Oscilloscopes for amp building...

[Paul-in-KC]

All,

I'd like to get an oscilloscope to be able to look at and see what is happening all along the signal path through an amp.

I know that any scope will cover the frequency range of interest, but what about input voltage specs?

What would you recommend for minimum max. voltages for AC and DC coupled?

I'd prefer to buy tools once. So, I'd like to get something that will do anything that I would need (for amp building).

Any favorites, or pitfalls?

Thanks,
-Paul

[skyboltone]

I used my Tektronics 453 scope for many years. The voltage issue is addressed with the probes you use. A 10X probe for instance will be reading 500 VAC on a 50 scale.

I managed to pick up a 2465 4 trace scope for a song because it was broken and I already had the parts.

The Tek is surplus to my needs now.

Dan

[husky]

All,

I'd like to get an oscilloscope to be able to look at and see what is happening all along the signal path through an amp.

I know that any scope will cover the frequency range of interest, but what about input voltage specs?

What would you recommend for minimum max. voltages for AC and DC coupled?

I'd prefer to buy tools once. So, I'd like to get something that will do anything that I would need (for amp building).

Any favorites, or pitfalls?

Thanks,
-Paul

You can deal with it on the probes but the multiplication factor of the probe doesn't = multiplying voltage handling capability. For instance mine is 150V with no probes and 350V with the 10x probes. There is a voltage rating on the probes. A 465B is a good choice for an older scope. I just treated myself to a bitchin tekTDS3012C which is amazing but pricey. You can save traces and view on a browser and do screen shots if you like. But... to get 500V it will cost me like $350 for the probes. Standard it is 350V I think. That is really fine just dont go probing DC up there.

[Paul-in-KC]

The Tek is surplus to my needs now.

Dan

Does that mean you might want to find it a new home?

[Paultergeist]

You can deal with it on the probes but the multiplication factor of the probe doesn't = multiplying voltage handling capability. For instance mine is 150V with no probes and 350V with the 10x probes. There is a voltage rating on the probes. A 465B is a good choice for an older scope. I just treated myself to a bitchin tekTDS3012C which is amazing but pricey. You can save traces and view on a browser and do screen shots if you like. But... to get 500V it will cost me like $350 for the probes. Standard it is 350V I think. That is really fine just dont go probing DC up there.

Respectfully, this post contradicts virtually everything I have ever read about oscilloscopes.

A 10x probe and a 1x probe is pretty standard fare for amp-tweakers -- what exactly do you mean by "no probes?"

[desu boi]

Just get a cheap 1X/10X probe from China. Mine are rated CAT II 150V AC at 1X and CAT II 300V AC at 10X. This means the probes have been tested and found ok at impulse voltages of 2500V on the 10X setting.

If that isn't good enough you could always make a voltage divider to go higher.

For a scope, the Rigol DS1052E is cheap and popular.

[surfsup]

I was debating the Rigol but got the Atten instead:

http://www.eham.net/reviews/detail/9840

They are about the same. I got it at $350 shipped to my door. I like the ability to hook it to the PC to pull up the screen shots but lately I just plug the USB stick in front and hit the "print" button and it saves the bmp to the usb. I have to open in paint and resave as JPG to reduce the size from around 1.5mb to 300k because bmp files are huge for some reason.

Works well, dual trace, etc. small and light, only about 3lbs? about 12"x4"x4"

Has been invaluable at watching signal traces, but I admit I am still trying to figure out how to isolate an oscillation problem. I can see it but not sure how to fix it

[skyboltone]

The Tek is surplus to my needs now.

Dan

Does that mean you might want to find it a new home?

Yes. I need to do a history check on Ebay for a price. I noticed last night there are a couple on there for $50. I'll be keeping mine for a back up at that price. This one came out of IBM surplus years ago. As compared to Chinese scopes it's MADE IN USA, and there is an abundance of service information available on line. I think there are two 10x probes. It's a 50 mhz scope.

