Idiots guide to tube amp design?

TheBigKevDogg · April 10th, 2006, 07:02 PM

Well I just pulled the trigger on a 5e3 kit (inspired by Kevin's build a little while back), and now I'd like to get a little understanding on how the things work! I can follow a schematic just fine, and have done some simple FX box mods (plan on swapping out the wiring on some tele's this weekend for the first time), but am just curious as to what really goes on in the signal path of a tube amp. I know the basics of preamp and power amp and I don't really want to know specifically why each resister/cap is that certain value, just a general flow chart thing, with some explanations of what stuff like B+ is (i've heard all of this talk but have no clue waht it is lol). Does anyone have any good online/free resources that aren't too dumbed down, but not too specific either? ¡Gracias!

Gord K. · April 10th, 2006, 09:47 PM

I don't know if it is an appropriate level for you, but...

The AX84 website has several models of tube amps. The P1 is around 5W and uses a 12AX7 and an EL84/6BQ5. On the page that has all the schematics for the P1 there is also a theory of operation document for the Rev 10 version of that amp.

HTH

Gord.

Scott S · April 10th, 2006, 10:20 PM

The important thing is just to keep reading. Check your library, search online for any unfamiliar terms, here and on Google, and don't worry when you can't understand something at first.

Dacious · April 10th, 2006, 10:48 PM

This is a good diagram:

http://www.hoffmanamps.com/charts/im...ntdiagram1.gif

When you pluck a guitar string, the vibrating string creates a tiny AC voltage in the inductor (wire coil around a magnet = pickup) which corresponds to the string motion. That's signal. Where it goes is the path. Although the signal is AC, you do not want it fed back into itself at any point prior to the power tubes. Nor do you want the 50hz AC ripple from the power supply in it.

The preamp tube has a large positive DC voltage present on the anode, or plate. This has dropped from 350-450 volts coming off the rectifier/filter caps/choke to 200-300 volts. That's what preamp tubes like to see. This is commonly referred to as B+ voltage. As it passes through the preamp it drops gradually.

The power coming straight off the rectifier is fed through several filter caps and either a choke or dropping resistor. This is the ripple filter - the diodes whether tube or silicon produce a series of short surges as the phase coming off the wall plate reverse. If this makes the plates of the preamps or power tubes it will be audible. It is not smooth. The filter caps are like little batteries filling up off the little spurts, which let power out on the other side as smooth, stable DC. If the ripple gets past the filters it will be audible as a deep buzz or thrumming.

Each of the preamps also has bypass caps on the plate and cathode load resistors so that stray hum from the heaters or other sources is not fed back into the system. You only want the signal propogated. The caps combined with certain value resistors knock out AC artifacts you don't want amplified.

TheBigKevDogg · April 11th, 2006, 03:37 PM

Wow guys thanks so much! Super helpful, all of you! I've got some studyin' to do!

April 10th, 2006, 07:02 PM	#1 (permalink)
TheBigKevDogg Tele-Meister Join Date: Jun 2005 Location: Santa Barbara, CA/USC Posts: 147 10 Photos	Idiots guide to tube amp design? Well I just pulled the trigger on a 5e3 kit (inspired by Kevin's build a little while back), and now I'd like to get a little understanding on how the things work! I can follow a schematic just fine, and have done some simple FX box mods (plan on swapping out the wiring on some tele's this weekend for the first time), but am just curious as to what really goes on in the signal path of a tube amp. I know the basics of preamp and power amp and I don't really want to know specifically why each resister/cap is that certain value, just a general flow chart thing, with some explanations of what stuff like B+ is (i've heard all of this talk but have no clue waht it is lol). Does anyone have any good online/free resources that aren't too dumbed down, but not too specific either? ¡Gracias! __________________ My Guitars (and Other Instruments) http://members.cox.net/thebigkevdogg/Guitars/Index.html

April 10th, 2006, 10:48 PM	#4 (permalink)
Dacious Friend of Leo's Join Date: Mar 2003 Location: Godzone Posts: 2,623 35 Photos	This is a good diagram: http://www.hoffmanamps.com/charts/im...ntdiagram1.gif When you pluck a guitar string, the vibrating string creates a tiny AC voltage in the inductor (wire coil around a magnet = pickup) which corresponds to the string motion. That's signal. Where it goes is the path. Although the signal is AC, you do not want it fed back into itself at any point prior to the power tubes. Nor do you want the 50hz AC ripple from the power supply in it. The preamp tube has a large positive DC voltage present on the anode, or plate. This has dropped from 350-450 volts coming off the rectifier/filter caps/choke to 200-300 volts. That's what preamp tubes like to see. This is commonly referred to as B+ voltage. As it passes through the preamp it drops gradually. The power coming straight off the rectifier is fed through several filter caps and either a choke or dropping resistor. This is the ripple filter - the diodes whether tube or silicon produce a series of short surges as the phase coming off the wall plate reverse. If this makes the plates of the preamps or power tubes it will be audible. It is not smooth. The filter caps are like little batteries filling up off the little spurts, which let power out on the other side as smooth, stable DC. If the ripple gets past the filters it will be audible as a deep buzz or thrumming. Each of the preamps also has bypass caps on the plate and cathode load resistors so that stray hum from the heaters or other sources is not fed back into the system. You only want the signal propogated. The caps combined with certain value resistors knock out AC artifacts you don't want amplified. __________________ My other Telecaster is a Thinline The Tele Bible, Ch 1, v 10 Love thy Telecaster, covet not thy neighbour's Strat!

April 11th, 2006, 03:37 PM	#5 (permalink)
TheBigKevDogg Tele-Meister Join Date: Jun 2005 Location: Santa Barbara, CA/USC Posts: 147 10 Photos	Wow guys thanks so much! Super helpful, all of you! I've got some studyin' to do! __________________ My Guitars (and Other Instruments) http://members.cox.net/thebigkevdogg/Guitars/Index.html

April 10th, 2006, 09:47 PM	#2 (permalink)
Gord K. Tele-Meister Join Date: Mar 2003 Location: Winnipeg, MB Posts: 154	I don't know if it is an appropriate level for you, but... The AX84 website has several models of tube amps. The P1 is around 5W and uses a 12AX7 and an EL84/6BQ5. On the page that has all the schematics for the P1 there is also a theory of operation document for the Rev 10 version of that amp. HTH Gord.

April 10th, 2006, 10:20 PM	#3 (permalink)
Scott S Tele-Afflicted Join Date: Dec 2005 Location: SW CR IA US NA PE Age: 28 Posts: 1,916	The important thing is just to keep reading. Check your library, search online for any unfamiliar terms, here and on Google, and don't worry when you can't understand something at first.