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Isolated variac suggestions - Printable Version

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RE: Isolated variac suggestions - bridkarl - 09-20-2025

I don’t necessarily need all
bells and whistles of a new scope. It’s just the price of a new scope isn’t much more than a used one.
What would I need for troubleshooting/repair of Philcos and table radios? Dual channel 15 mhz? I don’t do VHF work.

RE: Isolated variac suggestions - MrFixr55 - 09-20-2025

Hi Bridkarl,

I have used scopes for very specific jobs and have not used one to align a radio, but the following article gives an interesting perspective:

https://www.edn.com/scope-bandwidth-rise-time-and-the-rule-of-five/

For sinusoidal waves (What you would be looking at if aligning an AM radio), a 15 MHz scope would accurately display sine waves up to 3 MHz, which should be good enough for broadcast band. I am not even sure that you need dual trace. If you were to need to align an FM set, then all bets are off. IF on an FM set is typically 10.7MHz, and you need a "sweep" generator. Take this into consideration when you find the vintage FM set that you MUST have. (Never say never.)

RE: Isolated variac suggestions - bridkarl - 09-20-2025

I see I can get a brand new Hantek 2 channel 150 mhz scope with a built in signal generator for $200. Seems like that would be more than sufficient

RE: Isolated variac suggestions - DaleHCook - 09-21-2025

462ron Wrote:  As for an isolation transformer and variac, what I’ve been using for years is an RCA Isotap II that can be found sometime on eBay

I have used that same Isotap for decades as my isolation transformer. I built my own Variac box, with metering and fusing, using a GR Variac which I had in stock. Mine has a cover marking it portable, so I can use it in the field.

462ron - 462ron - 09-21-2025

With the Isotap having switchable voltages in 5V steps, I’m curious why you would need to add a variac to it? The Isotap is one compact unit that does both without taking up much bench space!

Ron

RE: Isolated variac suggestions - DaleHCook - 09-21-2025

463ron Wrote:With the Isotap having switchable voltages in 5V steps, I’m curious why you would need to add a variac to it?

My Variac box provides continuous control of the output voltage. Its input and output are fused, and the output has a voltmeter and an ammeter.

Note that I may be the only person in this topic who is actually using a Variac - that is a brand of variable autotransformer whose trademark was long held by the original licensee of patent 2949592, General Radio Company, and is now held by ISE, Inc. Calling anything else a "variac" is like calling every brand of automobile a "cadillac." Everything not made by GR or ISE is merely a variable autotransformer.

462ron - 462ron - 09-21-2025

Dale I do like that you have a voltage and amperage monitor on it. I have limited bench space so the compactness of the Isotap is a plus for me. It does have terminals to plug in a voltmeter and I usually run the output through a dim bulb that is built into my bench.

Ron

RE: Isolated variac suggestions - radiorich - 09-21-2025

Hello Ron,
That is too funny I also have ISotap but mine is branded RCA .
I guess since my shop was RCA dealer and warranty service shop .

Sincerely Richard

RE: Isolated variac suggestions - DaleHCook - 09-21-2025

462ron Wrote:  I have limited bench space ...

I do as well - see the pages for my Compact Shop. As one who has been collecting and using GR instruments for more than 50 years I had to have a GR Variac in the shop. They are the Rolls Royces of variable autotransformers.

RE: Isolated variac suggestions - radiorich - 09-21-2025

Hello Dale ,
Very Nice !

Sincerely Richard

462ron - 462ron - 09-22-2025

Wow Dale you did manage to stuff a lot into a limited area. My shop is in part of my son’s old bedroom along with some book shelves, a dresser, my wife’s multiple laundry baskets and I recently made a little more room by getting rid of a treadmill that was also there.

Ron

RE: Isolated variac suggestions - MrFixr55 - 09-22-2025

Hi Ron,

My comment is based on Kirk's signature stating the number of times that he was electrocuted. He must be a cat and have 9 lives. So if he has been electrocuted less than 8 times, He is good to go until the next time.

As for me, the fact that I made it so far is proof of a benevolent and loving God and a motherload of angels looking after me. My big claim to fame is that I caused the Big Blackout of November 1965 (According to my mom.

462ron - 462ron - 09-23-2025

MrFixr I always got a chuckle out of Kirk’s running total of electrocutions. My tongue in cheek comment was mostly to let everyone know Kirk was at Kutztown and doing well!
   
   As for blackouts, I too have caused one in our house. As a teen I had a small bench setup in my bedroom and one night did something that blew a fuse that caused no lights in the hall and other bedrooms. It was an old home close to 100 years old in need of an electrical upgrade!

Ron

RE: Isolated variac suggestions - MrFixr55 - 09-23-2025

Hi Ron, It was great to know that Kirk is able to practice the hobby again.

I didn't cause a blackout in the house in 1965, I took out the entire Northeast United States (At least that's what my mom accused me of.

I was playing with a Westinghouse 1/3 HP induction motor given to me by a teenager (I was only 10 at the time). I hooked it up, understanding what L1 and L2 meant). the motor hummed but did not start (I did not know about start windings and centrifugal switches at the time). It tripped the breaker for the "playroom". I unplugged the motor. When I reset the breaker, the lights dimmed, brightened, dimmed and went out. Mom, immediately screamed for me, thinking that I was playing with something. I told Mom that I reset the breaker for the playroom and did not touch the main breaker (I knew all of this by this time, as I read a lot about electricity).

Mom noticed that even the streetlights and lights in neighbors' houses were out and neighbors were gathering in the streets. Dad came home and having the only radio that worked (in the car said that the lights were out as far west as Chicago (not true but mist of Ontario, Canada was out). Mom screamed out "AND YOUR SON WAS THE REASON FOR IT!!!". Dad knew which of their 4 sons (and 2 daughters) Mom was talking about.

Did I actually cause the blackout? No. Dad understood that my experiments were merely a grain of sand in the truckload of sand that represented total electrical usage on the Northeast Power Grid. But Dad could not convince Mom for a long time. They all started calling me Con Edison (Although ConEd did not serve Long Island).

462ron - 462ron - 09-24-2025

Too funny MrFixr. The things we did as kids including things we had no right to mess with. I think I told this story before but when I first got interested in electronics as a young teen, I only played around with battery projects until one day a friend of mine and me found a floor model radio at the curb. Don’t remember the make or model but we dragged to his basement and removed the chassis and speaker. Put it on a table and started messing with it and me with no knowledge of radios or circuits at the time. Well my friend was leaning on the speaker which was upside down and at the same time he reached for one of the control shafts that had no knob on it. He screamed and was thrown against the wall which his mom heard. She comes down to find out what happened and after learning he gor a bad shock, she made us get rid of the radio and never mess with this stufff again! I now know that he probably was in contact with one of the field coil terminals with his arm and when he grabbed that bare metal shaft with his hand he got the full brunt of probably 300+ volts! He lost all interest in electronics after that while I continued on to this day.

Ron