Restoration

Funky-Fish Funk up your sound!

Restoration Echolette B40N by Funky-Fish

 

The amp

Echolette (KLEMT-Echolette) is a German brand that was famous in Europe during the 1950-1960. They produced audio equipment like delay effects and amplifiers. The B40N amplifier is an all tube bass amplifier, produced in 1963. The circuit looks very similar to an old Fender Bassman or a Marshall JTM45. My amp is repainted but besides that it is completely authentic, circuit, tubes, everything. It still works a bit but with a lot of distortion and almost no output power, after all, it is 50 years old! The schematic:

 

I didn’t take an old Fender, VOX or Marshall as an example of a restoration because in my opinion people pay ridiculous prices for this old stuff. There is some nice vintage equipment that sounds as good, that may get a change to be restored too. This amp is constructed on a PCB and with less common tube sockets, which makes it a bit more difficult than restoring amps of famous brands. Some pictures before the restoration:

 

  • A well build amplifier, with a lot of sense for details: look at the wires nicely bundled together, different colours of wire for every function, perfect solder joints. The potentiometers look and feel of good quality.

 

  • Some pictures of the outside. The chassis has no oxidation damage and the front panel looks in good condition.
  • The original Telefunken rectifier and preamp tubes and the Adzam (also rather old) power tubes. I dare to say that these are indeed the 50 years old original preamp and rectifier tubes since this amp was from a friend of mine and he bought it new back in 1963. Although a lot of people like these old tubes I will replace them by new tubes. I’ve seen too many amps with broken rectifiers and microphonic preamp tubes, so to start playing on stage with tubes that really have been used for 50 years is a bit tricky. There is no doubt that the power tubes need to be changed, since 40 Watts is not much for a bass amp and you may be sure that this tubes did suffer (even when it was just from transport). I’m 100% sure a nice amp will sound good too with new tubes, you don’t need 50 years old tubes for that.

Restoration

  • Let’s start easy and put some contact cleaner in the potentiometers and switches. There is none of them broken, so I chose not to replace them but just clean them to avoid bad contacts.

 

  • One thing I always do when I work on power amplifiers is checking that the fuses are correct. And indeed current rating and type (slow-fast) were wrong in this one. I’ve putted the correct type for this amp in the fuse socket. Different problems can occur with wrong fuses. If the current rating is too low or the fuse is too fast, the fuse can break without the amp having any problems. If the current ratings are too high or the fuse too slow, the fuse won’t break and you can damage parts of the amplifier or even more.

 

  • I can tell out of experience that an amp is sometimes noisy when the filament supply is not referred to ground or another potential. This amp uses two 47Ohm resistors to ground on the filament supply and they are still fine and resistance-free connected to ground. => ok!

 

  • Most often an amp of this age has bad contacts in its tube sockets. Or the sockets don’t have an infinite resistance anymore between the different pins and so noise or even worse will occur! I did change all tube sockets, since it is a complete restoration and the amount of tubes is rather limited. I didn’t use shielded preamp tubes and I needed to use my drill to put new tube sockets in it.

 

  • Next, I changed a few resistors. Most often in tube power amps the screen grid resistors have suffered or are even broken. I changed the original ones to metal film, 3W types (look at the previous picture).

 

  • At first instance I would like to keep the circuit unchanged, but one thing that should be added in my opinion is a variable bias circuit. If you thought that all EL34’s are the same, I’m sorry to disappoint you, it isn’t. If fact they differ a lot, even within one brand, that’s why we use matched tubes and we need a variable bias circuit to adjust the bias correctly for that specific pair of tubes. Otherwise you will feel like it is always a different amp if you change tubes (or even brake them!). Or you should be able to buy always tubes with the same ratings. So I changed the circuit a bit and added a trimmer to the original bias circuit.

 

  • Since the connectors are also 50 years old and not oxidation free, I wanted to change the input jacks. This high impedant inputs are very noise sensitive so let’s replace them.

