1973 Sound City Bass 150

The poor man’s Marshall - Sound City is the “other” English brand that never quite achieved the fame and recognition of Vox or Marshall. Sound City in many ways was the precursor to the very similar designs of Hiwatt. They are usually loud, heavy, semi-clean amps with little in the way of frills or effects. This one came in with a lot of grime and dirt covering everything - it had never been worked on with the exception of some tubes being changed. The filter caps were cracked and leaking caustic paste, all the tubes were shot, and a lot of components needed to be replaced. The customer wanted no expense spared here and the goal was to bring this monster of an amp (Output = 150 Watts RMS) back from the dead.

All the axial lead electrolytic capacitors were replaced with upgraded voltage and temperature rated MOD brand electrolytic’s. The multi-section cap can’s were replaced with new German made F&T 100/100uf 500v, and 32/32uf 500v type units. The power dropping resistors were upgraded to 2 watt metal oxide type, and 5 watt wire-wound type for better noise floor and reliability. The adjustable Fixed Bias was set to %55 Class AB Plate Dissipation with a B+ of 535 VDC. The KT88’s here use a strange mix of Ultra-Linear circuit design with Fixed Bias, concurrently with a very small amount of Cathode Bias. The tone stack in the amp (Semi-Active) uses feedback loops from the preamp stages which themselves use very unique circuit design of local negative feedback throughout. The “Overtone” knob controls a second gain stage designed to produce distortion only in the upper band frequncy range leaving the bass frequencies relatively clean. This is technically a Bass amp, but it sounds great on Guitar and that is how the customer uses it.

The amp was completely re-tubed with the following compliment. V1 = JJ E83CC, V2 = JJ 5751, V3 = EHX 12AT7, V4-V7 = JJ KT88 Blue Glass. I picked out this lineup specifically for this amp to give the best balance of tone, reliability, and low noise. This will be used for Post-Hardcore and the amp will be front loaded with a Dallas Rangemaster - These tubes worked best for this style. These Sound City amps - much like Hiwatt’s, can have issues with background noise due to the wiring and ground layouts. I addressed this with tubes and component choices. The 5751 in V2 was chosen to lower noise and so that the semi-active tone stack would not be overloaded with the hi-gain boost pedals the customer likes using.

All pots were cleaned and hardware tightened. A great deal of hardware had to be replaced due to how crusty/grimy things were - so much so that a lot of the screws that needed to be un-done to get the filter caps out actually had to be clipped out with screw cutters. The Neon pilot lamp was also disassembled and repaired. A lot of work here, but now this piece will live on for the coming decades.