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Trader
 
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Default Variac and New Amp

Hi,

I bought a small Cayin PP amp that puts out 12w per side(MT-12). The unit
was made for the Japanese market which uses 100v 50-50hz. On the back of
the amp (from the pictures) it looks to draw 120 watts. This would equate
into 1.2 amps. I wanted to buy my friends 3 amp variac. Will this get the
job done or should I be looking for a 5 amps Variac? Also, will the Variac
added any noise or to the output of the amp?

Thanks in advance


  #2   Report Post  
Patrick Turner
 
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Trader wrote:

Hi,

I bought a small Cayin PP amp that puts out 12w per side(MT-12). The unit
was made for the Japanese market which uses 100v 50-50hz. On the back of
the amp (from the pictures) it looks to draw 120 watts. This would equate
into 1.2 amps. I wanted to buy my friends 3 amp variac. Will this get the
job done or should I be looking for a 5 amps Variac? Also, will the Variac
added any noise or to the output of the amp?

Thanks in advance


Why buy a variac?

If someone dials up the wrong voltage, there could be some expensive
troubles, like all the heaters going open....

Why not buy a fixed voltage transformer to get from the mains you have to the
voltage of
the amp you bought?
It would need to be rated for about 150 VA at least.


  #3   Report Post  
Trader
 
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Patrick,

This makes great sense. I thought I could always use the Variac for other
things. My friend said that they cheap Variac I wanted to buy would add to
much noise to the line and kill the sound of my tube amp also.
I did located a 500 watt step down transformer. Do you think that this will
work without adding any noise the line and making my tube amp sound bad?
Here is the url
http://traveloasis.com/transformer2.html

Thanks in advance.

"Patrick Turner" wrote in message
...


Trader wrote:

Hi,

I bought a small Cayin PP amp that puts out 12w per side(MT-12). The

unit
was made for the Japanese market which uses 100v 50-50hz. On the back

of
the amp (from the pictures) it looks to draw 120 watts. This would

equate
into 1.2 amps. I wanted to buy my friends 3 amp variac. Will this get

the
job done or should I be looking for a 5 amps Variac? Also, will the

Variac
added any noise or to the output of the amp?

Thanks in advance


Why buy a variac?

If someone dials up the wrong voltage, there could be some expensive
troubles, like all the heaters going open....

Why not buy a fixed voltage transformer to get from the mains you have to

the
voltage of
the amp you bought?
It would need to be rated for about 150 VA at least.




  #4   Report Post  
Krzysiek Słychań
 
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Do you have 115 or 230V mains voltage? If you have 115V, you can use a 115/
15V power transformer with a primary winding connected to mains and a
secondary winding connected in series in counterphase (so that the voltage
that feeds the amp would be 115V-15V=100V) with the amp power iron's
primary. A nice method of stepping voltage down

Oh, and the 15V winding should be rated at least at approx. 1,5A (or more).


  #5   Report Post  
Patrick Turner
 
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Trader wrote:

Patrick,

This makes great sense. I thought I could always use the Variac for other
things. My friend said that they cheap Variac I wanted to buy would add to
much noise to the line and kill the sound of my tube amp also.


The variac will work OK, and it won't add the slightest noise to your tube amp,
providing there is an earth connection for where you plug in the
amp.


I did located a 500 watt step down transformer. Do you think that this will
work without adding any noise the line and making my tube amp sound bad?
Here is the url
http://traveloasis.com/transformer2.html


That should be perfect if you are going from 120v mains to the 100v required for
the
amp.

I assume you have 120v mains.

Patrick Turner.





  #6   Report Post  
Patrick Turner
 
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"Krzysiek Słychań" wrote:

Do you have 115 or 230V mains voltage? If you have 115V, you can use a 115/
15V power transformer with a primary winding connected to mains and a
secondary winding connected in series in counterphase (so that the voltage
that feeds the amp would be 115V-15V=100V) with the amp power iron's
primary. A nice method of stepping voltage down

Oh, and the 15V winding should be rated at least at approx. 1,5A (or more).


