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Can I use a 120V Variac to get 220V?



 
 
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  #1  
Old August 18th 06, 08:31 PM posted to rec.radio.amateur.homebrew
external usenet poster
 
Posts: 32
Default Can I use a 120V Variac to get 220V?

I want to reform the electrolytics in an amp I'm bringing back to life.
It runs high power, 220 volts ac only.

Can I use my 110 volt variac in conjunction with a 110V to 220V step-up
transformer to power up the amp? Obviously I'd not go key-down, but I
do want to ultimately get to the full B+ on the tubes.

How would I wire-up the variac / transformer, assuming it's possible?

Thanks in advance for the help, guys.

73,
Jeff
W8KZW

  #2  
Old August 18th 06, 09:59 PM posted to rec.radio.amateur.homebrew
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Posts: 58
Default Can I use a 120V Variac to get 220V?


wrote:
I want to reform the electrolytics in an amp I'm bringing back to life.
It runs high power, 220 volts ac only.

Can I use my 110 volt variac in conjunction with a 110V to 220V step-up
transformer to power up the amp? Obviously I'd not go key-down, but I
do want to ultimately get to the full B+ on the tubes.

How would I wire-up the variac / transformer, assuming it's possible?

Thanks in advance for the help, guys.

73,
Jeff
W8KZW


Hi Jeff, Wire the output of the variac to the primary of the
transformer, and the secondary to the 220V power input of the Amp. You
may want to remove the tube(s) or disable the filaments to reduce the
burden on the step up transformer.
If the power transformer in the amp has a 110v tap, connect it up and
then just use the variac. Be careful when you are doing this, there
are all sorts of lethal voltages present. Good luck.
Gary N4AST

  #3  
Old August 18th 06, 09:59 PM posted to rec.radio.amateur.homebrew
external usenet poster
 
Posts: 58
Default Can I use a 120V Variac to get 220V?


wrote:
I want to reform the electrolytics in an amp I'm bringing back to life.
It runs high power, 220 volts ac only.

Can I use my 110 volt variac in conjunction with a 110V to 220V step-up
transformer to power up the amp? Obviously I'd not go key-down, but I
do want to ultimately get to the full B+ on the tubes.

How would I wire-up the variac / transformer, assuming it's possible?

Thanks in advance for the help, guys.

73,
Jeff
W8KZW


Hi Jeff, Wire the output of the variac to the primary of the
transformer, and the secondary to the 220V power input of the Amp. You
may want to remove the tube(s) or disable the filaments to reduce the
burden on the step up transformer.
If the power transformer in the amp has a 110v tap, connect it up and
then just use the variac. Be careful when you are doing this, there
are all sorts of lethal voltages present. Good luck.
Gary N4AST

  #4  
Old August 19th 06, 01:40 AM posted to rec.radio.amateur.homebrew
external usenet poster
 
Posts: 32
Default Can I use a 120V Variac to get 220V?


Hi Jeff, Wire the output of the variac to the primary of the
transformer, and the secondary to the 220V power input of the Amp. You
may want to remove the tube(s) or disable the filaments to reduce the
burden on the step up transformer.
If the power transformer in the amp has a 110v tap, connect it up and
then just use the variac. Be careful when you are doing this, there
are all sorts of lethal voltages present. Good luck.
Gary N4AST


Thanks, Gary, but the devil is in the details.

The 220 out from the step-up transformer is from one end of the
secondary coil to the other.

The amp is essentially asking for two 110 V lines, working against a
common "ground".

So, somehow I must go from this:

0 -----220----- 0

to this:

0 0

0

and therein lies my confusion.

Here are the connectors labeled:


0 0
A B

to this:

0 0
C D
0
E

.... all I need to do is to connect the dots!

  #6  
Old August 19th 06, 08:55 PM posted to rec.radio.amateur.homebrew
external usenet poster
 
Posts: 58
Default Can I use a 120V Variac to get 220V?


wrote:

Hi Jeff, Wire the output of the variac to the primary of the
transformer, and the secondary to the 220V power input of the Amp. You
may want to remove the tube(s) or disable the filaments to reduce the
burden on the step up transformer.
If the power transformer in the amp has a 110v tap, connect it up and
then just use the variac. Be careful when you are doing this, there
are all sorts of lethal voltages present. Good luck.
Gary N4AST


Thanks, Gary, but the devil is in the details.

The 220 out from the step-up transformer is from one end of the
secondary coil to the other.

The amp is essentially asking for two 110 V lines, working against a
common "ground".

