Hello folks,
I recently got my hands on an EL84 PP valve amp output stage chassis (from a Dynatron Cavalcade GR1, I believe) and would like to turn it into a guitar amplifier.
Can anyone recommend any resources that would help me design a preamp for it? Or would it be better to just copy an existing design?
I have attached my attempt at tracing the circuit, along with some pictures of the chassis (please ignore the duplicate heaters).
Also, just out of curiosity, what are the two EL84 plate capacitors for (C7 and C8 - the two silver caps in the lower right corner)?
Many thanks,
Alex
I recently got my hands on an EL84 PP valve amp output stage chassis (from a Dynatron Cavalcade GR1, I believe) and would like to turn it into a guitar amplifier.
Can anyone recommend any resources that would help me design a preamp for it? Or would it be better to just copy an existing design?
I have attached my attempt at tracing the circuit, along with some pictures of the chassis (please ignore the duplicate heaters).
Also, just out of curiosity, what are the two EL84 plate capacitors for (C7 and C8 - the two silver caps in the lower right corner)?
Many thanks,
Alex
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It’s a zobel network - on the primary instead of the secondary. You WANT those on a guitar amplifier, to prevent HF peaking which can fry the transformer. It can get to kilovolts, especially if you try to run without the speaker. The 100 ohm load on the secondary helps with that too, but does consume a little of your power at all frequencies instead of just the way upper end you don’t need anyway.
Search AX84 site.
Exactly what you are looking for.
Killer guitar amps built around EL84
Besides, lots of people built them, you will find practical advice, resources, mods, tweaks, build pictures, the works.
It has been "sleeping" for a couple years now, only because "it already contains all there is to know about EL84 on guitar amps", it is THAT good.
Exactly what you are looking for.
Killer guitar amps built around EL84
Besides, lots of people built them, you will find practical advice, resources, mods, tweaks, build pictures, the works.
It has been "sleeping" for a couple years now, only because "it already contains all there is to know about EL84 on guitar amps", it is THAT good.
I wrote this, er, way back when - http://www.rru.com/~meo/Guitar/Amps/PA2Guitar/pa2g-notes.html
There's also https://www.diyaudio.com/community/...m-bogen-m330a-husk.410971/page-2#post-7664415
which may help get you going.
I suppose my suggestion is to try something different with it. As noted above, you'll need another tube to make it scream - all by itself.
On the other hand, these days there's nothing wrong with the so-called "full range" power amp / speaker cabinet approach, where literally all of the sound is created in today's ultra-sophisticated "pedals" upstream. Given you have a tube amp, that type of "FR" amp would compete with much more powerful SS amp in perceived sound.
There's also https://www.diyaudio.com/community/...m-bogen-m330a-husk.410971/page-2#post-7664415
which may help get you going.
I suppose my suggestion is to try something different with it. As noted above, you'll need another tube to make it scream - all by itself.
On the other hand, these days there's nothing wrong with the so-called "full range" power amp / speaker cabinet approach, where literally all of the sound is created in today's ultra-sophisticated "pedals" upstream. Given you have a tube amp, that type of "FR" amp would compete with much more powerful SS amp in perceived sound.
Thank you so much everyone for your great replies! Going to do some reading tonight and fire up the 'ol LTSpice before I blow up some parts IRL.
I think I will definitely go for a valve preamp, I have a bunch of 12AX7 to hand.
Never heard of it before but I wish I knew it sooner now.
I think I will definitely go for a valve preamp, I have a bunch of 12AX7 to hand.