Metalwork - Lathe and Mill topics

Sunday, 24 December 2023

Re: [Amateur-repairs] SETTING UP A TEST BENCH

Yep, I stand corrected! Variac, not rheostat.
--

Bob
KD8WU

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Re: [Amateur-repairs] SETTING UP A TEST BENCH

Another thing worth noting is that makers of variacs often skip putting a fuse on the output side. Think about transformer theory and you will see why this is important.

73

-Jim
NU0C

On Sun, 24 Dec 2023 09:03:18 -0500
"Tim Reimers KA4LFP" <treimers95@gmail.com> wrote:

> "A good rheostat for slowly powering up something that make have been turn
> off for the last 20, 30, 40 years."
>
>
> Couple of points here
> A Variac (what you're talking about when you say rheostat)
> Does NOT LIMIT CURRENT.
> A dead short in a DUT will still destroy components like the DUTs power
> transformer, even sometimes at the low voltage a variac provides.
>
> Also, a Variac does not protect you from the AC line. A large (massive)
> number of old shortwave radios and other audio gear had "hot chassis"
> designs, with no power transformer, and the chassis was physically isolated
> from the case.
> A so-called AC-AC design.
>
>
>
> Best design for a power system for your bench:
>
> Separate GFCI circuit feeding a large isolation transformer, in series with
> a Dim Bulb Tester in series with the Variac.
>
> The Dim Bulb Tester does limit current to protect you from those dead
> shorted dried out capacitors that will let all the unobtanium smoke out of
> your power transformer.
>
> 73, Tim KA4LFP
>
>
>
>
>
> Morse Code: The original digital mode.
>
>
>
>
>

--

73

-Jim
NU0C

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Re: [Amateur-repairs] SETTING UP A TEST BENCH

Excellent advice.

Gary

On 12/24/2023 8:03 AM, Tim Reimers KA4LFP wrote:

"A good rheostat for slowly powering up something that make have been turn off for the last 20, 30, 40 years."

Couple of points here

A Variac (what you're talking about when you say rheostat)

Does NOT LIMIT CURRENT.

A dead short in a DUT will still destroy components like the DUTs power transformer, even sometimes at the low voltage a variac provides.

Also, a Variac does not protect you from the AC line. A large (massive) number of old shortwave radios and other audio gear had "hot chassis" designs, with no power transformer, and the chassis was physically isolated from the case.

A so-called AC-AC design.

Best design for a power system for your bench:

Separate GFCI circuit feeding a large isolation transformer, in series with a Dim Bulb Tester in series with the Variac.

The Dim Bulb Tester does limit current to protect you from those dead shorted dried out capacitors that will let all the unobtanium smoke out of your power transformer.

73, Tim KA4LFP

Morse Code: The original digital mode.

Re: [Amateur-repairs] SETTING UP A TEST BENCH

"A good rheostat for slowly powering up something that make have been turn off for the last 20, 30, 40 years."

Couple of points here

A Variac (what you're talking about when you say rheostat)

Does NOT LIMIT CURRENT.

A dead short in a DUT will still destroy components like the DUTs power transformer, even sometimes at the low voltage a variac provides.

Also, a Variac does not protect you from the AC line. A large (massive) number of old shortwave radios and other audio gear had "hot chassis" designs, with no power transformer, and the chassis was physically isolated from the case.

A so-called AC-AC design.

Best design for a power system for your bench:

Separate GFCI circuit feeding a large isolation transformer, in series with a Dim Bulb Tester in series with the Variac.

The Dim Bulb Tester does limit current to protect you from those dead shorted dried out capacitors that will let all the unobtanium smoke out of your power transformer.

73, Tim KA4LFP

Morse Code: The original digital mode.

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Re: [Amateur-repairs] SETTING UP A TEST BENCH

One thing on my To-Do list is to install a dedicated power outlet for the Unit Under Test, a power consumption meter like a "Kill A Watt", and a BIG E-STOP button.

