Topics

(OT) repair tools: Autotransformers/variacs

@0culus
 

Is there a reputable source of new autotransformers/variacs that can handle relatively large current? I need one for my 585A repair, but it seems a lot of them are only a few amps. I think at least a 10 amp would be safer given the line fuse rating @ 117V (7A slow blow).

Thanks!

Sean

Eric
 

Sean,

Circuit Specialist

https://www.circuitspecialists.com/variac-with-digital-display-tdgc2-2d.html

they are a china reseller however they have auto transformers up to 30 amps I have the one linked. Build quality the metal is thin but the movement is smooth and the meter is accurate to +-1 Vac so good enough. And not bad current to price ratio.


Eric

On 6/23/2020 2:05 PM, sdturne@q.com wrote:
Is there a reputable source of new autotransformers/variacs that can handle relatively large current? I need one for my 585A repair, but it seems a lot of them are only a few amps. I think at least a 10 amp would be safer given the line fuse rating @ 117V (7A slow blow).

Thanks!

Sean


stevenhorii
 

Search eBay for "Variac".

Here's an example of a 10A one:

https://www.ebay.com/itm/Transformer-Variable-AC-Voltage-Regulator-Metered-1000w-10Amp-110V-Auto/173189420709

Not made in the US.

One thst is a known manufacturer (Staco):

https://www.ebay.com/itm/Staco-Powerstat-Variable-Autotransformer-Variac-1-4-KVA-10A-120-Volt/303359131963

Much higher price and used.

I have no relationship with either of these sellers.

Steve H

On Tue, Jun 23, 2020 at 2:05 PM <sdturne@q.com> wrote:

Is there a reputable source of new autotransformers/variacs that can
handle relatively large current? I need one for my 585A repair, but it
seems a lot of them are only a few amps. I think at least a 10 amp would be
safer given the line fuse rating @ 117V (7A slow blow).

Thanks!

Sean




Jack Reynolds
 

Hi Sean,

You said you were looking for a "new" autotransformer and you may want to think about that word.  Off the top of my head Superior Electric and Staco are 2 well known US companies that have been making 10 amp and above cased units for years.  They are still available new and are presumably made in the US more or less. However it would appear that the new ones go for around $400 and above.  There are however an abundance of used units on Ebay and they can be had for well under $100 including shipping (they are heavy).  The older US made ones are built like battleships or old Tek scopes and with the Ebay refund guarantee for NFG that is where I would put my money.  If you truly want to pay for a new one, google those two companies and you will likely find a bunch of dealers who sell them.  I hope this helps.

Jack Reynolds

On 6/23/2020 2:05 PM, sdturne@q.com wrote:
Is there a reputable source of new autotransformers/variacs that can handle relatively large current? I need one for my 585A repair, but it seems a lot of them are only a few amps. I think at least a 10 amp would be safer given the line fuse rating @ 117V (7A slow blow).

Thanks!

Sean


Ondrej Pavelka
 

They don't make them as they used to.... I would look for one of similar
vintage to your scope

On Tue, 23 Jun 2020, 20:58 Jack Reynolds, <jackandladyreynolds@...>
wrote:

Hi Sean,

You said you were looking for a "new" autotransformer and you may want
to think about that word. Off the top of my head Superior Electric and
Staco are 2 well known US companies that have been making 10 amp and
above cased units for years. They are still available new and are
presumably made in the US more or less. However it would appear that the
new ones go for around $400 and above. There are however an abundance
of used units on Ebay and they can be had for well under $100 including
shipping (they are heavy). The older US made ones are built like
battleships or old Tek scopes and with the Ebay refund guarantee for NFG
that is where I would put my money. If you truly want to pay for a new
one, google those two companies and you will likely find a bunch of
dealers who sell them. I hope this helps.

Jack Reynolds

On 6/23/2020 2:05 PM, sdturne@q.com wrote:
Is there a reputable source of new autotransformers/variacs that can
handle relatively large current? I need one for my 585A repair, but it
seems a lot of them are only a few amps. I think at least a 10 amp would be
safer given the line fuse rating @ 117V (7A slow blow).

Thanks!

