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 Post subject: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Wed 13, 2018 5:32 pm 
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Joined: Jan Mon 17, 2011 2:10 am
Posts: 115
Location: Revere,Massachusetts U.S.A.
Hi Folks, I’m trying to align an RCA AM/FM radio using the Heathkit scope, I can get the 10.7 MHz sine wave on the scope.
This radio works great I’m just wanting to learn how to use a scope, my question to everyone is :
Do I need more bandwidth? I really love this scope but I may need a much more modern version.
Thank You Tony


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Wed 13, 2018 6:10 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
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Location: Long Island
If you are getting 10.7-MHz on a Heathkit O-8 oscilloscope, you are doing better than anybody else has with done with one of them in the last 66 years. What sync speed are you using to see sine waves? The scope only sweeps to 100-kHz. The 3-dB high frequency vertical bandwidth of that model was around 1.2 MHz.

Generally speaking you do not need any kind of oscilloscope to align a radio, AM or FM. A scope can be used in place of the usual VTVM or other kind of meter. It is also customary to use a scope in conjunction with a sweep generator for sweep alignments, but for most radios is not necessary either.

Recurrent trace scopes like the O-8 went out of style in the early 1970s, so if the goal is to learn how up-to-date scopes work, you should probably look for something newer so you'll have AC and DC coupling, dual trace modes, and triggering. But for use with a sweep generator or for looking at audio waveforms the O-8 is okay.

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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Wed 13, 2018 6:41 pm 
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Joined: Jan Mon 17, 2011 2:10 am
Posts: 115
Location: Revere,Massachusetts U.S.A.
I should have said, i can’t get a 10,7 MHz sine wave . After reading your reading your posting there is no way I ever could.

One last question....Could I use a multiplier probe ???
Thanks Again Tony


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Wed 13, 2018 7:01 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 1924
Location: Sunbury, Ohio 43074
Welllll.... even if there were such a thing as a multiplier probe for a scope, you will still have the bandwidth limitation of the scope itself. You would need an "unmultiplier" probe if you will ... that would divide down the incoming waveform to a percentage that the scope could display. That process in and of itself would render a lot of waveforms useless.

So, in a word, no.

I second the opinion to get a more modern scope with which to learn. TV service grade scopes are plentiful, available, and cheap, usually from $50 to $100 in working condition. B&K and Sencore come to mind. Even the later Heathkit, some EICO, RCA etc. These would be excellent scopes to learn on, would be easy to re-sell, and also to keep even if you get a better one. If you ever need to WORK on a scope, you need .... wait for it ... a scope :)

A bit more money, and you can get a 100 or 150MHz scope with all the bells and whistles such as a Tek 453, 454, 465, or the like.

You should look for at minimum 50MHz bandwidth, dual trace with AC and DC coupling, A/B/ADD and invert mode, Triggered sweep, Possibly sweep delay. Even if the scope appears a bit more complex than you feel comfortable with, you can learn it, and it'll serve you well. or start with a lesser scope and trade up later.

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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Thu 14, 2018 6:15 pm 
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Joined: May Wed 06, 2009 7:01 pm
Posts: 801
Tony,

You can align FM radios with a low-end scope such as the Heathkit but you will need a demodulator probe and an accurate sweep generator. Basically, all the scope shows with the demod probe is a low frequency signal detected by the probe or the scope can be fed directly off the FM detector itself. That's how it was done in the days when low bandwidth scopes were the norm. You can get a good notion of how to do it from a book published by Sylvania using their low end scope at the time of publication. A pdf version can be found here
http://www.cfp-radio.com/documentations/Sylvania-scope.pdf

For accuracy in a signal generator used as 10.7 MHz marker, in the old days crystal-control was used. A cheap frequency counter is a good alternate these days assuming the generator is stable.

Sylvania's companion book on servicing with the VTVM is also useful
http://www.cfp-radio.com/documentations/Sylvania-VTVM.pdf

Best wishes,

-- Rich


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Thu 14, 2018 6:31 pm 
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Location: Annapolis, MD
This is a bit confusing......you never have to display or measure the 10.7MHz signal to align an FM radio.

Two standard methods:
1. Monitor 2 different test points in the detector circuit---one is for peaking up all the IF stages, and the other is for setting the center frequency of the detector. All you need is a basic signal generator and a VTVM or DMM.

2. Sweep alignment. Here, the scope is used as an X-Y display, and the frequency is typically only 60Hz.

A wide bandwidth scope is certainly useful for troubleshooting FM. My scope is spec'ed at something like 70MHz, and will easily display the 10.7MHz IF signal. It will also capture the local oscillator signal "well enough" to confirm it's operating and get the frequency within 5%.

