Fig. 1 — DC voltage leakage was one problem with this amp, but note the easy-to-access layout of the capacitors and wiring, which made replacing resistors and caps easier.
WARNING:All tube amplifiers contain lethal voltages. The most dangerous voltages are stored in electrolytic capacitors, even after the amp has been unplugged from the wall. Before you touch anything inside the amp chassis, it’s imperative that these capacitors are discharged. If you are unsure of this procedure, consult your local amp tech.
It’s time to get serious and start checking for bad components. I flip the chassis over and start measuring resistors. The first one reads more than double its value. Okay, so that one has drifted way out of range and needs to be replaced. Next one, same thing. Next one, even worse. Next one, almost open. Turns out almost every resistor, especially any that pass high voltage, has drifted so far out of spec that the circuit is barely functioning at all. I replace almost all the resistors, turn on the amp, turn up the volume, and … much better, but still weak and not good sounding. I go back in and start measuring voltages around the signal caps. Turns out that most all the signal caps have substantial DC voltage leaking through. Caps are supposed to block DC voltage and these are doing a particularly bad job. I replace all the caps showing DC leakage, turn on the amp, turn up volume and … we have an amp that’s sounding pretty respectable. At this point I’ve replaced almost all the resistors and capacitors (Fig 1), but it was necessary.
Fig. 2 — The amp’s major components were built in two parts, with the control section, in this photo, on the top and the main chassis, and with the transformer and tubes, on the bottom.
Now it’s time to check the tremolo, which, of course, is barely working. I swap out the tremolo oscillator tube, but no improvement. This amp is actually in two parts: the main chassis on the bottom of the cabinet with all the transformers, tubes, etc., and the control panel mounted to the top with the input jacks, power switch, and all controls for volume, tone, and tremolo. There is also a capacitor associated with the tremolo on this panel (Fig 2). I replace the cap and now we have a respectable tremolo. All is good … almost.
Fig. 3 — Once the amp was working again, the final touch was adding a hum balance resistor at the end of each of the filament lines and connecting them to ground.
The amp, while now functioning well, has a low-level hum. Well, I’ve gone this far and the customer tells me he wants to use it for recording, so why not try to get it a little more right? I clip some additional filter capacitors across the existing caps. If this minimizes the hum, then maybe the filter caps are not up to snuff and need to be replaced. Using alligator leads, I clip in some new filter caps across those caps, turn the amp on, turn up the volume, and … the same hum.
So okay, the filter caps are doing an adequate job on their own, as additional filtering doesn’t help. But where is this hum coming from? I realize this amp has an old-style filament wiring, found on many amps from this era including some tweed Fenders. One side of the filament winding coming from the mains transformer is tied to the chassis, with the other lead going from one tube to the next, connected to one of the tube’s filament connections. The other filament connection is connected to the chassis to complete the circuit. This wiring configuration seems to induce a low-level hum in amps. My solution: remove all filament connections to the chassis, including at the transformer, and run the second filament line to all the tubes. Once that’s done, I add a hum balance resistor at the end of each of the filament lines and connected to ground (Fig 3). I turn on the amp, plug in, and now the Electar is respectable sounding and probably quieter than when it was built. A little gem of the past resurrected.