A Valco variation on the famed Supro Thunderbolt, the Harmony 420 has a solid-state rectifier, verses the Thunderbolt’s tube rectifier, and individual bass and treble controls.

Harmony 420

Though this old Harmony 420 bass amp looks like I fished it out of a river, I found this one in an old bar/dance hall in Delaware where it served out its years as a backup stage amp. This poor old guy sure has been around the block a few times, or, as my grandpa used to say, it’s “been through the mill.”

This is another amp built by Valco and is pretty much the same as the more famous Supro Thunderbolt, except for a few changes. For one, these 420 amps have a solid-state rectifier and separate bass and treble controls (the Thunderbolt had a single tone pot). The 420 also has a different cabinet design, with the controls on the top of the amp rather than the lower back of the Thunderbolt. So does the 420 sound the same as the Thunderbolt? They’re very close, but the price comparison between the two amps makes for an easy decision because the 420 gets you at least 90 percent of the way there, often at less than half the cost. Both amps even featured the same Jensen C15P speaker.

A lot of amp makers in the 1960s struggled to create appealing models for bass guitar, and this one is no exception. Playing a bass through these amps is simply an uninspiring experience. Although the 420 is voiced darker than a regular guitar amp, it provides some really nice, glassy clean tones for guitars. Also, the amp takes pedals very well. The wood and the cabinet design on these amps is nice, and unlike Danelectro-made amps, they do travel well.

These cost around $200 in 1966 and were marketed as providing “powerful amplification” with “minimum distortion.” That does hold somewhat true, as the 420 used a pair of 6L6 tubes for the output. Later versions of this amp featured a cool red-racing-stripe motif, and, of course, following the Valco way, there were several similar amp circuits made under the Airline and Gretsch brand names as well.