Test Equipment - Tube Tester & OScope

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Test Equipment - Tube Tester & OScope

Postby Jamie on Thu Sep 24, 2015 9:45 pm

A local auction is coming up along with some ham radio gear are a couple of units I'm interested in. It's been 40 years since I've used an oscilloscope but would like to have one on hand for biasing. Pending these are in working order, they look to be taken care of well.

Precision 660 Tube Tester
Eico 460 Oscilloscope

Is the Eico sufficient for these tasks? Not looking to bid high on these. Thanks!
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Re: Test Equipment - Tube Tester & OScope

Postby PeterS on Fri Sep 25, 2015 1:16 am

That Eico is a fairly low-end scope. Perfectly adequate for audio troubleshooting etc but I wouldn't pay a fortune for it either. It 'only' goes to a few megahertz but that's not a problem for audio! I used to have an old Hewlett-Packard that went to 200kHz, laughably slow but plenty for audio. The beauty of those old scopes is they often have a very bright and sharp screen image that's better than cheap new digital scopes. :old:

I think Precision 660 is an emissions tester, but a high quality one - same story, it will do the job but I wouldn't overpay for it. I recently got an Eico 666 (satan's tube tester) which is a fairly similar design, and I feel like it does the job of separating good from bad preamp tubes about as well as my (now broken) Hickok 539B did. You can pick up an Eico 666 for $100-$200 because it's 'only' an emissions tester, while the Hickok in good shape sells for somewhere in the $1000 ballpark :shock: . Meanwhile, IMO they are both of very limited use for power tubes because the test voltage is too low (<200V).
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Re: Test Equipment - Tube Tester & OScope

Postby Jamie on Fri Sep 25, 2015 1:57 am

Thanks Pete. I have a B&K model 600. So, is that also not useful for power tubes? I have no idea what the test voltage would be. I understand that both are emission testers. I'm not planning on paying more than $50 for each. But I did pick up a mint EP-4 Echoplex from a local auction for $50. My son has that now, I'm not letting the EP-3 go yet..;)
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Re: Test Equipment - Tube Tester & OScope

Postby PeterS on Fri Sep 25, 2015 12:25 pm

is that also not useful for power tubes?


My experience with the Hickok 539B was that any power tube that wasn't broken would measure about the same transconductance. So I added a plate current meter - terminals are provided which make that easy. That was somewhat more useful - the bad tubes would stand out from the herd- and that measurement is pretty much reducing the fancy transconductance tester to an emissions tester. But I also found that a pair of tubes that drew the same current in the Hickok (at 150 volts) might be very different in an amp (at 450 volts). I have an AVO Mk 4 on loan, and it goes to 400 volts, and that provides useful results, but they are even more expensive to buy than a good Hickok. For power tubes I ignore the manual (which suggests testing 6L6GC at 250 volts) and just make up my own test conditions and measure the current, not the transconductance.
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Re: Test Equipment - Tube Tester & OScope

Postby Jamie on Fri Sep 25, 2015 3:46 pm

Thanks Pete on the info.. Lots to learn. I'm taking it that you are matching tubes with the AVO? Emissions and shorts are really all I'm concerned about. Not looking to spend big $ for my needs.
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Re: Test Equipment - Tube Tester & OScope

Postby PeterS on Fri Sep 25, 2015 4:09 pm

I'm taking it that you are matching tubes with the AVO?


Yes. But you could do that equally well in an amp. I thought about, but never got around to, building a simple tester that puts 450 volts on the plate, and either measures the current at a fixed grid voltage, or (cunning idea here) uses a solid state current regulator in the cathode circuit to set a current (say 40 mA), with the grid grounded, and measures the cathode voltage...
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Re: Test Equipment - Tube Tester & OScope

Postby Jamie on Fri Sep 25, 2015 6:10 pm

Well all that is a bit beyond me right now. I've been using a weber bias rite for biasing. Thought picking up a scope might be a good learning experience. My old tech used a scope like many of the guys here.
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Re: Test Equipment - Tube Tester & OScope

Postby PeterS on Fri Sep 25, 2015 10:03 pm

A scope is a lot of fun once you get familiar with it. Then you feel blind without one. My latest acquisition (hmmm, must stop hoarding) is a little tiny Philips one that has a screen about 3 inches across, one channel, and only half a dozen knobs. It has a 12ax7 for the front end...

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Re: Test Equipment - Tube Tester & OScope

Postby Jamie on Tue Oct 06, 2015 12:19 am

The Eico scope and the precision tester work fine. Transformer is ok, it lights up, meter can be zeroed. Tube sockets are a little loose, not sure how to get to those to tighten up. Located a manual for the tube tester, that should help. The test process is quite different than the B&K, fun stuff. Cool score for $40.

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Last edited by Jamie on Sun Oct 11, 2015 9:50 pm, edited 1 time in total.
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Re: Test Equipment - Tube Tester & OScope

Postby Jamie on Thu Oct 08, 2015 12:59 am

Looking a test probes, any recommendations for amp servicing? Eico made 3 probes, I'm not sure which of the two would be the best way to go. Direct probe or an attenuating low capacity probe. I'm guessing a demodulator probe wouldn't be necessary. Any suggestions appreciated!
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Re: Test Equipment - Tube Tester & OScope

Postby pdf64 on Thu Oct 08, 2015 8:42 pm

Jamie wrote:Direct probe or an attenuating low capacity probe

For tube amp work both will likely be needed (x1 and x10).
Maybe the attenuating probe is switchable (to non-attenuatiing)? If so that would be nice.
To monitor high voltages, eg power tube plates, a x100 attenuating probe is usually also needed.
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Re: Test Equipment - Tube Tester & OScope

Postby Jamie on Thu Oct 08, 2015 10:58 pm

pdf64 wrote:For tube amp work both will likely be needed (x1 and x10).
Maybe the attenuating probe is switchable (to non-attenuatiing)? If so that would be nice.
To monitor high voltages, eg power tube plates, a x100 attenuating probe is usually also needed.


Thanks, that was the input I was looking for. On a side note, wifey thought I finally scored an enigma machine.. ;)
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Re: Test Equipment - Tube Tester & OScope

Postby Jamie on Mon Nov 23, 2015 3:24 am

I'm going to restore the Eico 460 as a winter project but just landed an Iwatsu SS-5705. I'll go over it, it's a 40mhz scope should be good for my use. The $30 460 needs some tubes and calibration. The 1v2 half wave rectifier is shot. I'll step through the service manual, should be fun.

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