So, somehow I must go from this:

0 -----220----- 0

to this:

0 0

0

and therein lies my confusion.

Here are the connectors labeled:


0 0
A B

to this:

0 0
C D
0
E

... all I need to do is to connect the dots!


Jeff, I would just leave the ground floating and connect C and D to the
220V secondary of the transformer. All you are trying to do is
energize the HV supply of the amp. If you have a schematic of the amp,
you should be able to figure where to supply the 220 to do just that.

Gary N4AST

  #8  
Old August 20th 06, 09:11 AM posted to rec.radio.amateur.homebrew
mike
external usenet poster
 
Posts: 9
Default Can I use a 120V Variac to get 220V?

John, N9JG wrote:
Your advice is elegant in its simplicity.


And OPTIMISTIC in it's generality.
While one might imagine situations where this technique is
useful, it would be better to define a strategy that takes
into consideration the exact configuration of the PS in
your unspecified amplifier.

If your caps don't need reforming, any technique will work.
If they do, you're gonna have some current flow. It's not
hard to imagine a scenario whereby you have 25W or more
dissipated in your caps. I don't call this safe. A 100W
light bulb will keep you from blowing up the rectifiers while
you're blowing up the caps.

Assuming you have solid-state rectifiers, go back to the
variac and transformer. Depending on the value of the high voltage,
There may be issues if you just turn off the tube filaments.
The series lamp can still be helpful, but isn't the whole story.

It's always helpful to disclose the parameters of the situation
when asking for advice. Otherwise, you'll get 10 different
solutions based on 10 different assumptions, none of which will be
correct.
mike

"Andrew VK3BFA" wrote in message
oups.com...

wrote:

I want to reform the electrolytics in an amp I'm bringing back to life.
It runs high power, 220 volts ac only.

Can I use my 110 volt variac in conjunction with a 110V to 220V step-up
transformer to power up the amp? Obviously I'd not go key-down, but I
do want to ultimately get to the full B+ on the tubes.

How would I wire-up the variac / transformer, assuming it's possible?

Thanks in advance for the help, guys.

73,
Jeff
W8KZW


Its relatively simple and easy. Connect a 100w light globe in series
with the ac power input - this will limit current to a safe level. Run
for 10 hrs or so, will give caps a chance to reform....start with the
tubes in so the filament current draw limits cap voltage, then later
remove tubes to get virtually full voltage across caps....

Andrew VK3BFA.




  #9  
Old August 20th 06, 10:40 AM posted to rec.radio.amateur.homebrew
Andrew VK3BFA
external usenet poster
 
Posts: 28
Default Can I use a 120V Variac to get 220V?

mike wrote:
John, N9JG wrote:
Your advice is elegant in its simplicity.


And OPTIMISTIC in it's generality.
While one might imagine situations where this technique is
useful, it would be better to define a strategy that takes
into consideration the exact configuration of the PS in
your unspecified amplifier.


Gee, that sounds like the opening page of a PowerPoint presentation -
your not a manager by proffession, are you?

And if you have an engineering degree, and want to engage in endless
metaphysical speculation, thats a very good idea.....whatever it
was.....amongst the verbiage....

If your caps don't need reforming, any technique will work.
If they do, you're gonna have some current flow. It's not
hard to imagine a scenario whereby you have 25W or more
dissipated in your caps. I don't call this safe. A 100W
light bulb will keep you from blowing up the rectifiers while
you're blowing up the caps.


Rubbish. Where do you get this 25w figure from, and across how many
capacitors in a (typical) series string - oh, and lets ignore idling
current through transformer and bleeeder resistors, and filamnet
current drain, and blowers, and dial lamps, and.....which would further
reduce available volts across the caps.... And whats this "imagine a
scenario" stuff - I thought you were trying to be precise and were
chiding me for my lack of hard data....

Assuming you have solid-state rectifiers, go back to the
variac and transformer. Depending on the value of the high voltage,
There may be issues if you just turn off the tube filaments.
The series lamp can still be helpful, but isn't the whole story.


So, what voltage do you set the variac too? - how do you work it out?

It's always helpful to disclose the parameters of the situation
when asking for advice. Otherwise, you'll get 10 different
solutions based on 10 different assumptions, none of which will be
correct.
mike


True. There are probably 10 different ways of puting out a fire, but
the easiest is dumping a bucket of water on it.

Honestly, this is ridiculous - most modern (ie, last 40 years) caps are
fine, will survive horrendous abuse, and unless you have the
manufacturers data sheets for these capacitors, (and the power
transformer, and the rectifiers) how are you going to set these
parameters anyway? - this is a linear amplifier, not the space shuttle.