I seriously think you advice would confuse our original poster,
and place his amp and himself at some risk.

Patrick Turner.




  #7   Report Post  
Tim Williams
 
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Default

"Patrick Turner" wrote in message
...
I seriously think you advice would confuse our original poster,
and place his amp and himself at some risk.


Alright. Google "buck transformer" or something like that. I vote for this
as well -- it's a permanent solution.

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms


  #8   Report Post  
Doug Schultz
 
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Default


"Tim Williams" wrote in message
...
"Patrick Turner" wrote in message
...
I seriously think you advice would confuse our original poster,
and place his amp and himself at some risk.


Alright. Google "buck transformer" or something like that. I vote for
this
as well -- it's a permanent solution.

Tim

Yup
it works great the other way to bring newer mains voltage down to the level
of antique guitar amps spec too.

Doug


  #9   Report Post  
Jon Yaeger
 
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Default

in article , Patrick Turner at
wrote on 8/27/04 11:19 PM:



Trader wrote:

Patrick,

This makes great sense. I thought I could always use the Variac for other
things. My friend said that they cheap Variac I wanted to buy would add to
much noise to the line and kill the sound of my tube amp also.


The variac will work OK, and it won't add the slightest noise to your tube
amp,
providing there is an earth connection for where you plug in the
amp.


I did located a 500 watt step down transformer. Do you think that this will
work without adding any noise the line and making my tube amp sound bad?
Here is the url
http://traveloasis.com/transformer2.html

That should be perfect if you are going from 120v mains to the 100v required
for
the
amp.

I assume you have 120v mains.

Patrick Turner.



I don't necessarily agree. Sometimes an amp connected to a variac sounds
like crap. A fellow hobbyist I exchange notes with has had the same
experience - we have different variac models and each is capable of handling
the necessary current.

I can't explain why this is so but the amp improves markedly if plugged back
into the mains.

Many Japanese transformers have 120V windings but they may or may not bring
a lead out of the case. I would open the shell and see if there are other
options.

I've got some spare Kenwood and Pioneer transformers that would be suitable
for a 24W amp and which have multiple input voltage taps. They are pretty
easy to find, especially in a junked amp or one with a bad OPT.

Jon


  #10   Report Post  
Krzysiek Slychan
 
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"I seriously think you advice would confuse our original poster,
and place his amp and himself at some risk."

Why?




  #11   Report Post  
Patrick Turner
 
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Krzysiek Slychan wrote:

"I seriously think you advice would confuse our original poster,
and place his amp and himself at some risk."

Why?


Anyone farnarkling around with mains voltage without
considerable experience is likely to perhaps electrocute themselves or
burn something in the amp.

The fact that the original poster asked the question he did indicates
his knowledge/experience isn't high. If there is no obvious way to
voltage match from 120v to 100v,
say by rotating some voltage preset switch on the back of the amp,
then I assume that option is closed, so I thought it better to advise
some stranger
of the simplest and easiest and SAFEST way to achieve a wanted end
result,
and without the possibility of the variac being turned up to too high a
voltage
by accident, and not have that noticed by anyone.

Patrick Turner.




  #12   Report Post  
Trader
 
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As the original poster I would have to agree with Patrick. I ended up buying
a 500 watt step down/up transformer. I just hope it doesn't introduce noise
that is audible in my little tube amp.


"Patrick Turner" wrote in message
...


Krzysiek Slychan wrote:

"I seriously think you advice would confuse our original poster,
and place his amp and himself at some risk."

Why?


Anyone farnarkling around with mains voltage without
considerable experience is likely to perhaps electrocute themselves or
burn something in the amp.

The fact that the original poster asked the question he did indicates
his knowledge/experience isn't high. If there is no obvious way to
voltage match from 120v to 100v,
say by rotating some voltage preset switch on the back of the amp,
then I assume that option is closed, so I thought it better to advise
some stranger
of the simplest and easiest and SAFEST way to achieve a wanted end
result,
and without the possibility of the variac being turned up to too high a
voltage
by accident, and not have that noticed by anyone.

