Fender Super Reverb Power Transformer

[CJ]

It is about the regulation percentage, a nice core with some thick primary wire will have good regulation numbers.

A transformer with poor regulation will have a 6.3 volt wind whose voltage will vary with load. So let's say you hokkthe XFMR up to a lighter load than the label says. You might then experience an unwanted jump in heater voltage.

 

[dmp]

I recently got some small toroid power transformers from ebay wound in China and the no-load H+ was 7.3, hooked up to the tubes it dropped to 7.1
I guess that is poor regulation???? I guess the cheap material choices lead to poor regulation (but also the small size)
The transformer 6.3v is rated at 2.28 A and I was powering two 12AY7 (0.6A)
But with 1 ohm resistors in series the H+ dropped to 6.1v

 

[soapfoot]

Interesting!

Would be fascinating to see someone as knowledgeable as yourself dissect a Hammond 300 series (eg 370BX) one day and see what you can observe

When I was 23 and reading guitar forums, I believed that Hammond transformers were trash because that’s what guitar snobs said. I learned a little bit more and sort of challenged that assumption later on. It’d be interesting if the guitar snobs were right in the end.

 

[imaradiostar]

I wish all power transformer manufacturers would wind power transformers with -5% and -10% windings; extra primary turns to tweak the voltage on the secondary side. I don't think I have ever seen a properly loaded transformer with a true 6.3v on the filaments when powered with the 122v out of the wall!

A few vintage units are correct when fed 110 or 115v, though.

 

[CJ]

i might just have to hack one of them hammonds to get the full skinny,

heater winds are tricky because there are only about 14 turns, 1 turn over you get 7.1, one turn under you get 5.5,

so adjusting the primary turns is the easiest way to fine tune the 6.3,

 

[john12ax7]

Interestingly the Hammond 200 series has two primaries at 115 and 125 V to allow for adjustment.

 

[scott2000]

I recently got some small toroid power transformers from ebay wound in China and the no-load H+ was 7.3, hooked up to the tubes it dropped to 7.1
I guess that is poor regulation???? I guess the cheap material choices lead to poor regulation (but also the small size)
The transformer 6.3v is rated at 2.28 A and I was powering two 12AY7 (0.6A)
But with 1 ohm resistors in series the H+ dropped to 6.1v

eesh...

 

[Redhouse]

Interestingly the Hammond 200 series has two primaries at 115 and 125 V to allow for adjustment.

The only one I could find on their website with 115/125 was the 284X which has a 1200v CT secondary.
(too high for a Fender amp)

High Voltage (Plate) & Filament - 32 VA to 454 VA (200 Series)

 

[john12ax7]

The only one I could find on their website with 115/125 was the 284X which has a 1200v CT secondary.
(too high for a Fender amp)

High Voltage (Plate) & Filament - 32 VA to 454 VA (200 Series)

It's explained at the bottom of the page. Most of them have it, but it seems they haven't updated the table to make it clear. Click on the datasheet for something like 273BX and you will see 115 and 125 taps.

 

[Redhouse]

 

[soapfoot]

By the way, I had a look at a Hammond 370BX I bought in 2020. It says "Made in Canada" on the sticker.

 

[heatwalk]

By the way, I had a look at a Hammond 370BX I bought in 2020. It says "Made in Canada" on the sticker.

Checks out for other ones I have around also, Made in Canada on both a small power transformer and line transformer. That brings up a point - how official are "Made In" statements? If a PCB is made and loaded with parts in China, but assembled into a complete product, is it technically "made in usa" because American hands put the screws in a chassis? (vs manufactured, assembled, etc. Seems like marketing can always find a way to put similar sounding stamps on things)