The Amp Garage

KGW wrote: With 2 100W+ tapped WW resistors, this could easily be done.

Watch your individual power dissipations, though. 1/10 the length of a 100 watt resistor is only a "10 watt resistor."

--mark

The Jack Darr book ( in print again ) has a good, simple introduction to amp stages and how they work. Inside the Vacuum Tube (Rider) has a great explanation of how tubes actually work, and explains biasing, load lines, etc. Newer books I like include Valve Amplifiers and Building Valve Amplifers by...

Bias can be altered by a superimposed AC voltage on the cathode. Bias (in my mind) represents the static, steady-state, no-input condition. Once you add input (AC), then all points that are not AC grounds will change with the input. As KOC pointed out in one or more of his TUTs, the gain and freque...

On the airbrake discussed in the other thread, except in bypass mode, there is a fixed 25 ohm shunt, and a varying series resistance, as much as 175 ohms in 'bedroom mode.' This means the load seen by the amp varies as well, with a 30-something ohm total load at max attenuation. A better design woul...

I like the 'four 4x12 cabs in series' solution.

There's no easy way to make those useful that I can think of, short of rewiring a 4x12 cab with all four speakers in series.

--mark h

For a given resistance value, smaller resistors produce more noise. But, I don't know that this is an issue at this point in the circuit.

--mark

I don't think make-before-break helps in this situation, because it's the charge built up on the unconnected caps that causes the pops, and they will discharge with a pop when you make the connection with them, before or after breaking the previous connection.

--mark h

raiken wrote:

mhuss wrote: That said, the discontinued Aiken Tomcat uses a single 12AT7 as a preamp tube, so it seems extremely likely that that's the cascode one!

No, I don't use a cascode in any of my production amps.

Oops -- I misconstrued your "...your hunch is correct" comment!

--mark h

CathodeBiased wrote:...= .0635 Watts of power

I think you're off by a factor of 10 there ( = .635), but as you point out, 2w is still almost a factor of three margin.

I'm also curious why weight is a factor.

--mark h

Actually, as long as the OT has multiple output taps (as it typical for all but the weirdo Hammonds and the really old RadioSpares), just leave the NFB where it is. The two things that matter are the ratio (as Bob mentioned) and also the voltage coming in -- the 16 ohm tap will produce a higher volt...

Here are the heater to cathode ratings for the common preamp tubes: 12AT7 -- 90v 12AX7 -- 100v 12AU7 -- 180v It looks like the latter is the safest bet. Even though it has a low mu, the cascode circuit has so much gain, I don't think it will be a problem. That said, the discontinued Aiken Tomcat use...

Actually this is using a 12AU7 (which is much safer). The 12AU7 has a 180v H-K rating.

--mark h

What if you DC bias the Heater center tap to lets say 70VDC Good for the hum and heater to cathode voltage no??? Sure, if you do it for the one stage that has it cathode "way up in the air." But if you do it across the board, now you're stressing all the other cathodes (which probably have 2-3v on ...

I'm coming to the conclusion that Hiwatts are just better in person. At the last two ampfests, I've come away all gung-ho about the Hiwatt. Then, to try to keep the momentum going, I scour the web for clips and the results are a bit of a let-down. In person, it's raw power...like you'd imagine Town...

Yes there's a comprehensive discussion over at The Gear Page. The last five pages turned into My Dumble Is Bigger Than Your Dumble and the mystery, Who Blew Greg's Celestion Gold?! LOL, sadly true Dumbles, indeed! Gimme a 'Wreck, that's why I'm here! Amen, brother! Sorry, D-fans, but I just don't "...