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 tube osciloscopes: which one is right?

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Tubetechie105



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PostSubject: tube osciloscopes: which one is right?   Sat Oct 16, 2010 4:33 pm

well once again I am hunting a transistor-less piece of test equipment but I am a tad confused:
how much bandwidth does a radio/HF ham operator/Test equipment collector need?
what would you, the folks at ARF, recommend in the way of tube only scopes? a tek 585A? a tek 545?
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Dave Doughty



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PostSubject: Re: tube osciloscopes: which one is right?   Sat Oct 16, 2010 6:15 pm

Depends on what kind of circuits you need to test. A 20 mHz, dual trace, triggered scope covers 95% of most requirements surrounding vintage electronics. I know that you have a certain fascination with tube test equipment but a more modern solid state scope makes a lot more sense, in my opinion. I was trained using tube scopes but when they became smaller, more stable and with better performance due to solid state technology, they became much more useful to me for everyday troubleshooting.

Dave


Last edited by Dave Doughty on Sun Oct 17, 2010 8:10 am; edited 1 time in total
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burnt fingers



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PostSubject: Re: tube osciloscopes: which one is right?   Sun Oct 17, 2010 6:41 am

The problem with a 585A or similar is not only the power consumption but the cost of replacement tubes such as 6DJ8/6922 and nuvistors.

Altho I have a lot of restored HP, GR, Boonton, etc tube test equipment I tossed the 585A some years ago in favor of SS. My current favorite for compactness, features and reliability is a 70's 453.

The 585A was at the point that it needed more attention than the gear it was supposed to be testing.

Carl
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pixellany



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PostSubject: Re: tube osciloscopes: which one is right?   Sun Oct 17, 2010 7:12 am

burnt fingers wrote:

The 585A was at the point that it needed more attention than the gear it was supposed to be testing.

Carl
And then there is the 545---complete with the discrete delay line with about 50 adjustments. Working in the calibration lab (circa 1968), I could easily blow 3 hours setting up one of these beasts.
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Tube Radio



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PostSubject: Re: tube osciloscopes: which one is right?   Sun Oct 17, 2010 8:30 am

Yes Tektronix scopes will be the better choice far as vacuum tube scopes go. I have two (503 & 564) that need to be restored.

It has been my experience that sometimes the old scopes will display some analog signals better than the newer scopes will. I have had cases where my newer dual channel 20 MHz scope would not lock on to a signal right, yet an older DuMont scope displayed it perfectly.

Now if you desire portability then the newer scopes are the way to go.
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Steve Johnson

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PostSubject: Re: tube osciloscopes: which one is right?   Sun Oct 17, 2010 8:51 am

Vintage tube scopes are nice to collect but for the bench I would choose a solid state scope. Stability, lesser maintenance, and space make these a better choice for me.

I have two SS scopes currently on the bench. A Tek 465 (100 MHz) with DMM and a 475 (150 MHz). Purchased them both last month. Good Tek probes can cost more than a scope. I spent more time finding a good deal on 2 Tek probes than it took me to find two good scopes. I got two NOS 150 MHz Tek 10X probes with all the attachments for $50. I thought that was a good deal. One of the scopes I purchased came with a good Tek probe.
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Tube Radio



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PostSubject: Re: tube osciloscopes: which one is right?   Sun Oct 17, 2010 12:28 pm

Personally I prefer to use an old vacuum tube oscilloscope when working on anything such as an amplifier that has the potential to put out damaging voltages as the older scopes can handle that voltage better.

It's all up to personal preference though.
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radiotechnician



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PostSubject: Re: tube osciloscopes: which one is right?   Sun Oct 17, 2010 1:25 pm


If you find a DC tube scope that works properly like an Eico 460 dont worry
about a triggered scope.The issue is how much space you want to give up
and that points to 3" scopes. Those scopes are not sensitive but will handle a demodulator probe well. A low capacity X10 probe to stick on the plates of IF amplifier stages would be a good addition. TV bench techs always had a scope burning because they were a moneymaker.
for fast chassis throughput.

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burnt fingers



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PostSubject: Re: tube osciloscopes: which one is right?   Sun Oct 17, 2010 1:37 pm

I use tube scopes for modulation monitors for up to 1500W of AM as I dont want to chance RF running around in SS. These are stripped of functionality beyond the simple vertical and horizontal basics. One is a 1946 5" DuMont, another some 60's 5" Fairchild and an early HP.
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Tube Radio



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PostSubject: Re: tube osciloscopes: which one is right?   Sun Oct 17, 2010 1:53 pm

Burnt Fingers, What model is that DuMont 5" scope?
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dberman51



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PostSubject: Re: tube osciloscopes: which one is right?   Sun Oct 17, 2010 7:08 pm

I agree with the previous posts recommending an SS scope -- my favorite scope back in college was a Tek 547 (50 MHz) but when I got into industry we used 453s and then 465s. The 465 easily became my favorite scope and that is what I have now. I would have no fears of exposing it to RF or high voltages within its specs. I think the max voltage specs of the 547/1A1 and 465 are the same.

-David
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burnt fingers



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PostSubject: Re: tube osciloscopes: which one is right?   Sun Oct 17, 2010 7:25 pm

Tube Radio wrote:
Burnt Fingers, What model is that DuMont 5" scope?

Its a Type 208

I also have a 465/DMM that works well but the go to scope is usually the 453 as I find it syncs much easier plus I used one at work for almost 10 years, they couldnt pry me away from it.

