Oscilloscope?

alpha al

Active Member
Joined
Oct 19, 2017
Messages
115
Reaction score
157
Location
Gastonia, NC
Bench .JPG
This is my shop bench. Both scopes are old RCA WO-91 tube type scopes, built for TV servicemen. At home, I use an EICO 460 which is similar. These are low-bandwidth scopes, but fine if alll you need them for is audio. Thay can be found cheap.

 

Matthews Guitars

Well-Known Member
Joined
Aug 17, 2019
Messages
7,202
Reaction score
11,999
I have a Tektronix 2246A on one bench and a 2247A on the other. And a 2465B that I need to recap to put in service.

I have a modern Rigol scope that I only use for solid state gear. It isn't rated to handle tube plate voltages.

I'm very seriously thinking of buying a brand new Keysight EDUX1052G which lists for only $752.00. It includes Bode plots, FFT, function generator, and serial protocol analyzer. It's a lot of scope for the money.
 

KraftyBob

Well-Known Member
Joined
Sep 5, 2017
Messages
2,243
Reaction score
3,188
Location
Chicago Suburbs - USA
I have a Leader LBO-508A Analog scope. Perfect for tube amp work. I bought it from a retired TV repairman and it was in great condition - as was all of his stuff (I bought the Sencore from him as well). The only thing I needed to do was clean the pots and replace the caps (then calibrate).

IMG_5993.JPG
 

KraftyBob

Well-Known Member
Joined
Sep 5, 2017
Messages
2,243
Reaction score
3,188
Location
Chicago Suburbs - USA
I realized I missed the second part of your question about the oscilloscope kit. 100MHz is way more than enough bandwidth so no concerns there. It's only a single trace, and while I don't use both on mine all the time, it certainly comes in handy to have dual probes at times.

The big piece missing in my opinion is I don't see a voltage rating. Oscilloscope have a max input voltage rating that it's safe to operate up to. You have to pay attention to how it's spec'd out as well. For example, my scope is rated at 600V DC + ACp-p (since AC rides on top of DC). For amp work you'll want to keep the scope on AC Coupling to remove any DC voltage, and since it's rating is peak-to-peak, the 600v converts to 212vrms - which can easily be exceed when signal tracing. That's where your 10x probe comes into play as that will reduce the voltage the scope sees by 10 times. So the 212vrms is only 21.2vrms at the scope. I hope this makes sense.

I could be wrong by I'd be surprised if that kit was designed to handle the higher voltages found in a tube amp. Also, while it's only $60, I only paid $80 for mine. Yes, it's 1980's technology, and it's physically big, but analog scopes are perfect for this type of work.
 

KraftyBob

Well-Known Member
Joined
Sep 5, 2017
Messages
2,243
Reaction score
3,188
Location
Chicago Suburbs - USA
@KraftyBob
That SENCORE looks to be quite the unit! The scope looks nice also. For fear of getting ill, I won't ask what you paid for them! :rolleyes: Right place at the right time and all that!
Nice Toyz!
Gene
No worries, Gene, happy to share the details. I paid $80 for the oscilloscope and $50 for the Sencore. When he told me $50 I was floored as these are going for $400-$500 online. I asked if he was sure and he said yes, that he was happy his equipment was going to get some use again. He then threw in a B&K frequency Counter, which I told him I didn't need, but he said just take it.

A little off topic, but just this week I picked up a Sencore TC162 Tube tester that's in excellent condition for $75. It's an emission tester but I'm not looking to match tubes - just weed out some of the bad ones. I drove 2 hours for this one and a similar situation - a retired tech looking to unload stuff that's been sitting in his basement for years. All it needed was a little alcohol, q-tips and nylon brush to clean-up the switches. The tube chart looks like it hasn't even been touched. These typically sell for at least twice that, if not more, and often those need a lot of work to get up and running.

