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On Fri, Mar 8, 2024 at 03:23 AM, stevenhorii wrote:

The calculator takes unusual batteries - like current button cells, but
quite a bit thicker. Fortunately, they have not leaked. Unfortunately, they
are dead so I don’t know if the calculator works.

If you have access to a lathe it's a trivial task to make up a spacer that allows modern button cells to be used in place of those obsolete thicker ones (that possibly contained mercury). I have done that for old clocks with good results.

Obligatory Tek content: Mercury button cells were used in the 7S14 sampling plugin and possibly other products. The best substitute hack has been described on this group and doesn't requite machine tools!

Morris

Chris,

There is a TR-20 on eBay - for USD $16,800!


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and an EAI 180 for even more:


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Where are you located?

A friend of mine has one but wants to keep it. He uses it - after doing a
lot of repair work on it (power supply, many of the op amps). Besides doing
some analog computer work, he also uses it as a music synthesizer. He
thinks that besides the “young folks” who grew up during the
microprocessor-based computers and have an interest in early computing
stuff (and money to buy it - you probably heard about the Apple I that sold
for an astronomical price) there are those who have gained an interest in
analog music synthesizers and are partly responsible for driving up the
price on analog computers.

Steve H.


On Fri, Mar 8, 2024 at 12:43 Chris Wilkson via groups.io <cwilkson=
[email protected]> wrote:

I just missed out on a fully loaded EAI Pace TR-20 a few years ago. I'm
happy/sad about that. They aren't light and they aren't small!
I hesistated on shipping cross country. At the time they popped up fairly
regularly so I was hoping to see one within driving distance. I'm still
waiting....

On a happier note, I built a dedicated analog computer to implement a 1-
or 2-player Vector Pong game with score and sound. It drops into a stock
Asteroids Deluxe (cabaret style) arcade machine and makes use of the built
in power supply and audio amp/speaker and that glorious X-Y monitor. It's
a big hit when I take it to public arcade shows. I had obsessed over
Pong's unfortunately square ball ever since I was a small child. That itch
has been eliminated. Vector Pong draws a true circle! :)

I just missed out on a fully loaded EAI Pace TR-20 a few years ago. I'm happy/sad about that. They aren't light and they aren't small!
I hesistated on shipping cross country. At the time they popped up fairly regularly so I was hoping to see one within driving distance. I'm still waiting....

On a happier note, I built a dedicated analog computer to implement a 1- or 2-player Vector Pong game with score and sound. It drops into a stock Asteroids Deluxe (cabaret style) arcade machine and makes use of the built in power supply and audio amp/speaker and that glorious X-Y monitor. It's a big hit when I take it to public arcade shows. I had obsessed over Pong's unfortunately square ball ever since I was a small child. That itch has been eliminated. Vector Pong draws a true circle! :)

With analog computing, it's not a revival of the classical analog computer. We're at the cradle of something totally new coming up.

Try running up the external supply to a higher level. It's not precise. If it runs and ultimately regulates according to closed-loop conditions, it should be good to go. You know now how to tell if that's the case. The input should work around 43V, but a little more should be OK. If it has to reach say over 46 V, then maybe there are more problems. The main thing is to reach the closed-loop condition at a reasonable input, which should proof the circuit operation.

Ed

I got the TIP41C transistors and I swapped them in.

The power supply no longer oscillates at 1MHz, but the -8.6V rail is at -8.2V when I feed in 42V, and that's with the potentiometer turned all the way up.

Would it be a smart idea to bodge a 10k resistor in parallel with R937? Is there a better way of getting the voltage to match -8.6V? The current consumption is 800 mA, which seems a bit low. When I plug in the scope, it still doesn't power up.

How about pictures of the slide calculator, both sides.

Forgive my error in terminology. It is not grey as in color, it is Gray named for the author of the patent who gave it the name Reflected Binary.

I recently bought a “hybrid” - a slide rule with an electronic calculator
on the back. These were made by Faber-Castell but it was not long before
they were eclipsed by the electronic calculators that did the various
functions that slide rules do. To some extent, this makes sense - you don’t
do addition and subtraction on a slide rule. There was an earlier version
that that had an “addiator” on the back.

The calculator takes unusual batteries - like current button cells, but
quite a bit thicker. Fortunately, they have not leaked. Unfortunately, they
are dead so I don’t know if the calculator works.

I also have a Curta “pepper mill”. I’ve also used the Friden calculators. I
swear it’s where the term “crunching numbers” comes from. It’s amazing that
the Curta can do the same operations as the Friden though it does require a
lot of turns of the crank.

I still have my HP-35 calculator and it still works (with the AC adapter).
I have not gone through the effort of rebuilding the battery pack.

Steve H.

I remember them being advertised in so many techie magazines 50+ years ago. We called them "math grenades". I now have one, they are a work of art. The massive desktop calculators by Marchant, Monroe, Friden, and Burroughs are simply amazing as well.

?? Bruce Gentry, KA2IVY

Another marvel analog mechanical calculator , of more modern vintage
is the " Curta " , popular in the 1950's to 1970's, but then eclipsed by the pocket calculator.

