Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: eleventeen on November 02, 2013, 01:27:15 pm
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http://sfbay.craigslist.org/eby/ele/4161813554.html (http://sfbay.craigslist.org/eby/ele/4161813554.html)
5 MHz bandwidth (laughable) = perfect for audio. 2 probes, they even look contemporary style. Sick price.
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http://sfbay.craigslist.org/eby/ele/4161813554.html (http://sfbay.craigslist.org/eby/ele/4161813554.html)
5 MHz bandwidth (laughable) = perfect for audio. 2 probes, they even look contemporary style. Sick price.
Must be gone already. "This posting has been deleted by its author."
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Not surprising...I was too lazy to upload the listing to photobucket & store it for all eternity when I found it.
It was a compact 5 MHz dual-trace Iwatsu scope with probes for $20. Not that Iwatsu is a good brand (actually never heard of it before) but one really does not need a "good" scope to work on audio. Which was kind of funny because I can barely recall a "5 MHz scope"...even when I was a kid, in the very very last days of tube scopes, they seemed to have bigger bandwidth than that. But a 5 MHz bandwidth would be fantastic for audio.
My real point was that these things show up all the time used and really do not cost much more than a good quality DVM if you're patient and look around. And as I've pointed out...in many cases, it can definitely be better to go with a lesser-brand that was only occasionally used by a budget-minded hobbyist than buying a used high-end Tektronix that was the company-supplied scope for a field-service tech and shipped all over the place and beat to hell and which will cost a fortune to repair should it need such.
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> Not that Iwatsu is a good brand (actually never heard of it before)
Major old-school maker of telephone gear. Major supplier of radar from 1940. Pioneered improved production methods. Got into 'scopes in the 1950s. FAX 1960s.
I am suspecting that the Leader 'scope I bought in the late 1970s was an Iwatsu under a more US-friendly brand-name.
http://en.wikipedia.org/wiki/Iwatsu_Electric (http://en.wikipedia.org/wiki/Iwatsu_Electric)
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> I can barely recall a "5 MHz scope"...even when I was a kid, in the very very last days of tube scopes
EICO 427, still available 1972, was marketed as 450Kcps (0.45MHz) and that was a stretch. I thought it was a fine audio 'scope except for the gas-tube sweep.
At a yard-sale in the 1990s I found an older un-built HeathKit 'scope that was maybe 4MHz. That's about the upper limit of simple/cheap technology. There's 30pFd of deflection plates and stray C. At 5MHz that's about a 1K load. You need at least 50V of drive. 50^2/1K is 2 or 3 Watts. You can just do this with a medium transistor and a resistor. (Larger dissipation means heatsink and more stray C; or push-pull drivers.)
Out in the garage I have a huge H-P rack-mount 'scope, tubes, 450KHz bandwidth (model 130?). Since it has a solid sweep and calibration it will be a fine audio 'scope. H-P made these long after they were chasing Tektronix for the speed-market, since there ARE a lot of uses for a slow-speed reliable 'scope.
$20 sure was a deal. (I paid like $129 for the EICO, $35 for the Heath, $5 for the H-P.)
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Oh, and I once found a 50KCPS 'scope at the curb, gutted, and re-built it into a 19KHz transistorized 'scope for classroom demos.