Simple test method tube guitar audio amplifier using Oscilloscope Dummy Load and Audio generator
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- Опубликовано: 18 окт 2024
- This procedure has been on the request list for years.
I just finally got around to doing it.
Tube amp bench test method. Example: Fender Super Reverb guitar amp.
You do not need to be a test equipment expert to perform this test.
You also do not need an expensive oscilloscope. Many 10Mhz and under scopes can be purchased for under $100. Examples: Heathkit, Leader, Iwatsu, Hitachi, B&K.
Audio dummy loads can be purchased or construct your own using a resistor on a 1/4" plug.
So watch the procedure, let me know if you have questions. I also have a quick reference diagram .jpg available. E-mail me for that. I am doing my best to share this knowledge.
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I learn more here by accident than I did in school by purpose!
I agree, some years ago I was at home recovering an injured back, I stumbled across Terrys' channel and was absorbed instantly. He's got a way to make the beginner feel 'Hey, I can do this too' !
Thanx Terry👍
And here I thought the hum was caused by not knowing the words to the song!
Thanks Terry, for all you've done, for all you are doing, and for all you will contunue to do.
Great topic!! BTW I just listened to D-Lab on a 1937 GE f81 with an newly built am transmitter. All the radios were playing D-LAB at the same time. I liked it... but my wife was chagrined LOL.
Thank you, Terry! BTW, it's good to see The Cobbler on the bench, being very, very quiet!
Glad you reminded us about the Earth(ground) loop and how remedy it !
I have the device under test (amp in this case) on an isolation transformer(w/ground isolation), for the reasons you mentioned. I think it better to have the signal generator operate as designed (in my case the HP3325), has an equipment ground. I do sometimes breakout the old Heathkit audio generator though and it is not grounded.
Great advice re ground loops, recently had this exact issue
Nice one Terry..Lots more learned..Thanks for sharing..Ed..UK..😀
One of the most useful videos for amp repair. Thanks D-labs Electronics
Very good information. I’ll have to watch this a few more times. It seems like everyone has different takes on what should be powered through an isolation transformer. Some say the scope should always be isolated from ground, and others say never the scope and always the amp. Now I must ponder the function generator as well. I’m coming up with more questions, but hopefully simultaneously getting smarter 🤓😎
Hey Terry. Thanks as always for sharing. Learned so much from you over the years.
I see the Cobbler lurking in the corner so take care!
Yep, Cobblers always looking for a way in
Nice information sir thanks for sharing video.
Very well explained for us newbies in the hobby ! Thank you Sir !!!
This is great stuff. Thank you! I don't have an audio generator - Can you use your cell phone as an audio generator (with the right app)?
Also, could you use white/brown/pink noise to test the EQ?
Well done, as always 😀👏
Killer, thank you Terry! I get the dummy load but would you consider illustrating a layout with wiring, jacks, resistor specs, etc. Thanks again.
e-mail me, I have a diagram
@@d-labelectronics dummy load diagram request
thanks 👍
I'm wondering about a few things here. I have an old hp 200cd signal generator that I salvaged and rebuilt. The chassis is earthed by the green wire in the line cord. The actual circuit is floating at -135V above ground on the negative rail. I'm assuming a lot of older signal generators are designed this way so the ground loop is not an issue. Any thoughts?
Hi Terry, it's also good to use a ground buster on the power cord of the scope too, isn't it?
To check an unknown tone generator without disassembling it, do you just continuity check the case/output terminals to make sure there’s no continuity between the output terminals and the Earth or ground prongs of the mains plug?
Nice clean output. Does it stay that way, up to full power output of the amp? Most of you internet repair guys seldom show the output at full power.
As the amp is cranked up, you will see flat topping of the sinewave
I normally do not test a customers amp that way
@@d-labelectronics if you don't run the amp up to its clipping point you'll never know if that 50 watt at 8 ohms amp is putting out full power. Instead of 20 volts and you have only run it up to 10 or 12 volts, that's a big difference between actual and spec. Just saying! Not to over criticize your work however. Keep up the videos.
Roger that man, I understand
Simple, straight forward demonstrated procedure! Enjoyed watching, thanks.
I just read somewhere that one has to be careful sometimes if one side of the speaker out is grounded or also can create problems. They suggested first ohming out (with all turned off) the two speaker leads to chassis ground?
Also how do you check if signal generator is not grounded?
What size resistor should I use for the dummy load?
Wouldn't it be better to run the amp from an isolated supply ?? Cheers Matey
Still have a question,
Does your scope have to be isolated from ground to do save measurements??
And THX for all your good advice 👍🎸🎶
Hello, I have a 3 prong eliminator, that I leave on my scope. So, the AC ground lug is not connected.
how do the waveforms behave if running the scope through a high gain amp with alotta distortion? I'm trying to track down and minimize noise in my preamp
But Terry, what about the oscilating tv probe ground being a chassis ground? Do I need an isolation transformer?
It has a ground isolator on the power plug, no worries, e-mail me, I can send you a pic of the gadget
So you lift the earth ground from the osciloscope?
Yes, Best to eliminate multi grounds
So, if I use my dummy load, where do I pull the signal from out of the amp for the scope?
You simply connect your scope across the speaker jack. The load & scope are connected in parallel. Make sure the ground lead of your scope is connected to chassis