[Shermie]

Does anyone have a copy of the instruction manual or at best can explain to me how to operate an Otto-1 Multi Tube Tester. I recently restored a defective used one,  but am only able to partially understand how to operate this unit.

[markC]

How could you restore it if you don't understand how it works?

[Shermie]

Thanks for the help.

[markC]

Sorry for being a smartass, what is it that you are having trouble with? Perhaps if you post a pic. of the unit that may help.

[Shermie]

OK and thanks for opening up to my request for help.

I will snap a few photos under the chassis of the Noise/Trans-Match section.

The matcher part works. I am able to get the unit so far to match the Octal and 9 pin (EL84) tubes who share the same
basing, with pretty good results.

Replaced 4 burned 1.5Kohm, 3 watter resistors with some 5 watt sand types.

Previous owner had the unit on 24/7 for several years and this design does not look to be built for continuous duty operation.

When I replaced the burned resistors, I also saw that the tester had, on each of the power tube sockets,
a 10K-1/2 watt resistor soldered between two pins (I can't recall now what pins).

But these resistors measured all over the place.

One was 9.3K, the other 9.5K and two at 10.4K, the other four also were not matched (on the 9 pin sockets).

Replaced all 8 of them with new 1 watt 2% types just to make each socket electrically as close as possible.

I will post some detailed photos of the section in question. There are two TO-220 type regulators bolted to the chassis next to the PC board. Will take some readings of these also and post.

My hunch, that there is a bad component in the noise testing area. I see what looks like a transistor and some diodes, both Si and Ge types.

When I put a 12AX7 into the socket and fire up the controls, on my Grado SR125 (32 Ohm headphones), all I get is a noise that goes up and down with the level control. Does not seem to be working, but I could be listening for the wrong thing. w/o the manual?

I will snap some pics underneath and post ASAP.

The chassis is very sturdy, reminds me of a Leslie 147 amplifier, tough as nails.

My understanding of this matcher/tester, it was built by the Sovtek people in Russia and imported
to the US and sold by New Sensor as the Otto-1.

There may have been plans for an Otto-2 that never materialized ?

In lieu of the actual operating manual and schematic, I can and will reverse engineer the unit.

It would probably take me a few weeks of inspecting and drawing-out the diagram.

The two PC boards underneath are very simple one sided and have only two dozen parts, so I can follow the traces pretty well.

Remainder is point to point.

The only modification I plan to do is that the Meter Connection binding posts are de-threaded. Will swap them out for a pair
of Tip-Jacks for easier metering.

I measured the voltage on Pin 3 (Octal) and I get +300Volts with no tubes inserted. So as usual, this tester mimics the majority of current production units out there. This apparently tests the power tubes at +300Volts.

The power tubes get hot fast, so I imagine that the plate currents are quite on the high side. The transformers also have an audible buzz, not sure if normal, but the voltages all seem to be there and no bad smells or discolorations.

Have not really sat down with the Fluke to measure this thing well, so I am not yet sure if the biasing arrangement is Cathode based of if there an actual negative voltage fixed bias supply circuit.

Thanks for your interest, I am sure we can figure this guy out and when I get the schematic drawn-up, I will share it with all of you now
that this is a discontinued unit.

Looks like a good DIY project and platform on which to improve with Digital Meters, BNC scope connections, etc.

[Shermie]

Last night I managed to sit down for an hour with the Otto-1. I travel 90% of the time and last weekend the family had priority.
I sprayed the main function selector switch with some CaiLube and the transformer buzz disappeared. The tube matching readings are now steady and don't vary when I put some pressure on the switch.

The problem that the unit has is definitely in the Noise & Trans/Match section.

There are some IC's that I can easily identify but there is an odd looking 6 pin package that has no label or marking.

I see what looks to be like a Russian transistor marked 7BF1, the B is the Cyrillic character for B. There is a voltage drop across the outer pins of about 0.5 volts so It looks like that part is OK, or at least the DC voltages seem like typical for a transistor that is turned-on.

My oscilloscope shows me a Sawtooth waveform and also a distorted Sine Wave.

So my best guess is that that area of the tester needs some work. Will post some detailed photos over the weekend

New Sensor has not responded yet. Stay tuned!

[Shermie]

Link to photos of the tester. Already have matched several quads and duets with very good results. Works wonders with EL84 and 6550's.

http://shermanr.web.prw.net/Page0.htm

Here's the link to the fotos I took of the tester. The mystery IC chip is cracked, and put out a bit of smoke in the process. The uniy still works matching tubes. But the mystery board and chip make this repair an adventure in post cold war reverse engineering. I am lucky I have a friend who travels to Kiev regularly so I'll send him on a mission or mercy.

Still no manual. Started to draw out the PC boards. In a few weeks I should have a basic schematic minus the obvious details on several of the components that have so visible specs.

