O scope help

[KE5YTV]

I'm looking for some help. I would like to buy an O scope to monitor waveforms on my transmitter. I would like to get one that would do the job but spend as little as possible. Please tell me what I need to look for with possible model numbers. Thanks guys.

Mike

[ssbothwell KJ6RSG]

i dont know if you are looking for new or used. Dave over on EEVBlog.com does really fantastic tear-downs and reviews of new oscilloscopes here: http://www.eevblog.com/tag/oscilloscope/ not all the blog posts are reviews or teardowns so you may have to search around a bit but there are a ton of o-scope reviews on the site.

mike would you mind if i expanded your question to include spectrum analyzers as well? i am dying for a really cheap one.

[ke7trp]

If you want to monitor your waveform you can use almost any O scope.  I used a Techtronics Type 422 for years.  I got it for free.  Its fairly small and worked great.  I now use a Techtronics 2245 100mhz scope.

You can build your own scope pick up or buy one already made and ready to go.  There are easy designs all over the web and in the hand book.  Some work better then others.

I would start asking around.  Most of the time you can get an old POS O scope for free as nobody wants to deal with the large physical size or the low MHZ that old scopes typicaly have.

C

[KE5YTV]

Solomon,

Be my guest. 

[kb3rdt]

Mike try find a SB-610 or YO-100 there not too much you can find them at ham fest or ebay I need to get better scope myself I like to find one same as I told you or a SM-220 but kenwood get pricey!

[KA2DZT]

If you feed enough voltage onto the vertical plates directly you can use any old scope.  No need to worry about bandwidth as the plates along are good to about 80megs.  Some scopes have terminals on the back to make connections to the plates.  Scopes that don't have connection terminals can be modified to do the job.

Fred

[KE5YTV]

I found info on another site that the SB 610 is not a good scope for AM signals. 

http://www.amforever.com/phpBB3/viewtopic.php?f=2&t=750

Mike

[The Slab Bacon]

I found info on another site that the SB 610 is not a good scope for AM signals.  
Mike

HUH? ? ? ? ?      

I have used one for over 15 years till it just crapped a power transformer 2 weeks ago.
Screw their bogus trapezoid pattern as it is really not the proper setup for AM, but use their envelope waveform (which bypasses all of the vertical amps and feeds the RF right to the deflection plates) and they are OK-Fine. I have lab grade scopes but why burn them up running for hours and hours. The little SB-610 fit perfect right at the operating position.

However, being that they are of Griefkit Mfr and collectable they usually bring a lot more money than they are really worth. For what you now would have to pay for one, you could buy an older generation Tech or HP for less than 1/2 the price you would wind up paying for a 610.

[WA1GFZ]

I like TEK 7000 series. 7603 is a nice scope.
My 7904 will see a 1GHz sine wave

[kb3ouk]

ok, but with the evelope waveform, to display that you need a horizontal sweep circuit, right? i was told in another post on here this weekend that with my BC-1060A that i couldn't do waveform displays because it appeared to be an audio only scope, but i could do a trapezoid if i hooked the audio directly to the vertical plates and the rf to the horizontals. i looked in one of my books and it says for waveform you need the horizontal sweep circuit, then the rf input goes on the vertical plates, but for trapezoid the rf on the horizontal plates provides the sweep.

and i'm still in the process of getting my scope to work. i have a Caroled BC-1060A, got it friday, just need to get the CRT to work and it should be good.

[KA2DZT]

ok, but with the evelope waveform, to display that you need a horizontal sweep circuit, right? i was told in another post on here this weekend that with my BC-1060A that i couldn't do waveform displays because it appeared to be an audio only scope, but i could do a trapezoid if i hooked the audio directly to the vertical plates and the rf to the horizontals. i looked in one of my books and it says for waveform you need the horizontal sweep circuit, then the rf input goes on the vertical plates, but for trapezoid the rf on the horizontal plates provides the sweep.

