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 Post subject: Help with Olson TE-148 tube tester
PostPosted: Sep Mon 20, 2021 5:12 pm 
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Joined: Sep Mon 20, 2021 4:49 pm
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Hi,
Someone just gave me an Olson TE-148 tube tester and I am wondering if anyone has full schematics or could tell me what this (looks like a broken pot) component is and if it is an add on or part of the original circuit. I have included an image of the component of interest and also I created a PDF of the manual. The manual has a partial schematic but it does not appear to be complete. I fix a lot of tube guitar amps so this would be really useful for me if I can get it working.
Thanks


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Olson TE-148.jpeg
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Olson TE-148 Manual.pdf [29.49 MiB]
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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Mon 20, 2021 6:53 pm 
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It's a pot but doesn't look broken.


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Mon 20, 2021 6:59 pm 
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Location: Sunbury, Ohio 43074
It’s a wire wound trim pot. If you can take a picture of the other side where the guts are, we can probably see if it’s likely to be ok or not

You could measure the resistance across the outer terminals, then measure from either end to the center terminal while you rotate the adjustment

Make note of where it’s set now. Changing it may throw the tester out of calibration

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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Mon 20, 2021 7:19 pm 
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I found something on the net - "OLSON TE-148 TUBE TESTER This tester is { { VERY 'exact' to the EMC 211 } & similar to the EMC 213 in operations." If that is true, look here for a manual and kit instructions - https://bama.edebris.com/manuals/emc/emc211/. See if the EMC is similar to yours.
Attachment:
EMC 211.jpg
EMC 211.jpg [ 38.71 KiB | Viewed 343 times ]


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Mon 20, 2021 10:19 pm 
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Joined: Sep Mon 20, 2021 4:49 pm
Posts: 6
LOL, this is the first time I've posted on this form (new member) so I was not sure how many images I could upload. As you can see from the picture I just uploaded, this is just a shell of a trim pot, that's why I was not sure what value. In the pdf manual I posted, there is a schematic near the back, but it is not a full schematic and that component along with some switches are not shown.
Thanks for your help so far!


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IMG_0475.jpeg
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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Mon 20, 2021 10:27 pm 
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Joined: Sep Mon 20, 2021 4:49 pm
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Thanks for the link Tom, the manual is the same as what I have but the kit build instructions may have the answer!


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Mon 20, 2021 10:34 pm 
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Can you pull back and take another photo showing the entire back side of this unit?


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Mon 20, 2021 10:49 pm 
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Joined: Jun Sat 15, 2019 7:43 pm
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Looks like it is the 600 ohm resistor to adjust the meter sensitivity. Is it bad? what does the resistance read?

DM


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Mon 20, 2021 10:54 pm 
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What devilsmist said about the 600 ohm pot.

The big rheostat is the 2000 shunt control. You should have 1 more pot - the 600 ohm variable resistor. But per your photo, that pot is in the wrong place. That is why I asked for a photo. See if you have another pot in the circuit.


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Mon 20, 2021 11:57 pm 
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Here is the schematic.
Attachment:
211schematic.pdf [19.99 KiB]
Downloaded 19 times


DM


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Wed 22, 2021 5:50 pm 
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Joined: Sep Mon 20, 2021 4:49 pm
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I see now, the schematic is drawn a bit odd. Yes the broke component is the 600Ω rheostat/pot for adjusting the meter and it is open. 600Ω rheostat/pot appears to be difficult to find and fairly expensive, is there any reason I can't replace it with a 1k standard pot (wired wiper to one side, other side left open)? I uploaded more pictures. Also these large resistor are out of spec, I am guessing the 1.2k resistor is a 10 watt resistor and the 270Ω resistor is 5 watt, is this correct? I am also going to replace the 50µf electrolytic across the meter, I would think that a 450v cap should work.
thanks


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IMG_0474.jpeg
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IMG_0479.jpeg
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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Wed 22, 2021 6:12 pm 
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Regarding the the 1.2k and 270 ohm resistors - 10 watt and 5 watt look about right. Check all the resistors (since there are just a few) and maybe lift one end to avoid parallel items throwing off your readings.

Yes, replace that cap. See if you can lift it to find a voltage rating.

As for the 600 ohm pot - that is a weird looking pot. See if you can verify the end points on the pot and that they go to the correct locations. Per the EMC schematic, one end goes to the center wiper of the 2k rheostat and a switch and the other end goes to the (-) minus side of the meter. I cannot figure out where the center wiper goes.

If you search hard enough, you can find a 600 ohm pot. If not, see if you can find a 500 ohm and you can tack on a 100 ohm (depending on how that thing is connected). Some guys test and get prelim settings and then solder in permanent pots in lieu of a pot.


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Wed 22, 2021 6:50 pm 
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Joined: Jun Sat 15, 2019 7:43 pm
Posts: 1469
guitarpresence wrote:
I see now, the schematic is drawn a bit odd. Yes the broke component is the 600Ω rheostat/pot for adjusting the meter and it is open. 600Ω rheostat/pot appears to be difficult to find and fairly expensive, is there any reason I can't replace it with a 1k standard pot (wired wiper to one side, other side left open)? I uploaded more pictures. Also these large resistor are out of spec, I am guessing the 1.2k resistor is a 10 watt resistor and the 270Ω resistor is 5 watt, is this correct? I am also going to replace the 50µf electrolytic across the meter, I would think that a 450v cap should work.
thanks

The 600 ohm pot can be replaced with a 1K 1/2 watt pot. From the pictures the large resistor looks like a 3 watt and the smaller one a 1 watt. For the electrolytic across the meter, voltage is not critical, a 10 volt would work fine. Also replace the 1meg resistor for the shorts circuit, the white ceramic capacitor will be fine.
Keep in mind this is not a very high quality tube tester, You should search around for a more substantial tube tester if you are going to work on tube amps.

DM


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Sun 26, 2021 6:26 pm 
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Joined: Sep Mon 20, 2021 4:49 pm
Posts: 6
Thanks for all the help! The unit is up and running, I did use a 1K pot (wiper to one side, other side floating) and it works fine. I still have a couple of resistors on order and I replaced the 50µf cap with a 47µf, 50V.
Agreed that this is not a high precision tube tester, but I have gone without one for decades so, it will be fine for me, it is what it is :) .
The meter calibration procedure that the kit instructions recommends it to use a "known good tube" and adjust the the meter to 36. Of course, "good tubes" vary greatly, so not a very good way to calibrate the meter.
Any suggestion on a better way to calibrate the meter?


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Sun 26, 2021 7:00 pm 
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Actually, tubes don't vary enough to worry about. If you have a few good ones you can average them.


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Sun 26, 2021 7:03 pm 
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bob91343 wrote:
Actually, tubes don't vary enough to worry about. If you have a few good ones you can average them.

20% more or less in my experience, but still not enough to worry about. Unless you are selling them.

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Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


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 Post subject: Re: Help with Olson TE-148 tube tester
PostPosted: Sep Sun 26, 2021 8:16 pm 
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Joined: Sep Mon 20, 2021 4:49 pm
Posts: 6
Good to know, thanks!


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