IMG_7198.jpg

Apologies to Springfield Scooter for the thread jack...
 

tmingle

Well-Known Member
Joined
Jan 24, 2008
Messages
551
Reaction score
671
Location
Mifflintown, Pa.

I just bought a Siglent 1202 a couple weeks ago but, I haven't spent a lot of time with it yet.
Electronics school was 40 years ago so, I have a lot of re-learning to do before I stick 1 of the probes inside a tube amp!!!
A buddy gifted me an isolation transformer as well.
 

jmp45

Well-Known Member
Joined
May 5, 2016
Messages
3,783
Reaction score
7,424
Location
At Home
I have an Iwatsu SS-5705 40mhz scope, nice but I'm looking into an entry level digital scope. I'm eyeing an OWON SDS1022 20mhz. I have other OWON meters I really like.

Q, is 20mhz sufficient for amp / pedal projects?

I don't imagine I'd use it for anything else off hand.

 

XTRXTR

Well-Known Member
Joined
Feb 14, 2021
Messages
1,115
Reaction score
1,395
Location
Some City, USA
20MHz is well enough and is about the lowest they go these days. You might be able to find an old analog that is even lower but would still be sufficient for an amp.

Key features should be able to read 500 VDC and maybe 1000VAC but you can buy probes with 10x and maybe 20x that will allow you to see high voltages scaled back by 10x or 20x.

If It were me I would also want a FFT function. That will help you determine if you have an oscillation that is out of the hearing range but will definitely reduce life of the tubes or OT.

It would also be nice if it had a spectrum analyzer to determine the odd v even harmonic output, more odd harmonics fatigue the ears fast, you'll have ringing in your ears at lower volumes. But it is the by product of heavy distortion. I don't know if you can get an Oscope with a spectrum analyzer built into it but it would be nice.
 

neikeel

Well-Known Member
Joined
Feb 12, 2014
Messages
7,652
Reaction score
7,724
Hitachi v212 and Gould Advance OS250B and Gould Advance signal generator
Ancient basic kit, much mocked by my son and heir (who still borrows it) - he can buy his own high spec digital scope himself!
 
Last edited:

jmp45

Well-Known Member
Joined
May 5, 2016
Messages
3,783
Reaction score
7,424
Location
At Home
20MHz is well enough and is about the lowest they go these days. You might be able to find an old analog that is even lower but would still be sufficient for an amp.

Key features should be able to read 500 VDC and maybe 1000VAC but you can buy probes with 10x and maybe 20x that will allow you to see high voltages scaled back by 10x or 20x.

If It were me I would also want a FFT function. That will help you determine if you have an oscillation that is out of the hearing range but will definitely reduce life of the tubes or OT.

It would also be nice if it had a spectrum analyzer to determine the odd v even harmonic output, more odd harmonics fatigue the ears fast, you'll have ringing in your ears at lower volumes. But it is the by product of heavy distortion. I don't know if you can get an Oscope with a spectrum analyzer built into it but it would be nice.

Thanks XTR... I chose the Owon, had good luck with their meters. SDS1022, has FFT, no spectrum analyzer, 20mhz, 2 chan. Ch1 300v, Ch2 400v, the x10 probes should be safe. Sale on Amazon, picked it up cheap. I have the Iwatsu on hand if I need it, it works just fine. Just curious about the digital scopes. Cheaper than a decent pedal.

IMG_3726.jpg
 
Last edited:

rockgod212

Active Member
Joined
Mar 20, 2010
Messages
247
Reaction score
50
i think both of mine are protek's, simple scopes.

i am curious what you guys are plugging the amps into for safety- what transformer? how to do guys run your test equipment, does everything (signal gen, scope, amp under test) get plugged into xternal transformer for safety or just the amp? curious on the ground lugs on scopes too, do you keep them or not? ive seen or heard of guys that ditch them. lots of questions, but ive never used my scopes for not having lots of knowledge on hook everything up and not get shocked or destroy the amp.
 

Latest posts



Top