1. Yes, download the tube data sheets to find out which you need.slashfan wrote:Ok!! I still don't get 70% of the stuff written above, I'm still learning. Okay, now my doubts. Try to answer simply. Still a newbie here.
1) Are there different sockets for different types of tubes? If yes then which ones have common sockets?
2) I have a schematic diagram of a JCM 800 combo which is a 50 watter. How can I re-design the circuit to make it around 20 watts?
3) What are gain stages.
4) What function does a choke do?
5) What does the amount of gain depend upon?
6) How can I choose a proper output/matching transformer?
7) Does the number of output tube have anything to do with the amount of gain, because the SL 5C has only 1 output tube and still delivers lots of gain.
What dies biasing an amp do? What is cold bias?
2. Well you can graft on a 20w output stage onto a Marshall preamp but it might not sound like a Marshall any more because the output stage is all part of the sound.
3. Any stage that amplifies the signal, usually, but not always, each tube in the schematic, dual triodes can be 2 gain stages. (Some exceptions are cathode followers (no voltage gain) and phase inverters,)
4. Simply put it passes low frequencies and blocks higher ones dependant upon value, but there is quite a bit more to them than that.
5. Several things, the 'gm' of the tube, the type of circuit and component values.
6. You need some experience at designing tube amps, or copy an existing design.
7. No, the output tube is usually an impedance converter that takes a voltage signal from the preamp stages and boosts the available current (hence power) to drive the speaker.
8. Not easy to explain to someone who knows nothing about tube amps. Look up class A, and AB power amp theory. Biasing is necessary in push pull amps to minimise unwanted* distortion.
*As opposed to wanted distortion that you are trying to replicate.
All the above is very simplified. Designing tube amps is not something you learn from reading posts on the net.
From these questions I would suggest that if you are hell bent on building a tube amp you should start with a kit ,or at least an existing design, rather than trying to design your own low power Marshall. It will probably be way cheaper, quicker, and less frustrating because you need a certain level of knowledge of how they operate before you can even start to design your own.
I am sure other FSB members will clarify these points (and correct me if/where I am wrong).