Sean





Dale H. Cook
 

On 6/23/2020 2:05 PM, Sean wrote:

Is there a reputable source of new autotransformers/variacs that can handle relatively large current?
If you want a quality autotransformer to handle large currents I strongly suggest that you forget new, bite the bullet, and buy a used General Radio Variac. GR Variacs are the Rolls Royce of variable autotransformers. I own several of them. Buying them other than in person, say at a hamfest, can, however, be risky. You need to be able to see that the track is not damaged and has not been sanded down (GR used a special silver alloy coating for the track which must be intact) and that the brush is intact and not badly worn.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcity/radios/

snapdiode
 

I wish people would put their location when asking for things like this.

https://www.kijiji.ca/v-appareils-electroniques/ville-de-montreal/variacs-a-vendre/1470224804

Jim Ford
 

Yeah, Sean, I have a Staco 7.6 A autotransformer rescued from work trash. It's pretty beefy and vintage, complete with crinkle-paint finish. I've not used it for anything yet, but perhaps soon as I delve into vacuum tube audio. Personally, I can't see having vacuum tubes in a scope except for the CRT (come to think of it, all 4 of my scopes have CRTs) because I tend to want to go to high frequencies, but that's me.
Maybe a TWT would be in order for moon-bounce someday...

Anyway, I would second the search for a more vintage autotransformer.
Of course, I don't buy anything from China, anyway. I'd encourage others not to as well. Good luck!

Jim Ford

------ Original Message ------
From: "Jack Reynolds" <jackandladyreynolds@...>
To: TekScopes@groups.io
Sent: 6/23/2020 11:57:43 AM
Subject: Re: [TekScopes] (OT) repair tools: Autotransformers/variacs

Hi Sean,

You said you were looking for a "new" autotransformer and you may want to think about that word. Off the top of my head Superior Electric and Staco are 2 well known US companies that have been making 10 amp and above cased units for years. They are still available new and are presumably made in the US more or less. However it would appear that the new ones go for around $400 and above. There are however an abundance of used units on Ebay and they can be had for well under $100 including shipping (they are heavy). The older US made ones are built like battleships or old Tek scopes and with the Ebay refund guarantee for NFG that is where I would put my money. If you truly want to pay for a new one, google those two companies and you will likely find a bunch of dealers who sell them. I hope this helps.

Jack Reynolds

On 6/23/2020 2:05 PM, sdturne@q.com wrote:
Is there a reputable source of new autotransformers/variacs that can handle relatively large current? I need one for my 585A repair, but it seems a lot of them are only a few amps. I think at least a 10 amp would be safer given the line fuse rating @ 117V (7A slow blow).

Thanks!

Sean




@0culus
 

Thanks everyone! I found a decent deal on a Staco 10 amp variac thanks to John Griessen...I may pull the trigger on that as a stopgap. I definitely wouldn't mind finding a nice GR model...if local hamfests ever come back, I'll definitely keep my eyes open for one. Thanks for the tips on what to look for Dale!

Sean

Greg Muir
 

Sean,

I picked up the 20A/2KVA autotransformer several years ago that Eric previously cited in this topic. It is a very beefy unit that is well constructed and meets the stated specifications. I also have it set up to reverse feed a used Cutler-Hammer/Westinghouse 3 KVA dry-type distribution transformer to give me selectable voltage anywhere between 208-240VAC when needing to work on higher current equipment requiring the higher input line voltage.

I’m not saying that this unit is only from Circuit Specialists I have also seen it in the ads from other sellers as well as on ePay. And if you need the high current capacity, the $95-$100 price gives you a very solid unit. Some sellers even offer spare replacement carbon brushes for it – not something you really need but nice to have on hand anyway.

What I have found buying used brand name autotransformers (Staco, General Radio) is that you often pay high prices for the name on them. If the name is important then it is understood. I do have a couple of lower current GenRad autotransformers but they are relinquished to smaller equipment work with lighter current needs. When looking at the insides of this 20A unit one cannot really tell the difference in construction between it and an American made product. Judging from all of the identical looking units at various current ratings it seems that these Chinese make autotransformers must be coming from the same manufacturer.

Greg

 

Hi Sean,

I bought in January an autotransformer to resuscitate my old 547 oscilloscope, whose maximum power consumption is around 500 watt.

