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Old 15th March 2009, 09:45 PM   #1
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Default Has anyone built this amp??????

Couldn't find it in the archives:





KT88 SET





I like it because:

1. I want to build a SET or UL.
2. Big shiny tubes.
3. Simple Power Supply.
4. It has an economy of components.


I'll have buckets of questions and require handholding all the way. But the more I learn the more I can give back to the community!

First Q: I don't want to put a pot on it. Just want a power amp, I don't just delete that 100k pot right, I need to put a resistor in it's place. But what value??? And how does one arrive at that conclusion?

Second Q: Any idea what the gain would be on this badboy as shown? And so I don't need to ask every time: How do you arrive at the answer?


Thanks in advance for all knowledge disseminated.
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Old 15th March 2009, 09:57 PM   #2
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That's diyaudio member alexg's amp.
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Old 16th March 2009, 02:18 AM   #3
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Do the search on "Abdellah" and you will find plenty.
This for eaxample:
Improvements for the Mikael Abdellah KT88???

I like KT88 too - 4 off them per channel in parallel push pull.

Cheers,
Ian
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Old 16th March 2009, 03:13 AM   #4
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IMHO, I've always felt that design was incredibly overrated. No modern touches like CCS's or diode biasing, and the 6N1P datasheet only specs transconductance at between 3.5 and 5.5 mA/V, not very impressive.
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Old 16th March 2009, 03:59 AM   #5
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Thanks ginger.

I think the SimpleSE is still a strong contender. I'm going to price out parts for this and then the Simple, see if dollars and cents can help make up my mind for me.
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Old 17th March 2009, 06:49 AM   #6
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Default Re: Has anyone built this amp??????

Hi,

I just finished one shown here:
Photo Thread

It may not be the most modern design, but it is very tractable for a first-time
builder and with only a few components you can spring for higher quality
without breaking the bank. The TubelabSE is also a very good bet, particularly
if you want to easily tinker with the circuit.

To answer your specific questions:

Quote:
Originally posted by raypalmer

First Q: I don't want to put a pot on it. Just want a power amp, I don't just delete that 100k pot right, I need to put a resistor in it's place. But what value??? And how does one arrive at that conclusion?

Second Q: Any idea what the gain would be on this badboy as shown? And so I don't need to ask every time: How do you arrive at the answer?
Replace the 100k pot with a 100k resistor. Higher values will just cause more
noise. Lower values will attenuate the input voltage slightly, although anything
above 10k is probably OK.

As for gain, I never actually worked this out, and in general it will depend on
the impedance of your output transformer and the tubes you use. One of the
first circuits analyzed in detail in "Valve Amplifiers" by Morgan Jones is a
similar SET design. I would strongly recommend buying this book. Power
output at given distortion level is usually a more meaningful metric than
gain anyways.
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Old 17th March 2009, 05:23 PM   #7
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Default Same boat / different paddle...

Sorry to butt in but,

Help!

My grandfather left me two things, an old pair of needle nose pliers and a shoe box full of Tung-Sol 6550s (some are actually good).

I have been drifting back and forth as to what is the best direction to go as far as PP or SE KT-88 design. with two simple PP kits under my belt I feel I would like to build something that will rattle the windows and yet make me weep from the three tenors. Is there enough loss in an SE to make PP worth the extra work and cost? If the ultimate 50watt per channel amp were to be made and a guy had more money than brains...

Parts? brand and type Transformer & OPT Choke(Hammond? Edcor?), Caps, resistors, Rectifiers,

Thank you.
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Old 18th March 2009, 04:38 AM   #8
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This is the amp design I was going to base from for my first SE amp. I tweaked the design a bit to use a 12AT7, since I had some on hand. I acquired some of the parts and then I found Tubelab's Simple SE and decided to save some time and build one of those instead of rolling my own. My other amps are all point-to-point...well the Dynaco is both...so I wasn't sure about the PCB. I suspect it will be fine, though. It was certainly easy to build and it is tough to get it wrong as long as you follow the directions.

The chassis work is always the long pole for me....
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