Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: Willabe on September 25, 2015, 08:17:34 pm
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A friend just gave me a Tektronix 2445A 150MHz 4 channel scope with a high voltage probe. Looks to be in good shape. :icon_biggrin:
Is this a good scope for tube amps? Anybody familiar with this scope?
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From what I understand any scope in the 50MHz range is fine. I just bought a Rigol DS1054Z because it gets rave reviews for having 4 channels and 50MHz. The audio range of most guitar amps is like 10Hz to maybe 20kHz. So 50MHz is well within range.
~Phil
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I'm not familiar with that particular scope, but it is more than perfect (as long as you have a 10x probe) for working on any kind of audio gear. You received a great gift. My everyday scope is a 15 MHz Leader LBO-514, though I do have a Tektronix 556 (100 lbs, 44 tubes, 800W). Oh, here's a picture of one stack of my test equipment when I was moving it earlier this year.
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Nice looking stack of test gear. :icon_biggrin:
Yes it came with a 10x probe.
A friend from church is coming over this week to show me how to use it.
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I was under the impression that a 10x scope probes can't take over 300v and guitar amps regularly go up to 500 or 600 in some cases. I bought a few 100x scope probes so that I can go higher. Anyone want to confirm that for me?
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I was under the impression that a 10x scope probes can't take over 300v and guitar amps regularly go up to 500 or 600 in some cases. I bought a few 100x scope probes so that I can go higher. Anyone want to confirm that for me?
I don't know for a fact. My lbo-514a label on the bnc input says 600V max. My tek p6103 says it's good to 500v. The voltage ratings for your probes should be on the data sheet.
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The 2445 Max input voltage is 400V (dc + peak ac) or 800 V pp ac @ 10KHz or less.
Here's the operators instruction manual. You can probably find a service manual also.
http://www.mit.edu/~jhawk/tek2445.pdf (http://www.mit.edu/~jhawk/tek2445.pdf)
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Voltage rating on probes depends more on the caps they use than the X-factor.
Since 'scopes don't need more than a Volt to get a full picture, 100X probes may be useful for a 'scope which has little turn-down for large inputs.
Note that the OT plate leads of a 400V DC amp will kick to 700V-800V.
In many practical cases, you do not need a precision probe. 10Meg and 100K gives 100X reduction, stands high voltage, and uncompensated bandwidth is beyond the audio band.
IMHO 1MHz is more than ample for 99.44% of guitar-amp work. 100KHz is often fine. I have used a 19KHz 'scope and learned stuff. With the transistorization of 'scopes, you can't hardly find anything under 5MHz. Bandwidth is a non-feature. Easy controls may be far more useful.