To be on the super safe side I bought a 20 amp one, or 2000VA, 0 - 130V, at Amazon for $93. It is without doubt a Chinese one, identical to many other cheap ones.
For $20 less I could have bought a 10 amp. But the bigger one was worth to me for the difference in price.

There are few electrical devices that are simpler than an autotransformer, and more everlasting. The toroidal core will not wear out. The compact winding will not wear out. The carbon contact that slides over the stripped upper portion of the winding may wear out, but probably not in a lifetime.

This inexpensive unit has given me a perfect service. It seems to be solidly built, has a power switch, a fuse, two AC outlets and a basic meter. Connector cable and plug seem solid.

I consider myself an American patriot, but I have been fortunate buying inexpensive Chinese electrical, electronic products.
I see no reason to spend more money on an autotransformer of prestigious brand.
IF... if the Chinese one would fail.... (horror!)... it should be 1000 times easier to fix than the simplest Tektronix oscilloscope.

Ernesto

Dave Seiter
 

In the past year I've come across two low power units that both had open windings with the break right at one end of the coil.  I repaired one for personal, light use, but other one had more problems, so it's in the junk box.  I try to buy any I come across, but they seem to come in two flavors: very cheap (or free) because the person doesn't know what they are, and expensive, because it's a name brand, heavy, and/or fancy looking.  
-Dave

On Tuesday, June 23, 2020, 05:31:03 PM PDT, Ernesto <ebordon@...> wrote:

Hi Sean,

I bought in January an autotransformer to resuscitate my old 547 oscilloscope, whose maximum power consumption is around 500 watt.

To be on the super safe side I bought a 20 amp one,  or 2000VA, 0 - 130V,  at Amazon for $93.  It is without doubt a Chinese one,  identical to many other cheap ones.
For $20 less I could have bought a 10 amp.  But the bigger one was worth to me for the difference in price.

There are few electrical devices that are simpler than an autotransformer, and more everlasting.  The toroidal core will not wear out.  The compact winding will not wear out. The carbon contact that slides over the stripped upper portion of the winding may wear out,  but probably not in a lifetime.

This inexpensive unit has given me a perfect service.  It seems to be solidly built, has a power switch, a fuse,  two AC outlets and a basic meter. Connector cable and plug seem solid.

I consider myself an American patriot, but I have been fortunate buying inexpensive Chinese electrical, electronic products.
I see no reason to spend more money on an autotransformer of prestigious brand.
IF... if the Chinese one would fail.... (horror!)... it should be 1000 times easier to fix than the simplest Tektronix oscilloscope.

Ernesto

 

Dave:

If it's not too difficult, could you describe how you repaired the
broken winding?  I have a Superior Powerstat "Type 10" 1.25 amp unit
with a winding break that is accessible- it's located within the contact
area where the brush rides- but I can't figure out any way to attempt a
repair.

I'm not sure if I should be sending this back thru the Tekscopes
reflector, or directly to you.  I hope other Tekscopes group members
won't be irritated by my going thru the group to pose this question. I
see that there are already about 10 responses to the original post, and
maybe this is getting too far afield from Tek equipment as such.

Dave, thanks for any suggestions you might be able to offer.

Mike Dinolfo N4MWP

On 6/24/20 1:51 AM, Dave Seiter wrote:
In the past year I've come across two low power units that both had open windings with the break right at one end of the coil.  I repaired one for personal, light use, but other one had more problems, so it's in the junk box.  I try to buy any I come across, but they seem to come in two flavors: very cheap (or free) because the person doesn't know what they are, and expensive, because it's a name brand, heavy, and/or fancy looking.
-Dave
On Tuesday, June 23, 2020, 05:31:03 PM PDT, Ernesto <ebordon@...> wrote:

Hi Sean,

I bought in January an autotransformer to resuscitate my old 547 oscilloscope, whose maximum power consumption is around 500 watt.

To be on the super safe side I bought a 20 amp one,  or 2000VA, 0 - 130V,  at Amazon for $93.  It is without doubt a Chinese one,  identical to many other cheap ones.
For $20 less I could have bought a 10 amp.  But the bigger one was worth to me for the difference in price.

There are few electrical devices that are simpler than an autotransformer, and more everlasting.  The toroidal core will not wear out.  The compact winding will not wear out. The carbon contact that slides over the stripped upper portion of the winding may wear out,  but probably not in a lifetime.