From there I hope to somehow determine with some luck, what that board does. I did measure some sawtooth wafeforms and some DC values prior to the chip finally dying.

Thanks,
Rich

[markC]

Never seen a chip like that b4. What vintage is this unit?

[Shermie]

Update:

Tester is about 10 years old. Original owner purchased it in 1998.
Did retrieve some DC measurements prior to the part smoking.
A 6922 tube inserted into the corresponding socket, Gain pot set in the middle of rotation.
About 5 minutes into the DC readings, the chip suddenly smoked, and cracked on one side.

The DC voltage readings were as follows:

Measuring DC from the pin next to the black dot down the same side:

Pin 1 (Dot): 0 VDC
Pin 2 : 8.8 VDC
Pin 3: 17.7 VDC

The chip is symmetrical and the same DC voltages are mirrored on the other side of the chip on Pin 4, 5 and 6.

The other components are the 7BF1 transistor and the 1 watt Audio Amplifier chip.
There is a 3 pin potentiometer and also a diode.

The board is single layer and pretty simple to draw out, even shows the polarity of the electrolytics on the foil side.

On the transistor the board has marked B, K and E. Probably for Base, Kathose and Emitter in cyrillic (will check with my Russian friend)

After removing the faulty chip, the unit still is able to match power tubes well.

Now the focus is on that particular board I would like to fix.

I have a hunch, that this 6 pin chip is a dual transistor package.

Now whether it's a dual FET, PNP, NPN is now only a guess as well as my hunch.

Strange that the chip has no markings at all.

Maybe someone took some fine grade sandpaper prior to installation as the surface
looks rough, unlike any other chip I have seen that has a smooth black surface.

If the dot was indented, I would have noticed that the chip was sanded, but the
dot is raised (like braile) and it also is roughened.

On some old Grundig Reel to Reel units, all of the components are placed
writing down on the PC board so that one cannot see the readings. Maybe
a bit of sand paper keeps the circuit proprietary ? Just another guess.

Can't seem to include the image, I select Insert Image and all I get is a [img][img] ?

Thanks,
Rich

[Shermie]

Snoooing around some 6 pin IC's I see that an Optocoupler may be one application.
The PC board has the 0V pins connected in common.
More as I develop the diagram..

[Shermie]

I pulled the cracked case open and see that the 17.7 Volt DC pins are internally bridged, both pins are bridged as a single piece of metal inside the chip. So, this leaves me with a device that has the 17.7 Volt DC pins internally bridged, and the zero volt pins bridged by the PC board itself. The 8.8 volt middle pins are fed by two white wires soldered to the pins on the board right behind the chip in question. I'll check to see where these wires are coming from and also scope and DC the wires to check for possible input signals. (need to get home this evening to find out.)

Stay tuned as I piece this board together on paper.

[Shermie]

I got the info on the parts I needed from my friends in Ukraine.
The transistor is a medium power NPN and that mystery 6 pin chip is a
small bridge rectifier.

Here's the data sheet info... I am on my way now to fix this tester.

Transistor 7BF1:
http://www.chipinfo.ru/dsheets/transistors/1817.html

Bridge Rectifier:
http://www.chipinfo.ru/dsheets/diodes/407.html

I will let you know how my restoration work goes...

BR/
Richard

[BillB]

Great detective work! 

[Shermie]

Okay I am back again and the Otto-1 is operational.

- I replaced the defective Russian bridge rectifier with a Radio Shack 100V, 1.5A Bridge. A few jumper wires were needed as the holes on the PC board were too small.

- The Russian NPN transistor has a cracked Base pin. I jumpered.

- Also replaced a burned 430 Ohm resistor.

I said a prayer, fired it up, and BINGO!

Everything works, except the noise test has a hum I need to sort out.

So far so good. Even the 6550 tubes are now measuring properly as do the 6SN7's.

I can help anyone who has one of these. I also got a scanned copy of the instruction manual from a
helping soul (Thanks Bart!)

The difference here was having a friend with a contact in Kiev who knows Russian parts well.

The people at New Sensor were ZERO help...

[Madmolecule]

I have just purchased an auto Otto-1 off eBay. With your help I was able to find replacements for the chips on the board. I have started to draw up the schematic but I did not know if you had made any progress. Also I would love to get a copy of the manuals if it all possible. I know this thread has been dead for over 10 years but I am trying to resurrect my unit.

[Mightyfine]

Newbie to this forum. I realize this thread is quite old, but giving this a try anyway.

I was recently given a non-working Otto-1 tube tester and have been scouring the web looking for any schematics, instruction manual, etc that I might find. Not much out there, and no luck so far. I'm answering the most recent post in this thread in hopes of getting a reply. And may start a topic on the Otto-1 if this doesn't work. Thanks!