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Thread: What's the deal with Bad Cat amps?

  1. #1
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    What's the deal with Bad Cat amps?

    Last week I fixed two Bad Cat amps for a customer -- a Lynx 50 head and a Black Cat 30R 2x12 combo. Both had power section failures. The customer is a Bad Cat endorser and so I had to deal directly with Bad Cat for all parts -- they were very nice and easy to work with and overnighted the stuff to me. The overdrive sound isn't my bag but the clean sound is fantastic. The Black Cat has an EF86-based preamp channel, very cool.

    Guts-wise, they have their own house brand of capacitors... so I don't know whose stuff they're relabeling. Both amps were carbon comp resistors throughout. Both were cathode-bias, which I don't really see much of (I do a lot of huge high-power amps for metal guys). The Lynx had an arc on a power tube socket, pins 2-3 (bad cabinet wiring), the Black Cat had leaky phase inverter coupling caps that had melted down the output tubes. Both amps had bad phase inverter tubes, not sure why.

    Anyway...

    Both also had insanely high idle current in the power amp. The Lynx 50 runs 2x EL34s in push-pull cathode-bias, and they idle at 35W a piece! The Black Cat has 4x EL84s and each of them is idling at 16W. I had to contact the company to see if this was correct, and they assured me it was. The customer complained that the amps are not reliable at all (duh) and that some previous tech told him they had "design flaws" that he wanted to correct at a later date. As far as I can see, the only thing that needs correcting is the cathode resistor values.

    Anybody else had experiences with Bad Cats? They didn't give me a schematic for either amp, so I just had to eyeball it. Are these basically souped-up Vox circuits? I guess I always assumed they were just clones of some classic amp with some extra boutique mojo.

  2. #2
    Supporting Member Jazz P Bass's Avatar
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    Sounds to me like you simply had tubes that went bad.
    Now it may be the high idle bias or tubes that just went south.
    Seeing as the factory stands behind the bias setting, that must be what they want.
    Doesn't mean that you cannot set it lower hint, hint.

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    Old Timer tedmich's Avatar
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    wow what a mess! People do like the Lynx...


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    what mess?

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    Bad Cat amps are amp designer Mark Sampson's subsequent venture after Matchless. The 30R is basically the same as the DC30, and like Matchless, the caps are branded. The power section is Class A like Vox and normally runs hot. Just sounds like you had bad tubes to me. FWIW- I love those amps. Some of the best-sounding ever to come through the shop.
    John R. Frondelli
    dBm Pro Audio Services, New York, NY

    "Mediocre is the new 'Good' "

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    IMHO those printed circuit boards are cheating. Either this guy does 100% PTP or NOT!

    Those caps look like MKT.

  7. #7
    Gaz
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    Quote Originally Posted by jrfrond View Post
    Bad Cat amps are amp designer Mark Sampson's subsequent venture after Matchless. The 30R is basically the same as the DC30, and like Matchless, the caps are branded. The power section is Class A like Vox and normally runs hot. Just sounds like you had bad tubes to me. FWIW- I love those amps. Some of the best-sounding ever to come through the shop.
    I know tube amp need some sort of maintenance over their life-span, but why did the amps 'come through your shop'?

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    I'm not sure what they have on the Lynx cathode resistors but when I was doing a Hot Cat build I found the individual 270 ohm resistors were correct for class A 30 watts according to a manual for EL34's. They might need to be NOS tubes to survive though as current production tubes seem to get eaten alive. I took the advice of some other more experienced techs and dropped the dissipation with individual 400 ohm resistors and didn't notice a night/day change in the tone.

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    Thanks for the insights. Here are the gut shots I took of the two amps I worked on:

    Black Cat 30R

    Lynx 50

    Yeah, the Lynx has 270R cathode resistors. It does look right on paper but I'm uncomfortable putting current-production EL34s in a spot where they're near 38W dissipation.

  10. #10
    Senior Member hasserl's Avatar
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    Quote Originally Posted by jamesmafyew View Post
    Thanks for the insights. Here are the gut shots I took of the two amps I worked on:

    Black Cat 30R

    Lynx 50


    Yeah, the Lynx has 270R cathode resistors. It does look right on paper but I'm uncomfortable putting current-production EL34s in a spot where they're near 38W dissipation.
    Links no worky

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    beauties

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