What and how do i determine what transformers to get for this schematic???

[ThKind]

these are a preamp and power amp i am building there is no transformer info at all and wondered how to figure it out ???

[kleuck]

If your supply voltage is actually 300 volts, you need a 4K transformer, it's explained here The Valve Wizard -Single Ended and the example is an EL84 under 300 volts

[kleuck]

EL34, sorry, i can't edit my message.

[Steve Conner]

Take your pick of output transformers from here. The Edcor looks like a bargain. Budget OPT's

The 20 watt rating is optimistic. You'll be lucky to get 10.

[loudthud]

There are serious problems with that schematic. It won't work as drawn. There is no practical way to get 20W through a 10K 10W resistor in series with the B+. The bias filter will produce a positive voltage and it won't work if you reverse the diode and cap polarity. The audio part of the circuit looks ok, sort of a Marshall 2203 feeds an EL34 Champ, but the power supply needs attention.

[ThKind]

this is an updated powersupply schemtaic .... again a new builder here but worked it out with may uncle will it give close to 20w???

[eschertron]

I have some comments about the tube you've chosen, regardless of the power supply and amplifier gain.

Find some EL34 datasheets. From them you will see that while the tube dissipates 25W as a design nominal value, in single-ended mode the power that it can transfer to the OT is less, around 10W as Steve Conner mentioned. Having said that, guitarists and amp builders rarely stick with design center limits and you can get more than 10W audio power out. It won't be clean power, and there will be quite a bit of power tube distortion by the time you pass the 10W mark. Can you get 20W of audio power out of this amp? Maybe. Will it sound like a chainsaw by the time you reach 20W? Likely. Loud enough to smoke the pants off anyone in your basement while you play?

So don't expect 20W of clean power out of a single EL34. Won't happen.

[ThKind]

ok thanks for the clarity will have to look a little deeper for some el84 power amps i guess?

[loudthud]

There are very few transformers like the one in the schematic that are available off the shelf. The Bridge rectifier is not used very often in tube circuits below 100 Watts. The bias supply has not been corrected.

The bias filter will produce a positive voltage and it won't work if you reverse the diode and cap polarity.

That circuit will never produce 20W with a 300V B+. Maybe you could get 12W with a B+ of 450V. It would need a completely different power supply design. Study this: http://www.hammondmfg.com/pdf/5c007.pdf

There are hundreds of designs to be found on the internet that have been built and actually do work. Why are you so obsessed on this one? Can you make your own chassis? How do you intend to connect all the resistors and capacitors? Where do you intend to buy the components? Buying a kit will solve all those problems, and at a lower overall cost. If you simply must do it the hard way, get this book: TOT - Tonnes of Tone

[eschertron]

ok thanks for the clarity will have to look a little deeper for some el84 power amps i guess?

I'll echo Loudthud here and suggest that you look around at the different guitar amp designs, and start with a schematic (or kit) of an amp that appears to be close to your design goal. There are some design 'types' that tend to sort the existing amps into classifications. One example is single-ended versus push-pull designs. Not only do push-pull (PP) designs tend to be more powerful - 15W and up - they 'sound' different to a lot of discerning ears. This is only one of MANY design types. Do some reading, and find out as much as you can about the history and evolution of amps, and then you will be better positioned to make informed choices about what design parameters you want to start with.

[jazbo8]

The diode for the bias supply is backwards as mentioned earlier, hope no one builds this, it will destroy the EL34... But perhaps the 20W is simply the recommended power rating for the speaker and not the actual output power...

[Joe L]

I've never heard of anyone that is sorry they built a Deluxe 5E3 kit as a first project. Bruce of Mission Amps sells one of the best.

A few pedals and this what you get - 100 Riffs (A Brief History of Rock N' Roll) - YouTube