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Hi everyone,At Mike's suggestion, I post a few photos of the prototypes.
This one is a headphone amp/preamp using the TL-818 (custom TL-404) autoformer. Separate power supply unit, not shown, uses 6DM4 rectifiers.
Gain tube is 6C45Pi, with hybrid 12HL7 constant current source. 0D3 are used for shunt regulation. It was recently auditioned as a preamp with FM Acoustics amplifier and JBL DD67000 speakers - and performed well with the uber priced equipment and versus the FM Acoustics preamplifier.
The case is made of specially pressed bamboo to provide increased density and strength.
Edits: 03/08/15 03/08/15 03/08/15Follow Ups:
Mikey what's a TL818?
G.
J. Gordon Rankin
It is a custom TL-404 and the customer wanted an eight hundred series part number to complement his brand name "Sideways 8" which, of course, is the symbol for infinity.
MSL
Builder of MagneQuest & Peerless transformers since 1989
Fantastic work. Especially love the alternating pressed bamboo.
Is the TL-404 available again from Magnequest?
Yes. I have three or four pairs of the XL's in stock.
MSL
Builder of MagneQuest & Peerless transformers since 1989
Is the XL nickel core? How much is a pair?
Hello hvbias;None of the TL-404's have ever been built on nickel.
And they perform exceptionally well on the core material which we use for them.
Check out http://magnequest.blogspot.com/(hot link provided below)and scroll down a few entries and you'll find some square wave and frequency response test results on a pair of our TL-404's. And these results were with a source (driving) impedance of 2400 ohms.
rounding off a bit... the 404 is within half a db from 20 hz to 100 khz. And,again,that is with a relatively high driving source impedance.Had that source impedance been say 800 ohms it probably would have gone down a further octave on the bottom end.
Which tells me that the core material we are using is good for this design. And for some historical perspective... This design dates back to 1946 and was built for MGM recording studios.
Our current production uses a lamination grade with greater perm and lower core losses than the original design from 1946.
I'm pretty happy with the design the way it is. And we've had a lot of builders who have been very pleased with the TL-404's.
The XL version is the same as the non XL except that it has more stack. The larger stack is offered for those who would like to build with a 45 SE output tube (or say a 71A) and has a two watt MOL.
And you can still use the XL version as a line level (i.e. preamp) output.
The XL's are $600 a pair. And I have some in stock. I am sold out of the smaller cored TL-404's for the time being.
MSL
Builder of MagneQuest & Peerless transformers since 1989
Edits: 03/26/15 03/26/15 03/26/15 03/26/15 03/26/15 03/26/15 03/26/15
.
To infinity and beyond!!!
This one is a prototype KT88/6550 triode-connected SE amplifier using DS-025 output transformers. Separate power supply, not shown, uses 6DM4 rectifiers. To achieve greater output, production model likely will use the RS-500 output transformers and pentode mode with regulated screen supplies.Driver is a beta follower 12BZ7, cap coupled to BCP-16 grid choke. Local feedback works well to reduce distortion and optimize sonic performance. Despite the lower power output, triode connected KT88 sounds exceptional and competitive against directly heated triodes at similar output levels.
The case shows the alternating layers of the specially pressed bamboo.
Edits: 03/08/15 03/08/15 03/08/15 03/08/15 03/08/15 04/17/15
Those look great...
I agree the DS025 and KT88 are not a good match and triode mode is really not that good sounding for any of those Pentode/Tetrode tubes.
But if you go regulated screen (really best sounding) you should note your damping is going to be really really high without some global feedback.
Something you may want to try is something I did on a guitar amp. The driver stage was a 6SN7 with an unbypassed cathode resistor. I used a high voltage resistor from the plate of the KT88/6550 to the cathode of the 6SN7 (yes current through it) and recalculated the 6SN7 bias resistor accordingly (400V-Bias6SN7)/Rfeedback =iFeedback. Bias resistor equals Bias6SN7/(iFeedback + 6SN7current).
I did -3dB here and it really made things sound really good. But the damping was still like 20. But for a guitar amp, who cares... its all about zing in that world.
Thanks,
Gordon
J. Gordon Rankin
Top view of the headphone amp/preamp.
Edits: 03/08/15
Beautiful work! I hope to see more of it in the future!
Hopefully Sideways 8 will get some international distribution and an American importer\representative. It's gorgeous stuff. And uses all quality parts and components throughout. I think the designer builds the best amp he can and then prices it... rather than first establishing a price point and then seeing how much "quality" he can get into that matrix.All of the best sounding and best built products are done in this order... the opposite way just seems to result in "who can slide on their belly the furthest"... not a good approach for music nor for longevity.
And MQ has another long term OEM who has always used the same approach... he'll call me and ask for guidance and advice on the selection of ironware and then he'll optimize around the recommended iron choices. The opposite is you get OEM's (and some diy'ers) who call and want to dictate what the iron should or must be with little to no understanding of the physics, optimalities, and the inter-relationships between a multitude of various performance factors...
Another misguided demand I often have to deal with is the sort of "there's only one parameter" that is important... say low dcr in a choke... nothing else matters... core losses could be ten times greater than the copper losses... but it's a good choke because it SIMPLY has low dcr. Nope. That's not the way I roll in designing\building magnetics.
Or the transformer must use a specific core material... independently of how or if or when such an option might be optimal or actually provide the end user (or OEM) with a real world benefit.
Or they will adopt a generalization like higher primary impedance is better (i.e., has lower distortion) than a set of operating points with a lower bias current and\or lower nominal primary impedance. Never stopping to think about or take into account that the plate curves they are relying on are drawn from purely resistive loads on the tube. Sorry folks output transformers (which you'll be using with your tubes) are not purely resistive--- wouldn't it be smarter to look at the output stage holistically--- as you'll want to optimize the operating points with consideration of the output trans which will be loading your anodes.
Haven't been on the soapbox for a while... felt good... hope ya'll enjoyed my ranting.
MSL
Builder of MagneQuest & Peerless transformers since 1989
Edits: 03/26/15 03/26/15 03/26/15 03/26/15 03/26/15 03/26/15 03/26/15 03/26/15
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