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artosalo 20th December 2012 04:06 PM

EL509 SE
 
I was asked to design a SE amplifier above 10 W power level.
The customer let me suggest him new ideas, but the main target was to create a relatively "clean" amplifier. I planned to try something new for the tone stack and I also wanted to try something else than conventional EL34 as an output tube.
One design goal was to keep all supply voltages adjustable to find the best possible result.

The prototype has no been built and is under initial tests.
Output power exceeds 15 W.

Since this is my first guitar amp, all comments are welcome.

http://img845.imageshack.us/img845/5307/vahv2.gif


http://img51.imageshack.us/img51/8946/poweri2.gif

tinitus 20th December 2012 07:22 PM

hi, looks interesting

but do I need new glasses, or...?

vinylkid58 20th December 2012 07:30 PM

Quote:

Originally Posted by tinitus (Post 3293007)
but do I need new glasses, or...?

I can't read the main schem values either, and I've got my "extra powerful" reading glasses on.;)

jeff

tinitus 20th December 2012 08:04 PM

great, thanks, I got a bit scared ....no worries then :D

artosalo 20th December 2012 08:23 PM

Imageshack seems to decreased the resolution too much.
I try to get better pictures tomorrow.

http://img845.imageshack.us/img845/5307/vahv2.gif

artosalo 21st December 2012 06:44 AM

http://kuva.termiitti.com/image/28372.gif

tinitus 21st December 2012 07:32 AM

thanks
a buffered line out with attenuator looks very nice

I suppose the 6F12P is a compactron
any reason why not just another 6n1p ?

OPT impedance ?

6n1p, 250V plate voltage ? is it not a bit on the high side ? ( no plate load resistor on buffer ? )

GeorgK 21st December 2012 08:18 AM

looks quite interesting with the pentode input and the active tone control.

what's the idea behind R4?

Do you plan to leave the HV supplies adjustable or ist this for prototype only?

artosalo 21st December 2012 08:51 AM

Quote:

Originally Posted by tinitus (Post 3293626)
thanks
a buffered line out with attenuator looks very nice

I suppose the 6F12P is a compactron
any reason why not just another 6n1p ?

OPT impedance ?

6n1p, 250V plate voltage ? is it not a bit on the high side ? ( no plate load resistor on buffer ? )

6F12P (6Ф12П) is Soviet triode-pentode with two very efficient tube halves.
Both pentode and triode have very high Gm (~19,5 mA/V) and the triode part has = 100.

The reason why not an other 6N1P is that a pentode was wanted as a voltage amplifying stage.

OPT impedance is 2k5, but it could also be up to 3k5 with essentially similar performance. There will only be slight difference between the level of 2nd and 3rd harmonic.

The anode (to cathode) voltage is some 120 V, because there is R5 (22k) as cathode resistor. This means that the DC-voltage at the cathode is some 130 V.

artosalo 21st December 2012 08:56 AM

Quote:

Originally Posted by GeorgK (Post 3293656)
looks quite interesting with the pentode input and the active tone control.

what's the idea behind R4?

Do you plan to leave the HV supplies adjustable or ist this for prototype only?

R4 forms local negative feedback at the output tube only and thus improves the linearity of whole amplifier, as does the global negative feedback due to R24 as well, but with different way.
The total NFB can be adjusted with P6 at the output trafo.

The tests will show which supply voltages should be left user-adjustable.
I do not know yet.


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