Oscilloscope Basics for Vacuum Tube Audio Testing
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- Опубликовано: 2 янв 2022
- This video covers the basics of using a scope on Tube Audio gear. I cover the various types of scopes, how the controls and probes work, some safety concerns, and how to use a signal generator to do a quick test of a tube amp's power output.
Here are two very good videos going into further detail on ground isolation of the device under test and how not to blow stuff up. NEVER try to isolate or float the scope, always float the device you are testing!
• EEVblog #279 - How NOT...
• Isolation Transformers...
I plan to go into more detail on using a scope in the Nobsound 6P1 series, but I wanted to do a stand alone basics video for beginners before we get started.
Again, tube audio gear has lethal voltages inside them, even after they have been powered off. DO NOT OPEN THEM UP unless you 100% understand all the safety protocols needed to work on them safely!! 
Хобби
Excellent video Stephe.Very informative
Awesome video! Easy to watch and understand. Thanks for sharing!
Just go my first scope (siglent 1104E-X) for home. I'm used one in work for years but this is the first for my home bench. Having built a couple of guitar tube amps for gigging it will be nice to finally see whats going on in the amp, stage to stage to output, and how the signal changes over different gain/volume settings. So vids like this help to give confidence on what I'm looking at and why its happening. Thank you for your efforts putting these videos out! I definatly get something out of them.
Great timing! I just ordered one yesterday. Along with a signal generator, variac and isolation transformer.
Nice!
I just got the digital 2 in1 Oscilloscope and Generator and couldn't find how to connect the signal generator. This is the first video on youtube that I has looked since yesterday that saves my time to look around, right on time :) Thank you so much to be a mentor/instructor for DIY. At 14:30, I saw you pulled out the clip and I tried but didn't come out. I was afraid to break it....lol......but did tried again and it worked. Looking forward to see more measurement videos.
Glad I could help
You have just brought me to the next level. Luckily I have the same 2235 scope and a very similar Leader audio generator so that really helped. Thank you so much for helping me tie it all together finally!
Cool! It's so much fun running audio gear on a scope and being able to see the output!
Good one...really enjoyed it. Thanks for the detail.
Glad it was helpful!
Thank you. Oscilloscopes have always been 'black boxes' for me, so this helps a lot
Great video! Thanks for the information
Glad it was helpful!
Very informative. Thanks.
This is great advice and if you are unable to use an isolation transformer another option is a differential probe on the scope.
Great tip!
Skunkie Designs, you are talking about the old power panels. The new ones do not join neutral and ground. But I just picked up (3) Triad N-92MD 500VA, and (1) N-90MD 250VA isolation transformers for hospitals, FREE! About $700 worth of transformers between all four!
I don't think the US wiring has changed. hyperphysics.phy-astr.gsu.edu/hbase/electric/hsehld.html
I prefer the analog scope too. B and k made some nice scopes too. the 1400 series 1476 etc. The tektronix 5100 series nice too but may need some work by now . I have the bk 1476 and happy with that. Used to do TV repair.
thanks for the videos, Newbie here, can you tell me how you solder the two wires (signal) together to put into your amplifier. thank you
cool stuff
A lady who understands residential line power service!!!
Thank you, I learned a lot. Would to hear your opinion on how the headphone jack perform on the 6P1?
Oh we are gonna dive DEEP into this 6P1 soon!
It’s definitely nice to view analog waveform on an old analog scope for me it is easier on the eye. However the features including automatic readings of frequency and voltage and FFT spectrum analysers on even a low cost digital scope really take the work of it. Regards distortion if you can see it on the sine wave it’s really really bad but I guess it will show gross distortion.
Yeah, if you can see it on a scope, it's really bad :P
I could be wrong on this but I think I remember a figure of 20% harmonic distortion before it’s visible to the human eye etc on a scope
Very good instruction. Thank you! One question. Do you connect the isolation transformer to the Oscilloscope or the DUT?
DUT
This was fun because I have the same scope... almost, 2235A (it has one extra knob for backlighting grid). I was wondering how you hooked the signal generator up to the scope and the amp. You mentioned connecting it to the scope and said something about RCA plug to FG (I presume that was the amp input), but are you running them parallel out of one FG output or from 2 different channels?
I simply connect the signal gen output to the amp and connect one probe also to the signal gen output. Then I have 2 dummy loads connected to the amp outputs and connect a probe from the other channel of the scope across one of the dummy load resistors.
Could you advise where and how you hook up the isolation transformer please?
Plug the isolation transformer into the wall and the device under test into it.
@skunkie What kind of scope probes are those? Make/model?
Ghad I have no idea, I bought them 20 years ago!
Thank you for this video! Just bought a digital oscilloscope and tested my Type 45 triode amp. Worked out fine but what caught me off guard was that at higher frequencies I could faintly hear the signal from the Lundahl output transformers! Started panicking a little but after googling discovered that singing OPT on a dummy load are not unusual. Can you make a video how to detect and hunt down oscillations and other issues best detected with a oscilloscope? My amp measured really nice up to full power over the whole frequency range (20-20khz) but I was wondering how I could see parasitic oscillation at higher frequencies or is it ok if 20khz look exactly like the input? I have a very small phase difference between input and output, is this normal? Thanks again for your valuable videos!! Best F
Looking at the square wave is a good indicator of oscillation issues. And yeah, depending on the amp design, not unusual to see a little phase shift.
@@SkunkieDesignsElectronics thank you! I spend more time with the oscilloscope yesterday and I think I nailed the issue! I was hearing a high frequency hiss as soon as the amplifier warmed up, redid all solder points multiple times and also switched solder from 95/5 Ag to the spool of 60/40 I had left just to eliminate any cold joints that might be. I had the scope at the ready when it happened again and measured the amp on the spot, well nothing to be seen on the scope, reconnect and it hisses!! Then it dawned on me to look at the input side and lo and behold, the cheap Bluetooth adapter I added in the chain so my wife and daughter can connect the phones was making crazy spikes in the signal path and my passive channel switcher fed it to the other channels. What a relief! I reworked the passive switcher because the scope showed little spikes even with the BT gone and now I get a flat line just connecting my dac to input and the scope on the output! Oh I love this thing, why didn't I get one earlier?! Sorry for the long story but I'm so glad your videos encouraged me not only to rework my amp but also to poke around in it with the Oscilloscope ! Thanks again
Great video, I'm just learning this stuff and a little confused on how you came up with 1.9w. isn't 11Vpp x .707=7.7rms?
It was 9Vpp on 110V is 3.18V RMS 11Vpp is 3.89RMS. You are doing the calculation for voltage peak (Vpk), not peak to peak (Vpp).
@@SkunkieDesignsElectronics your right, thanks for clarifying, still learning. I really appreciate you taking time to teach.
So in short, can my oscilloscope still be plugged into my house ground? Or should I float my oscilloscope ground? Because you still need to reference your DUT right? Hard to find the info out there on this
Do NOT float the ground of the scope!
Can you link this isolation transformer you use? Thanks!
This one is $49 on Amazon
smile.amazon.com/Jameco-Valuepro-ITR300-Transformer-Isolation/dp/B00B886DGS/
@@SkunkieDesignsElectronics This one has 2 prongs inputs, do I use it with those 3 prong to 2 prong adapters?
@@bernardosilva7306 Yes, or do like I did and dedicate a IEC power cord for this use and remove the ground pin on the end that plugs into the isolation transformer.
@@SkunkieDesignsElectronics Good, that's the one i ordered.
@@SkunkieDesignsElectronics Awesome, thanks a lot!!! :)