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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Thu 14, 2018 6:56 pm 
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Joined: Jan Mon 17, 2011 2:10 am
Posts: 115
Location: Revere,Massachusetts U.S.A.
Thank You Rich for you reply regarding my Heathkit scope, I received from another collector that
The scope only has under 2mhz bandwidth? I’m wanting to learn how to properly use a scope,
And I do have the Sylvania book. It’s a really easy book to understand. What do think about a
a 10X probe. Do you think it would help ?
Thanks Tony


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Thu 14, 2018 8:54 pm 
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Location: Annapolis, MD
10X probes don't do anything for bandwidth---they are used to get low impedance---and especially low capacitance.

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"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Thu 14, 2018 11:15 pm 
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Joined: May Wed 06, 2009 7:01 pm
Posts: 801
Tony,

Here's another free book, by Rider on meters. He has a schematic on page 92 of a peak to peak demodulator probe. Easy to build your own if you don't have one. That's the probe used for FM alignment. Rider shows it hooked up to a VTVM but it also works with a scope for FM alignment.
https://www.americanradiohistory.com/Archive-Rider/BOOKS/How-to-Use-Meters-Rider-1954.pdf

A 10X capacitive divider probe can be used with your Heathkit assuming it is designed for the proper impedance. It just reduces the loading on a high impedance circuit being tested but as pixellany pointed out, nothing external will change the bandwidth of the scope. Check the specs on your Heathkit. The input impedance for many older scopes is 1 megohm but I don't know the specs for yours. A 10X probe also reduces the voltage getting to the Heathkit's vertical amp by a factor of 10, a problem when measuring small signals.

I started my scope experiences with an Eico 425, vintage 1950 or so. With the proper probes and skill of the user, it can still perform service work as described in the Sylvania book. Over time, I have acquired better scopes but that old scope was used to align TV sets back in the day.

Best wishes,

-- Rich


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Fri 15, 2018 4:11 am 
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Joined: Jan Mon 17, 2011 2:10 am
Posts: 115
Location: Revere,Massachusetts U.S.A.
Hi Again, Ok lets say I retire my Heathkit scope and buy a new Hantek scope. I can spend around $300.00 and buy a lot of bandwidth, I’d be happy with 70 or 100 MHz.

My only concern would be how to protect a solid state scope from the high voltages from tube electronics.


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Fri 15, 2018 10:48 am 
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Location: Annapolis, MD
My concern would be spending that much money for something without having established a need. The classic chicken and egg problem is applicable. You have to spend a lot of time using scopes and other test equipment before you can appreciate what an upgrade would do for you. If you are going to be doing a lot of FM work, you might want to consider a sweep generator first.

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"It's always something". --Gilda Radner (1946 - 1989)


Last edited by pixellany on Jun Fri 15, 2018 2:40 pm, edited 1 time in total.

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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Fri 15, 2018 12:00 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 10115
Location: Powell River BC Canada
For AM FM radio repair I have never needed to see RF of IF waveforms.
If I want to measure the voltage of an AC signal, I have an old HP
VTVM that can go up to about 900 mHz.

If I measured a RF voltage, the meter would tell me what the meter
thought the voltage was.

The phrase 'can be heard' is used to describe the nth harmonic of
a dial setting on a particular signal source. It is also why, for example,
bands D, E, and F on low cost signal generators are all accessed on the
last position of the band switch. Staring at a bent 30 mHz sin wave
isn't going to tell you much. (Use a spectrum analyzer) .

Radios can be adjusted with a pulse generator. A 1 uSec pulse
at a repetition rate of 1 kHz can be heard way up many bands.
If you wanted to see if the 1 mHz pulse had sharp
corners, then a 100 mHz scope would be useful.
It would be as accurate as signal used to calibrate the probe.

My HP and TEK scopes, good to above 100 mHz, have switches
limiting them to 20 mHz. This is because trying to view a 10 mHz.
signal on a 100 mHz scope might have garbage you don't care about
gobbling up the 2 or 3 windows you may need.

Old beater HP and TEK can be found for little money. Find and play
with one of those , then buy the expensive solid state. Good manuals
are on line.

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de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Fri 15, 2018 2:56 pm 
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Joined: Jan Mon 17, 2011 2:10 am
Posts: 115
Location: Revere,Massachusetts U.S.A.
Thank you to all for your time and effort,but my question is : what precautions Should I take to protect a much younger scope?

Solid state scopes can’t the pounding like my old girl and of course our little Pocket Radio.


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Fri 15, 2018 3:11 pm 
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I'm not sure what you are concerned about.....

All things equal, good S/S equipment should be more reliable than tube stuff.

