low plate/high plate

[jestaudio]

At the risk off looking a total idiot can someone enlighten me on low plate and high plate layouts, ie which particular part of the circuit

[Structo]

That refers to the plate load resistors on V1 and V2.

High plates are usually 220K/150K (V1a and V1b) with corresponding 3K3/2K2 cathode resistors.

While low plate refers to 100K plates and 1K5 cathodes.

The #124 ODS amp has 100K or low plates.

Robben Ford's #102 ODS has high plates.

[David Root]

V1 and V2. You will see 220K plate, 3K3 cathode, 180K pl./2K7 cathode, 150K pl./2K2 cathode, and 120K pl./1K8 cathode. Sometimes all 220K/3K3, eg #183 ODS, sometimes low plates on V1 and high plates on V2, or vice versa, it all depends what you are trying to achieve tonally.

The rule is divide the plate value by 66 to get the cathode value. This keeps you in the middle of the load line, same as low plate, 100K/1K5.

The higher you go the smoother the tone, other things being equal of course. Also the current drops as you go higher. If you were to go to say 330K/5K your current would be down around 0.3 mA, maybe even less, which is generally not a good idea.

All above applies to 12AX7 of course, not necessarily any other type.

[jestaudio]

got it looking at my ceriatone based build it would appear to a high plate, how much can you mix and match between ,ie. if i modded it to go low plate would i have to change the cathode resistor, probaly a stupid question but i,m learning as i go

[T Wilcox]

At what value does a Low plate become a High plate?
Does refering to an amp as high plate or low plate only correspond with D-styles, or could I say a Marshall 2550 is a low plate?
Where is the happy medium plate?JK
Thanks for asking this BTW Jestaudio!

Todd

[Structo]

I've really only heard high/ low plate in relation to Dumble amps, but I'm not the most experienced here.

[David Root]

Yes, you can't screw around with the 66 rule in a Dumble.

Don't get "creative" if you don't know what you are doing! It will NOT sound good in a Dumble circuit. Did you understand what I meant by by being in the middle of the load line? If not, you have some reading to do.

If you're doing an SLO or Marshall style amp, sure that's different, the tonal balance is designed to be different. But you have to understand what they are doing too, and why.

Bottom line, if you don't understand it, get to the point where you do understand it. Then you can do anything!

[jestaudio]

Yes, you can't screw around with the 66 rule in a Dumble.

Don't get "creative" if you don't know what you are doing! It will NOT sound good in a Dumble circuit. Did you understand what I meant by by being in the middle of the load line? If not, you have some reading to do.

If you're doing an SLO or Marshall style amp, sure that's different, the tonal balance is designed to be different. But you have to understand what they are doing too, and why.

Bottom line, if you don't understand it, get to the point where you do understand it. Then you can do anything!

I pretty sure i,ve got the gist of it, the general problem i have is my area of electrics uses different terms to describe the same theory, and from what i gather different amp builders seem to have there own pet names for what is essentially the same bit of circuit
Maybe someone should put together a glossary of commonley used terms with a brief explanation then newbies like me would,nt ask the same stupid questions over and over