Vintage tube amplifier repair!

  A friend of mine brought in a really old ELKA TRX-20 amplifier. It's not the same amp I've restored in the past but it's the exact same model:  http://guitar-dreamer.blogspot.gr/2013/03/vintage-tube-amplifier-restoration.html 
  This is a vintage 1969 tube amp combo made by an electronics company based in Italy that was called "ELKA". This is their TRX-20, 2X10", 20Watts guitar amplifier model and here's all the info I first found about it online:
"Elka TRX-20 valve guitar combo, reverb and tremolo effects, year: 1969 , 2x EL84 "


Specs and features:
 This 2X10" tube combo has two channels and four guitar inputs (two for each channel). The channels are named "Normal" and "Vibrato".There's a dedicated volume control per channel but the treble and bass EQ controls are common for both channels. The "vibrato" or "effects" channel has an on-board tremolo effect with "intensity" (level) and "frequency" (rate) controls. The "effects" channel has also a genuine spring reverb effect with a level pot called "reverb dimension". The reverb and tremolo effects are switchable via an external dual button plastic foot-switch.

Tubes, there are lots of 'em!
 I opened the amp and noticed that it's some kind of a Marshall 18w replica as far as the power amp is concerned but the preamp is pretty fender-like. This amp has 10 tubes in total!
 An EZ-81 tube is in charge of the AC to 350Vdc B+ voltage rectification while two Philips el84 power tubes deliver 20Watts of power to a set of 10" Celestion 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 "reverb driver" board mounted at the bottom the wooden cab. The  reverb tank is also placed at the bottom of the cab inside a wooden box.

The repair:

 This particular amplifier was in a much better condition than the previous ELKA I've worked on. The only problem was that there was no sound coming from the speakers... At first I removed its backplate and cleaned up everything. Boy there was dust inside... I then replaced a broken speaker cable but there was still no sound. The next things I checked were the tubes. Most tubes were changed and upgraded but there was an Ultron 12at7 that looked suspicious. I opened up the amp and found that the Ultron tube did not work due to an arc discharge that happened in the past. The arc has shorted out three electrolytic capacitors as well so they had to be replaced.

 I bought a set of power supply 450Vdc/47uF capacitors and replaced the old leaky and slightly burnt ones. I also replaced a 4.7uF/50V cathode bypass cap located near the Ultron tube. Once the new caps were soldered in, the Ultron 12at7 was changed with a newer Ruby ecc83 tube.

Footswitch: 
 The effects of the vibrato channel did not always work properly. So, I checked the footswitch which was in pretty bad shape. Once I got it opened, I noticed that most of its solder joints were broken off. I rewired its dpdt switches and cables to get both the tremolo and reverb effects working.

The result:
 The amp was finally turned on and I heard its sound! Man, what a sound! Crystal clear highs plus a deep and musical reverb effect that made my mexican strat sing like a bird. Even split-coil humbuckers sound classic and clear through this amp. There's definitely no overdrive channel here and the clean headroom is quite high. Turning the tone down and placing an overdrive effect pedal in front of this amp will get you some really good distorted sounds with plenty of low end bass. 

Here are a few pictures of this classic amp:

-Thanos
guitardreamer.gr@gmail.com