Trapezoid pattern you use the audio on the horizontal plates, the modulated RF goes to the vertical plates.  You can just use the vertical plates and any of the medium sweep rates to see the envelope waveform.  You need a fair amount of voltage (RF) to the vertical plates (60-70 volts)

I use a HP-120 1/2meg scope, but it needs to be modified.  You're better not using the vertical amps in the scope, hence feeding the plates directly.  The plates alone are good to about 80megs.

Fred

[Pete, WA2CWA]

Mike try find a SB-610 or YO-100 there not too much you can find them at ham fest or ebay I need to get better scope myself I like to find one same as I told you or a SM-220 but kenwood get pricey!

SM-220 CRT's are no longer available and no one makes even a close substitute.

[KE5YTV]

Slab,

I have a SB 610 that I can purchase for $50. I was buffaloed into thinking that it wouldn't work due to what I read "over there". I will pull the trigger tomorrow. Thanks ! 

Mike

[kb3ouk]

hmm, i'm gonna have to check that book again then, i'm certain it said audio to vetical and rf to horizontal. looking in another book i have shows it the right way: audio horizontal, rf vetical.

[w3jn]

Although the SB-610 will "work", why spend $50 on a one-trick pony?   Find a decent triggered sweep scope - any hamfest  can usually cough up a B&K, HP, or older Tek scope for well under that.  Last hamfest I went to I got a Tek 7603 with a dozen plug-ins, including the rare 7CT1 curve tracer, for $25.  Works FB.   A good scope is invaluable around the shack for troubleshooting and building.

[WA1GFZ]

I think the 7603 is a great scope. I also have a 7634R storage scope that uses all the same plug in modules.
I bought my 7904 for $75 and about $150 for a bunch of plug ins. Then a friend gave me 2 NIB CRTs when he moved west.

[The Slab Bacon]

Mike,
       Johnny is right, but sometimes you dont have room at the operating position for a full sized scope. Hence the little 610 or HoHo-10 doesnt take up much space.
I used mine for what seemed like forever till it crapped a power transformer. You must use the envelope waveform on them to be accurate. They arent the best scopes in the world, by far. But they are good enough to see your percentage of mod (positive peaks) and whether or not you are hitting the baseline or not. And that is all that you really need.

Their trapezoid pattern on those is not really what you want to use as it does NOT put the audio onto the horizontal plates. As far as those things go, $50 these days is a pretty reasonable price for one. I've seen people asking much more than that for them.

If it has been around for a while, give serious consideration to replacing the 3
.1 @ 1600v caps and possibly the 2 diodes in the HV voltage doubler circuit, also be sure that it is fused properly, IIRC the line fuse is .6 amp. Any combination of the above is usually what takes the power transfoma out. (so will an extremely damp environment as mine did)

[Opcom]

Many an inexpensive modulation scope capacitor couples one side of the power transformer B+ winding to one horizontal plate and cap couples the other plate to ground. This gives a decent sweep as the voltage is lare enough that only the rather linear portion of the sine wave is displayed on the screen, the peaksetc being well off the screen to the right and left. Sweep is therefore free. The Wawasee Catalyzer 3" modulation scope uses this method and I find it satisfactory for what it is. So, if you have a 600-700VCT transformer, there is the filament voltage of 6.3, the source for sweep, and a decent voltage to double or triple for the anode.

Some scopes run the cathode at a high negative voltage and the anode and plates near ground, saving $ on the coupling capacitors for the deflection plates. A filament transformer rated for HV insulation must be used.

When powering a CRT filament from a regular filament winding which is not insulated for high voltage, the circuit is arranged with the grid at ground potential (cathode is 0 to -100 for brightness control) because the heater to cathode rating of the CRT is like any other tube. So, you use 2KV coupling caps on the deflection plates.

one way or the other.

You can build with both positive and negative high voltages to realy jack up the brightness, but it is not necessary for good brightness in mod scope service.

If you want a free 5" CRT suitable for mod scope use for the shipping, PM me. I will pick out one that will run on relatively low voltage and send it. Or you can look here for my list: www.magnetosphere.net  I have some 5CP1 which will run on 2-4KV.