I found out how to send pictures of the 'scope screens
This link shows TP75 on schematic 9 in yellow and the collector of Q1062 in
Purple. 10 uS/div and 5v/div
The 'scope ground is on Ref 1 just marked REF on the 2465 schematic (see
2465B schematic to compare the two reference * and **)

and this shows the same signals at 1 second/div

I hope everyone has access.
I am moving my attention to the U1030 circuit and how it regulates.
This has to be a common fault. Two out of Four 2465 that myself and a
friend own have the problem of clicking for several minutes before settling
down.
Several people have told me it is a common problem. No one says what causes
it. The common repair is to replace all capacitors and a few other
components.




On Wed, Mar 6, 2024 at 10:32?PM peter bunge via groups.io <bunge.pjp=
[email protected]> wrote:

Thanks Mark, I replaced R1020 although it was not bad. The troubleshooting
for that circuit using a power supply says the switch should activate from
20 to 25 volts. Mine latches at 17.5 volts. I don't think it is
significant.
I replaced C1024 with no change.
The RIFAs look good so I did not change any. They don't fit with the
symptoms.
I don't know if C1051 would cause my problems. I won't discount it.
CR1110 would show in the current sensing if it was shorting. There is no
evidence of a problem after T1060.
I don't think the doublers would cause my symptoms but I may change them. I
have the ones recommended.
I'm thinking that something in the U1030 circuit is acting up.Maybe U1040
feedback optocoupler? I need to see what its supposed to do.
I have good 'scope pictures of the signals but cannot post them. They show
the drive signals suddenly stopping after running from 1 to 5 seconds. The
recovery to working happens when the interval DECREASES. It seems that
there is something like overvoltage that needs to drift down to a control
range.
Peter

On Wed, Mar 6, 2024 at 8:15?PM Mark Vincent <orangeglowaudio@...>
wrote:

Peter,

R1020 is known to go bad. That should be 2W. Make sure to get a resistor
that is about 15mm long. Some 2W resistors are 3.68 x 8.72mm which is
smaller than a 1/2W. C1034 is originally a tantalum. I replaced the three
on that board with 50V film types to ensure low ESR. C1055 and a few

others

are the clear amber tinted RIFAs that are known troublemakers. I used

630V

film types to replace them. C1051 is another condenser that is a RIFA

type.

Look to see if those were replaced. CR1110 is known to go bad. It is a
Schottky rectifier. I replaced mine with a Si type and it worked with the
proper voltage out. Mine is 200V, I think, because I have some in stock.

If

you decide to replace the doubler condensers, I suggest using Nichicon

LGR

types. I put in 390mfd in mine. Make sure the diameter is small enough to
fit where the originals are. Add wires from the lugs/pins of the LGR type
to the board.

Mark

Thanks Mark, I replaced R1020 although it was not bad. The troubleshooting
for that circuit using a power supply says the switch should activate from
20 to 25 volts. Mine latches at 17.5 volts. I don't think it is significant.
I replaced C1024 with no change.
The RIFAs look good so I did not change any. They don't fit with the
symptoms.
I don't know if C1051 would cause my problems. I won't discount it.
CR1110 would show in the current sensing if it was shorting. There is no
evidence of a problem after T1060.
I don't think the doublers would cause my symptoms but I may change them. I
have the ones recommended.
I'm thinking that something in the U1030 circuit is acting up.Maybe U1040
feedback optocoupler? I need to see what its supposed to do.
I have good 'scope pictures of the signals but cannot post them. They show
the drive signals suddenly stopping after running from 1 to 5 seconds. The
recovery to working happens when the interval DECREASES. It seems that
there is something like overvoltage that needs to drift down to a control
range.
Peter

On Wed, Mar 6, 2024 at 8:15?PM Mark Vincent <orangeglowaudio@...>
wrote:

Peter,

R1020 is known to go bad. That should be 2W. Make sure to get a resistor
that is about 15mm long. Some 2W resistors are 3.68 x 8.72mm which is
smaller than a 1/2W. C1034 is originally a tantalum. I replaced the three
on that board with 50V film types to ensure low ESR. C1055 and a few others
are the clear amber tinted RIFAs that are known troublemakers. I used 630V
film types to replace them. C1051 is another condenser that is a RIFA type.
Look to see if those were replaced. CR1110 is known to go bad. It is a
Schottky rectifier. I replaced mine with a Si type and it worked with the
proper voltage out. Mine is 200V, I think, because I have some in stock. If
you decide to replace the doubler condensers, I suggest using Nichicon LGR
types. I put in 390mfd in mine. Make sure the diameter is small enough to
fit where the originals are. Add wires from the lugs/pins of the LGR type
to the board.

