Bad Cat Hot Cat 15 build ?

[chuckb]

Hey guys, I want to build a 15w Bad Cat Hot Cat using EL84's. The schematic I have is a 30w with EL34's. What changes do I have to make to the the preamp and power section to acomplish this?the attachment is a schematic of the 30w Bad cat.

Chuck

[Chuck H]

To keep all else equal (or more so) you may want to consider using 6V6's instead of EL84's. This consideration is because EL84's need less than half the signal voltage of EL34's to perform. You would have to make changes that alter the tone and performance of other circuits in the amp to do this. What you would end up with would be more different than similar to a Hot Cat. 6V6's are similar to EL34's in their drive voltage needs so the rest of the circuit can remain unaltered.

For example... If you were to pad the signal into the PI for use with EL84's, the PI would not be at the same level of clipping for the amount of power tube clipping as with the EL34 amp. If you don't pad the signal the EL84's will be well into a full square wave by the time the PI starts to clip. 6V6's would almost be a plug and play alternative.

There is the option of padding the signal after the PI, but I've never seen it done that way. Reducing PI output with the circuit values is already present in the design. I could be wrong but I don't think you'd want to raise the cathode resistance much further or cool the bias much more than it already is on that PI. So maybe a simple post coupling cap shunt resistor across the PI outputs would be an option. I never see this done either, with the exception of post PI master volume type circuits. I think this is because designers have an aversion to generating gain just to throw some away. Anyway, if you must go with EL84's the post PI shunt may be your best option.

This is just the big macro stuff. There would need to be other changes too.

Also, I don't know where you got the schem but I'm wondering about the master volume circuit. The way it's wired there would be a post preamp shunt of 220k with the control full down and a shunt of 320k with the control full up??? That doesn't seem like it would be very effective as a master volume control.

Chuck

[chuckb]

Hey Chuck, thanks for the reply. I may indeed go with the 6v6's seeing how they're similar to el34's and I don't have to deviate for the schematic to much. Your right about the Master volume though, Loudthud pointed it out to me before in another tread and sent me this revised schematic. I want to retain the hot cat tone as much as possible and if using el84's will change that then 6v6's it is. As allways I appreciate your input.

Chuck

[JoeK]

Hi bit late to chip in on this thread but I'm perusing things black and cat myself. As it's a bit hard to find details and schematics I thought this page of hi-res photos was nice it's a club with reverb.

Image hosting, free photo sharing & video sharing at Photobucket

If anyone can point me to a hot30R page of high res I'd love to see them. cheers Joe.

[guitarmike2107]

Check out this page for photo's

Index of /projetG5/Images Amplis/Bad Cat

[JoeK]

Thanks for that link. Some useful stuff in that collection. Cheers Joe.

[dobrota]

It seems power amp of Bad Cat is very similar to power amp of Vox Ac15 but with EL34 instead of EL84. For EL84 use common cathode resistor about 130 ohm / 5W and one 220uF capacitor and decrease grid 2 resistors to about 100-470 Ohm for 1 or 2W

[leadfootdriver]

Gotta say, I hate the wiring on the BC. Are those 1 watt resistors? They're huge. Isn't that supposed to cut down on resistor noise?

Any insights on the construction techniques?

[HTH]

Hey Chuck, thanks for the reply. I may indeed go with the 6v6's seeing how they're similar to el34's and I don't have to deviate for the schematic to much. Your right about the Master volume though, Loudthud pointed it out to me before in another tread and sent me this revised schematic. I want to retain the hot cat tone as much as possible and if using el84's will change that then 6v6's it is. As allways I appreciate your input.

Chuck

I've build a Hotcat 30 from that same schematic and was sceptical about it working as a master volume in practice - it didn't is the short answer. Gonna rewire it and go with my gut instinct (same as your revised schematic).