Homemade Hot Rod Plexi Part 4 – Preamp B+ Cap

Let’s be definitive on at least one issue: a preamp filter cap located inside a small jtm45 chassis is a major source of hum. It is no wonder that the “lower gain” jtm45 and early plexi50w have it on the board, while every “higher gain” mod.1987 from the mid70’s onward have it on the chassis…

Homemade Hot Rod Plexi Part 3 – Snubber Caps

Snubber capacitors in parallel with each rectifier diode will go a long way towards reducing the high frequency parasitic oscillation in some tube amps by clamping down the diode’s switching noise. Typical values range from 1nf to 47nf. Coupled with relocating the bridge rectifier on the far side of the chassis, this has had a…

Homemade Hot Rod Plexi Part 2 – Superlead vs. Superloud

In the heyday of non-master volume amps, i.e. during the late 60’s, your garden variety 100W amp was supposed to blast away on stage without P.A. reamplification and would typically be connected to dark-ish sounding speakers à la Greenback. Think Hendrix at Woodstock. A far cry from today’s typical set up. Back then, a lot…

Homemade Hot Rod Plexi Part 1 – Presentation

I embarked on a homemade 50W English-style head “from scratch” project a few weeks ago, and I managed not to blow things up entirely, which is quite a feat considering the amp was built mostly with parts laying around i.e. an OT and a choke scavenged from a 1976 JMP, JTM45 reissue PT, unmatched carbon…