Correcting electrical safety issues in a Bad Cat ‘Classic Cat’

Bad Cat 0159Hello again. In this week’s blog we look at correcting some electrical safety issues in a Classic Cat 1×12 combo from Bad Cat amplifers, of the USA. This particular Bad Cat would appear to be a limited edition, maybe even a one-off custom order, and we could find no reference to it at all on their website.

Bad Cat 0163Most Bad Cat and Matchless amplifiers are derived in some way from (or inspired by) vintage 1960’s made-in-UK VOX amplifier circuits. This model is completely different, and is obviously derived from 1950’s Tweed/Fender and Valco/Supro amplifier designs. Classic Cat controls and functions are really sparse – just a pair of input jacks plus volume and tone controls. That’s it ! The design follows the classic Supro pattern of a pair of 5881 or 6L6 output valves, cathode-bias, for a nominal output of 24 watts rms at the onset of clipping.

Bad Cat 0164There is a single 12AX7 gain stage followed by interactive volume control and single (“tweed”) tone control. The effectiveness of the tone control depends on the position of the volume control and also offers no control at all over bass or lower midrange frequencies. This stage is followed by a 12AX7 valve employed as a “paraphase” (self-balancing) phase-inverter, very similar to some mid-1950’s Fender (“tweed”) designs. However, this type of phase-inverter is not known for achieving perfect balance or low distortion, and so adds to the raw vintage character of the amp’s performance.

Bad Cat 0154Our good customer Danny brought this amp into the workshop to resolve some electrical safety issues. The most obvious sign of trouble is the broken IEC 240V power inlet. Further investigation revealed a lost earth connection, plus a loose mains fuseholder which could not be tightened. This latter component was also not compliant for 240V in the first place. We replaced the IEC inlet and installed a dedicated chassis earth point. We replaced the dodgy fuseholder with a compliant component and installed a T1A fuse.

Bad Cat 0155The amp now passed the Workcover NSW electrical safety test with flying colours, meaning that we achieve an earth test of less than 2 ohms from the earth pin of the 240V plug to any exposed metal part on the amp. You can see from the next photo the IEC inlet and fuseholder wired correctly, plus the dedicated earth connection to the chassis. The final photo shows the internal layout of the chassis, and hand-wiring Bad Cat/Matchless style.

Bad Cat 0158We would like to thank Danny for his continued custom, and for supplying us with the subject matter for this blog. We offer world-class service, restoration, repairs and advice re most boutique level valve (tube) musical instrument amplification.  It HAS been a lifetime obsession.

 

Bad Cat 0156Please check out our earlier blogs re amplifiers by Matchless, DR-Z, Landry, Jackson, Morgan, Matamp and others, plus our own Richards custom design amplifiers.

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