Patrick Turner.






  #13   Report Post  
Sander deWaal
 
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"Trader" said:

As the original poster I would have to agree with Patrick. I ended up buying
a 500 watt step down/up transformer. I just hope it doesn't introduce noise
that is audible in my little tube amp.


Just put it away far enough.
I'd say about half a meter or so would be enough.

--
Sander deWaal
"SOA of a KT88? Sufficient."
  #14   Report Post  
KeithW
 
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Default

Hi K & P,
As an Master Electrician of some 28 years I would have to agree with
Patrick on this. There's something counterintuitve about connecting the
secondary of a transformer in series with the primary and I still have to
study a diagram. I see nothing wrong with a properly sized/fused Variac,
perhaps somehow locked/restricted to the correct setting. That's how I'd do
it and I are an Electrician. After all...

- Nothing is so Smiple That You Can't Screw it Up. keithw...

PS: For those of you that would like to see a small tutorial on the subject
refer to

http://www.solaheviduty.com/products...t/bbeconns.pdf

H1-4 is the primary of the transformer and X1-4 is the "UNKNOWN" secondary.
SO for 120volt primary H1 & H3 would tie together and H2 & H4 would tie
together and primary voltage would be applied to H1 & H2. For 240volt
primary H2 & H3 would tie together and primary voltage would be applied to
H1 & H4. Basically connecting the "Two 120 Volt Coils" in parallel or
series. Same applies to the secondary of the transformer

"Patrick Turner" wrote in message
...


"Krzysiek Słychań" wrote:

Do you have 115 or 230V mains voltage? If you have 115V, you can use a

115/
15V power transformer with a primary winding connected to mains and a
secondary winding connected in series in counterphase (so that the

voltage
that feeds the amp would be 115V-15V=100V) with the amp power iron's
primary. A nice method of stepping voltage down

Oh, and the 15V winding should be rated at least at approx. 1,5A (or

more).

I seriously think you advice would confuse our original poster,
and place his amp and himself at some risk.

Patrick Turner.



  #15   Report Post  
Krzysiek Słychań
 
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OK, EOT.

Personally I'm advanced and careful enough to do mains wiring




  #16   Report Post  
Patrick Turner
 
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Trader wrote:

As the original poster I would have to agree with Patrick. I ended up buying
a 500 watt step down/up transformer. I just hope it doesn't introduce noise
that is audible in my little tube amp.


It definately won't make things noisy.
If anything, the amp should be further isolated from the mains and be quieter.
And noise or hum heard will be due to an existing problem in the power supply,
or an earth loop from some other gear.

Patrick Turner.



"Patrick Turner" wrote in message
...


Krzysiek Slychan wrote:

"I seriously think you advice would confuse our original poster,
and place his amp and himself at some risk."

Why?


Anyone farnarkling around with mains voltage without
considerable experience is likely to perhaps electrocute themselves or
burn something in the amp.

The fact that the original poster asked the question he did indicates
his knowledge/experience isn't high. If there is no obvious way to
voltage match from 120v to 100v,
say by rotating some voltage preset switch on the back of the amp,
then I assume that option is closed, so I thought it better to advise
some stranger
of the simplest and easiest and SAFEST way to achieve a wanted end
result,
and without the possibility of the variac being turned up to too high a
voltage
by accident, and not have that noticed by anyone.

Patrick Turner.





  #17   Report Post  
Tom Schlangen
 
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Hi Jon,

Sometimes an amp connected to a variac sounds
like crap.


I would second this, but would underline the word
"sometimes".

The most noticable improvement when going from variac
to normal mains was with a Klein+Hummel VS-55 amp
(6BM8 PP) I had to restore, which sounded like crap
at the variac, but got much better when directly
connected to mains.

Other amps (some with much higher power requirements
than the VS-55 mentioned above) showed no or only
hard-to-reproduce differences in sound w/ or w/o
the (same) variac.

I don't have an explanation, either.

Tom

--
A gleekzorp without a tornpee is like
a quap without a fertsneet (sort of).
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