Power amp design. Resources?

[pinkphiloyd]

I've dug up and acquired some great stuff on designing preamps and power supplies, but I can find very little, if any, on output section design. Anybody point me to something good?

[Jazz P Bass]

Mr Elloitt is always a help.
Simple Class A Amplifier
Edit:
Forgot about this one from Motorola.

[J M Fahey]

That one sure *is* a practical design Bible.
Have been using it from the early 70's, when I switched from Tubes to SS.

[Raybob]

SS is against my religion. For Tube amps, Randall Akien has some good info at Aiken Amplification
For PT current calculations, there's a handy spreadsheet available at PT Current Draw

[pinkphiloyd]

I guess I should have been clear, I was referring to tubes. Thanks anyway, though.

[J M Fahey]

Why would anybody design a *Tube* power amp?
It's all already there, on black and white, and has been so for the last 50 years.
Now, SS, that's where innovation lies.
Besides, not even Leo, Jim or Dick designed, they used datasheet examples or copied each other

[Enzo]

I agree, little has changed in how a tube power stage is designed in just forever. Read the Radio Design Handbook from the 1930s, and the designs there are just as valid now as they were then. Look at the suggested circuits in the back of the RCA tube manual. Look well, because they are the source for many commercial amps you have seen over the years.

The power amp includes the power tubes, output transformer, and phase splitter/inverter. SOme more involved amps add a driver tube between phase inverter and power tubes. You can chose appropriate tubes for the power level you want, and a transformer to suit them. Chose the phase inverter type from the short list. Provide power to it all, and voila.

Look at the power stage of a Fender Bassman, then a Marshall something or other. Not much difference. At least not in the circuitry.

[trem]

Am I high-jacking this thread if I ask a quick question.? If so, my apologise.......
It has been on my mind for quite awhile, but Enzo just brought it up again.
If the phase inverter is considered part of the Power Supply, do you guys ground the PI tube along with the power tubes, and perhaps the speaker jack.?
Thank You

[Wombaticus]

I agree, little has changed in how a tube power stage is designed in just forever. Read the Radio Design Handbook from the 1930s, and the designs there are just as valid now as they were then. Look at the suggested circuits in the back of the RCA tube manual. Look well, because they are the source for many commercial amps you have seen over the years.

The old sources are great but never contemplate how the power section behaves when overdriven. Richard Kuehnel's "Guitar Amplifier Power Amps" book attempts to fill that gap.

[J M Fahey]

True.
Yet the solution is easy.
To protect from over-dissipating screen grids (dissipation rised exponentially when overdriven) current limiting resistors were added .
Old schematics often connected screens straight to their supply source or at most through small value (say 100 ohms) resistors. Datasheets still show it that way.
Today 1K , 2K2 and even 4K7 are used, if needed.
The other problem is ugly blocking distortion, unheard of in clean amps.
It was also solved by a grid series resistor ; 1K5 to 4K7 on power tube grids, and up to 220K or 330K in series with *veeeery* overdriven triodes , coupled to lower value coupling capacitors.
Beyond that, very little change, if any.
Well, let us not forget Gary's Led biasing.

[Intergalactic Tourister]

What kind of PI tube?

I have an amp with 7199 phase inverters and pin 8 is grounded via a 48k resistor.
And pins 1 & 9 are grounded via a 47pf cap.

Or perhaps you're wondering whether to gnd them together at one point? Or at different stages?
The speaker jack is connected directly to the output xformer (the + side and - side). The grounded side is not the side you connect to the spker jack. Your amp may different though.