DIY Valve Amplifier – Part 1 – Amplifier Section

Components
Components

Here are a few details of a valve amplifier I am building, using the valve related parts from a 1960’s reel to reel tape recorder.

This amplifier is based on an a Mullard ECL82 triode/pentode valve, with an EM84 magic eye tube for level indication.

Beginnings Of The Amplifier
Beginnings Of The Amplifier

Here the first components are being soldered to the tags on the valve holder, there are so few components that a PCB is not required, everything can be rats-nested onto the valve holders.

Progress
Progress

Progressing with the amplifier section componentry, all resistors are either 1/2W or 2W.

Valve Sockets Fitted
Valve Sockets Fitted

Here the valve holders have been fitted, along with the output transformer, DC smoothing capacitor & the filament wiring, into the top of the plastic housing. At this point all the components that complete the amplifier section are soldered to the bottom of the right hand valve holder.

Wiring
Wiring

Starting the wiring between the valves & the power supply components. The volume control pot is fitted between the valve holders.

Valves Test Fit
Valves Test Fit

The valves here are test fitted into their sockets, the aluminium can at the back is a triple 32uF 250v electrolytic capacitor for smoothing the B+ rail.

Amplifier Section First Test
Amplifier Section First Test

First test of the amplifier, with the speaker from the 1960’s tape recorder from which the valves came from. the 200v DC B+ supply & the 6.3v AC filament supply is derived from the mains transformer in the background.

Magic Eye Tube Added
Magic Eye Tube Added

Here the magic eye tube has been fitted & is getting it’s initial tuning to the amplifier section. This requires selecting combinations of anode & grid resistors to set the gap between the bars while at no signal & picking a coupling RC network to give the desired response curve.

Final Test
Final Test

Here both valves are fitted & the unit is sitting on it’s case for final audio testing. the cathodes of the ECL82 can be clearly seen glowing dull red here.

 

In the final section, I will build a SMPS power supply into the unit to allow it to be powered from a single 12v DC power supply.

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