 

  • Next, capacitor time! Capacitors do have a hard live in tube amps (high temperature, high voltage) and are not intended to live forever. They are intended to work on this high voltages, nonetheless they will age and get a lot of stress by working on these high voltages. Every type of capacitor has its own problems and eventually they will be aged so much that they will prevent the amp from working correctly. If people ask for a repair I just replace the broken ones or the ones that prevent the amp from working correctly but in an amp of this age I prefer to replace them all, since all of them will be aged and cause problems now or within the next days, years?

 

  • The first type of capacitors that I replaced are the electrolytic capacitors, mainly used in the supply. They start “leaking” or “drying-out”, in fact to put things easy, they do age and are surely not within specs anymore after 50 years (even after 30 or 40 years…). But most of the time the amp keeps on working with this bad supply caps. They won’t filter the mains supply ripple that good, their internal impedance changes. So with new supply caps you will have less supply hum, sometimes higher supply voltage and most often a bit more output power. So, no doubt they should be replaced!

 

We could use caps with a higher capacitance to filter out the mains supply noise better, but watch out, tube rectifiers can’t handle that much capacitive load, check the datasheet of the rectifier tube! You can see a big electrolytic capacitor on top of the chassis. It has two capacitors of 50µF 500V in its package, so it replaces the 2 caps of 32µF around the inductor in the circuit. 50µF filters out the main supply hum better and is still a safe load for the GZ34 rectifier.

 

Inside the amp you can see the other replaced electrolytic capacitors. One of them is decoupling the cathode resistor of the first preamp stage.

  • Often under-estimated but very important is that the coupling capacitors should be in perfect condition. These are the capacitors that link two amplifier stages. At one side connected to 150V DC or more and at the other side connected to the control grid very often at 0V DC. If they do leak even less than 1 volt DC to the next tube, that tube will work differently or sometimes will stop working at all. Distortion or no sound at all will result. Most often not really “nice” distortion and certainly not how the manufacture intended the amp to sound. Tube amps have the extra difficulty that the control grids are very high impedant, so a decoupling capacitor should have a very high insulation resistance for DC.

 

Very often older tube amps have bad (leaking) decoupling capacitors and they need to be replaced. Since all caps in this amp are aged (value, insulation) a lot, I chose to replace all capacitors. Lots of literature is written about what is the best type of capacitor for which job in a tube amp. I most often use film capacitors in the audio path, polyester or polypropylene. Only the very small values are implemented by ceramic capacitors.

 

  • If all electronics is finished, I’ve put new tubes in the amp.
    1. GZ34 of TAD, Premium selected
  • Matched duet JJ EL34’s.
  • 2 JJ ECC83S
  • The first tube is a selected ECC83 from TAD.
  •  

    • By figuring out how the output impedance switch works (5 or 20 Ohm), I found out that the output impedance switch was broken. So I replaced that switch and replaced one of the loudspeaker connectors from cinch to Jack. Originality is fun but I would like to have an amp that is practical in use too. And since every Ohm loss in a loudspeaker connection is a lot, I did replace the whole output section to have a resistance free connection towards my loudspeaker.
    • Such a nice, brand new amp, may look good too, so I cleaned all the knobs, buttons and front panel. The final result:

    Testing

    1. I’ve putted the amp on and everything works nicely. I adjusted the bias of the output tubes and got an acceptable 25W rms undistorted sine wave at the 5Ohm output.
    2. I was not completely happy with the plate voltage supplies for the different amplifier sections. First tube rather low, phase shifter rather high (450V). One could keep the circuit original but I changed the series resistors of the supply a bit, to get some more common bias voltages everywhere.
    3. Sound testing! The amp is clean and noise-free. The sound is rather familiar and clean and breaks up nicely. But I have problems adjusting the equalizer. I will use the amp mainly for guitar and not for bass, since the power output is a bit limited for modern bass in my opinion. I changed the tonestack values a bit towards the values of a Fender tonestack since I like that sound the most. Better sound but still difficult to adjust, especially the bass pot. I changed that pot from a linear to a logarithmic pot and the feel was much better.
    4. Same problem occurred with the volume pots, so I changed them too from linear to logarithmic potentiometers.
    5. Like this the amp is perfect for me and ready for the next 50 years!

     

    Price

    I used for almost 160 Euro materials: tubes, electronic components, tube sockets,… To restore this amplifier I needed around 8 hours of work before everything was completely finished.