I am low budget aka retirement.
I will try the 50ohm load.
I been using a coil of wire around the antenna.
If had a HP I would not need to build VTVM. I did not used as too many in the pass has made adjustments and or modifications .
Dave
I will try the 50ohm load.
I been using a coil of wire around the antenna.
If had a HP I would not need to build VTVM. I did not used as too many in the pass has made adjustments and or modifications .
Dave
Hi Dave,
No problem, and I get it.
All I'm trying to do is teach a little. Just so you understand the broad limitations of that probe and meter. Overall you did a great job, and I like how you handled range calibration.
Okay, so things to watch for in general:
1.) Cheap meters tend to be non-linear across their scale. That is a fact of life, they are all non-linear. Some much worse than others. All you can do is calibrate F.S.
2.) If the movement is "sticky", the meter movement is garbage. Don't try and clean it. You can only make things worse.
3.) The accuracy degrades badly near the bottom of the scale, the further down you go, the worse it is. Accuracy specs apply at full scale only.
4.) Range resistors drift with time and temperature. New, good meters have the divider formed on a thick film base to keep the temperature more or less equal across all of them.
5.) The divider is also low and controlled capacitance. Better meters have trimmers across the higher range resistor elements. These days done electronically.
6.) meter probes made for higher frequency use have compensation capacitors as part of the design. That means the input impedance drops with frequency, but it is the only way to get a flat frequency response.
Just understand the limitations of your equipment and how it may impact the circuit under test. Any stray capacitance can detune the circuit you are trying to align and there are steps you can take to minimize that.
Everything seems to simple until you really look at it closely. It's the details that will get you! Just try and be aware of them, that's all. For your input divider, i% metal film, low TC resistors should be used. For the high range I would use resistors rated at 3,500V. By the way, resistors have voltage breakdown ratings, some as low as 50 VDC. You must read the datasheet. When we were younger, carbon composition resistors had a breakdown rating of 500VDC and we simply assumed this was the standard. It isn't. We also thought the maximum voltage was limited by dissipation - NOPE! Also, I have seen inductive metal film resistors. Carbon composition types are not. So there are locations in a circuit where you should use a carbon composition type. Overload characteristics are also better.
Read the data sheets! 🙂
-Chris
No problem, and I get it.
All I'm trying to do is teach a little. Just so you understand the broad limitations of that probe and meter. Overall you did a great job, and I like how you handled range calibration.
Okay, so things to watch for in general:
1.) Cheap meters tend to be non-linear across their scale. That is a fact of life, they are all non-linear. Some much worse than others. All you can do is calibrate F.S.
2.) If the movement is "sticky", the meter movement is garbage. Don't try and clean it. You can only make things worse.
3.) The accuracy degrades badly near the bottom of the scale, the further down you go, the worse it is. Accuracy specs apply at full scale only.
4.) Range resistors drift with time and temperature. New, good meters have the divider formed on a thick film base to keep the temperature more or less equal across all of them.
5.) The divider is also low and controlled capacitance. Better meters have trimmers across the higher range resistor elements. These days done electronically.
6.) meter probes made for higher frequency use have compensation capacitors as part of the design. That means the input impedance drops with frequency, but it is the only way to get a flat frequency response.
Just understand the limitations of your equipment and how it may impact the circuit under test. Any stray capacitance can detune the circuit you are trying to align and there are steps you can take to minimize that.
Everything seems to simple until you really look at it closely. It's the details that will get you! Just try and be aware of them, that's all. For your input divider, i% metal film, low TC resistors should be used. For the high range I would use resistors rated at 3,500V. By the way, resistors have voltage breakdown ratings, some as low as 50 VDC. You must read the datasheet. When we were younger, carbon composition resistors had a breakdown rating of 500VDC and we simply assumed this was the standard. It isn't. We also thought the maximum voltage was limited by dissipation - NOPE! Also, I have seen inductive metal film resistors. Carbon composition types are not. So there are locations in a circuit where you should use a carbon composition type. Overload characteristics are also better.
Read the data sheets! 🙂
-Chris
The Resistor, 1/4w 1% metal film Resistor,
Low cost too.
Only need 100 volts if need higher voltage then use probe to cut down to 100 volts to the meter.
All AC, AF and RF are in the probes not meter.
Dave
Low cost too.
Only need 100 volts if need higher voltage then use probe to cut down to 100 volts to the meter.
