recommend marshall 50 watt OT and PT

[daz]

I'm thinking of building a 50 watt EL34 PA and using the same pre as in my current 18 watter. can anyone recommend a good tranny set? (will be using a tube rectifier) Cost IS a consideration, so bang for the buck sets are especially desirable as long as there is no no non subjective sacrifice.

Also, anyone know of a EL34 schematic that is cathode biased, and especially designs known to have a less than nuclear volume output like the typical marshall 50?

[Bruce / Mission Amps]

I'm thinking of building a 50 watt EL34 PA and using the same pre as in my current 18 watter. can anyone recommend a good tranny set? (will be using a tube rectifier) Cost IS a consideration, so bang for the buck sets are especially desirable as long as there is no no non subjective sacrifice.

Also, anyone know of a EL34 schematic that is cathode biased, and especially designs known to have a less than nuclear volume output like the typical marshall 50?

Shouldn't be any problem to just build a 50w Marshall type amp and use a pair of grounded 150K grid load resistors on the EL34s.
Hold the two EL34 cathodes up by 270 to 360 ohms... use at least a 10 or 15 watter... bypassed with a 47uF@100v to 100uF@100v cathode bypass cap.
The "relatively" inexpensive transformers from Antique Electronic Supply are made in the USA and are pretty good.

http://www.tubesandmore.com/scripts/...P?item=P-TM050
http://www.tubesandmore.com/scripts/...?item=P-TM-P50
http://www.tubesandmore.com/scripts/...m=P-TM800-C-CE

[daz]

Thanks Bruce. But one question...why the choke? Can i just use a power resistor, and if so whats the diff?

[Bruce / Mission Amps]

Thanks Bruce. But one question...why the choke? Can i just use a power resistor, and if so whats the diff?

Yes, but it seems to me most El34 amps work better with a choke because the screen current can be VERY high compared to other 25-30 watt power tubes such as KT66 or 6L6s.
A choke has pretty low DC Resistance so the voltage drop across it under high load/high current will be much lower then say a 500-1000 ohm screen node resistor. That can be a little problematic if the DCR of the OT is too high and the plate B+ turns out to be much lower then the screens!
A good choke, under a current load, should always have much better AC ripple rejection then any screen node resistor.
Screen resistors are OK for low powered amps... 18 watts or less, but I don't think they are a good choice for higher powered amps.
However, there are exceptions, such as some Traynor EL34/6CA7 amps at well over 50 watts. Check out a YBA-1A Bassmaster MKII with a 10 watt 470 ohm resistor with a screen node branch... followed by another 470 ohm 10 watter, dedicated one at the common screen supply.

[daz]

Thanks Bruce. Thats good info to know, tho since i posted this i've pretty much decided to go with a four EL84/36 watter. i was convinced there would be enough clean headroom for me, and having built a 18 i'm more comfortable with this since it's about the same thing. Any advantage to going with a choke on this one, and if so how would i pick one that would match the current schematic's voltages it gets with a resistor?