Least expensive output transformer option for ST-35?
Posted: Wed Nov 14, 2012 8:44 amHello DIY Tubers -
The cold weather is finally approaching here in the Midwest and it's time to turn my attention from outdoor projects to indoor projects.
I have a couple of DIY Tube projects that have been idling on the back burner for awhile. First up is a ST-35 that I started a couple of years ago. I acquired the board for free and my original ST-35 (made 9.5 years ago in college!) is working so well that there's been no need for a second one.
The populated ST-35 board has accumulated enough dust and it's time to finish it.
I know exactly how good an ST-35 with the 'spec' components sounds, but I thought I'd take a different approach with this build. The iron and tubes make up a huge percentage of the total amplifier cost, so I'd like to find output transformers that provide reasonable performance - let's say +/- 3dB response between 120Hz to 15kHz with appropriate power handling - for as modest a price as possible.
Ultimately, I plan to use this back-up amplifier with a pair of Akai Jet Stream SW-30 speakers that I was given recently. Clearly, the 40-something year old speakers aren't a mark of sonic excellence, but they don't sound too bad, either. I'm trying to match the performance of this ST-35 to bookshelf speakers like the Jet Streams.
The Triode Dynaco repros are great and I wouldn't hesitate to buy them for a top-flight build. I've also used and enjoyed Edcors and my original ST-35 uses Hammond 1650s that I am very, very happy with.
In general, these transformers run north of $75, each.
What's out there for half that amount?
My first stop was Hammond - and it looks like the 125E transformer could work. Wired to work with an 8 Ohm speaker the resulting primary impedance is 8200. I don't know what the center tap is wired at, but presumably it's between 20% and 40%.
Does anybody have any thoughts on how well these would or would not work?
Mouser sells them for about $46, each.
How about other options?
I'd also be interested in hearing about the lowest cost power transformer - but I recognize that there are more concrete limitations on power transformers because they handle a fairly consistent amount of power and there isn't a trade-off curve for cost vs. fidelity like there is on output transformers.
Thanks for your input guys - I'll look forward to hearing about what's out there -
Drew
The cold weather is finally approaching here in the Midwest and it's time to turn my attention from outdoor projects to indoor projects.
I have a couple of DIY Tube projects that have been idling on the back burner for awhile. First up is a ST-35 that I started a couple of years ago. I acquired the board for free and my original ST-35 (made 9.5 years ago in college!) is working so well that there's been no need for a second one.
The populated ST-35 board has accumulated enough dust and it's time to finish it.
I know exactly how good an ST-35 with the 'spec' components sounds, but I thought I'd take a different approach with this build. The iron and tubes make up a huge percentage of the total amplifier cost, so I'd like to find output transformers that provide reasonable performance - let's say +/- 3dB response between 120Hz to 15kHz with appropriate power handling - for as modest a price as possible.
Ultimately, I plan to use this back-up amplifier with a pair of Akai Jet Stream SW-30 speakers that I was given recently. Clearly, the 40-something year old speakers aren't a mark of sonic excellence, but they don't sound too bad, either. I'm trying to match the performance of this ST-35 to bookshelf speakers like the Jet Streams.
The Triode Dynaco repros are great and I wouldn't hesitate to buy them for a top-flight build. I've also used and enjoyed Edcors and my original ST-35 uses Hammond 1650s that I am very, very happy with.
In general, these transformers run north of $75, each.
What's out there for half that amount?
My first stop was Hammond - and it looks like the 125E transformer could work. Wired to work with an 8 Ohm speaker the resulting primary impedance is 8200. I don't know what the center tap is wired at, but presumably it's between 20% and 40%.
Does anybody have any thoughts on how well these would or would not work?
Mouser sells them for about $46, each.
How about other options?
I'd also be interested in hearing about the lowest cost power transformer - but I recognize that there are more concrete limitations on power transformers because they handle a fairly consistent amount of power and there isn't a trade-off curve for cost vs. fidelity like there is on output transformers.
Thanks for your input guys - I'll look forward to hearing about what's out there -
Drew
