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Old 6th February 2011, 05:49 PM   #1
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Default KT90 Simple SE

I am thinking about a Simple SE build using KT90 output tubes. I am not terribly knowledgeable about tubes, so I want to make sure I am not missing something... My proposed parts list and construction plan is below.

*** Tubes:
- EH KT90
- some brand of 12AT7.... Any suggestions? Tubes by JJ, JAN-Philips, EH, and Mullard all look affordable.

*** Power
- Antek AS-4T360 transformer (can be wired 360-0-360 at 550mA, which is way overkill, but I do want headroom)
- Hammond 193M choke (10H, 300mA)
- Welborne Labs PS10 high-voltage regulated power supply (target is about 450V), solid state rectified
- DC (possibly regulated) heater supply

*** Output
- Hammond 1628SEA

I think I feel comfortable sourcing the other parts on my own. My thought is to bias the KT90's at about 100mA each. The regulator and DC heaters are intended to keep hum and noise to a minimum. My hope is that this amp will not only be a good introduction to tubes, but that it will also outperform my high-end Class A solid state power amp (hence the overkill power supply and high bias).

Does this look like a reasonable list? I guess I am looking at about 15W ultralinear and maybe 8W triode, right?

Thank you for any suggestions.
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Old 6th February 2011, 06:13 PM   #2
6L6 is offline 6L6  United States
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Why do you want a regulator on the B+ when you will have a big choke?

Tube or SS rectification?

If you want a killer sound, you should get a killer output transformer - My favorites are Electra-print. They are huge!! I've been using them for 10 years or so, never a problem and great service. You get what you pay for.
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Old 6th February 2011, 10:07 PM   #3
rknize is offline rknize  United States
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I can/do run my Simple SE with EH KT90s at 100mA. I have no problems with hum on my 98dB speakers. I have a 220uF C2 plus a 80uF motor run cap in parallel with it. I'm using the cheap Allied 6H choke. Spend your money on output transformers instead of regulators. There you will hear a difference. Go for the big, honkin Edcors at least. One Electron or Electraprint, if you want to splurge.

EH 12AT7 is fine. I've had all of my JJs getting weak after a few 100 hours. I won't be buying any more. NOS JAN is good too and will probably outlive anything else. Those military Mullards are excellent too...grab them now if you can afford it.
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Old 6th February 2011, 10:35 PM   #4
rknize is offline rknize  United States
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Sporting EH KT90s in triode. They do sound nice with my speakers and can rock in UL if needed.
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Old 6th February 2011, 11:18 PM   #5
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Quote:
*** Output - Hammond 1628SEA
I have a pair of 1628SEA's. They were in a Simple SE, and they have been in a few other amps. These transformers do bass better than any other SE transformers, unfortunately that is their only trick. If you want a good all round OPT look elsewhere. I like the big Edcor CXSE25-8-5K, but I limit myself to a near $100 budget. If you have the $$$ look to Electra Print.

Quote:
DC (possibly regulated) heater supply
Not needed. The SSE has a very low hum level. A poorly implemented rectifier may create switching noise that could be coupled through the power transformer into the amp. A toroidal transformer is more likely to couple noise than a conventional transformer


Quote:
- Welborne Labs PS10 high-voltage regulated power supply (target is about 450V), solid state rectified
Maybe a good thing, but I never tried it. As stated before, if you are going to regulate, you don't need a mega choke, a cheaper one, or possibly none at all, depending on the regulator, will do.

I use laboratory quality bench supplies to design and develop my amplifiers. The sound is excellent. The Simple SE with a choke and the suplemental motor run cap is 95% of the way to a fully regulated supply.
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Old 6th February 2011, 11:31 PM   #6
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I like KT90... though I don't have enough current capacity to run them to their full potential. I think you do need to run them at a fairly high current to get them to sound their best.

Click the image to open in full size.
http://i69.photobucket.com/albums/i4...E/P1120152.jpg
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