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Oscilloscope probing high voltage valve amps

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diy didi

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Hi.
Its been a while since I have worked on valve gear. I was wondering if someone could clear out something for me. I have a Tektronix 453 Scope, as well as a Rigol DS1102E scope.
Can I probe those 250V-550V DC Valve- plate pins if I set my probes to x10 and the scope to AC coupling????
If not, how would I go about doing so?
 
A decent scope, and a x10 probe is all you need.

But to be fair, there's little reason to ever use a scope on a valve amp.
Why is a valve amp different from a solid-stage amp in that respect? Or are you saying there's little reason to use a scope on any audio amp? :confused:
 
Why is a valve amp different from a solid-stage amp in that respect? Or are you saying there's little reason to use a scope on any audio amp? :confused:

No, just that valve amps are so crude and simple there's rarely ever any need to use a scope - a multimeter (and a wet finger!) is almost always all you need.
 
So long as your scope is rated fpr 4 to 500v should be fine.
Nige has a point theres not a great deal to a valve amp, and you'd only need a high volatge probe on the power supply or anodes.
I've checked bias current on o/p stages by measuring the voltage accross the cathode bias resistors with a meter.
 
Nige has a point theres not a great deal to a valve amp, and you'd only need a high volatge probe on the power supply or anodes.

I've been repairing valve amps professionally for over 40 years, I don't recall ever having needed to use a scope on one? - and I'm the sort of person who would use a scope to repair a torch :D
 
No, just that valve amps are so crude and simple there's rarely ever any need to use a scope - a multimeter (and a wet finger!) is almost always all you need.
Fair enough. But I don't think I would want to put a wet finger on a 300V anode. :rolleyes:
 
You got me on that one, I spent 5 years repairing musical equipment, not all of that time on valve amps, but I had my fair share of them.
And as for using a 'scope to repair a torch, I have one I use a lot that spent some time on the end of my scope, here it is:

Picture 006.jpg

A ubiquitous joule thief, its been used the last 3 years while working on and fabricating industrial machinery, so it looks a little worse for wear now.
 
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Never worked on a valve amp but have worked on plenty that used vacuum tubes. :)

Ron
 
Wet finger, bzz bzz.
The type of bzz produced can tell you a lot about the fault.
 
Oh man, my reply went away. :) A victim of the big crash I guess.

Anyway, since Americans began calling them tubes before my time I have no clue. Personally I think valve is more fitting and likely why the inventor called them valves. Makes more sense to me.

Ron
 
For further info

They were called valves by the inventor ( as Nigel so rightly pointed out). However!! That was just the diode ( Valve... makes sense )... The triode, pentode etc... Were always called vacuum tubes... As the man who invented them called them.. I think he was Austrian or something..

Its called CRT not CRV...
 
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The word tube is used in The Netherlands too. ( Buis ) ( Buizenversterker ) Tube, tube amplifier
 
However, don't set your 453 to 5mv/DIV and than attach your probe to the plate of the output amp. The charging of the input coupling capacitor (sorry, blocking cap for your limeys) have been known to blow FET front ends. The proper procedure for Tektronix scopes is to set the input coupling switch to GND (ground), connect the probe and then swich the coupling switch to AC. On Tek scopes, this will precharge the coupling cap so that when you switch to AC, there's no major spike to be fed to the input amp. Just connect and disconnect probes with the coupling switch set to GND and you won't go wrong.
 
As I'm sure you're aware, the 'wet finger' is for grids only :D
Actually I'm not, never having worked at repairing "valve" amps (although I did build some stereo tube equipment kits back in the 60's). But I think I would be quite wary of poking around a tube circuit with a wet finger in case I miscounted the tube terminal numbers. ;)

Regarding tube versus value, vacuum tube is a more general term as not all vacuum tubes are necessarily valves.
 
Actually I'm not, never having worked at repairing "valve" amps (although I did build some stereo tube equipment kits back in the 60's). But I think I would be quite wary of poking around a tube circuit with a wet finger in case I miscounted the tube terminal numbers. ;)

For the normal double triodes, Anode, Grid, Cathode, Heater, Heater, Anode, Grid, Cathode, Heater CT - counting from pin 1 :D

I can still remember it :p

Regarding tube versus value, vacuum tube is a more general term as not all vacuum tubes are necessarily valves.

Not here (or most places), vacuum tube is never used.
 
My boss when I was serving my time allways called them 'bottles'.
 
Does it really matter whether they're called tubes or valves; hoods or bonnets; trucks or lorrys; windshields or windscreens; grounding or earthing; gasoline or petrol; or whether we end words like theater differently as in theatre or spell them differently such as color vs. colour or aluminum vs. aluminium or tires vs. tyres? At least we can all understand each other and I'm thankful for that!
 
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