The 465 is also a very fine instrument. A little bigger and heavier. Don't get any Tek scope newer than the 2465 series. They were the last with ordinary components inside. The newer ones have a lot of OEM parts that are pretty much unobtanium. Tek learned that it's more profitable to require factory service.
Dan

[cpollack]

I have a Tek 546 (tube-era) that's about as old as I am and an old rack-mount tube HP, as well. The Tek is a 50MHz scope, dual trace, and does anything an amp builder would need. Tunnel diodes and replacement CRTs are a little tough to find if they require replacement, but I've got $75 into it, so no worries. The HP is single trace and uses mostly common tubes.

For sussing out guitar amp circuits just about any older scope will fill the bill. Dual trace is nice to look at the "before and after" of a particular stage.

Non-technical guitarists are a funny lot. I've had guys tell me that "you really need to keep it all tube" when they see my tube scopes and Eico signal generator. "Yeah man, that makes a HUGE difference! I've even got a vacuum tube volt meter!" FWIW, I think Mike Soldano's scope is an RCA even older than my tek and HP.

[Paul-in-KC]

You guys are great.

I really appreciate everyone taking the time to post and share their knowledge.

I ended up getting an HP 54501A that looks to be in good shape and guaranteed to be working (at least for a couple of weeks); for a winning bid of $153.00 plus shipping (on eBay).

That's without probes, but still, I think that's a pretty good price on a nice old piece (not that old really) of test equipment made here in the USA.

Now to find some probes...

-Paul

[husky]

You can deal with it on the probes but the multiplication factor of the probe doesn't = multiplying voltage handling capability. For instance mine is 150V with no probes and 350V with the 10x probes. There is a voltage rating on the probes. A 465B is a good choice for an older scope. I just treated myself to a bitchin tekTDS3012C which is amazing but pricey. You can save traces and view on a browser and do screen shots if you like. But... to get 500V it will cost me like $350 for the probes. Standard it is 350V I think. That is really fine just dont go probing DC up there.

Respectfully, this post contradicts virtually everything I have ever read about oscilloscopes.

A 10x probe and a 1x probe is pretty standard fare for amp-tweakers -- what exactly do you mean by "no probes?"

I mean if you plug right in with BNC clip leads, no probes as marked on the front of mosts scopes there is a voltage rating on the scope.
What I wanted to make sure he wasn't mistaken on is that the voltage rating of the scope is one thing and the probe also has a rating which must be observed. You don't want to go looking at AC signal on the plate of a power tube with a 300V probe (You could use a blocking cap of course if it didn't skew your measurement)

For instance the input of my scope is 150V
P6139B which it comes with are 10x 300 V CAT II
P5100A are 2500VPeak 1000VRMS 100X

[husky]

The 465 is also a very fine instrument. A little bigger and heavier. Don't get any Tek scope newer than the 2465 series. They were the last with ordinary components inside. The newer ones have a lot of OEM parts that are pretty much unobtanium. Tek learned that it's more profitable to require factory service.
Dan

Agree, I have a 2465 and a 465B, The 2465 even can be more expensive to service. The 465B you can almost throw out and just get a new one or another for parts. When I buy analog I get certified calibrated units, it is worth it in the long run unless you like to tinker. I'm hooked though on the new one though, being able to capture is so sweet. Then get a sweep generator and you can do frequency plots and print them right off your computer.

[xtian]

I just ordered a BK Precision 2120B scope. Is this what we're talking about when we say, "cheap asian probes":

http://www.ebay.com/itm/Two-10X-100MHZ- ... 0129798160

These are 10X. Will that cover what I want to measure in my tube amps?

I've never owned a scope, and I'm not even sure what I will want to measure!! Whee! New tech!

[vibratoking]

I'm a fan of good probes. The cheap ones don't last, IME. You should always consider the price of the probes when considering the purchase of a scope. For used scopes, the price of the probes can dwarf the scope. I've now seen quite a few guys buy a $150 scope and then spend that much or more on the probes.

[xtian]

I appreciate well built equipment…but that's not what I'm after. Right now, I want really inexpensive, "test the waters" stuff. I don't care if $20 probes break. I just want to experiment with the scope, to see if it's really important to my work.

So, quality issues aside, do I just need one or two 10X probes, or will I want other probes as well?

Probably the highest voltage I'll want to touch is the reservoir caps, in order to learn about 60 and 120 cycle hum. So, when there's 450vdc+ on that cap, what probe will I need to scope the ac there?

Or is this a stupid idea, and who would do that?