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 Post subject: SE Guitar AMP with existing OPT
PostPosted: Mon Mar 28, 2011 3:42 am 

Joined: Fri Mar 19, 2010 8:59 am
Posts: 21

Looong time ago, I promised a friend of mine I'll build a small practice guitar amp for him.

I Live in Spain and power transformers and OPT are wayy expensive here, buying them overseas (e.g. Edcor) adds a lot in terms of shipping.

I recently got a couple of Old Telefunken SE OPTs from Germany, theoretically intended for use for EL95, 12K:4 Ohm, they were cheap and rumor is they sound really good.

My first idea is trying to use one in the guitar amp, with a 6P15P and two 8 Ohm "Full Range" (70Hz-17kHz) 96dB Beyma speakers in parallel (hence 4Ohm) and relfected OPT impedance of 6K?

I thought on using the same AX84 P1 amp circuit, but using tube rectifier or hybrid, 6N2P-EV instead of the 12AX7 (rewiring, of course) but instead a EL84 / 6P14P use a 6P15P which AFAIK has higher Anode resistance and approaches the more "theoretical" 10:1 in terms of Anode Resistance/Primary Impedance OPT ratio .

However, I understand guitar amps are part of the instrument, and as such must distort; as long as these distortions are euphonic.

Is there any way I can predict which kind of distortions? which route of experimentation would you seek? Paralleling more speakers (they're rather good and cheap, 8") using just one speaker and other means? I understand I must seek 2nd order distortion?.

I also got a suitable power transformer, with secondaries intended for "el84 SE use": 320V HT, 6.3V and would prefer to use one of these...

 Post subject: Re: SE Guitar AMP with existing OPT
PostPosted: Mon Mar 28, 2011 7:46 am 
Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7317
Location: Pleasant Hill, California
Hi Pukkita;

if you connect a pair of 8 ohm speakers in parallel you still would have 4 Ohm and 12 Ohm reflected.

For higher 2'nd order harmonic I would probably go with triode mode, with lower plate voltage and lower load resistance. But 12K and 400-450V B+ in pentode with 200V on G2 may sound nice as well! For a sag/compression you should select proper value of screen grid voltage divider and the value of the capacitor shunting it.

For the rest of you project; yes, 6N2P will be fine there instead of 12AX7.


А женщина даже в мужской рубашке выглядит гораздо приличнее, чем мужчина в женских колготках! Be-be-be!

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