Hey - clever people.
What's the best way to get a scope to be able to interrogate my old pre amp further to reduce hum, conventional means have not got to the bottom of it ...yet.
Many years ago I used to be a senior lecturer in engineering, and of course used these with load cells etc regularly, but many years later I doubt I could even find the power switch :-(
I only want this for my preamp hospital treatment, however I prefer using old stuff that was well built, rather than more landfill 2.4" LCD Display Fully Welded Assembled Digital Oscilloscope With Probe Tool UK | eBay
However it of course is a case of $=results too
ideas?
What's the best way to get a scope to be able to interrogate my old pre amp further to reduce hum, conventional means have not got to the bottom of it ...yet.
Many years ago I used to be a senior lecturer in engineering, and of course used these with load cells etc regularly, but many years later I doubt I could even find the power switch :-(
I only want this for my preamp hospital treatment, however I prefer using old stuff that was well built, rather than more landfill 2.4" LCD Display Fully Welded Assembled Digital Oscilloscope With Probe Tool UK | eBay
However it of course is a case of $=results too
ideas?
Check out Soundcard Scope - Soundcard Scope you can use it with just your PC's SC though an exterior decent SC or audio interface is better. It has a scope, low THD sig gen, THD meter and FFT . All you need is a 10:1 attenuator, EG a 10k pot and 1k fixed resistor as well as a test lead, EG a bit of coax or screened cable, screen to ground, positive inner with a 630v 100n cap on a stick or croc clip.
Andy.
Andy.
The nature of the hum tells you a lot before you even start. For example is it 50 or 60 Hz pure and deep in tone or is it harsher and more raspy at 100 or 120Hz, the latter indicating power supply noise from the rectified AC.
Amazing that you can by a new "scope" for less than £20 but to be fair they are little more than toys although the frequencies involved here are well within its reach. You you need to be very very careful looking at high voltage lines with something like that and possibly rig up an external protection circuit (couple of Zeners) to protect the scope input.
Amazing that you can by a new "scope" for less than £20 but to be fair they are little more than toys although the frequencies involved here are well within its reach. You you need to be very very careful looking at high voltage lines with something like that and possibly rig up an external protection circuit (couple of Zeners) to protect the scope input.
Get yourself a real oscilloscope, best is a tec scope but a very functional one
v´can be bouth for EUR52 :
Philips Storage Oscilloscope PM3315, 125 MHz, 2 tastkopfe, Cover, Power Cord | eBay
v´can be bouth for EUR52 :
Philips Storage Oscilloscope PM3315, 125 MHz, 2 tastkopfe, Cover, Power Cord | eBay
I think the problem lies in sensitivity of the scope esp the low cost one as you will need to detect hum as low as 1mV. Most analog scope is 5mV-5V scale and more for low cost one. So I believe you can step up the hum level with a transformer step up probe to be detected?
OTL designed by Tim Mellow with 4 6C33C?
I use it on OTL amp, hum level is already very low due to high capacitance of PSU but still a little visible on the scope with step up probe.
OTL designed by Tim Mellow with 4 6C33C?
I use it on OTL amp, hum level is already very low due to high capacitance of PSU but still a little visible on the scope with step up probe.
I only want this for my preamp hospital treatment, however I prefer using old stuff that was well built, rather than more landfill 2.4" LCD Display Fully Welded Assembled Digital Oscilloscope With Probe Tool UK | eBay
However it of course is a case of $=results too
ideas?
And by sheer chance I came across this today:
UK Vintage Radio Repair and Restoration Discussion Forum
Once I knew an older person who repaired tube radios and amps by injecting hum at different locations of the circuit with a special screwdriver (the electrician version with the lamp inside). He had much knowledge, no Oh-silly-scope needed. The same with doctors. Modern ones need for everything an MRT and CT, older ones can diagnose with just two fingers, eyes and experience.
Over ~60 years ago, I didn't have a scope. So when amp or RX developed hum, first thing I did was dig up an electrolytic cap, test it by charging and discharging (spark + bang) and when OK, connect it in parallel with the 1st cap after the rectifier (taking into account its maximum current of course). When the hum became less or disappeared, case solved. When that didn't happen, investigate eventual ground loops: disconnect the humming equipment from every other equipment, connect a headphone to the output and listen. No hum, case solved (ground loop issue). Usually this procedure was enough, even when tubes like E443H were involved.
+1
These days the TEK2215 can be had for not that much money. I still have the one I bought used when I was in high school.
If you're looking to spend a bit more, but not overload the credit card, the educational options of the Keysight DSOX1100/1200 series provide a lot of scope for the money.
