OK, so the look may be sixties scientific equipment, but its full name is ‘Laney Supergroup Series Mk1 Session Amplifier 50W’, and I guess this is from some time around 1967-8, with plexiglass creamy white front and back panels. At that time ‘The Smoke’ had Marshall, ‘Brum’ had Laney. Actually, look inside and there’s not all that much between them, the significant influence of the Fender 5F6-A Bassman (this one top-mounted so even closer physically to the Fender than Marshall was) very obvious, but both using EL34 power valves and pretty much the same components from the same suppliers, apart from the transformers.
This only has one input for each channel, so they can’t be as easily bridged as was often done at the time with a simple patch lead for gain with the four hole Marshalls (Y-cord input adapters easily solves though); there are ‘Boost’ switches voiced for the treble and bass channels (though these have decreasing effect at higher volumes).
With this one you could see the valves lit up through the ventilation grill, but there was no sound. As soon as I had picked it up from the weight I knew it had to be a transformer missing, and sure enough when opened up – no output transformer. Which is a shame as these used Partridge, reckoned to be about the best, and probably the biggest single difference from the Marshalls of the time with their Drakes or Dragnells. That and the 10 ohm cathode resistor it has on the power valves; however this is not a cathode biased amp as there is also a circuit to supply a fixed negative bias voltage. That cathode resistor sure is convenient for measuring the bias across though.
This amp needed to be got up and running cheaply, which made tracking down a rare Partridge out of the question, so I installed – you’ve guessed it – a Marshall 50W replacement output transformer. Renewed all the rectifier diodes and the filter caps, replaced the mechanically stressed output jacks, installed a bias adjustment network, biased it up, renewed screen grid resistors (from 470ohm to 1kohm). Tested through a Marshall closed back cab, I’ve never played a vintage plexi Marshall, but this did sound like the recordings I have heard. How spot on close it is can be left to the cork sniffers, but these amps are typically sub £1k if you can find one; the same period Marshall can easily be two or three times that.
Here is another later one from ’69 or ’70 waiting for its replacement filter caps (most of the filter caps are on the main circuit board with these, whereas by this time Marshall had moved to using quite a lot more filtering and clipping the canisters to the outside of the chassis); this one sits on the bottom of its case like a Marshall, and retains all of its original Partridges intact. The model has now become a four hole input (so channel bridging is only a matter of a simple patch cord), and is rated at 60W output according to the back panel.
Laney, Marshall; Marshall, Laney – was this the Brum heavy blues rocker’s dilemma? With the 100W version of the Laney Supergroup, we can be grateful that for Tony Iommi it wasn’t.