Hi,
This is my first build into the tube world and I'm currently shopping for outputs. I'm building Tom's DG300B SE amplifier and it requires 5K primary and I'd like to get 4 and 8 ohms taps. Tom suggest 15W+ outputs in the manual so that's what I'm aiming for.
Here's what I found so far and I'd appreciate all the feedback about the models/brands if you're experienced with them and I welcome any suggestions as I'm new to tube amp building.
So here's the list I've eyeing
Monolith Magnetics S-11
Hashimoto H-20-7U
SILK (SEC) S-525F
James tranformers JS-6123H (but way overprice on ePay) Unobtanium...
Thanks for your help
This is my first build into the tube world and I'm currently shopping for outputs. I'm building Tom's DG300B SE amplifier and it requires 5K primary and I'd like to get 4 and 8 ohms taps. Tom suggest 15W+ outputs in the manual so that's what I'm aiming for.
Here's what I found so far and I'd appreciate all the feedback about the models/brands if you're experienced with them and I welcome any suggestions as I'm new to tube amp building.
So here's the list I've eyeing
Monolith Magnetics S-11
Hashimoto H-20-7U
SILK (SEC) S-525F
James tranformers JS-6123H (but way overprice on ePay) Unobtanium...
Thanks for your help
James are nice, but IMO you can do better, so don't stress over those. Hashimotos are nice too, but a bit bass-shy. I'd go for Monolith, by reputation alone.
I dont call Hashimotos bass shy. I'm very happy how hashimoto sound. I have ISO FC20s too and like Hashimotos more.
The most of "general" 300B SE transformer will be in trouble at 20Hz 15W.
10W is more believable.... at 30Hz. 😉
If you use 5k transformer for 300B SE, the estimated output power (for example with 400-420V PSU) in A1 mode 6-7W, in A2 even 10-11W (depends of driving ability, OPT primary, secondary DCR, loss etc.).
Monolith is good candidate.
I had sent an email to Monolith but got an answer a week later, telling me they are in a production run and cannot take orders and will contact me later. Are they a small shop? Products look great though.
I also saw Toroidy have some and I’ve been a customer of them for many years for the power transformers but there’s not so many reviews of their output.
Do
I also saw Toroidy have some and I’ve been a customer of them for many years for the power transformers but there’s not so many reviews of their output.
Do
Don't discount the Edcor GSXE15-5 units. Some of their other OT aren't anything to jump up and down about but the 15W GSXE are really nice for small $$. I do believe these are single output secondary only though. Another brand to consider is Thermionic labs. Musical Power Supplies might also have something worth considering and/or call Heyboer and see what they suggest. The transformers Heyboer manufactures for those ST70 kits are REALLY good. I personally use ISO FC-30-3.5II for my 300B amps, but those are just outside your price range posted.
I agree!
I also preferred the Hashimoto H203U to my Tango/Hirata U808. A couple of years ago, I built a pair of SE300B monoblocks using the H30-3.5S and found it to have the edge in the bass region over my 90s vintage Tango NY15s and Tamura F7002.
Just to throw another option. Musical Power Supplies makes a 20W rated SE output. I've used a pair that I had stacked for parallel feed. They measure and sound very well. I'm using them in a SE GU-50 amp for about 15W. The 1W FR is -3dB at approx 5Hz and the top end if flat +/-0.5dB to 100kHz. There is a supersonic peak of 3dB above 100k but in a non GFB amp it does seem to cause any audible effects. These numbers both roll off a bit more at full power and the peak is damped down. And they are about $75US each plus some shipping from Tennessee.
I have also used the 15W Edcors in a SE 6V6 amp and they sounded good but not quite as smooth sounding as the MPS and they start rolling off about 15kHz. Down slightly at 20kHz which isn't necessarily a big deal.
I have also used the 15W Edcors in a SE 6V6 amp and they sounded good but not quite as smooth sounding as the MPS and they start rolling off about 15kHz. Down slightly at 20kHz which isn't necessarily a big deal.
Maybe send Victor an email. He is the Elekit distributor out here on the west coast. He always seems to have transformer upgrades for the single ended amp kits, Lundahl etc. https://www.vkmusic.ca/
jeff
I already PM'd Pinnocchio my preference but I would like to raise a somewhat provocative question: does anyone really believe Monolith freq response specs? -3dB at 4Hz? really? There is only so much you can do with coiled copper and iron cores even after extensive computer sims to figure out the best coil arrangement and core shape.
That spec would be at 1 watt is my guess.the real speac for output transformers is there max output power at the lowest freq with specified distirtion before the core saturates.my tango xe 3.5 s are ratrd 30watts at 40hz. At 1 watt is more like 20hz to 160khz.
I'm collecting parts for a 300B SET with pretty much the same basic OPT requirements.
After considering a lot of different options I finally went for a pair of Lundahl LL1679.
After considering a lot of different options I finally went for a pair of Lundahl LL1679.
When looking at the transformer graphs, do we need to consider the frequency response graph or the primary impedance graph or both are very important? As an example, the Hashimoto H-20-7U, the frequency response seems to be pretty linear from ~20Hz to ~50Khz but then starts dropping like a rock, on the other side the primary impedance for 5K shows pretty linear from ~50Hz to ~30Khz, then drop. This is just an example though and not all manufacturer provide a graph for the primary impedance, mostly frequency response.
Thanks
Do
Thanks
Do
Attachments
Small signal frequency response of an OPT can't be described without specifying the driving (source) impedance. In the simplest case, like a 300B amp, no feedback, usual operating conditions, etc. that number is the output valve's "plate resistance", R-sub-p. We can't compare frequency responses unless this source inpedance is the same for all tests. In the case of an SE OPT the DC current must also be specified, because it changes primary (also called magnetizing) inductance.
The low frequency rolloff (at small signal) of a transformer is a simple linear function of source impedance and primary inductance. It's a textbook example of an RL high pass filter, but both values must be known. Specs and curves that are made with one assumed source impedance can be shifted to a different source impedance with a simple linear shift, but comparisons without that shift are meaningless.
All good fortune,
Chris
The low frequency rolloff (at small signal) of a transformer is a simple linear function of source impedance and primary inductance. It's a textbook example of an RL high pass filter, but both values must be known. Specs and curves that are made with one assumed source impedance can be shifted to a different source impedance with a simple linear shift, but comparisons without that shift are meaningless.
All good fortune,
Chris