Funky-Fish Funk up your sound!
Restoration Echolette B40N by Funky-Fish
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:
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.
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.
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.