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-Mark http://pixellany.com

"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Fri 15, 2018 3:27 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 1924
Location: Sunbury, Ohio 43074
transoceanic 8523 wrote:
Thank you to all for your time and effort,but my question is : what precautions Should I take to protect a much younger scope? Solid state scopes can’t the pounding like my old girl and of course our little Pocket Radio.


Sure they can. You just have to observe reasonable limits; for instance, a 200V input if the scope is set for 10V won't hurt a thing. If the scope is set for 0.1mv, it may, but if it's a well designed scope, it won't hurt that either. Good instruments are engineered so you could, if needed, look at a low level AC signal riding on a high level DC signal ... that's what they do.

Can you exceed what the instrument can handle? Yes, but it would take some effort, and during normal use, you will be just fine. I cannot recall an instance in all my 50 some years of using scopes, where I damaged an input. I'd avoid DROPPING the instrument, however. Don't ask.

You can get a high quality full featured scope, as was mentioned earlier in this thread, for well under the $300 you mention. I would avoid Ebay like the plague however. Unless you are buying from a company with a guarantee, you should SEE before you BUY. Hamfests, Flea Markets, even the occasional Estate sale or auction... and you can do much better than Ebay prices. I've been at auctions where good scopes go for $25 or even less, VERY good ones under $100, and usually work when you get them home. If you have the patience, you can plug them in ahead of time and check.

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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Fri 15, 2018 7:42 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 10115
Location: Powell River BC Canada
transoceanic 8523 wrote:
Thank you to all for your time and effort,but my question is : what precautions Should I take to protect a much younger scope?

Solid state scopes can’t the pounding like my old girl and of course our little Pocket Radio.


There was a post about the overpass that collapsed. An engineer was
using his scope to look at strain gauge signals. His scope had a sign that
read ....Keep you hands off my scope....

Where I worked, a very young engineer blew up the brand new
Fluke Scopemeter in a short time.

If it is yours, and your dollars bought it, you will be very careful
to keep it away from things known to throw sparks. Any scope for
general purpose use isn't likely to need to be EMP tested,

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Fri 15, 2018 9:09 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 1924
Location: Sunbury, Ohio 43074
It's always possible to blow up your test equipment. But it's seldom if ever the instrument's fault. I think if a bridge fell on a scope, a tube scope won't fare much better than a solid state one ;-)

And of course, anyone can blow up anything if it's misused.

If you want a tube scope, that's fine. Many prefer them for a variety of reasons; nostalgia, familiarity, second use as a room heater, whatever, ..... But not because they will hold up better :)

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Preserving the history of electronics, one boat anchor at a time! :)


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Tue 19, 2018 2:31 am 
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Location: Beaver Falls, PA. USA
Just about any modern scope has a switch in the input circuit for AC or DC coupling. In the AC mode, a DC level on the input will be ignored. There will be limitations, however; follow the instructions in the manual, and you'll be OK.

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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Tue 19, 2018 6:40 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 7889
Location: Long Island
Quote:
Thank you to all for your time and effort,but my question is : what precautions Should I take to protect a much younger scope?

Solid state scopes can’t the pounding like my old girl and of course our little Pocket Radio.


There are two separate issues. One is the voltage rating of the scope, the other is the voltage rating of the probe(s) you connect to it. Modern scopes do not have very high voltage inputs; even with AC coupling you will be limited to a couple hundred volts at most. And yes you can damage a modern scope very badly if you exceed its input voltage on AC or DC by a sufficient amount. So most people put X10 probes on them straight away in the hope that higher voltages will be reduced by the probe and the scope won't get hurt. But that won't happen if the probes are only rated for a couple hundred volts themselves!

The thing to understand is, in aligning vintage FM radios you normally start off by centering up the discriminator or ratio detector. You are basically adjusting a test point for zero volts DC when you do this. A zero-center vacuum tube meter is the easiest way to do this. The IFs are then adjusted for best gain over their bandwidth. There are a number of ways you can proceed, but the most common is to peak up the AGC voltage, looking at the VTVM, or use a sweep generator and look at the demodulated output on a scope. In any case you are looking at low voltage DC or audio frequencies. At no point in time do you need to connect the scope to high voltage.

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"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


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 Post subject: Re: Heathkit Scope Model 08. Bandwidth Issues.
PostPosted: Jun Wed 20, 2018 9:06 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 10115
Location: Powell River BC Canada
Vintage these days can encompass the short period of time that
tube multiplex decoders were part of FM receiver alignment and
they operated at B+ voltages. Tracing the various paths to see
if signals were on coils could easily exceed a solid state scope
input voltage. My Heath 4850 has a maximum of 125 V peak + DC
rating on the channel inputs. That model is a hair-pulling nightmare
of relays and resistors. It was an $800+ , 50 mHz kit when I built it.

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de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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