PT, OT and tubes. How do they interact.

[shocki]

I have read quite a lot of stuff about preamp design lately and have a great book dealing with that. I am still learning. But I have good resources.
I don't have much information about the ouput/transformer side of the amp though. Wow does the OT (for example the actual size.) die PT voltages and corresponding tubes influence the breakup up, bass response und power exactly?

You could have an amp with low voltages, 6V6 and a big transfomer (more iron).
Or you could have an amp with high voltages, 6l6 but a smaller transformer. In this case the OT would be driven into some kind saturation and the bass would not be as tight I think.

Obviously you can use tubes like 6l6 with different plate voltages as long as you are not going over the maximum specs.

So it depens what you want to archieve. Is there any information on how all those parts interact exactly?
What makes a tiny Bandmaster OT a Bandmaster compared to the bigger OT of the Super Reverb ? (if you would use the same primary and secondary on both)

[Chuck H]

The details would need to be bypassed for any explaination that would fit in a post. And the important stuff is in the details. Basically:

A bigger OT will have more and tighter bottom, is typically a little more efficient, flatter top end and is a lot more expensive.

More plate voltage will be louder, have tighter bottom and more top end detail.

A bigger PT will sag less. Providing more of the power needed for dynamics. Where a smaller (actually lower rated) PT may actually drop more voltage under higher current demands and lose detail.

A little about the details: If a PT or OT is already rated high enough to provide for any circuit requirements, a bigger PT or OT may make no notable difference.

Anything I said above about dynamics, tighter bottom, etc. does not mean "better". It just means different. Some amps have a characteristic sound that is dependent on the sort of transformers and plate voltage they use. Be it a moderate sized PT with moderate voltages and a large OT or a large PT with high voltages and a moderate sized OT or small PT with low voltages and a small OT. Mix and match as you like so long as nothing is under rated for the application.

Tubes, transformers and voltage levels are only part of what makes different amps sound different. There is also the speakers, type of cabinet, feedback arrangement, class of operation and circuit specifics that affect frequency balance.

How it all works together in every possible scenario is impossible to cover. If you pay attention you will develop a feel for it. An amp with a small PT, low voltage and a small OT is going to sound boxy, overdrive easily and compress a lot. Great for blues. Not so much for metal. An amp with big iron and high voltage will be loud, tight and compress very little. Better for metal or country steel guitar. Not good for 50's rock. etc. etc. etc.

Whenever you get the chance, compare the sounds and circuits of different Fender blackface type amps at every oportunity. They are all similar circuits component wise with variable iron sizes, plate voltages and tubes. Probably the most consistent format for comparison of different features such as these.

EDIT: Note that none of this takes into account the effects of different tubes within the same "type" or different primary matching impedances. Both of which are also significant considerations within the subject of power amps.

I just noticed that you already have a thread started on basically the same subject!?!

[shocki]

Thanks alot for your reply. Great forum with very helpful people.

[Zozobra]

I like you started out reading about preamps and then got confused about poweramps as I wanted to understand them well enough to design my own or at least verify that the designs I was using weren't stupid.

Merlins website (I think I saw that you've got his preamp book somewhere else?, his power supply book is also excellent but it took me a good while to get the beneft from it as its a bit more subtle) has some good basics on it which gave me enough understanding of the topic to then have a crack at Richard Kuehnel's book on poweramps which is comprehensive to a fault