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 Post subject: Starter Kit
PostPosted: Nov Sat 23, 2019 10:25 pm 
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Joined: Nov Sat 23, 2019 10:00 pm
Posts: 7
Opening up a discussion to rack your brains.

What is the best set up for an amateur tube radio repair starter kit?

Multimeter can do it all?


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 Post subject: Re: Starter Kit
PostPosted: Nov Sun 24, 2019 1:03 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 4233
Location: Florida
You can do most of it with only a DMM or VTVM. The most important thing is knowing basic theory and how the circuits of a radio work. Without this basic knowledge all the test equipment in the world isn't going to help.

RRM


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 Post subject: Re: Starter Kit
PostPosted: Nov Sun 24, 2019 2:36 am 
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Location: Ohio 45177
DVM has advantage of having modern safety features and battery powered(handheld types) so that you do not need an isolation transformer to make checks on AC-DC type sets with no transformer. Although I am not sure how really safe the hardware store 15$ meters are. An isolation transfomer is good to have if you work on typical table radios that are AC DC types. A basic signal generator of some sort so that you can align the radios. That will get you basically started. A tube tester would be nice. Or a friend that has one. As it will not be in constant use like a meter, sharing is practical with those. You get a radio, you test the tubes and then can put it away till the next radio. Unless you have spare tubes to try if a radio seems to have a problem in one area and you have no tester. You need the generator for IF alignment, but if you have the knowledge you can often do the RF alignment on a radio that is not really messed up, by ear with stations on the air with known frequencies, at least on typical AM radios. I have a strong station at 610 for setting the low end and can use something like the station at 1410 for the high end adjustments. Or even higher up the range if I can ID them with a digital tuning radio. Most radio dials in consumer radios have big fat pointers and dial markings that are also big and fat and you are not tuning to the closest kilocycle as you can't with those. Like they are in the correct neighborhood on the dial.

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 Post subject: Re: Starter Kit
PostPosted: Nov Sun 24, 2019 9:55 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
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Location: Long Island NY
99 years ago I would have said a decent meter is all you needed, but nowadays most tube amateur equipment has been pawed over and gone through many times by many people. You’re going to spend more time cleaning up other peoples’ mistakes and poor parts substitutions than much of anything else. In addition to the meter, a signal generator should be on hand. Doesn’t need to be fancy or expensive, and you don’t have to rush right out and buy a frequency counter for it unless you start tackling really advanced receivers. Being able to force signals through dead RF and IF stages is what a signal generator is good for, besides alignments.

As for the meter, the term “multimeter” connotes an analog VOM. Not a bad thing to own but a good VTVM will serve you better under a radio chassis. DMMs are good to have for situations where you need two or three decimal places accuracy, but those don’t occur often in tube electronics. If you have coin for it, best approach is to get a reasonably good quality DMM and use it to calibrate the VTVM you use day to day for radio work.

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 Post subject: Re: Starter Kit
PostPosted: Nov Sun 24, 2019 11:23 pm 
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Joined: Nov Sat 23, 2019 10:00 pm
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Great insight everyone, thank you.

I am going to try repairing the radio (that has not been plugged in for 70 years) and then when I'm ready to test it, I'll get myself an isolation transformer & a VARIAC.

I am looking at these two:
https://www.amazon.com/gp/product/B00006HPFH/ref=ox_sc_act_title_1?smid=ATVPDKIKX0DER&psc=1
or
https://www.amazon.com/dp/B000LDLF3M/ref=psdc_10967671_t3_B00006HPFH

and one of these:
https://www.amazon.com/gp/product/B07JZ2Z3PG/ref=ox_sc_act_title_2?smid=A3GRIWLFOYL9K2&psc=1

Would you plug the VARIAC into the isolation transformer and then the radio into the VARIAC?


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 Post subject: Re: Starter Kit
PostPosted: Nov Mon 25, 2019 3:59 am 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 713
Location: St. Louis, MO
You'll need more than just a meter. That solder ain't gonna melt itself. I recommend a good soldering station. You can probably get by with just an iron, but if you need to do anything like attach a lead to the metal frame, you'll need the station to crank up the heat.

An isolation transformer is nice, but not always necessary depending on the individual radios you'll be working on. A variac is also nice, but it depends on how much of the original components you'll be using. If you're going to completely gut the thing and replace everything inside it with brand new components, then you probably won't need one.

You'll also need a signal generator to align that radio once you've replaced everything. For just starting out, I'd recommend getting a working, aligned one. You'll need even more equipment to align one. That can include frequency counters, oscilloscopes, RF millivoltmeters...

A VTVM is nice to have. A lot of alignment requires peaking voltages, which honestly is easier to do with that analog needle. I suppose you could do it with an analog multimeter, I've never tried.

Then there's all the junk you'll need for refinishing wood cabinets.

edit: plug the variac into the isolation transformer, and the isolation transformer into the wall, preferably a GFCI.


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 Post subject: Re: Starter Kit
PostPosted: Nov Mon 25, 2019 5:57 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 2533
Location: Dallas, TX
There are probably some old salts around that have so much knowledge and experience they can troubleshoot a radio just using a paperclip, a wooden match and a wet finger.
Seriously though it somewhat depends on what kind of radios you want to work on.
If you only work on radios with power transformers then a isolation transformer isn't needed. On AC/DC radios an isolation transformer is nearly mandatory for safety of yourself and the test equipment.
How big an isolation transformer again depends on the type of radio. Most AC/DC sets use less than 100 watts (100 VA) or 1 ampere. Some of the old console radios from the 1930's had two dozen tubes and draw over 200 watts, but they have power transformers. If you ever get into TVs or stereo consoles they also take more power, again most have power transformers.
A variac would have to have similar power ratings and may still be used even on a set with a power transformer. Something that is needed with a variac is an AC current meter to monitor as you increase the voltage. The point is to discover a problem before something is damaged.
Whether the variac or the isolation transformer is first in the hookup isn't that important, it make a bit more sense if the one with the higher power rating is first.
An emission tube tester is nice however for All American Five AC/DC radios you can get a small variety of NOS tubes to try by substitution for less money.
For AM radio alignment you usually only need a meter (analog, i.e. needle, is best), RF signal generator with modulation, sometimes a variable low voltage source (0-4V) if using a technique that forces the AVC line. Add a frequency counter for accuracy if you want.
FM radios require more for a good alignment, like sweep gen, oscilloscope, etc.

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Tim
It's not the Destination, It's the Journey.


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 Post subject: Re: Starter Kit
PostPosted: Nov Mon 25, 2019 6:58 pm 
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Joined: Jul Mon 26, 2010 8:30 pm
Posts: 29031
Location: Annapolis, MD
Here is a mantra that you might find useful:

"If you don't know WHY you need something, then you don't need it."

Loosely translated this means avoid the temptation to acquire lot's of test equipment all at once. You can get a lot done with nothing more than a good digital multimeter. This combines the convenience of a digital display with the high impedance of the traditional VTVM.

When I started with this stuff at the age of 13, I never met anyone with a Variac or isolation transformer. I DID, however, learn about "ground-breaker" plug adapters at a very early age. Thankfully, I also learned about ONLY ONE HAND IN THE WORKS WITH POWER ON..... Now I regard a Variac and isolation transformer as required

I will NEVER be without a scope---but partly because I used them extensively in college and my career--AND i once worked full time in an instrument lab repairing all manner of strange stuff.

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-Mark
"Voltage is fun to watch, but it's the CURRENT that does the work."


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