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Some Vintage Test Gear Madness

Mine's an older unit, too, and I like it for the same reasons you'll like this one - tweak a knob or two, and you're there. It also has one of those big vernier-actuated variable capacitors in it.

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I attached an 8 ohm 100W resistor to the top to use as a dummy load for amps. No rare tubes, though. You lucked out.
 
They work ok for me. I don't think you see 'em in a lotta labs, or at least not the ones I've been in. Not sure why - My 'scope is a B&K as well, and both items seem to be pretty good units. But, most of what I've seen and used professionally has been Tektronix, Dranetz, Fluke, Norton, HP... like that.
 
Yep - all old super-hetrodyne sets had variable capacitors like that.  Then people got smart and started using *digital* <shudder>
 
Well, here we go - I fired it up on the dim bulb tester and checked out the power rails.  All voltages were present and accounted for.

So then I got out my 'scope and had a look.

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Holy crap!  It's doin' stuff!  The square wave looks like crap mind you with a lot of oscillations on the edges - seems the schmitt trigger circuit is not that happy.  Waveform symmetry is not really spot on either.

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But then I got brave and flipped it to full power.  Much nicer looking waveforms, although the square wave has some slope issues.  So in summary - it's worth saving!!

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That link leads to that type tube, but it's unavailable, that's why it's only $50. If they were available, they'd probably cost a lot more. But, they've gotta make some more new old ones first, and production is currently tied up making new old 12AX7s labeled with a defunct company's name. Yours is likely an old old one, from the company that actually made them back when they made tubes. Plug that baby into an old Fender amp, and outside of the terrible S/N ratio it might sound almost as good as an AxeFx :laughing7:
 
I spent a long afternoon calibrating the unit using the heathkit manual.  That's the great thing about old heathkit gear - you can get a very complete manual for it  :)  But I digress.  As you can imagine, the unit was very much out of calibration. 

Among other things, the calibration procedure calls for the use of a VTVM!  This is specifically for calibrating the frequency (you use a beat frequency with the VTVM grounded to the filament supply).  That got me surprisingly close.  I got it the rest of the way using the frequency counter built into my scope  :headbang:

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The waveforms look much much better now - they are very usable.  But then I found another problem.  The unit only works on the X100, X1000, and X10,000 CPS settings.  It won't oscillate on the X1 and X10 settings!  This means that I can't generate anything below 2KHz - which is rather annoying actually.  Need to sort that out...

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Waveforms do look better in all aspects. The missing lower freqs are maybe the selector switch?

I love that little 'scope, but I wonder what possessed them to put a marketing blurb on the front? Seems wrong for a test instrument just on general principles, but particularly out of character for Tektronix.
 
I never really noticed it until I looked at the photos.  Maybe I'll pull it off of there...
 
It's just a pet peeve of mine. They got your money, fer crissakes, do they really need to keep selling it?
 
So I've got a pile of parts on order for this guy - including a new set of tubes for it. 

But first, let's deal with that line cord and lack of a fuse.  Still can't believe that this old stuff never was fused!  What were they thinking??

1/2 amp slow blow and new polarized line cord installed!

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BTW, those things to the left that are in what look like fuse holders are Silicon Diodes  :eek:

What will they think of next?  :headbang:
 
Silicon diodes, eh? Amazing. Well, if they work, I'm guessing that's gonna wreak havoc on Sylvania and RCA's rectifier tube sales.

Speaking of silicon diodes...

I learned about those things before I learned about some other things, so in a fit of clever one day back when I was a puppy, I decided to replace the rectifier tube with some solid state goodness in an old Fender Pro Reverb so I wouldn't have to worry about that  stupid tube. Got ahold of some IN4004 diodes (1A, 400 PIV) from Radio Schlock and made a full wave bridge. Soldered that little cluster of modern engineering right to the rectifier tube socket, and cranked 'er up. Seemed to work ok, although the amp didn't sound very good. But, I was never very impressed with the sound of the thing anyway, so I let it go. I didn't own a multimeter back then, and didn't know anyone that did, so I had no idea what I'd done to the poor thing. Imagine my surprise when the filter capacitors turned out to be bad, as they blew up a few days later. That  pissed me off, as high voltage electrolytics aren't cheap. Never connected the mod to the failure until a couple years later, when realized I was probably putting 600V+ on those 400V caps  :laughing7:
 
:) :) :) :)  and  :eek:ccasion14:

Here's to experience!  especially learned the old-fashioned way  :headbang:
 
Mayfly said:
:) :) :) :)  and  :eek:ccasion14:

Here's to experience!  especially learned the old-fashioned way  :headbang:
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You obtained experience the old fashioned way, you burned it!  :icon_jokercolor:
 
Yeah, well. The only people who aren't making mistakes are the ones who aren't doing anything :laughing7:
 
Cagey said:
Yeah, well. The only people who aren't making mistakes are the ones who aren't doing anything :laughing7:
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I must be doing a lot more than I thought I was.
 
Hehe! Yeah, I know the feeling.

The trick is to learn from mistakes while not dwelling on them.
 
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