The LED leads and series resistors then attach to pads on the board for support and interconnections. There is just enough room for this between the bottom of the sampler box and the delay line bracket below it. Alternatively, the LEDs could be glued into the holes, and air-wired to the circuitry elsewhere.

When the sampler boards are remounted, there will be a driver LED sticking up through the box under each of the holes. Then a generator LED is mounted upside down over each one, attached to the pads where the Hg cells were. It is a tight squeeze, but there is just enough total height available to clear the LEDs standing up as long as the leads are bent right in close.

I set up the drivers so each channel has two LEDs in series, then a resistor, and a reverse protection diode, so I could get about 2 to 8 mA through each one, and hooked up to drive from an external supply so I could experiment with it. When powered up, the generators should all be illuminated, and it is then possible to bend them around a little, to maximize and match their outputs. This can be done on the bench - the sampler doesn't need to be installed or powered up.

I added a large bypass capacitors across each generator to make sure there would be no extra effects on the loop dynamics, but I'm not sure how much is actually needed. I had some 4.7 uF high-k chip caps, so in they went. It takes a few seconds to charge them up, but that's less than the CRT filament warmup time, so OK. Since the LEDs are much smaller than the Hg cells, I am sure that this setup has much less stray capacitance than the original circuit.

When all was said and done, I could run the 7S14 in a 7704, with the driver power supplied from a variable external supply, and I had already roughly characterized the generator voltages during alignment, so I could remotely set them from 1.3 to 1.4 V - it was all set for experimenting.

Stay tuned for Part 3, hopefully concluding the story.


Ed Breya
 

Part 3: Findings and recommendations.
I fired it up and applied a fast pulse input, and had the supply set to make 1.35 V on the generators. Everything seemed to be fine, so of course I had to mess with it. Running from about 1.3 to 1.4 V, it had no apparent effect on gain or risetime, and a small effect on offset - it would shift up about a minor div at typical settings. At maximum sensitivity 2 mV per div, it obviously would move up several divisions as the generators went from 1.25 to 1.4, and you could clearly sense the "knee" of the diode shunting effect - the change in voltage, hence offset, with increasing drive power, was very rapid and then compressed as the regulation flattened out.

Then I tried it with NO drive, and was surprised to see that it still gave a pretty good representation of the signal. The sampling diodes were rectifying the input signal and charging the caps up most of the way anyway! All it did was clip the overshoot and square it off a bit. Increasing the drive, you could clearly see that it started working again as the generators got back up to about 1.2 V - this was with input level about 25 percent above the p-p spec input range. I found the same effects on the other channel.

Conclusion: There is nothing magic about the 1.35 V or its precision. If that voltage changes a bit, the display will move a little, but the effect is probably less than the normal drift of the system anyway. The front panel offset pots have a huge range compared to the drift caused by changes in the bias voltage, and the samplers probably also have a bigger effect. I could not find any spec about this in the manual, so I assume it's either perfect (unlikely) or very loose. The main thing is that the bias voltage shouldn't change too rapidly, or way too far, so anything that hits close enough and is reasonably stable, should work just fine.

Knowing what I know now, if I was to "fix" another 7S14, I would not worry too much about the exact voltage and its regulation. So, I would back up a few steps to my original idea of using conventional LED/transistor optocouplers, but with no fancy regulation schemes needed.

The design would require five commonly available optocouplers (such as 4N26) per channel, with their LEDs in series and a current set resistor from one of the supplies, and outputs (B to C&E) all in series. When activated by around 5 to 15 mA through the LEDs, it should produce about 2.7 to 3 V. This voltage is just right and stable enough, but since it's an odd number of devices, it has to be split by a divider of say 47 k ohm resistors across the middle coupler of the string, to provide the center point. Add a couple of bypass caps to make sure the AC impedance is low, some pigtail leads to connect and support it, and that's it. The assembly could be built on the bench with the couplers lined up end to end, and just chained together on each side (if you think about the pinout you'll see what I mean) with air wiring, and then fitted into the sampler assembly. Three leads would connect to the original cell pads, and two leads would need to pick up power from + or - 15 V and ground. Since my LED version works just fine, I have no need to build this type, but I am virtually certain it will work.

There are also available photovoltaic MOSFET gate drive couplers that easily supply enough voltage from a single device, which would be much more compact, but then it still needs to be regulated back down, and split, adding a few more components. They are readily available new in the US$ 3-5 range. I have a sample one from many years ago, but couldn't find it when I started this experiment, so didn't look to see if it would work, but I think that any that can deliver a few uA or more at 3 V should be enough to operate some kind of shunt regulator junction devices or IC plus a resistive divider. I prefer to use good old LED/Q types (at least for low V, anyway) because they are cheap and plentiful, and pack a pretty good punch - tens of uA, although only about 0.6V max.

