Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joesatch on January 09, 2023, 09:00:27 am
-
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?
-
Those are not grounds. They are all tied together then run into a 47k resistor to ground.
-
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
-
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???
-
marshall has a LTP this looks different. the resistor is a 10watt 150 ohm. I have a choke.
-
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 (https://el34world.com/Hoffman/files/Hoffman_Plexi50.pdf). It's drawn the same style as his 18W stereo poweramp.
You cannot replace that 10watt 150Ω cathode resistor with a choke!!!
-
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?
-
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!
-
I will study the your schematic and try to incorporate the two
-
All you need...
-
What do you think about adding this gain stage before each channel ? This is what the mesa 50/50 has
-
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.
-
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.
-
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
-
It is for guitar but i would like it to be clean and not overdriven.
-
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.
-
Tidying things up. It works!
-
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.
-
More headroom. Several of the big Fender amps use 450V.