Mark

Peter,

R1020 is known to go bad. That should be 2W. Make sure to get a resistor that is about 15mm long. Some 2W resistors are 3.68 x 8.72mm which is smaller than a 1/2W. C1034 is originally a tantalum. I replaced the three on that board with 50V film types to ensure low ESR. C1055 and a few others are the clear amber tinted RIFAs that are known troublemakers. I used 630V film types to replace them. C1051 is another condenser that is a RIFA type. Look to see if those were replaced. CR1110 is known to go bad. It is a Schottky rectifier. I replaced mine with a Si type and it worked with the proper voltage out. Mine is 200V, I think, because I have some in stock. If you decide to replace the doubler condensers, I suggest using Nichicon LGR types. I put in 390mfd in mine. Make sure the diameter is small enough to fit where the originals are. Add wires from the lugs/pins of the LGR type to the board.

Mark

I checked the Inverter Drive power supply and it works for seconds until something shuts the drive off.
The power supply draws normal current for up to 5 seconds and the pulses appear on TP75 then stop abruptly.
This repeats faster and faster until the 'scope stays on. It is accelerated by hot air down the slots in the top plate.
It is NOT current limiting.
Maybe something is shutting down U1030. I replaced C1034.

I posted this once but it did not show up.
I put a power supply in from another 'scope. It starts right away. The problem is definitely in the power supply.
The power supply runs out of the 'scope with a load per the manual.

Installed in the 'scope and running on an isolation transformer so I can attach another 'scope:
I shorted the current sense resistor and put a 'scope on the collector of Q1040. The PS does not start. No sign of Q1040 turning on. I put an analog meter on the current sense resistor. The voltage is steady at 103 mV (515 mA). It is not overcurrent preventing starting.

Heat blown into slots in the top cover does speed up recovery. It does not take much and I don't really know what I'm heating. Something center or more to the front I think.

When running the AC current flickers at 1.1 amps and seems to want to drop to 1 amp. I have seen it running at 1 amp with jumps to 1.1 amps.
My other 2465 runs steady at 0.95 amps. It has one less option board.
There is something surging power. If the current surges were caused by any of the regulators after T1060 it would show in the current limit sensing.
Same goes for anything in the Q1060 and Q1070 drivers. It only leaves the Q1062 circuit or the voltage doubler input. I did not change the voltage doubler capacitors.
Any suggestions? Remember I have to disconnect 18 cables, remove the top cover with the CTS and GPIB option boards, and remove the power supply for every test.
All aluminum electrolytic capacitors except the doubler pair have been replaced. CR1022 and Q1040 have been replaced, so has C1024.
Q1050, Q1060, and Q1070 would show up in the current sense if they were the cause.

On Wed, Mar 6, 2024 at 7:48?AM Christian F1GWR <f1gwr.groups@...>
wrote:

When rotating Vert, Horiz and Step/Offset front panel knobs large
unexpected jumps in settings occur.

My $0.02 bet is that you didn't entirely get the grime/oxidation off the
contacts, so spraying with something like DeOxit and working the encoders
might clear it up.
Note that gray codes (including the quadrature code) are bounce resilient,
so if this is a contact issue, this has to be due to contacts that are
intermittent as they're wiping.

Alternatively if you can get a scope on the encoder pins, you'd be able to
see what's happening - this could be a circuit problem as well.

I have stopped refurbishing test gear for fun to focus on other more RF-ish design pursuits. As I can't abide having stuff around that isn't being used, I have started pulling equipment from my bench and storage, figuring out its condition, and selling it.

I am located in Portland, Oregon. While I prefer local buyers, I will ship anywhere in the United States as long as the buyer covers the actual cost. I am sorry but I don't want to deal with customs and overseas shipping right now. I am also willing to drive within an hour or so of home to facilitate a transaction. Think my prices are ridiculous, make me an offer. Payment terms: cash, Zelle, USPS money order or bank check (gear shipped when cleared). If you are interested in something, please send me an email (K7WXW at qrpdx dot net) in preference to responding here, which will be easier on everyone involved.

In this batch:

- Tektronix 2465, SN B025686. In working condition, w/ original service and operators manuals, all knobs intact, intermittent light fan noise, excellent cosmetic condition. $250 plus shipping.
- Tektronix 475A, SN B016612. In working condition, all knobs intact, good cosmetic condition. $200 plus shipping
- (2) Tektronix 485s, SN B155585 and B061036. Sold as a pair only. B155585 in working condition, all knobs intact, some sticky actuators and switches, good cosmetic condition.
B061036 powers up, screen illuminates, no traces, a couple of cracked knobs, for parts. A refurbishing project I never got around to doing. $225 for the pair plus shipping.

I have other non-Tektronix gear for sale or to be sold, which will be listed on other forums. Let me know if you want to know where.

Thanks for looking - Bill

The CRT face looks small.? On mine, the CRT area goes from the middle of the power switch to the middle of the top control.? I suspect that you have one that has been modified.? Look for the mod perhaps on the back of the scope.

My guess is that it has been modified for very high writing speeds to drive a camera.? Look for a P11 (blue) phosphor in that case.

Harvey

That will be a nice scope once you get it cleaned up and repaired. Congratulations on finding one. Careful, though, as they're addictive.

Barry - N4BUQ