Need Bad Cat "Black Cat 30R" Schematic

[bobloblaws]

Hello, anyone know of a schematic for an older Black Cat 30R by Bad Cat Amps? I sent a message to Bad Cat as well but so far no reply.

[nickb]

I've spoken to them in the past, they were very helpful. My understanding is the documentation control in the early days, prior to the current management, just didn't exist so the early schematics are no longer around. The good news is they are easy enough to draw out just by looking at one.

[alexradium]

it should be very similar to the DC30 Matchless wiith reverb,what's the problem?

[nevetslab]

I'll have to confirm this with the manager of our Guitar Dept (@ CenterStaging, LLC Burbank, CA), but I thought I heard him say the owner of Bad Cat had passed on, and that they're no longer in business. I had just gone thru the three Bad Cat Combo amps we have...a Cub IIR, a Hot Cat 30R and a Hot Cat 40R. Beautifully built amps! The Hot Cat 30R has an amazing range of tonality....very impressed with that amp!!

I just got thru installing new front panel lamps to back-light their Bad Cat logo (takes (5) CM259 type T-3-1/4 Wedge Base Type 259 6.3VAC/0.25A 5000hr lamps. The outside mating sockets on the 30R and 40R refused to light up the new bulbs, and, unless you remove the spkr baffle or unmount the bulb mounting assembly, they are a PITA to swap out bulbs on. Minor detail with such beautifully crafted amps!

[bobloblaws]

it should be very similar to the DC30 Matchless wiith reverb,what's the problem?

The owner told me it suddenly died during a gig. The fuse was blown. After replacing the fuse the amp is stable (does not continue to blow fuses) but there is no signal coming through, only a steady hum. So far I've checked all the tubes, the preamp tubes and rectifier are fine but all 4 EL84 power tubes are completely dead.

[The Dude]

What do you mean by, "completely dead". No filament, etc.? What are the voltages on the output tubes?

[bobloblaws]

What do you mean by, "completely dead". No filament, etc.? What are the voltages on the output tubes?

Meaning my tube tester shows them to be dead, in terms of transconductance. I have known good EL84's that test fine on my tester, so I trust it. Filaments are OK. With the bad tubes back in I took a bunch of voltage readings and most everything appears normal as far as I can tell, with the possible exception of the voltages on the cathodes which differ radically depending on whether the amp is in full or half power mode. To your question re: output tube plate voltages, I measured between 350V and 370V, depending on whether it is switched to half power or full power. In full power mode the cathode voltages are as follows, from left (rectifier side) to right: V1 -> 7.3V; V2 -> 9.0V; V3 -> 9.0V; V4 -> 7.3V. In half power mode the values are: V1 -> 32.3V; V2 -> 10.6V; V3 -> 10.6.V; V4 -> 32.3V. Obviously V1 and V4 cathodes are connected, as are V2 and V3, also borne out by the Matchless DC30 schematic, which is indeed pretty close. Also, this assumes the switch is the right way up, it was loose when the amp came to me. I think it's oriented correctly but there is an outside chance it's backwards. Anyway, I don't know if those voltages indicate an anomaly or not, and if they do I don't know if it is to be expected since the tubes are no good. I'm a little hesitant to pop new tubes in to see what happens as I don't want to end up frying perfectly good tubes if there is in fact a problem somewhere which caused all four power tubes to fail simultaneously. Is it possible they were all weak and some random event that caused the fuse to blow also caused the tubes to finally give up the ghost? I guess at minimum I'd want to start with a pair, one on either side of the OT, as opposed to a full quad, right?

Matchless-DC30-Old-Schematic.pdf

[alexradium]

These amps are all biased very hot,that coupled with upside-down chassis and 100 ohm screen grid resistors is calling for premature failure.
If all the surrounding components are ok including the OT,i would put 4 new tubes in and check for anomalies like red plating and such.

[bobloblaws]

These amps are all biased very hot,that coupled with upside-down chassis and 100 ohm screen grid resistors is calling for premature failure.
If all the surrounding components are ok including the OT,i would put 4 new tubes in and check for anomalies like red plating and such.

Ok, that's what I did, played it for 10 minutes or so, seems Ok. Thanks!

Recommend different value screen resistors?

[The Dude]

IMO, it'd be a good idea to check bias. I can't remember if this particular model is cathode biased, but I have upped cathode resistors in the BadCats, for lower dissipation and improved reliability. They tend to run the hell out of output tubes.

[bobloblaws]

IMO, it'd be a good idea to check bias. I can't remember if this particular model is cathode biased, but I have upped cathode resistors in the BadCats, for lower dissipation and improved reliability. They tend to run the hell out of output tubes.

I'm measuring about 15.5W dissapation per tube, so yes, that is hot. Cathode resistors currently are 120R. What would you bump it to? Or experiment until it gets down to about where in terms of dissipation?

[The Dude]

Experiment and do recheck, yes. I would start with 180 ohm and see where that get you.

[bobloblaws]

Experiment and do recheck, yes. I would start with 180 ohm and see where that get you.

Question re: hot bias. At least with the tubes I used to test I'm noticing some hum, enough to be annoying and the owner says it didn't hum previously. Does a hot bias increase noise at all? Given that apparently the tubes were used until the last gasp (he admitted that they had not been changed since "forever") is there anything else that might have suffered enough to introduce the hum, like screen resistors etc?

[The Dude]

I'd imagine the bias was hot from the factory. That's the way they build 'em. There could be lots of sources of hum. Is it there with nothing plugged in and volumes down? If so, check for power supply ripple. If idle current is extremely high, any hum will be more noticeable, but usually negligible.

[alexradium]

Power stage and PI can hum if unbalanced, otherwise it could be a bad filter cap,bad connection,or open resistors in filaments center tap eventually.
Scope is your friend,put it at work.