Why do people insist on making things sooooo complicated, almost
theoretical physics level - it isnt. Dont let irelevant theory get in
the way of practical electronics.

The intial switch on of ANYTHING that hasnt been powered up for years
is going to be the time it dies - at least the bulb will stop it
bursting into flames, the variac method will jsut slowly ramp up volts
until something blows catasphropically (I know, used to do this, got
sick of replacing fuses in the variac.)

As well, you have the added complication of multiple, lashed together
transformers which MUST all be correctly phased and able to take the
load current . a recipe for confusion at least.

And no, I cant spell. Spend too much time with soldering irons rather
than physics journals.

Andrew VK3BFA.

"Andrew VK3BFA" wrote in message
oups.com...

wrote:

I want to reform the electrolytics in an amp I'm bringing back to life.
It runs high power, 220 volts ac only.

Can I use my 110 volt variac in conjunction with a 110V to 220V step-up
transformer to power up the amp? Obviously I'd not go key-down, but I
do want to ultimately get to the full B+ on the tubes.

How would I wire-up the variac / transformer, assuming it's possible?

Thanks in advance for the help, guys.

73,
Jeff
W8KZW

Its relatively simple and easy. Connect a 100w light globe in series
with the ac power input - this will limit current to a safe level. Run
for 10 hrs or so, will give caps a chance to reform....start with the
tubes in so the filament current draw limits cap voltage, then later
remove tubes to get virtually full voltage across caps....

Andrew VK3BFA.





  #10  
Old August 20th 06, 10:58 PM posted to rec.radio.amateur.homebrew
external usenet poster
 
Posts: 58
Default Can I use a 120V Variac to get 220V?


Andrew VK3BFA wrote:
mike wrote:
John, N9JG wrote:
Your advice is elegant in its simplicity.


And OPTIMISTIC in it's generality.
While one might imagine situations where this technique is
useful, it would be better to define a strategy that takes
into consideration the exact configuration of the PS in
your unspecified amplifier.


Gee, that sounds like the opening page of a PowerPoint presentation -
your not a manager by proffession, are you?

And if you have an engineering degree, and want to engage in endless
metaphysical speculation, thats a very good idea.....whatever it
was.....amongst the verbiage....

If your caps don't need reforming, any technique will work.
If they do, you're gonna have some current flow. It's not
hard to imagine a scenario whereby you have 25W or more
dissipated in your caps. I don't call this safe. A 100W
light bulb will keep you from blowing up the rectifiers while
you're blowing up the caps.


Rubbish. Where do you get this 25w figure from, and across how many
capacitors in a (typical) series string - oh, and lets ignore idling
current through transformer and bleeeder resistors, and filamnet
current drain, and blowers, and dial lamps, and.....which would further
reduce available volts across the caps.... And whats this "imagine a
scenario" stuff - I thought you were trying to be precise and were
chiding me for my lack of hard data....

Assuming you have solid-state rectifiers, go back to the
variac and transformer. Depending on the value of the high voltage,
There may be issues if you just turn off the tube filaments.
The series lamp can still be helpful, but isn't the whole story.


So, what voltage do you set the variac too? - how do you work it out?

It's always helpful to disclose the parameters of the situation
when asking for advice. Otherwise, you'll get 10 different
solutions based on 10 different assumptions, none of which will be
correct.
mike


True. There are probably 10 different ways of puting out a fire, but
the easiest is dumping a bucket of water on it.

Honestly, this is ridiculous - most modern (ie, last 40 years) caps are
fine, will survive horrendous abuse, and unless you have the
manufacturers data sheets for these capacitors, (and the power
transformer, and the rectifiers) how are you going to set these
parameters anyway? - this is a linear amplifier, not the space shuttle.

Why do people insist on making things sooooo complicated, almost
theoretical physics level - it isnt. Dont let irelevant theory get in
the way of practical electronics.

The intial switch on of ANYTHING that hasnt been powered up for years
is going to be the time it dies - at least the bulb will stop it
bursting into flames, the variac method will jsut slowly ramp up volts
until something blows catasphropically (I know, used to do this, got
sick of replacing fuses in the variac.)

As well, you have the added complication of multiple, lashed together
transformers which MUST all be correctly phased and able to take the
load current . a recipe for confusion at least.

And no, I cant spell. Spend too much time with soldering irons rather
than physics journals.

Andrew VK3BFA.


All he was asking was how to hook up a variac. Seemed simple enough.

Gary N4AST

 




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