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Old 14th March 2010, 10:24 PM   #1
newtube is offline newtube  United Kingdom
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Default supercharging a simple se?

Hi everyone. .
I built my simple se a fair while ago and i'm as pleased as a very pleased thing with how it turned out, but for some reason i have the itch to meddle with it a little

I built the bog basic amp, no optional switches, no uprated parts etc but i did use good quality ingredients.

I have fairly hefty output transformers from a 300b of the past, a hammond 373bx mains, and a hammond choke, chinese 6l6gc valves / tubes.
The output trannies have no facility for U/L and have taps for 4/8/16 ohms and i currently use the 8ohm tap for my 3 way 8ohm speakers of 90.5db. they are 2k5 - 3k5.

I have plenty of bass and a great sound but i know it can be souped up a little without spending the earth. . .

What do you recommend guys? and what output do you think i have at the moment, 3w?
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Old 15th March 2010, 01:19 AM   #2
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The quickest way to eek out a little more performance would be to stick a pair of Fairchild ISL9R8120P2 solid state rectifier diodes in place of the vacuum tube rectifier. You'll get a higher B+ voltage and a stiffer power supply. While you're at it, put in the auxiliary capacitor (25uF ~ 80uF motor run capacitor). These two changes will net you a little more power and tighter bass.
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Old 15th March 2010, 02:52 AM   #3
rknize is offline rknize  United States
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Swap out the cathode resistor and use KT88s to get a couple more watts.
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Old 16th March 2010, 09:23 PM   #4
newtube is offline newtube  United Kingdom
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Quote:
Originally Posted by rknize View Post
Swap out the cathode resistor and use KT88s to get a couple more watts.
Which is the cathode resistor rknize? and what do i change it for matey?

Sorry for the questions
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Old 16th March 2010, 09:45 PM   #5
rknize is offline rknize  United States
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Take a look at this table. It's just a simulation and is used for a guide only, but it will help you answer that very question.

Tubes & Transformers

It's a little overwhelming, but lets narrow it down. Your OPTs have 3500k primaries? Your B+ is probably around 400V? What value resistor did you used for R17/R27? Assuming you used the one listed in the parts list (560 ohm), you can find the row that is the closest match to your operating point in the table:

Tube Type = 6L6GC
B+ voltage = 400
Rk = 560

Row taken from the table:
6L6GC 450 3000 444 37 560 67 28 5.19 10 0.4 2.37

If any of my guesses are wrong, adjust accordingly. You are running them fairly hot and getting roughly 5W out. Now scroll down to the KT88 section and choose an operating point. If you don't change anything and just run with the 560 ohm resistor, expect about 7W output. This is running them fairly cold which affects the distortion numbers. Using Diss as a rough guide so that the KT88s are run at about the same level the 6L6s were, a 470 ohm resistor seems appropriate.

Good luck! If you feel like experimenting, buy a few different sets of resistors to try and see what you like.
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