This inexpensive unit has given me a perfect service.  It seems to be solidly built, has a power switch, a fuse,  two AC outlets and a basic meter. Connector cable and plug seem solid.

I consider myself an American patriot, but I have been fortunate buying inexpensive Chinese electrical, electronic products.
I see no reason to spend more money on an autotransformer of prestigious brand.
IF... if the Chinese one would fail.... (horror!)... it should be 1000 times easier to fix than the simplest Tektronix oscilloscope.

Ernesto



Dale H. Cook
 

On 6/24/2020 1:51 AM, Dave Seiter wrote:

... and expensive, because it's a name brand, heavy, and/or fancy looking.
General Radio Variacs are expensive not because they are a name brand, but because they are the best quality, including a proprietary silver alloy coating on the track that provides superior operation. While that many not be important for electronics hobbyists is sometimes an important consideration for electronics professionals.
--
Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcityeng/index.html

David Berlind
 

Sean, before you buy, how about I gift you mine?My form of paying it forward given the generosity of other forum members. It's a Superior Electric Powerstat Type 116 rated for 7.5 amps. It weighs a lot. You would just need to pay shipping. You would also just need to replace the plastic thumb-cover (retainer) on the fuse holder. Mine went missing somewhere in transit.

David

On June 23, 2020 4:41:52 PM sdturne@q.com wrote:

Thanks everyone! I found a decent deal on a Staco 10 amp variac thanks to John Griessen...I may pull the trigger on that as a stopgap. I definitely wouldn't mind finding a nice GR model...if local hamfests ever come back, I'll definitely keep my eyes open for one. Thanks for the tips on what to look for Dale!

Sean

Dave Seiter
 

Hi Mike,
I was able to bend up both sections of the break (it was actually a burn-through, I think) , trim the ends a bit, then bend them down and solder them together with a bit of extra flux.  I think the solder bridged to the next coil, but it's just a 3 amp unit, so I didn't care.  My break wasn't on the contact path, it was just "around the corner" from it.
-Dave

On Wednesday, June 24, 2020, 07:28:30 AM PDT, Mike Dinolfo <@mdinolfo> wrote:

Dave:

If it's not too difficult, could you describe how you repaired the
broken winding?  I have a Superior Powerstat "Type 10" 1.25 amp unit
with a winding break that is accessible- it's located within the contact
area where the brush rides- but I can't figure out any way to attempt a
repair.

I'm not sure if I should be sending this back thru the Tekscopes
reflector, or directly to you.  I hope other Tekscopes group members
won't be irritated by my going thru the group to pose this question. I
see that there are already about 10 responses to the original post, and
maybe this is getting too far afield from Tek equipment as such.

Dave, thanks for any suggestions you might be able to offer.

Mike Dinolfo N4MWP

On 6/24/20 1:51 AM, Dave Seiter wrote:
  In the past year I've come across two low power units that both had open windings with the break right at one end of the coil.  I repaired one for personal, light use, but other one had more problems, so it's in the junk box.  I try to buy any I come across, but they seem to come in two flavors: very cheap (or free) because the person doesn't know what they are, and expensive, because it's a name brand, heavy, and/or fancy looking.
-Dave
      On Tuesday, June 23, 2020, 05:31:03 PM PDT, Ernesto <ebordon@...> wrote:

  Hi Sean,

I bought in January an autotransformer to resuscitate my old 547 oscilloscope, whose maximum power consumption is around 500 watt.

To be on the super safe side I bought a 20 amp one,  or 2000VA, 0 - 130V,  at Amazon for $93.  It is without doubt a Chinese one,  identical to many other cheap ones.
For $20 less I could have bought a 10 amp.  But the bigger one was worth to me for the difference in price.

There are few electrical devices that are simpler than an autotransformer, and more everlasting.  The toroidal core will not wear out.  The compact winding will not wear out. The carbon contact that slides over the stripped upper portion of the winding may wear out,  but probably not in a lifetime.

This inexpensive unit has given me a perfect service.  It seems to be solidly built, has a power switch, a fuse,  two AC outlets and a basic meter. Connector cable and plug seem solid.

