Oscope?

[JustMike]

I have a Solid State Marshall 5212 on my bench an it has a couple of problems. 1- the owner says it shuts down after a few minutes of playing at gig volume and 2- there is no gain/distortion on the gain/distortion channel. All of the controls work except for the Boost knob.


 I resoldered the entire board and it doesn't cut out on me, but I'm not playing at gig volume. I'm going to run it into an attenuator and crank it up.


 As far as the boost channel not boosting, it seems like a scope is the best way to troubleshoot this but I haven't used one since electronics class back in the '70's! I noticed that incredibly cheap ones can be found on Amazon and I'm just tracing audio so maybe it's not a bad idea? I can get a 200mhz scope and a signal generator for less than a hunnert bucks!
 
https://www.amazon.com/ETEPON-Oscilloscope-BNC-Clip-Assembled-Finished/dp/B081Q2KDJT/ref=sr_1_14?dchild=1&keywords=oscilloscope&qid=1613488283&sr=8-14


 Thoughts?

[glass54]

Couple questions JustMike,
Will you use an oscilloscope again? Are you going to play with/experiment on amps? And a third question (just cause I can ) do you have a reliable multimeter that does rms voltage.
I would be lost without an oscilloscope!! You can view waveforms or actual presence of a signal stating from Input Jack to Speaker Output terminals. You can use various frequencies and roughly determine Bandwidth of amp. For example you can go to input jack of recent Fender amp, set your oscillator at a level as shown on Schematics and trace it though to the output (1kHz test tone).
I would recommend a 100MHz 2 Channel oscilloscope (50MHz is fine) and it will do all you will ever need with Tube amps. A bonus with the modern SS compact oscilloscopes, you can set the display to read Volts (rms, Pk, etc) and display Frequency on the side section of display. Heaps of other parameters can be displayed. So you end up with a very reasonable AC multimeter and a freq counter
Unlike you 1970s CRO, Push the "Auto" and "measure" buttons and you have an almost instant result ie display of signal.
I am attaching something from Amazon that would be a little more money but well spent. As I don't know you location, I cant guide who to buy from BUT if you are in the USA, maybe Sluckey, HotBluePlates, PRR or others can steer you in the right direction ie Models and US dollars for good value.

https://www.amazon.com/Hantek-DSO5102P-Oscilloscope-Oszilloskope-Channels/dp/B071P97RLC/ref=psdc_393269011_t3_B01EJLZYN8

My go to Oscilloscope these days is (Not because its the best instrument in the world but very useful)
https://www.globalmediapro.com/dp/A26DH2/Rigol-DS1102CA-Digital-Oscilloscope-100MHz/
Another useful feature (from specifications for my oscilloscope) "Maximum Input Voltage 300 V (DC + AC peak)" ie safe with high-ish volts and obviously you have to remember to use probes correctly.
Trust this helps
Kind regards
Mirek

[thetragichero]

having the scope would've probably prevented you from having to touch up all the solder joints. i'm lazy and prefer diagnostic tools to figure out where the signal dies. second most useful tool for working on solid state amps (all amps) to a lightbulb limiter (maybe not with newer, smarter amps like this but older solid state amps will absolutely ruin your wallet burning out parts if you haven't fixed absolutely everything in the output section)

on the plus side, the old 'boat anchor' scopes can be had for little to nothing these days if you look around facebook marketplace/craigslist/local ham radio clubs/somebody's attic or garage (my tek 453 spent about 20 years in my father's attic before i scooped it up). can generally be had for less than a good quality multimeter. ebay if you're on a time constraint

[PRR]

I can 99% be quite happy with a 200kHz 'scope rather than a 100MHz speedster.