Anyone build a Hot Cat from the schematic I saw here.

karl82 · Post by **karl82** » Mon Jan 08, 2007 4:57 am

Just wondering if anyone has had success with this as I consider building one myself.

ampdoc1 · Post by **ampdoc1** » Mon Jan 08, 2007 7:55 pm

Sorry, no. But I must have missed this schematic. Got a copy to repost??

ampdoc

unklmickey · Post by **unklmickey** » Mon Jan 08, 2007 8:53 pm

hey guys,

i sent you both a PM with links to the original thread and download.

but of course, this still doesn't address the question Karl asked:

Just wondering if anyone has had success with this as I consider building one myself.

cheers,

unk

rfgordon · Post by **rfgordon** » Tue Jan 09, 2007 1:24 am

I haven't built one, but I've thought about it! I have two slightly different version schematics, if anyone wants them. The main difference is the first triode--one has cathode to ground, the other one a cathode resistor/cap.

I played a Hot Cat at the Crossroads show in Dallas a coupla years ago. Very crunchy as I recall. Nice amp, if a bit bright for my tastes.

ampdoc1 · Post by **ampdoc1** » Tue Jan 09, 2007 5:31 am

If you got 'em,...post 'em

ampdoc

rfgordon · Post by **rfgordon** » Tue Jan 09, 2007 10:44 pm

OK, here are my Bad Cat Hot Cat files. I post these with the caveat that I've never seen the inside of one, so I can't vouch for the accuracy. Posting for educational purposes only, blah blah blah, yada yada yada.

rfgordon · Post by **rfgordon** » Tue Jan 09, 2007 10:46 pm

OK, here are my Bad Cat Hot Cat files. I post these with the caveat that I've never seen the inside of one, so I can't vouch for the accuracy. Posting for educational purposes only, blah blah blah, yada yada yada.

VacuumVoodoo · Post by **VacuumVoodoo** » Tue Jan 09, 2007 10:53 pm

You need a grid leak resistor in the range 5-15Mohm, 1 Mohm will bias the tube near to cut off. It must be mounted directly on the tube socket.

unklmickey · Post by **unklmickey** » Tue Jan 09, 2007 11:30 pm

VacuumVoodoo wrote: ...1 Mohm will bias the tube near to cut off. ...

i'm pretty sure it's the opposite.

i don't think the grid-leak version will ever be near cut-off. it should be operating near saturation.

or am i missing something?

unk

drz400 · Post by **drz400** » Wed Jan 10, 2007 5:38 am

VacuumVoodoo wrote:You need a grid leak resistor in the range 5-15Mohm, 1 Mohm will bias the tube near to cut off. It must be mounted directly on the tube socket.

I'll confirm that the cathode is direct to ground on the one I saw and the grid resistor was a 1M

Darkbluemurder · Post by **Darkbluemurder** » Wed Jan 10, 2007 8:44 am

rfgordon wrote:I played a Hot Cat at the Crossroads show in Dallas a coupla years ago. Very crunchy as I recall. Nice amp, if a bit bright for my tastes.

That's interesting. I thought it was extremely midrangey sounding in the lead channel.

VacuumVoodoo · Post by **VacuumVoodoo** » Wed Jan 10, 2007 12:17 pm

drz400 wrote:
VacuumVoodoo wrote:You need a grid leak resistor in the range 5-15Mohm, 1 Mohm will bias the tube near to cut off. It must be mounted directly on the tube socket.
I'll confirm that the cathode is direct to ground on the one I saw and the grid resistor was a 1M

Ok, should work with a very leaky tube. Still, try higher value - be brave and daring!

drz400 · Post by **drz400** » Wed Jan 10, 2007 4:44 pm

VacuumVoodoo wrote:
drz400 wrote:
VacuumVoodoo wrote:You need a grid leak resistor in the range 5-15Mohm, 1 Mohm will bias the tube near to cut off. It must be mounted directly on the tube socket.
I'll confirm that the cathode is direct to ground on the one I saw and the grid resistor was a 1M
Ok, should work with a very leaky tube. Still, try higher value - be brave and daring!

I totally agree it is WRONG
I double checked the grid resistor and cathode connection many times to make sure I wasnt seeing things, I agree 100%

VacuumVoodoo · Post by **VacuumVoodoo** » Wed Jan 10, 2007 7:20 pm

Let's not get into a quarrel and analyze the circuit instead (the pdf available in this thread)

317V supply and 99V plate voltage say the tube is drawing 1mA.
Tube characteristic curves then say that this operating point requires -0.5V grid bias rel gnd/cathode.
Further, tube data specify grid leak current as 0.5uA MAX. Typical value should be 5-10 times lower.

This is why I said "very leaky tube": 1M grid leak resistor will generate correct grid bias voltage IF grid leak current is close to specified max value.

12AX7 data specify 10M grid leak resistor.

So, the question is whether current production 12AX7 have much higher grid leak current.

Experiment with grid resistor value, it WILL have influence on the amps behaviour.

daz · Post by **daz** » Mon Feb 26, 2007 10:53 pm

the handdrawn schemos you posted I believe are inaccurate. Someone I know on the other forums built it from that schematic and said it sounded nothing like a badcat. Not even that good at that.

Might be interesting to do a group collaboration build??

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Anyone build a Hot Cat from the schematic I saw here.

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