Friend brought me his recently acquired HD-130 Reverb head, saying the Reverb sounds great - when it works. Apparently the Reverb cuts out and stays off at inopportune times. Then returns just as abruptly. It was not working when I got it on the bench.
It's an early unit with 12AX7 PI, all parts date from early to mid 1974. It is very dirty, but has a strong clean tone. Both channels work fine, Tremolo is good, Bright switch works well, Deep switch works but is subtle.
A quick inspection revealed the main filter caps were physically deteriorating, so I replaced them. Will do a complete cap job when I receive the other parts ordered.
Cleaned and tightened everything - pots, jacks, plugs, switches, tube sockets, IC sockets, board screws, etc. The Reverb tank and cables look/measure fine. Set the bias to .5 volts DC as per the directions,
Amps sound great both clean and dirty (Volume up, Master down). Reverb was working and sounded good - until it stopped working again. Still intermittent.
When I chopstick the board where the Reverb control wires connect (wire solder points), I sometimes hear the tank crash.
Moved some of the ICs around to see if that made any difference, Reverb has not failed since but I only checked it over an hour or so.
I will reflow some solder joints and check for bad or out-of-spec resistors in the Reverb circuit. Sugestions welcome.