A good rheostat for slowly powering up something that make have been turn off for the last 20, 30, 40 years.

Besides ham radio stuff, I've been contemplating vintage audio equipment and what I would need for that. 8Ω dummy loads, AF power meter, AF spectrum analyzer (?)
--

Bob
KD8WU

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Saturday, 23 December 2023

Re: [Amateur-repairs] SETTING UP A TEST BENCH

Thanks, Bob KD8WU, for your thoughts. I, too, have eyes that are getting older. "Setting up a test bench" to me is one of the "fun" things to do during inclement weather - or when something new needs to be done - or when you're going a bit nutty because you're feeling a bit lazy and stuck inside. Let us know how it's going. I'm interested in seeing other hams' workspaces.

Dave W9OCM

Fairmount, IN 46928

On Sat, Dec 23, 2023 at 6:59 AM bobcolenso via groups.io <bobcolenso=yahoo.com@groups.io> wrote:

All this is giving me some ideas also. I like the big screen TV for reading schematics. My eyes are starting to get old.

A lot of people have mentioned a good soldering iron(s). This is very important! Mine is variable up to 750° or so, But I also have different size tips, normal for regular PCB components, and a BIG tip for things that have more thermal mass.

My sig gen is an HP-8648C has more than what I really need (9K to 3G, -139 dBm to +14.5 dBm) [Below 30 MHz S9 is defined as -73 dBm, S1 is -121 dBm, so you want that covered. 40 over S9 is a pretty strong signal AT -33dBm]

Don't go with an elCheapo multimeter with a dial and a needle, you'll get elCheapo results. Get something decent. I have a Boonton 92C, it's an RF mV meter calibrated to 700 MHz has a max full scale of 3 volts, the bottom FS is 3mV and I can read 250, maybe 100 µV.

Also a VTVM for peaking and nulling non-RF levels. Here I use an HP-410-C, which is actually a transistorized VTVM.

A good Frequency Counter.

One thing I just got is a 0 to 450 volt power supply. This I can use on spare part electrolytic caps sitting around.

On the want list is another dummy load and coax so I can put it in the far corner of the basement.

One thing you can do is look at web sites of people who work on radios and see what they use and get ideas from there. You know what you want to do with it, you know your skill level, ect.

Above all; HAVE FUN!

--

Bob
KD8WU

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Re: [Amateur-repairs] SETTING UP A TEST BENCH

All this is giving me some ideas also. I like the big screen TV for reading schematics. My eyes are starting to get old.

A lot of people have mentioned a good soldering iron(s). This is very important! Mine is variable up to 750° or so, But I also have different size tips, normal for regular PCB components, and a BIG tip for things that have more thermal mass.

My sig gen is an HP-8648C has more than what I really need (9K to 3G, -139 dBm to +14.5 dBm) [Below 30 MHz S9 is defined as -73 dBm, S1 is -121 dBm, so you want that covered. 40 over S9 is a pretty strong signal AT -33dBm]

Don't go with an elCheapo multimeter with a dial and a needle, you'll get elCheapo results. Get something decent. I have a Boonton 92C, it's an RF mV meter calibrated to 700 MHz has a max full scale of 3 volts, the bottom FS is 3mV and I can read 250, maybe 100 µV.

Also a VTVM for peaking and nulling non-RF levels. Here I use an HP-410-C, which is actually a transistorized VTVM.

A good Frequency Counter.

One thing I just got is a 0 to 450 volt power supply. This I can use on spare part electrolytic caps sitting around.

On the want list is another dummy load and coax so I can put it in the far corner of the basement.

One thing you can do is look at web sites of people who work on radios and see what they use and get ideas from there. You know what you want to do with it, you know your skill level, ect.

Above all; HAVE FUN!

--

Bob
KD8WU

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Sunday, 24 December 2023

BobKD8WU

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Saturday, 23 December 2023

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Bob
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Bob
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Bob
KD8WU

Bob
KD8WU