3" (which run on 600-2000V) are in too much demand to give away, but what the heck bigger is better.. got to cut a hole anyway. I also have some 4MP1 which are rectangular but you need 3KV. steal it from the TX..

I do have some 3AP1, which are 3" and run on 600-1500V, BUT they have a 2.5V filament, and for some reason they don't sell well. If you want one of those, I would do that. Just remember that voltage=brightness!

[Opcom]

very simple mod scope. Ther eis a mistake in the schemaic though as the grid of the CRT should go to the left  side of the brightness pot. Transformer is about 700VAC, only a few mA. The fil winding is insulated to 2500V.

The transistor circuit and iron core inductor can be ignored as this was intended to energize the inductor and magnetically pull the trace off the screen when no carrier is present. Its a little solenoid from a relay.

[KE5YTV]

Slab,

I picked up the SB610 today and also got the matching station console. Both are perfect like new condition. I got the pair for $75. I will change the caps and diodes as you advised. Thanks for all of the help.

Johnny,

I am also going to be on the lookout for a good deal on a real o scope at the next fest.

Mike

[W8ACR]

This is a great thread. I never knew that the trap pattern on the SB-610 was "fake". So if I understand correctly, I can feed the modulated RF (tapped from the RF final tank circuit) to the vertical input of the scope, and audio (tapped from the modulator output) to the horizontal input of the scope and this will give me a true trapezoid pattern - correct? Furthermore, I should be able to do this with the SB-610 or any "real" oscillloscope.

Thanks, Ron

[KA2DZT]

You have to look at the circuit for the plates.  There may be DC voltages on the plates which controls the centering of the sweep.  So usually you will be connecting through capacitors.  If you are using coax to feed your signal to the scope plates, one plate is grounded through a cap (.01) that needs to be added in.  Your center wire would go to the other plate, again through a cap (.01).  You may also need a RFC on that lead to isolate the RF from passing back into the vertical amp.

Fred

[W8ACR]

Thanks Fred.

A couple more questions. Upon further examination of the SB-610 schematic, it appears that the antenna jacks do feed the vertical plates directly through an attenuator and the vertical amplifier is designed for examination of a signal from a receiver IF strip. If I read this correctly, I would just attach the transmitter to the so239's in the usual fashion for applying the modulated RF to the vertical plates. Or would it be better to apply sampled RF into the vertical input jack and then bypass the vertical amplifier?

With regard to the audio, should I apply the sampled audio signal to the horizontal amplifier or bypass the tube and apply the audio directly to the plates?

Thanks, Ron

[The Slab Bacon]

I just simply run a piece of RG-142 (or RG-58) from one of the SO-239s to a "T" in the transmitter output coass. This does the same thing electrically as running the transmitter outpoot to the scope and back. The inpoot impedance to the deflection plates is high enough and the capacitance is low enough that neither the transmitter or receiver know it is there. It is just looking to sample the RF voltage from the transmittah. This saves a few pieces of coass snarling up the back of the operating desk and keeps it a bit simpler.

Screw the trapezoid, real men look at the outpoot waveform! ! !  Why have more cabling than you need? I changed the IF amp can in my 610 to a 455 Kc can and use the other inpoot and the vertical amp for looking at the received signal waveform just to help minimize the baseline screen burn while everything is idling and I'm not transmitting.

Those little scopes do have a problem with asthignatism. There is a simple mod that gives you an asthignatism adjustment. I dont rember what it was (I did mine 15 years ago) but it was pretty simple to do. It required adding 1 pot and moving a few wires around. I eliminated the tone generator switch (I never used it) and put it in that hole so I wouldn't have to drill another hole in the front panel.

[KA2DZT]

Ron,

I not familiar with the SB-610 so I can't help with that.  My comments are for an ordinary scope in general.

I use a HP 120 audio scope that I modified to make it work.  My xmtr is HB and it has circuit built into it to feed the modulated RF to the vertical plates.  I use the wave envelope pattern and the audio is used to trigger the scope.  The scope only lights with modulation.  I use the internal horizontal sweep, any medium sweep rate.

Fred