For those who want to stick with batteries, I would recommend using a single 3 V Li cell such as CR2032 (220 mA-hr), which is available with solder tabs, thus solving the attachment problem. It just needs to be split with a high resistance divider (500 k to 1 M) range (and bypassed with caps). The Li chemistry has a very low self-discharge rate, so life would be limited mostly by the divider current, so it may be worth experimenting to see how high the resistance can go and still work. At 1 M, I think the life should be in the six to seven year range for a fresh cell. Also, the battery can be checked without removing the cover by having small holes drilled through it in the right places (don't hit any of the runs), to poke test leads through to to access the ends or other test points.

So, whether you've "seen the light" or want to stick with batteries, there are a number of ways to solve the problem.

Ed


jones_chap
 

I don't mean to flame anyone including the original poster, but let's get to the meat of this repair, please...

I can tell that "we" are on two different wavelengths concerning this repair.  As a "scientist"your approach is awesome.  There is yet another way to deal with bias current.  If silver oxide batteries go the way of the mercury cell and no replacements are out there, great way to get it done-->possibly; why later.  If I'm developing a circuit and need such, I have yet another cataloged topology/choice!

As for the 3v cell, what? 

The "what" and "why later part":  Research & Packaging.

Research:  Before Stefan's contribution, I had already bought silver oxide battery replacements.  Why?  A Google search revealed that the original mercury cells were used to provide a stable voltage reference with most circuits not being ill effected by the swap.  Checking most web links revealed that most of these were mercury type cells were used tremendously by the photographic community in light meters doing the same thing as they are in the 7S14/5S14.

Packaging:  Which will be easier to implement, 3V cell & voltage divider, photonic power, or just a simple battery/holder swap.

_______________________________________________________________________________________________________________

KISS!  I've restored/repaired vintage audio equipment.  I've even dabbled in the modification scene but only after exhausting all other means of REPAIR.  Why?  The simple battery repair should be acceptable/appealing to beginner, amateur, or expert.

After reading your original post, I went ahead and stop procrastinating, did five more minutes of research and ordered the holders for what should be a $20.00--20 min repair!  It will look GREAT & basically not a change a thing on the schematic except the voltage source designation/name.  Have you ever gotten a used plug-in with undocumented repairs/modifications?  Hmm, that's for another discussion.

I'd buy a 7S14 with the silver oxide repair.  I'd be leery of one with all that other stuff (even if it works).

_______________________________________________________________________________________________________________

With this information, I'm simply posting this so that anyone reading or attempting the repair with the extra complexity will just take a look and see that at this time, THERE IS A BETTER WAY, PERIOD.  Beginners like me need to see the light (basic and get it done while looking clean and not unsightly).  Not to flame your posts or scientific way; however, I'd preamble any more posts with the extra complexity with "There is a better way."  Notice I didn't say an alternative.  This repair is just superior, not me.  Don't send those googling or yahooing into a trap.  As a reaaaaal beginner, your post would scare me away easily.  However, this easy repair would draw me more into Tekscoping.

Just Keep It Simple, Stupid.


stefan_trethan
 

I don't agree.

Basically you replace a programmed failure point with a permanent solution by using optical power.
Had Tek used optical power, we wouldn't be here talking because there would be nothing to fix.

They did not do that because mercury cells were just fine for the design lifetime and then some, and cheap too.
Same reason why aluminum electrolytic capacitors are used, they are "good enough", and dirt cheap.

I have an aversion to batteries and anything that wears out by design.

And I think it's pretty arrogant to determine one way to be better, "period", but that's just a personal opinion.

Anyway, I'd take a modified optical power 7S14 any day should you come across one and want to be rid of it.

ST



On Sun, Nov 7, 2010 at 1:04 PM, Johnny Chapman <jones_chap@...> wrote:


I don't mean to flame anyone including the original poster, but let's get to the meat of this repair, please...

I can tell that "we" are on two different wavelengths concerning this repair.  As a "scientist"your approach is awesome.  There is yet another way to deal with bias current.  If silver oxide batteries go the way of the mercury cell and no replacements are out there, great way to get it done-->possibly; why later.  If I'm developing a circuit and need such, I have yet another cataloged topology/choice!

As for the 3v cell, what? 

The "what" and "why later part":  Research & Packaging.

Research:  Before Stefan's contribution, I had already bought silver oxide battery replacements.  Why?  A Google search revealed that the original mercury cells were used to provide a stable voltage reference with most circuits not being ill effected by the swap.  Checking most web links revealed that most of these were mercury type cells were used tremendously by the photographic community in light meters doing the same thing as they are in the 7S14/5S14.

Packaging:  Which will be easier to implement, 3V cell & voltage divider, photonic power, or just a simple battery/holder swap.

_______________________________________________________________________________________________________________

KISS!  I've restored/repaired vintage audio equipment.  I've even dabbled in the modification scene but only after exhausting all other means of REPAIR.  Why?  The simple battery repair should be acceptable/appealing to beginner, amateur, or expert.

