Guitar amp with 2 x EL86 push-pull

[EL504]

Hello all,

New member, first posting.

I have recently finished and tested the electronic part of a guitar amplifier. All that is left to be done, is making and installing the bottom plate (MDF with an aluminum cover on the amplifier side as a screen).

The amplifier is loosely based on the clean channel of the Vox AC15. I have built it to combine it with a guitar amplifier with EF86 + 2 x ECL86 pp i have built before so i can play stereo with them.

Because the figures for a pair of EL86's in push-pull are a little bit better than those for a pair of EL84's in push-pull, I wanted to build an amplifier using EL86's for some time now.

One of the design problems was to keep the needed 200 V supply voltage for the screen grids of the EL86's constant (enough) while the anode supply voltage has to be 250 V. The screen current varies from 4 mA (no signal) to 26 mA (full power). Dropping the 250 V to 200 V with a resistor would cause too much voltage sag. But by using two ZZ1040 voltage stabiliser tubes i solved this problem.

The amplifier works very well except that the 6.3 V winding for external effects measures open (i will try to fix that when the amp has its bottom plate installed so it can stand upright; then i can access the power transformer better). The amp has no noise at all with the volume turned down and is very loud when the volume is turned up. And the ZZ1040's give off a lovely bright-purple glow which diminishes a bit when you give the guitar a good 'hit'.

[Colossal]

Gegroet en welkom bij Robert,

That is a very cool design! I like the voltage stabilizer, quite clever. The transformers look substantial. I bet the low end is tight and punchy. What kind of speakers in your 2x12 cab? I really like that Strat!

[EL504]

Thanks Colossal.

The OPT is indeed oversized (30 Watt; intended for Hi-Fi). I fitted 2 x Jensen C12Q-8 in the cabinet (mono = 4 Ohm).

It sounds very promissing but I did not play long and loud on it yet because of the neighbours. When completed it will move to our attic where I can play more freely and where I can also try it out on my other cab (Marshall 1960AV with 4 x Celestion G12 Vintage).