What to do with 100v tube amps? What step down should I use?

[Galaxie65]

So I have a set of 100v tube amps and I want to make sure that I take care of them. I have heard that I can use the standard socket value without much issue. However I would like to be smart about it and have these last for a long time without issue.

Is there a brand or model that anyone would recommend that I should use? I know that I can use a Variac but it would be nice to have a little unit that I can slide into my rack vs the large cylinder and knob

Any help would be appreciated!

 

[RS Steve]

This is what I run for my Luxman tube amps, didn't purchase from this site though.

https://www.ebay.com/itm/Voltage-Co...1500W-for-Japan-products-Coiled-/252638746244

Edit, I run two of these, one for each amp.

 

[Retrovert]

One can use the external Japanese transformer adapter, which is a bit pricey, or add a bucking transformer of 20 VAC to the primary to normalize 100 VAC to 120 VAC. Since this is done at the primary the current may be lower so the transformer is consequently not that expensive.

Other discussions on AK contain the details.

 

[trainbuftony]

Additionally you could order 2 new power transformers with the correct primary voltage and the same secondary setup. Swap them out snd use them like they were made for use on 120vac. Save the originals in case you decide to sell.

 

[Blue Shadow]

New transformers for the amps could be expensive. The amps only draw a couple hundred watts and to get going you could use one transformer that can supply that with ease. The use of two 1500 watt units is overkill but when you get them fixed and want to use them in the rig, using overkill might be worth the trouble.

 

[Retrovert]

A bucking transformer is a lot less expensive than new transformers and it won't affect the value as would removing existing parts and losing them.

 

[petes'picks]

Bk precision tr110 depending on your current needs.

 

[gadget73]

If they don't have a 120v tap inside that could be used, a bucking transformer is the easy way. Quite possible the commercial products are electrically the same, a simple autotransformer with the appropriate taps rather than a full on iso trans.

 

[Retrovert]

Bk precision tr110 depending on your current needs.

That is over $200 delivered.

A 20 VAC bucking transformer is $15 delivered.

 

[Retrovert]

If they don't have a 120v tap inside that could be used, a bucking transformer is the easy way. Quite possible the commercial products are electrically the same, a simple autotransformer with the appropriate taps rather than a full on iso trans.

The B&K Precision TR110 is a full isolation transformer. Fancy fancy, pricey pricey.

 

[petes'picks]

The B&K Precision TR110 is a full isolation transformer. Fancy fancy, pricey pricey.

I just paid 50 for one with a little patience, and you can select different output voltages.

 

[Retrovert]

I just paid 50 for one with a little patience, and you can select different output voltages.

Nice.

At that price it's hard to justify adding a bucking transformer inside the cabinet.

 

[Sound Dragon]

What about a Variac?

 

[Retrovert]

What about a Variac?

An autotransformer is not the optimal solution here. It's always on, with some heating, the maximum current must not be exceeded, the wiper isn't really designed to sit in one position forever, it must be adjusted with a meter, and if the knob is bumped the voltage is altered and the equipment can be damaged or destroyed.

Variac, BTW, was a specific trademark of General Radio often used as a generic name. GR let the trademark lapse at some point.

 

[Blue Devil]

An autotransformer is not the optimal solution here. It's always on, with some heating, the maximum current must not be exceeded, the wiper isn't really designed to sit in one position forever, it must be adjusted with a meter, and if the knob is bumped the voltage is altered and the equipment can be damaged or destroyed.

I've read this elsewhere too. How does McIntosh get around a couple of these issues I wonder.

 

[Retrovert]

Many transformers are constructed such that the primary has multiple taps and acts like an autotransformer.

The jumper for voltage is selecting where the mains enters the transformer.

 

[blhagstrom]

120v-100v step down transformers are readily available at reasonable prices on eBay and Amazon.

All they are is a transformer in a box with a switch and outlets and a cord.

Transformer manufacturing is not a difficult or expensive or precision thing. Millions of transformers (billions? Baaaajillions?) have been made and work forever. The Marantz 2500 POS is an exception.

I’ve salvaged nice 100v secondary transformers from things and turned them into stand alone step downs. I’ve even done some 110 secondary for tube gear use. Nothing tricky if the transformer has the windings.

If you’re a little handy, you can probably find a 120v 100v secondary transformer online and build a unit in an evening or two. The case is the toughest part unless you’re handy at making cases.

I nice toroid would be the nicest. They are stronger versus size than the standard frame transformer.

Bucking transformers do seem to be the cheaper route and are smaller. I haven’t gotten around to playing with those yet.

 

[craggd]

I have several Sanyo-TSD-N15LU-Step-Down-Transformers-120V-Input-100V-Output-15A- and think they are great. One quite reasonable now on the bay.

 

[Sound Dragon]

An autotransformer is not the optimal solution here. It's always on, with some heating, the maximum current must not be exceeded, the wiper isn't really designed to sit in one position forever, it must be adjusted with a meter, and if the knob is bumped the voltage is altered and the equipment can be damaged or destroyed.

Variac, BTW, was a specific trademark of General Radio often used as a generic name. GR let the trademark lapse at some point.

Learned something new! Thanks.

 

[ducati_EL34]

A bucking transformer is a lot less expensive than new transformers and it won't affect the value as would removing existing parts and losing them.

Huh? I don’t lose good iron!