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pixellany



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PostSubject: Re: tube osciloscopes: which one is right?   Mon Oct 18, 2010 10:36 am

Tube Radio wrote:
.....potential to put out damaging voltages as the older scopes can handle that voltage better.
I'm not sure why that would be true.....I would think that any professional test equipment could handle the voltages it is rated for---and that the ratings would encompass most equipment likely to be tested.
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Dave Doughty



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PostSubject: Re: tube osciloscopes: which one is right?   Mon Oct 18, 2010 12:51 pm

My daily driver Hameg 20 mhz solid state scope has been checking the waveforums of many tube circuits including looking at power supply ripple for at least 15 years without a failure. If someone is nervous about checking a high voltage waveform (or a low voltage waveform riding on a high DC voltage potential), build a high impedance pad to reduce the input level to the scope.

Dave
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Tube Radio



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PostSubject: Re: tube osciloscopes: which one is right?   Mon Oct 18, 2010 3:09 pm

I guess the reason I say that is a lot of newer scopes are made with solid state circuits in mind which operate at lower voltages. I'd much rather trust a scope with an input coupling cap rated at 1,600 volts for HV measurements versus a newer solid state scope, besides what happens if someone is measuring the ripple of a hv dc power supply and they accidentally switch the solid state scope to dc coupling while on a lower v/div range. Poof there goes some transistors or integrated circuits up in smoke and if it is certain models of tektronix scopes it may be a proprietary maybe unobtanium chip that blows. Also some of the older scopes just seem to lock onto certain signals better than some of the newer scopes do.

Sure one can build a high impedance pad, but what if the AC signal is very low. A high impedance pad may make the ac signal not show on the scope.
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smeezekitty

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PostSubject: Re: tube osciloscopes: which one is right?   Mon Oct 18, 2010 8:56 pm

Tube Radio wrote:
I guess the reason I say that is a lot of newer scopes are made with solid state circuits in mind which operate at lower voltages. I'd much rather trust a scope with an input coupling cap rated at 1,600 volts for HV measurements versus a newer solid state scope, besides what happens if someone is measuring the ripple of a hv dc power supply and they accidentally switch the solid state scope to dc coupling while on a lower v/div range. Poof there goes some transistors or integrated circuits up in smoke and if it is certain models of tektronix scopes it may be a proprietary maybe unobtanium chip that blows. Also some of the older scopes just seem to lock onto certain signals better than some of the newer scopes do.

Sure one can build a high impedance pad, but what if the AC signal is very low. A high impedance pad may make the ac signal not show on the scope.
They are usually more resilient then this.
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Tube Radio



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PostSubject: Re: tube osciloscopes: which one is right?   Mon Oct 18, 2010 9:30 pm

That may be true, but if you're on a low volts/div range and you're measuring for instance an ac signal riding on 1,600 Vdc and you accidentally switch to dc coupling it could quite possibly damage the scope or at the least damage the input over-voltage protection device if the scope has one.
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Sal Brisindi



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PostSubject: Re: tube osciloscopes: which one is right?   Mon Oct 18, 2010 10:07 pm

I have a couple of Tek 453's, great scope and super sharp razor thin trace!

I've mentioned this before on the "old" forum. The company I work for used a sledge hammer on every 453 and 454 scope to scrap them years ago. It broke my heart...

Sal
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Dave Doughty



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PostSubject: Re: tube osciloscopes: which one is right?   Tue Oct 19, 2010 4:49 am

Tube Radio wrote:
Sure one can build a high impedance pad, but what if the AC signal is very low. A high impedance pad may make the ac signal not show on the scope.

In that case I would insert a high voltage coupling cap (with a suitable bleeder resistor) in place of the pad. I just can't see myself trying use any scope with circuits carrying super-high voltages without taking precautionary measures.

Dave
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dberman51



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PostSubject: Re: tube osciloscopes: which one is right?   Tue Oct 19, 2010 12:25 pm

Tube Radio wrote:
That may be true, but if you're on a low volts/div range and you're measuring for instance an ac signal riding on 1,600 Vdc and you accidentally switch to dc coupling it could quite possibly damage the scope or at the least damage the input over-voltage protection device if the scope has one.
You will blow both types of scopes. According to the book "Oscilloscope Circuit Design" which I have packed away here somewhere, published by Tektronix, the max DC voltage rating of an oscilloscope is determined by the DC rating of the input blocking capacitor. I just checked the schematic for the 465B and this capacitor is rated at 600V, as I suspected. I seem to recall that the input capacitor for the 1A1 plug-in for the 547 and 545 is also rated at 600V.

The entire Tektronix line, including the 465 and 453 models, is intended for research/industrial/commercial environments which are far more demanding than an old radio! When I was in broadcasting, B+ meant 16kV and plate current meant 4.4 Amps, and yes, we used solid-state scopes.

-David
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burnt fingers



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PostSubject: Re: tube osciloscopes: which one is right?   Tue Oct 19, 2010 7:52 pm

But a sudden parasitic or other unexpected oscillation or event in a transmitter is less likely to take out a tube input stage while it could domino thru a whole bunch of SS in a couple of microseconds.

Carl
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dberman51



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PostSubject: Re: tube osciloscopes: which one is right?   Tue Oct 19, 2010 10:00 pm

Tek scopes seem to be able to stand up to a lot. Can't say we ever saw any parasitic oscillations though -- these were real good transmitters, and if they ever oscillated where they shouldn't have the FCC would have had something to say....

-David
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MM



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PostSubject: Re: tube osciloscopes: which one is right?   Fri Oct 22, 2010 12:35 pm

hello Dave,

a very nice one is the 422.
There are 2 Series, the newer one come up in 2 seconds, the older one in 20 seconds.
The older one have nuvistor inputs, this is a perfect choice Cool
The screen looks much better then 453, the price is low. (I have an 453 also)

look self, 422 (dual beam means: 2 scopes Razz )


greetings
Martin
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