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Old 16th August 2011, 07:01 PM   #1
jule is offline jule  Slovenia
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Default help me designing parallel SE guitar amp with 12at7 as power tube

My schematic came so far by now(lower it is)

I am aiming to get that early blues sound.

I got 24k/8ohm/2W output transformer which is almost like the one Fender used in reverb units (23k/8ohm/3.5W).

They used parallel SE design:
Click the image to open in full size.

So there is loadline for each half:

Click the image to open in full size.

I am probably going to use 200V B+, so my calculatoins got like this:

From graph I get 6.5mA per stage, so togheter 13mA and -2V on grid. So I would need 154 ohm resistor(not marked value on schematic I suppose it would get 0,3W output power.(Ia*Ua/8) and 0.8W of dissipation.

But how could I get a little more power out of it? Can it be done? I would like at least 0.5W if possible.

I am going to use 8' ,8 ohm, 15W speaker.

Also check component values on the schematic, suggestions are welcome. This is my first design of an amp. (But I already built one 5W SE with el84)

Click the image to open in full size.

Click the image to open in full size.
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Old 16th August 2011, 07:51 PM   #2
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Should word as drawn, and might be fun.
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Old 17th August 2011, 10:40 AM   #3
jule is offline jule  Slovenia
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what about bias of power tubes?
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Old 17th August 2011, 11:35 AM   #4
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More power? Try operating the 12AT7 in push-pull. Yeah, it would need a PI stage, but it would make the whole thing even more unique!

Dave
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Old 18th August 2011, 01:59 AM   #5
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Quote:
Originally Posted by dcgillespie View Post
More power? Try operating the 12AT7 in push-pull. Yeah, it would need a PI stage, but it would make the whole thing even more unique!

Dave
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You could run in push-pull in a self-split arrangement. I did one version of my amp with it but with 6AQ5's. Another amp used 6AU5's I think, about the same power level as yours. I used a 70V audio matching transformer, think his was a 100V. You could add a PI stage. Come visit, looks like your amp would fit right in.
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Old 18th August 2011, 08:27 AM   #6
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for an early 'blues' sound use the pre circuit fron princeton 5F2A -- simpler and will give you more fat crunch
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Old 18th August 2011, 08:29 AM   #7
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more power ? use a voltage doubler on PS ? fender ran 400V on 12AT7..
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Old 18th August 2011, 11:03 AM   #8
jule is offline jule  Slovenia
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Now I decided to dump at7 as power tube and run ecc99 in push pull mode. For better performance
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Old 18th August 2011, 04:04 PM   #9
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Quote:
Originally Posted by jule View Post
Now I decided to dump at7 as power tube and run ecc99 in push pull mode. For better performance
A wise choice I think....

There's a few double-triodes like the 7119, 5687 and my personal favorate, the 7044 that should do well for your amp as well...
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Old 18th August 2011, 04:31 PM   #10
Fenris is offline Fenris  United States
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Mine is using 6N1P tubes in P-P with the triodes in each tube paralleled. Should be about 3 watts of power.
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