I consider myself an American patriot, but I have been fortunate buying inexpensive Chinese electrical, electronic products.
I see no reason to spend more money on an autotransformer of prestigious brand.
IF... if the Chinese one would fail.... (horror!)... it should be 1000 times easier to fix than the simplest Tektronix oscilloscope.

Ernesto




 

On Wed, Jun 24, 2020 at 07:34 AM, Dale H. Cook wrote:


General Radio Variacs are expensive not because they are a name brand, but
because they are the best quality, including a proprietary silver alloy
coating on the track that provides superior operation. While that many not be
important for electronics hobbyists is sometimes an important consideration
for electronics professionals.
Hi Dale,

I am an electronics hobbyist and former electronics professional. Could you explain what "important consideration" is different for the hobbyist and the professional?
Also, what difference can a proprietary silver alloy on the exposed track do in a simple variac?
The variacs I know operate with volts, not microvolts.

Ernesto

Dale H. Cook
 

On 6/24/2020 3:35 PM, Ernesto wrote:

Could you explain what "important consideration" is different for the hobbyist and the professional?
A professional needs equipment that will withstand frequent use, much more frequent than a hobbyist.

Also, what difference can a proprietary silver alloy on the exposed track do in a simple variac?
It reduces long-term wear of the track. See US patent application 2,949,592.
--
Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcityeng/index.html

 

Hi Dale,
Thank you for the Variac patent information. In appearance it seems like such a simple design but that is deceiving. The resistance of the brush is a critical design consideration that makes it possible for two adjacent windings to be connected together without causing a short. The silver alloy applied to each copper winding where it makes contact with the brush stabilizes the contact resistance between the winding and the brush. Otherwise the exposed copper would oxidize in a matter of days increasing the contact resistance between the winding and the carbon brush resulting in excessive heating of the brush causing the Variac to eventually fail.

The Variac is one of those very rare electrical devices that have been so useful for so long. General Radio originally patented Eduard Karplus's unique variable autotransformer design in 1933. The name GR chose for the device came from a contraction of "Variable" and "AC". The design is so simple and reliable that in all probability it will still be useful 50+ years from now.

Eduard Karplus, along with 2 other GR Engineers, created the famous GR-874 connector which also had a long useful life because of its outstanding bandwidth and its unique sexless design. Like the Variac, the GR-874 connector is simple and reliable.

General Radio, like Tektronix, was a company where the engineers were known for creating outstanding products.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dale H. Cook
Sent: Thursday, June 25, 2020 6:23 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] (OT) repair tools: Autotransformers/variacs

On 6/24/2020 3:35 PM, Ernesto wrote:

<SNIP>
Also, what difference can a proprietary silver alloy on the exposed track do in a simple variac?
It reduces long-term wear of the track. See US patent application 2,949,592.
--
Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA https://plymouthcolony.net/starcityeng/index.html





--
Dennis Tillman W7pF
TekScopes Moderator

KeepIt SimpleStupid
 

Usually a Variac is coupled with an isolation transformer when servicing "stuff".

The Variac wiper MUST be fused. 3 V at 20A is only 60 VA, but it will blow away a 10A wiper.    Sencore fused both in their devices that had metering and the ability to do leakage testing and had an electronic, e.g. Sencore PR570, fuse.
Many isolation transformers earth ground the secondary.  I used my home made system for working on TV's with polarized 2 prong plugs and audio amplifiers.I have no idea how I connected it, since I was probably 10 years old when I put it together.  Isolation came much later.
At work we had Variacs at the output of phase angle fired controllers to run 40V heaters.  I fixed the original designers mistakes and later replaced an entire panel (thermometer, ersatz V and I meters, Variac, fuse) with a DC power supply and temperature controller.  We got better heater life too.

On Thursday, June 25, 2020, 9:26:48 AM EDT, Dale H. Cook <bridgewaterma@...> wrote:

On 6/24/2020 3:35 PM, Ernesto wrote:

Could you explain what "important consideration" is different for the hobbyist and the professional?
A professional needs equipment that will withstand frequent use, much
more frequent than a hobbyist.

Also,  what difference can a proprietary silver alloy on the exposed track do in a simple variac?
It reduces long-term wear of the track. See US patent application 2,949,592.
--
Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcityeng/index.html