R Core Transformers for tube amps

El Famoso

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Has anyone used an R core type power transformer for a build? I have used them for DIY hifi, especially for preamps because they are supposed to be a lot quieter than the old school type.

I know some folks like toroidal for this same reason. Thoughts? Opinions? Just looking for info from folks with more experience.
 

Nickfl

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Has anyone used an R core type power transformer for a build? I have used them for DIY hifi, especially for preamps because they are supposed to be a lot quieter than the old school type.

I know some folks like toroidal for this same reason. Thoughts? Opinions? Just looking for info from folks with more experience.

Do you have any sources in mind? From what I've read they tend to be hard to source in the specs you want and expensive. I'm not sure the reduction in noise would be worth the hassle and expense in a guitar amp.
 

El Famoso

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Do you have any sources in mind? From what I've read they tend to be hard to source in the specs you want and expensive. I'm not sure the reduction in noise would be worth the hassle and expense in a guitar amp.

I don’t really have any sources in mind. I see them online prices reasonably, but the voltages are too low for a guitar amp. The last one I purchased was around 280v for the high voltage side, which is great for a tube preamp but way too low for a gituar amp.

I have sent out for a couple quotes. I had my doubts too that it would be worth the hassle for this, hence my question.
 

tubegeek

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I don’t really have any sources in mind. I see them online prices reasonably, but the voltages are too low for a guitar amp. The last one I purchased was around 280v for the high voltage side, which is great for a tube preamp but way too low for a gituar amp.

I have sent out for a couple quotes. I had my doubts too that it would be worth the hassle for this, hence my question.

In theory they should be really great.

I saw that James Transformers sells them, they make output transformers for hifi power amps too, so maybe they'll have a good selection.

The way they're made it seems it'd be reasonably easy to customize them, even to rewind them yourself if you want to get crazy.
 

danlad

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Hypothetically I guess there could be scope for a voltage doubler circuit to raise voltages for the power amp. There are some old Aussie guitar amp schematics out there that do all sorts of ingenious things to get by with what they could get their hands on.
 

El Famoso

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First quote came back from a US company. More than double what I would be spending on a new Hammond, and minimum order of 2. @tubegeek I reached out to James for a quote. Thanks for the heads up. I am also checking with some suppliers in China. I imagine it will be pricey for a one off. I don't mind paying a little extra, because I think it would be cool to use one, but within reason.
 

tubegeek

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First quote came back from a US company. More than double what I would be spending on a new Hammond, and minimum order of 2. @tubegeek I reached out to James for a quote. Thanks for the heads up. I am also checking with some suppliers in China. I imagine it will be pricey for a one off. I don't mind paying a little extra, because I think it would be cool to use one, but within reason.
Be sure to ask James what they have as in-stock items too. Could be somewhat better priced.
 

El Famoso

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Found a Chinese supplier who does custom R-core one offs. Not much more than buying a standard i-core, even with shipping. I went ahead and ordered one to the specs I want. Ordering took a little while, trading messages back and forth due to the time difference, but I think we got it figured out. Pictures help, as my Chinese is, well, I can say hello and that's about it. :D

It would be nice to see these come into common use, as they are a better design. But I think a lot of people don't like deviating much from past amplifier designs, for fear of somehow affecting tone. Even hi-fi gets plagued by this, except when noise really matters, like in a phono preamp stage.
 

tubegeek

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Found a Chinese supplier who does custom R-core one offs. Not much more than buying a standard i-core, even with shipping. I went ahead and ordered one to the specs I want. Ordering took a little while, trading messages back and forth due to the time difference, but I think we got it figured out. Pictures help, as my Chinese is, well, I can say hello and that's about it. :D

It would be nice to see these come into common use, as they are a better design. But I think a lot of people don't like deviating much from past amplifier designs, for fear of somehow affecting tone. Even hi-fi gets plagued by this, except when noise really matters, like in a phono preamp stage.
I'll be interested to see how this plays out - please post pics when you get yours?
 

El Famoso

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Well, it shipped finally. Maybe that's a good sign that they actually customized it. Seller has been in business for 7 years so I don't think there will be any shenanigans. Fingers crossed and all that. Hopefully it gets here in the next month.
 

El Famoso

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Well it showed up today. I can’t believe it got here so fast. Just unboxed it. Construction looks pretty good. It was well packaged but the mounting bracket still got a little bent on one corner. Should be easy enough to straighten out.

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I’ll have to take it out to the shop and check the voltages. I’m pretty excited about this though. I love these transformers.
 

El Famoso

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Unloaded voltages about 10% high, which is good I think. I have 7v at 6.3v winding, 5.5 at 5v winding, and 385v at 355v to center tap winding. Can't do leg to leg with the high voltage winding, bc my multimeters all max out at 600v :rolleyes:. Thought my fluke was good but it only does 600v. The fancy fluke is at work, and I am at home at the moment. Still, very promising.

I know there are a couple of effects that happen with transformers to bring the voltage down when you actually wire them up. Voltage drop, loss of efficiency, and some voltage regulation effect. Hoping that ends up adding up to around 10%. :D. If not, well, it's a guitar amp, not rocket science, so I'm fine with close enough.
 

Nickfl

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Well it showed up today. I can’t believe it got here so fast. Just unboxed it. Construction looks pretty good. It was well packaged but the mounting bracket still got a little bent on one corner. Should be easy enough to straighten out.

View attachment 788550 View attachment 788551 View attachment 788552 View attachment 788553

I’ll have to take it out to the shop and check the voltages. I’m pretty excited about this though. I love these transformers.

Nice! If I may ask, how much did that end up costing all together by the time it showed up at your door?
 

El Famoso

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Nice! If I may ask, how much did that end up costing all together by the time it showed up at your door?
Right around $100 with shipping. So all told not much more than I would have paid just buying a Hammond or something off the shelf.

I will probably mount this inside the chassis. With the copper shield and transformer construction these things make almost no noise. I used one in a tube based phono stage and even before I put a metal divider between the power section and the signal section there was no noise from the transformer.
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You can see how close it is. It’s a huge amount of gain and I couldn’t believe how little noise comes off it.
 

tubegeek

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Right around $100 with shipping. So all told not much more than I would have paid just buying a Hammond or something off the shelf.

I will probably mount this inside the chassis. With the copper shield and transformer construction these things make almost no noise. I used one in a tube based phono stage and even before I put a metal divider between the power section and the signal section there was no noise from the transformer.
View attachment 788634

You can see how close it is. It’s a huge amount of gain and I couldn’t believe how little noise comes off it.
What circuit did you use for your phono pre? & what were your tube choices?
 

El Famoso

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What circuit did you use for your phono pre? & what were your tube choices?
That’s a copy of an Ear 834P circuit. You can find PSBs of them on the bay or other online places. I used old Soviet 6n2p tubes. These are very similar to a 12ax7, with a slightly different pin out.

The good folks at Lenco Heaven have several epic threads on these clones, including some tweaks to make sure the RIAA correction is accurate. Helped me get a very nice sound from mine.

I love the internet for being full of people who are enthusiastic and helpful about niche interests. One of the reasons I love TDPRI.
 

El Famoso

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Here’s a glamour shot :). I used an old commercial kitchen access panel I scrounged off a job. Walnut sides from wood scrounged off another job. Stainless was a bear to drill thru, but it came out ok.
 




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