Power amp schematic on this site question

[joesatch]

Looking to start on a stereo poweramp. I initially sourced parts for a mesa 50/50 style build but the schematic for that is too blurry for me to safely use.  There is a schematic posted on this site. I have a question about this schematic i have circled some traces.  Are these grounds or all tied together then run into a 47k resistor to ground?

[sluckey]

Those are not grounds. They are all tied together then run into a 47k resistor to ground.

[joesatch]

Thanks, what would i change to use EL34's (2 per channel)  and is there a Negative Feedback option? i will swap that giant resistor with a choke

[sluckey]

Thanks, what would i change to use EL34's (2 per channel)  and is there a Negative Feedback option? i will swap that giant resistor with a choke

Start by looking at a Marshall 50 watt schematic.

What giant resistor???

[joesatch]

marshall has a LTP this looks different. the resistor is a 10watt 150 ohm. I have a choke.

[sluckey]

marshall has a LTP this looks different. the resistor is a 10watt 150 ohm. I have a choke.

It may be drawn differently but it is the same except it has NFB added. Look at Hoffman's 50W Marshall. It's drawn the same style as his 18W stereo poweramp.

You cannot replace that 10watt 150Ω cathode resistor with a choke!!!

[joesatch]

what's that resistor do? that must be an el84 thing. Can i take that 47k to ground resistor and connect it to the 8 ohm tap on the OT instead?

[sluckey]

what's that resistor do? that must be an el84 thing. Can i take that 47k to ground resistor and connect it to the 8 ohm tap on the OT instead?

LOOK AT HOFFMAN'S 50W MARSHALL SCHEMATIC!

[joesatch]

  I will study the your schematic and try to incorporate the two

[sluckey]

All you need...

[joesatch]

What do you think about adding this gain stage before each channel ? This is what the mesa 50/50 has

[sluckey]

I don't think it's necessary. Won't hurt to include if that's what you want. .1µF input cap is way too big.

[joesatch]

Thanks again, i'd like to  include an input level control. I have gone through many power amps for guitar schematics and they all have a triode stage before the PI. I guess i will use it and put a 22nf. appreciate your help.

[shooter]

this is for guitar, not audio?


in either case, if you have a "proper" pre-amp, as Steve pointed out, not necessary.
if it's for guitar then maybe as an OD stage
for audio I like that stage to be a CF

[joesatch]

It is for guitar but i would like it to be clean and not overdriven.

[joesatch]

Getting things together. working on arrangement of parts in this 2U case. like this is close to the mesa 50/50. Anyone have experience with 120v fans like i have in here?  Most of the poweramps i see use a 12 vdc fan.

[joesatch]

Tidying things up. It works!

[joesatch]

One of my 6l6 wxt+ red plated.  Gonna chalk that up to a bad tube that thing always biased way hotter than the rest.  I've ordered a new set.  What is the effect of having a high B+ supply for the LTP?  I'm measuring 400vdc. 

[sluckey]

More headroom. Several of the big Fender amps use 450V.