Magnepan High Frequency Tube Amp

[john65b]

Hey all, Can anyone recommend a tube amp design for the High Frequency Panels of a Magnepan Tympani IVa? This tube amp will take from 400hz and up. It will be fed from a DCX2496 active XO, and an Aikido 6SN7/6SN7 in front of the DCX.

Here is what is in my parts bin: all sorts of 6SN7, 6SL7, matched quads of KT88, 6550, 6L6GC, and EL34, pair of Hammond 1650n output trannies, 5U4, 5R4, (and maybe a pair of 5AR4) Rectifiers, as well as tons of 1N400X diodes, pair of industrial no name 400-0 400-0 power supplies, pair of Thordson chokes for dialing in my B+ on Choke input PS. The caps and resistors are also high-ish quality...

With parts I have, I can easily do a dual power supply.

My chassis has eight octal sockets. All four in line in back are for the output tubes, whichever I end up using. So either I can use remaining four for two sockets for an Input and Phase Splitter with SS rectiification, or single input/phase splitter and tube recitifier...

I also have plenty of 12AX7. 12AT7, 6922, 6N1P, but I really want to stick with Octals since the chassis already has them...



I have thought of a Williamson circuit, but I have read it may be challenging to get working correctly...

I have tried a couple tubeamps on teh panels and they did not impress me as much as my Krell KSA-50 Clone (Dynaco ST70, Quicksilver GFA??)

Anyway, would love to have a cleaner config with a tube amp in the system instead of teh huge hot KSA-50 (which sounds superb)

Any advice?

[HollowState]

Originally Posted by john65b

Can anyone recommend a tube amp design for the High Frequency Panels of a Magnepan Tympani IVa?

I have tried a couple tubeamps on teh panels and they did not impress me as much as my Krell KSA-50 Clone (Dynaco ST70, Quicksilver GFA??)

Hi John,
Ok, I'll give you my opinion and advice for better or worse. First, you have a fine collection of parts to build a nice amplifier, except for one thing. The Hammond output transformers. Compared to the dozens of transformers out there, Hammonds are pretty low on my list for sound quaility, and I think I'm fairly safe in saying this. Of all the parts to a tube amplifier, the OPT is the most important of all. Regardless of circuit design style, tubes used, power supply or capacitors/resistors used, it's the OPT that can make or break an amplifier.

I'm not going to recommend any specific brand because I'm old school and have always prefered and used the vintage units like Acrosound, Peerless, UTC, Citation (actually Freed) and even Thordarson, Triad & Chicago Standard. But I have read, here on this forum, that there are many equally as good or better (?) units from manufactures like Hashimoto, Heyboer, James, MagneQuest and others that I've never personally used. TransformerSuppliers - diyAudio

I do know that your Maggies, when properly placed, are very capable of producing delicately detailed highs, but will also reveal an amplifier's shortcomings at the same time. They're also hungry and need power. So unless you're willing to spring for some high quality output transformers, you'll probably be disappointed with whatever you build around yours.

This all leads to my second thought that if you want a tube amp for your HF panel that will feed them what they deserve, you might want to consider an output transformer-less amplifier. But this is another whole subject and probably not what you want to read.

[Eli Duttman]

I have thought of a Williamson circuit, but I have read it may be challenging to get working correctly.

Williamson style circuitry is vulnerable to low freq. instability. Control of the high pass poles' F₃ and employment of high quality O/P "iron" deals with the issue. A yield of 60 WPC from KT88 pairs should be plenty, even for power hungry "Maggies".

HS is correct in stating the Hammond trafos in your possession are not up to snuff for this job. Talk to Purvine, Eliano, or Lefevre. Costs will not be too bad, as response down to 20 Hz. is unnecessary.

[john65b]

Yes, yes, you are not the first to tell me of the Hammond OPT issue...

I have asked about this particular amp design on Maggies before, and was somehow hoping if the Bass was removed from the equation, the answer would be different...i guess not. Anyway, I may just pony up for new OP trannies and build an amp. I know a friend at work bought some nice Edcors he is happy with...are they also OK for the task?

Maybe I will run up to Triode Electronics on North Side of Chicago....

[rock4016]

I would use these
EDCOR Electronics Corporation. CXPP100-MS-3.3K

With Pete's Red Board. With right output tubes, you'd be good for 100 watts or more output.
DCPP Amp

Here's the info on getting up to 250W
Posted new P-P power amp design

[Eli Duttman]

John,

The Hammond 1650Ns mate well with EL34 family tubes. A Mullard style circuit avoids the instability issue associated with Williamson style. An Octal small signal lineup that maximizes gm to protect against slew limiting is a 6AC7GT voltage amplifier and a 6SN7 LTP. Be sure to 10M45S CCS load the LTP tail, which may require a B- supply. Energize the 6AC7 heater with DC, per the data sheet recommendation. You might as well take advantage of the UL taps too.

Use high PIV Schottky diodes in the B+ supply, to eliminate SS diode switching noise.

[john65b]

Some very good info for me to noodle on...I also have a little issue...I really do not know i the tranny I have is truley a Hammond 1650N. The overall dimensions and bolt hole measurements were close (if I remember correctly) but primary/secondary wires are same colors as a 1650N, so I assumed it was...a pic is attached. The original designer painted the trannie after removing the ID sticker on top. Any identification factors I can use to determine if really a 1650N or if its really even a Hammond?