BadCat - Classic Cat - Hot! Hot! Hot!

[nickb]

I have a Classic Cat here. The 6V6's are dissipating 20W. Now I know Badcat like to run their output's hot (see here) but that is in crazy territory. The glass envelope is running 205C - the typical max is 180C worst case.

It's a PP class A output with 425v on the plates. The two sides are separately cathode biased with 500 ohms. The resistors are dropping 25V, that's 50mA x 400V= 20W. These little guys will die in no time.


Anyone any experience of these and can tell me if my B+ is anomalous?

[Jazz P Bass]

As you well know, some tubes will dissipate more than other tubes.
Same type, same brand.

Are the tubes 'original' from the factory?

I would imagine that mass producing a cathode biased amp entails either selectively picking tubes or not giving a hoot.

[nickb]

They were Ruby's. I don't know if they were originals. One had am internal short and the other was EOL.

I think they just don't give a ....

[Leo_Gnardo]

They were Ruby's. I don't know if they were originals. One had am internal short and the other was EOL.

I think they just don't give a ....

Ruby sells China-made, Russian (EH) and JJ, all tested, matched but not of course identical. A long envelope with round dome top would indicate JJ. Elliptical cross-section grey plate, EH. Black inside the glass, China.

If you want 6V6 that would survive under Bad Cat conditions, JJ would be the pick. Others are fit for the litter box.

FWIW EH and Tung-Sol appear to be identical to me, except for the paint & price. OK if your B+ is say 375V or less. Sound good but NOT tough.

[nickb]

Ruby sells China-made, Russian (EH) and JJ, all tested, matched but not of course identical. A long envelope with round dome top would indicate JJ. Elliptical cross-section grey plate, EH. Black inside the glass, China.

If you want 6V6 that would survive under Bad Cat conditions, JJ would be the pick. Others are fit for the litter box.

FWIW EH and Tung-Sol appear to be identical to me, except for the paint & price. OK if your B+ is say 375V or less. Sound good but NOT tough.

In that case they were Chinese. I've always liked JJ. I popped in a a pair of Russian (Reflecktor) 6P6S's Still, I've changed the cathode to 750 ohms to bring things down to a more sensible 13W - still hot IMHO. Power out is slightly higher, gain is down a teeny bit as would be expected.

On the input, one half of the 6072 (12AY7) is unused. Just begging to be used to give a bit more gain or at least paralleled with it's brother to lower the stage noise.

[Leo_Gnardo]

In that case they were Chinese.

Can't see how anyone could expect those Chinese firecrackers to hold up under those operating conditions. OTOH old Russian "blackout" 6V6 do surprisingly well, usually. Good move in dialling back the bias. I am surprised Bad Cat didn't do anything with that unused preamp triode. I thought those guys were supposed to be on the ball. Maybe, not so much, just got a big rep because certain rock stars got their amps? Meeeoooow!

[nickb]

Hmmm..

If you rearrange BadCat you get BadAct. And Classic Cat to Licc Cat Ass. And it just goes downhill from here on...

Anyway here is the schematic for the benefit off all.

[Gregg]

Usually ALL combos get hot. In cases like this I would mount a fan. It doesn't need to be something big and/or powerful. You just need some air movement under the chassis. I'm usually using a small (40x40x20mm) silent (13db) DC fan powered from the heaters that takes care of the heat issues.

[The Dude]

In my experience, this is somewhat typical of the Badcats. I've changed many a cathode resistor in those things after an explanation and discussion with the customer. I hate to modify an amp without discussing it with the customer, but it's just plain stupid to run tubes that hard. I've never had a customer complain afterwards. In fact, many have said the amp sounded better.

Edit: On the heat: Even after re-biasing, they do still run a bit hot, but not nearly as hot as before the resistor change. I have told a few customers that if they still have a heat problem we could install a fan. Never heard back from them, so I assume the temp was brought down enough for them to deal with. I have seen some get so hot that you could feel the heat when making amp adjustments prior to a cathode R change.