I wouldn't bother with the USB scopes, especially not for tube work. That said, a sound card interface and some software will get you quite far sometimes. Or if you want actual knobs to turn, something like the HP 3581 frequency-selective voltmeter can be excellent for debugging hum issues.
Tom
That was quite a good Oscilloscope- some 40 years ago.
We used those on the workplace where I learned all about electronics.
That is all a long time ago- this is such an old, ridden down the road kind of gear with thousands of work hours load on it. The ray tube may be outworn or the beam might be bleached out, don't expect this to be like new.
The asians bomb this and those alike into the ground.
For a little more cash, you wil receive a new, digital one which will work in 20 years from now. If this retired and worn out scope will make it through another three years, you can be lucky.
I would never pay a penny for such an unknown history gear that old from the stone age of measurement. Not in my whole life, the times, they are a changing. You don't want to ride a 40 year old car, never restored, as daily driver. Go, get a new one for nearly the same prize.
Oh, my goodness! This is a serviceman oscilloscope, the screen so small you have problems to see anything. Its hillarious what kind of oldtimers are being advised for buying here. I had one like this some 40 years ago, it was more a toy than a serious electronic measuring device. Never ever. After that, had Hameg analog/ digital scope. That was standard at that time, it was able to measure and store signals. Thats what every digital could do today for a fraction of money.
Worked long to be able to purchase this, but it was quality build.
What, if this TEK from stone age will have a defect? Did you have looked inside those gears? Nobody can repair those, because the special parts are long obsolete. And if someone manage to do so, it would cost more than the gear is worth. A no brainer not to buy such things. And of course, everyone is in pristine condition. Until the moment you open the parcel and see the crap.
Its an illusion, those have been stored in a room and never been used. And even if so, the parts are all overaged and prone to fail instantly.
In my experience a scope is not much use for low level hum tracking, as has been mentioned by a number of other members.
You may have better results using a sound card to record the DC at various points in the circuit (with appropriate blocking caps) and do an fft of it to see what frequencies you have noise, and their levels.
An instrumentation amplifier in between to boost the levels may also help.
Tony.
You may have better results using a sound card to record the DC at various points in the circuit (with appropriate blocking caps) and do an fft of it to see what frequencies you have noise, and their levels.
An instrumentation amplifier in between to boost the levels may also help.
Tony.
Member
Joined 2009
Paid Member
I had a really weird hum issue caused by a parasitic oscillation long ago. An emitter follower that controlled a mute relay oscillated. It worked on an unstabilized supply with very limited filter capacitance so the relay would turn off quickly at power down. As a result the oscillation got modulated by mains hum. The signal path unintendedly detected the RF signal, and that caused the hum. It would have been easy to find this if I had had an oscilloscope with a bandwidth large enough to see the oscillation back then.
More normal hum issues are probably easier to find with something that can do a narrowband measurement at the hum frequency. Your ears, for example, using a headphone and a headphone amplifier with a very limited maximum power, so you don't become deaf when something goes wrong. A portable recording device is also very handy, so you can more easily compare the hum before and after some change.
More normal hum issues are probably easier to find with something that can do a narrowband measurement at the hum frequency. Your ears, for example, using a headphone and a headphone amplifier with a very limited maximum power, so you don't become deaf when something goes wrong. A portable recording device is also very handy, so you can more easily compare the hum before and after some change.
Hey - clever people.
What's the best way to get a scope to be able to interrogate my old pre amp further to reduce hum, conventional means have not got to the bottom of it ...yet.
Many years ago I used to be a senior lecturer in engineering, and of course used these with load cells etc regularly, but many years later I doubt I could even find the power switch :-(
I only want this for my preamp hospital treatment, however I prefer using old stuff that was well built, rather than more landfill 2.4" LCD Display Fully Welded Assembled Digital Oscilloscope With Probe Tool UK | eBay
However it of course is a case of $=results too
ideas?
I have used one of these. And it works just fine. The screen is
about as large as some phones, which seems to be acceptable for many.
Looking at the price ( USD50) if that holds, it cannot be beaten.
As for the philips scope, if it has been working 40 years, there is no reason
to think it won't last a few more years.
I'd encourage you get something - anything. As a note of encouragement, I had a wicked hum in a linestage I was breadboarding (2C22>#76 tubes). I hooked up a free to me old Hickok oscilloscope and there it was-clear as day!
I subbed in a choke in place of the 270ohm resistor and.....See pics below.
Unit sounds wonderful and I'm working on a final build.
I subbed in a choke in place of the 270ohm resistor and.....See pics below.
Unit sounds wonderful and I'm working on a final build.