After reading your original post, I went ahead and stop procrastinating, did five more minutes of research and ordered the holders for what should be a $20.00--20 min repair!  It will look GREAT & basically not a change a thing on the schematic except the voltage source designation/name.  Have you ever gotten a used plug-in with undocumented repairs/modifications?  Hmm, that's for another discussion.

I'd buy a 7S14 with the silver oxide repair.  I'd be leery of one with all that other stuff (even if it works).

_______________________________________________________________________________________________________________

With this information, I'm simply posting this so that anyone reading or attempting the repair with the extra complexity will just take a look and see that at this time, THERE IS A BETTER WAY, PERIOD.  Beginners like me need to see the light (basic and get it done while looking clean and not unsightly).  Not to flame your posts or scientific way; however, I'd preamble any more posts with the extra complexity with "There is a better way."  Notice I didn't say an alternative.  This repair is just superior, not me.  Don't send those googling or yahooing into a trap.  As a reaaaaal beginner, your post would scare me away easily.  However, this easy repair would draw me more into Tekscoping.

Just Keep It Simple, Stupid.





jones_chap
 

I.  Original Schematic...Silver Oxide

II.  Original Look...Silver Oxide

III.   Cheaper...Silver Oxide

IV.  Can fit within the case with minimum fuss...Silver Oxide

V.  Effective...Both

VI.  Wiz-bang...Silver Oxide

**Everything rots; that's the circle of life, even our thoughts on this subject : )

***Your implementation was great but not original, so I don't value your "God" like retort on the subject (do like you and your efforts though).  I just never got around to doing it, as I'm not retired and quite busy with another little one on the way.

*****************
The Period or my absolutism comes from those criteria above.  It is period from that standpoint.  Looking 1000 yrs into the future of electronics or whatever is...makes my head hurt.  However, if my son gets my 7S14 and begins to investigate years down the road, the battery stuff will be like a bump in the road.  With that other stuff, well, lets sit down and figure out this undocumented modification--wow, a stroke of genius, but why just not replace the battery.

*****************

I've posted several times to get flamed by modifying things to fit my needs, sometimes desires, or mere curiosity.  I've been molded by posts, some not so nice, to be a pragmatist.  Right?  Wrong?  Relative, but from above; Period, do you get it?

As I've heard sooooo much last year with testing in schools, "It is what it is."  The Tek 7S14 is what it is.  We can't change the criteria of the repair condition; we can only effect the repair.  I'd even place spares somewhere in a neat place (not many) if so concerned.

*****************

Basically I agree that absolutism is generally shunned but agree to disagree and still value you and all whole-heartedly.

*****************

As our principal and superintendent told us, "Get it done."   Hated it, but got it done...  Years ago, I could play around with the innovative and do research to be valued down the road, but not now with high stakes testing.  I want to visually verify the waveform of several stimuli; this repair gets it done looking clean and not too shabby keeping to the original schematic.

Blessings.


jones_chap
 

Ooops...

V.  Wiz-bang...Photonic Power

Oh yeah, not arrogant but confident.  Check out my horoscope (Korean, Chinese, or Gregorian).  Mine is one of which where they all agree!  Wood Tiger.  Don't get well placed (just being VERY FACETIOUS) confidence misplaced for arrogance.

Still love ya  :  )






Ed Breya
 

Hi Johnny,
I had no idea that this would be a controversial subject. I had a problem, thought of a possible solution, tried it, and it worked. My criteria were apparently different from yours. Here's what I thought was important:

1. Get the instrument working again
2. Eliminate the batteries

These and others are also essential, so must obviously be met:

3. Must not take too much work or time (subjective)
4. Must not cost too much (subjective)
5. Must be physically realizable and fit the space available

These of course are all interrelated. I must admit that I never once worried about matching the original appearance, affecting the resale value of my plug-in, confusing anyone by having to change the original schematic, or tricking the naive into adding complicated circuits when they could just put in new batteries.

If you follow this thread to the very beginning, you will see that I mentioned what I had done, and offered to share information about it. It appeared there was some interest, so I composed (I think) a fairly thorough, informative, coherent, and hopefully entertaining description, roughly along the lines of the scientific method - the problem, hypothesis, experiment, and conclusion. I had to satisfy my own curiosity about how the bias affects the instrument. Along the way, the knowledge I gained caused other options to become evident, so I added them, with one of the main goals still being never to change batteries, or at least to maximize the interval between changes.

I had no idea that adding battery clips was already the "best idea, period," so to speak, and all my work was for naught. So I thought about yanking out all that complicated circuitry I added, and getting some battery clips to put in, but then I remembered how cool it looks with the bluish-white light shining in there, lighting up the guts of the plug-in, so I think I'll keep it like it is - it's gangsta.

Regards,
Ed

--- In TekScopes@..., Johnny Chapman <jones_chap@...> wrote:

I don't mean to flame anyone including the original poster, but let's get to the
meat of this repair, please...

I can tell that "we" are on two different wavelengths concerning this repair.
As a "scientist"your approach is awesome. There is yet another way .....