All AC, AF and RF are in the probes not meter.
Dave
Hi Dave,
I know. I'm looking at voltage vs resistance effects. Normally you want to use the 0.6 watt resistors, and you have to look at TC and stability vs temperature. Just being a 1/4 metal film resistor says nothing.
I know. I'm looking at voltage vs resistance effects. Normally you want to use the 0.6 watt resistors, and you have to look at TC and stability vs temperature. Just being a 1/4 metal film resistor says nothing.
When Calc out wattage it is 0.000909091 for 100 volts.
I know look a lot what Eico, Heathkit and HP use 1/2 watt resistors at 1% for 1,000 volts.
The only have on the resistor is what posted.
I will change the 250 volt probe to America made resistor
Dave
I know look a lot what Eico, Heathkit and HP use 1/2 watt resistors at 1% for 1,000 volts.
The only have on the resistor is what posted.
I will change the 250 volt probe to America made resistor
Dave
Hi Dave,
It isn't the power in this case. It's the voltage and temperature dependance. It just depends on how well you want it to hold it's calibration over time and as you use it (drift).
I'm not saying you need to change those things, but just you have to be aware of characteristics of some parts you wouldn't normally think of (most techs are unconscious to this stuff!).
It isn't the power in this case. It's the voltage and temperature dependance. It just depends on how well you want it to hold it's calibration over time and as you use it (drift).
I'm not saying you need to change those things, but just you have to be aware of characteristics of some parts you wouldn't normally think of (most techs are unconscious to this stuff!).
It is something that did look at
The wattage on the resistor was so low did not go beyond that point for calculations.
Thank you
Dave
The wattage on the resistor was so low did not go beyond that point for calculations.
Thank you
Dave
I use the 324 for alignment of tube AM/FM and short wave receivers. Don't think I'll ever use for TV alignment...
Unless in the near future, there's a swell of interest/ market value for this field.
Jim
ps. like that TV emoji, tho
Chris,
Where are the locations you recommend using carbon comp's over films?
And by that I mean, metal and carbon film, or are they the same?
Jim
There also wire wound too.
Now been too longe since I in class on why use each type. It was mainly found in working with tubes.
The wire wound in some RF circuit could give problems. That what I can remember
Dave
Hi Jim,
Wire wound resistors have high surge capability, and in a power supply can help isolate sections due to their inductance (which is actually small).
Okay, carbon composition types are used in RF and in grid / gate dampers where low inductance is important.
It will not, it will lower the amplitude in fact. However the circuit is designed to work into either a 0 ohm or 75 ohm load. It should be noted near the output jack.
Metal film is different than carbon film. Metal film resistors are more stable. Carbon film types can be low quality, but you can easily get junk metal film parts. End cap attachment is critical, so guess where they go cheap?
Wire wound resistors have high surge capability, and in a power supply can help isolate sections due to their inductance (which is actually small).
Lol!
You do know that is from the 1960's! That edition may even be from the 1950's!
I had a real colour bar generator, and the connection was not like that at all. What you have there is a "make it go" scenario. Something a small shop might do but not a larger shop or shop authorized for warranty.
Ever read "Jack Darr's" TV clinic? He had a column in Radio Electronics I think. Popular Electronics would have had something similar.
You do know that is from the 1960's! That edition may even be from the 1950's!
I had a real colour bar generator, and the connection was not like that at all. What you have there is a "make it go" scenario. Something a small shop might do but not a larger shop or shop authorized for warranty.
Ever read "Jack Darr's" TV clinic? He had a column in Radio Electronics I think. Popular Electronics would have had something similar.
The data come from 1950's.
In 1960's they where pushing color bar generators.
I found this data from repair techs from 1950's. Only found in print this year.
The simple bars on RF generator I did long time ago. Just turn to channel 3 or 4 and set the AF to 400 Hz. Now bar generator FYI it works on today's TV's too.
In 1960's they where pushing color bar generators.
I found this data from repair techs from 1950's. Only found in print this year.
The simple bars on RF generator I did long time ago. Just turn to channel 3 or 4 and set the AF to 400 Hz. Now bar generator FYI it works on today's TV's too.
FYI
What did for a live till 2004 is in my avatar. I designed, engineered and built aircraft hangar doors ship world wide including Canada 🍁.
In High school and college I was a iron worker.
I had plan in 1960's be in electronics did not work out now a hobby.
Dave