UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Guitar amplifier with 2 x EL86 push-pull

Robert Gribnau · 28th Jun 2020, 4:59 pm

Hello all,

I have just 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).

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 to much voltage sag. But by using two ZZ1040 voltage stabiliser tubes i solved this problem.

The amplifier works very well. No noise at all with the volume turned down and very loud when 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'. I can not wait to see how it will look after sundown.

Edit: Because the schematic is hard to make out, a link to the schematic on my internetsite: https://1.bp.blogspot.com/-SwqQZAEWU...600/Schema.png

Greetings,
Robert

28th Jun 2020, 4:59 pm	#1
Robert Gribnau Heptode Join Date: May 2017 Location: Konongo, Ghana Posts: 516	Guitar amplifier with 2 x EL86 push-pull Hello all, I have just 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). 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 to much voltage sag. But by using two ZZ1040 voltage stabiliser tubes i solved this problem. The amplifier works very well. No noise at all with the volume turned down and very loud when 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'. I can not wait to see how it will look after sundown. Edit: Because the schematic is hard to make out, a link to the schematic on my internetsite: https://1.bp.blogspot.com/-SwqQZAEWU...600/Schema.png Greetings, Robert Attached Thumbnails Last edited by Robert Gribnau; 28th Jun 2020 at 5:27 pm.