James Horrocks is the bass player in the Lol Goodman Band a top class blues band that can be seen at blues venues and festivals around the UK. He called in with a Trace Elliot Boneville C50 1×12 lead combo. It was sounding rubbish, kept cutting out and the reverb was weak and had a hiss. It needed a new pair of EL34 output tubes and some fresh resistors in the reverb circuit. I have never encountered one of these before. It is unusual in that it has two foot switchable channels but volume level is the only parameter you can set independently. The GAIN control and PREAMP STYLE are common to both. Also, it has an FX loop switch on the front panel that cuts off the guitar signal completely when the rear FX LOOP switch is set to SERIES. I thought this was a fault at first but when I looked at the circuit, it was designed this way. The FX OFF switch works as expected when the rear switch is in PARALLEL mode. Despite it’s quirks, it sounds and looks good, especially if you’re into motorbikes. Like the green tolex too.
James said: “Amp sound great Dan …. good job well done :)”
Lol Goodman Band
I had a pair of Peavey UL-12 speakers in for repair from Barry Barnes of the band Sinnerboy, the excellent Rory Gallagher tribute. (See www.sinnerboy.co.uk). The recently re-established Peavey UK distributor were taking ages to get me some replacement Black Widow baskets so I ended up cancelling the order and getting them reconed at RMJ in Keighley. I sketched out a schematic for the crossover (I have just included the passive setup. There is an alternative connector for active).
Peavey UL-12 PA speaker schematic – passive
The tweeter fuse is a polyswitch or resettable fuse which I replaced with TE Connectivity RXEF040 which opens the circuit at about 400 mA RMS and dissipates excess energy in the 2.5 Ohm resistors and the bulb. The fuses had exploded in a puff of soot which I am sure isn’t meant to happen. The tweeter coils were intact though.
I have had a Marshall 1960A Lead 4×12 cabinet in with problems.
Only two out of the four drivers were working on mono 4Ω mode and one of the four was making bad noises. This cab relies on the switch contacts on the two jack sockets to connect the two pairs of drivers in series (16Ω) or parallel (4Ω) depending on which socket is used. The switch contacts on the original sockets are nickel silver or tin plated and can’t stand much current without burning out. This is what happened in this case. The arcing had heated the contact enough to melt the plastic body.
To fix the fault I replaced both switch jacks with gold plated Neutrik / Rean NYS2152G replacements. They fit perfectly and should last a bit longer than the originals. I also sprayed the centre Mono / Stereo switch with contact cleaner. There was also a loose spade connector on one driver which I pinched up with pliers to solve the bad noises.
1970’s VOX AC30 in with a loud mains buzz. Main fault was the HT smoothing capacitor (the old one is the blue thing on the top). It also needed a new quad of EL84 tubes and a small repair to one of the speaker cones. All done, it was very hum free and hiss free. It is hard to fix the date for this one. It had 1976 on the POT’s date code. It looks like a Rose Morris era AC30 Top Boost amp without the voltage selector on the front panel and with PCB strips wired to valve sockets, not tag boards. The PCB’s are the superior glass fibre bluish ones. This is one of the better models to get. The 1970 to 1973 Birch-Stolec era models are to be avoided because the resin bonded paper PCB with directly mounted tube sockets degrades with the heat and the copper tracks come loose. Tag board wired models are easiest for techs like me to work on.
This is a nice little SJB Ant Combo valve amp. Unusual valves in this one: One 6SJ7Y pentode, one 6N7 double power triode, one 5Y3WG rectifier and two Brimar 6V6GTY power pentodes.
This is an SJB combo valve amp that might be called a Hornet.