Thomas has also stated that he favours Tango/ISO XE/FC-20S for use with Type 45, others have said it is a poor choice configured at 5k primary, so who knows.
Then theres the fact that its gapped for 100mA and can accomodate the 300B, so it might not be the best fit, and they're not inexpensive, probably not too disimilar in price as a pair of custom double C core, ~40H, ~35mA, ~20:1, ~6W. Its hard to see how that is not the least compromised solution and I think I'll go that way.
Thanks to all.
JP
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Another one is Audio Feast, they look alot like noguchi but are in the USA, finemet transformer cores. Loads of transformers on their website. They say they do custom transformers, although their standard FM-3ws or fm3wsl might suit.
8 x 20 x 20 = 3K2 or: 6x20x20= 2K4
Why not opt for 1:26 for 6R x 26 x 26 = 4K and 1:33 6R x 33 x 33 = 6K5?
When using 1:26 the redundant turns give small P-S parasitic capacitance and inductance. Using 1:33 there would be no bother.
4K gives highest power (still with low distortion) while 6K5 would give better damping.
The reason I take 6R is because my loudspeaker (speaker in cabinet) has this impedance at resonance and the bass region is the hardest part to get right with small power. Another approach is to get the best out of the available power and accept the compromise of a lower power bandwith, say 50Hz-25KHz. Those are the borders where reproduction gets 1dB down from center frequencies. The advantage is the OPT can be made smaller, with less copper loss and improved coupling. These are design goals you must decide upon first 🙂
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I've always favoured a higher primary - sounds cleaner to me.
For a 300b I like 5K, so for a 45 I'd go for 5k to 7.5K.
For a 300b I like 5K, so for a 45 I'd go for 5k to 7.5K.
The difference here is with the available output power. You must not expect the 1,6W amp to deliver the same LF reproduction as the 8W amp or it must be at very low listening levels.
Yes, well... low insertion loss gets important with lower power tubes I reckon. But there was another argument against using too powerful iron. It had to do with the hysteresis curve I thought. A bigger airgap was to no benefit in this case.
Quite the contrary. This is especially true if EI laminations are used. In a single ended amplifier if you use a bigger transformer than necessary it will work at lower B and thus it will be more linear (in terms of magnetic hysteresis). By definition Bac cannot be bigger than Bdc (induction due to signal cannot be bigger than static induction due to dc anode current and this is what basically sets the lowest frequency where the rated power can be achieved).
The fact that the transformer is rated for higher power doesn't really matter if it has enough inductance.
At the low frequency the maximum output voltage into the nominal load is proportional to the product of anode current and inductance. The anode current is the one by design so the inductance determines the performance. The higher the better.
The Tango XE/FC-20S is fine to use with the 45. It has enough inductance for 5K load and is excellent for all other aspects.
It has 18H inductance which means that the maximum undistorted power at 30Hz will be: 1.5W. More at higher frequency. This is more than good enough. At 40Hz where most loudspeakers start to give up (especially those with high efficiency) the max undistorted power is more than 2.5W....
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I still suggest you keep looking for the F-475 and if you can't find it then just go for the small Lundahl LL1682 or the Sowter SA02. Both are good reliable products. Personally I prefer the Sowter because the Lundahl is rated as 5K into 5R which means 8K into 8R. So I would only use it with actual 5R speakers. With true 8R speaker it has a better use the 46.
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Ah, I was forgetting that if the XE20 is an option than you might be better off with the smaller U-808. This has more inductance and is perfect for the 45. The reason why I did not mention it before is that transformers with multiple configurations were not desirable. Great little transformer, surely superior to both Lundahl and Sowter but more expensive. Can be found on Ebay as well for sale from Japan.....
Well I have. By true 8R speaker I mean that for most of the spectrum it's around 8R, minimum 6R. There are several commercial speakers like this. For 6R the 5K transformer will provide 3.75K which is about the optimal value for max power at 260-275V with 35-36 mA anode current. I have experimented with 45 in all possible ways. For SE, for me, 5K is the best all around choice. Loudspeakers need to be well-behaved in terms of impedance otherwise they are rarely a fair match with SE amps.
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i was just wondering how this project went(without the need to revive this older post) ? Which route was chosen component - wise?
Cheers!
Cheers!
