Vintage tube amplifier restoration!

 This is a vintage 60's tube combo made by the ELKA company. It's the TRX-20 model and here's all the info we first found about it:
"Elka TRX-20 valve guitar combo, reverb and tremolo effects, year: 1969 , 2x EL84 "

Specifications:
 This 2X10" tube combo has 2 channels: "normal" and "vibrato". There are 4 inputs on it, two for each channel and a dedicated volume control per channel. The EQ controls (treble and bass) are common for both channels . The vibrato channel has an on board tremolo effect with intensity (level) and frequency controls. The reverb effect has also a level pot called "reverb dimension". The reverb and tremolo effects are switchable via a 2-button plastic foot switch.

Tubes, lots of 'em...
I opened the amp and noticed that it's some kind of a marshall 18w replica but it had 10 tubes in it!...
 An EZ-81 tube was in charge of the voltage rectification while two Philips el84 power tubes delivered 20Watts of power to a set of 10" guitar speakers (8Ohms total impedance).
 There were also seven ecc83-81 preamp tubes inside the amp. Two of these tube were located outside the amplifier chassis, on a separate effects board(reverb) mounted inside the combo cab. The open reverb tank was at the bottom of the cab.

The complete restoration:
  When the amp came in, it was in a really bad shape, everything was covered in dust and nothing quite worked... So we decided to fully restore the amp without altering its original specs.
  First, I stripped the combo cab and cleaned everything up. Then, I replaced every electrolytic capacitor on the pcb and all the power resistors with brand new JJ and ELNA ones. The power wires and power switches were also replaced and all the pots and jacks were cleaned with contact cleaner.
  All the preamp tubes had metal covers that were connected to ground. Grounded covers reduce electromagnetic interference, heat build up and noise but all these covers were rusty and worn out. So I disconnected and cleaned them using deoxit and vinegar before putting them back on amp.
  The Philips preamp and power tubes were in a good shape but the ez81 rectifier valve was dead. So, we changed that as well. The reverb tank was not working as the springs were disconnected at one end. We reattached the loose spring ends and the echo-type reverb effect was ready to work again.
  There was still one major issue we had to address: the power transformer was overheating and the ac voltages were not right. Then, smoke came out and it was time to look for a new PT. We ordered a custom made PT from "Giatras" company and the result was awesome. We received a brand new large and sturdy PT and it cost around 40Euros! The new PT was mounted on the chassis and we hit the power switch...

The result:
 The amplifier came back to life, after so many years! These Philips NOS tubes are glowing, the amp sounds loud and clear and the tone is just awesome. Mission accomplished!

Here are some photos taken during the restoration:



The pcb with the old caps and resistors:

Metal tube covers removed:

The pcb traces and the tube sockets:

Some of the old parts removed:

Soldering new parts on the pcb:

The fx board outside the chassis:

The chassis:

Installing new capacitors on the reverb/fx board:

The reverb/fx board with its own reverb transformer:

The new electrolytic caps are in!

New power switches:

The old rusty Power Transformer(PT):

The new PT is in place:

4 guitar inputs!

The amplifier is ready to rock and roll again!

The new PT and components:

The fixed reverb tank and both speakers:

The Output Transformer (OT):

The fx boand under its metal shield:

The new power transformer (PT) and a brand new JJ ez-81 rectifier tube:

Here's the ELKA trx-20 live on stage in July 9th, 1976 !