Hi! I am making a mesa boggie mark II diy. I made almost parts and I already test of the pré amplifier. I made transformer of power.
So, I still missing the output transformer and inductors of EQ.
Does anyone have the specification of output transformer? I'll wind the transformer myself.
So, I still missing the output transformer and inductors of EQ.
Does anyone have the specification of output transformer? I'll wind the transformer myself.
Actually I got a little confused. To calculate I need the input voltage on the valve plates, right? And having the reflected impedance of the valve +- 4000k 6l6 and El34?
This is a 6L6 pair?
Refer to RCA datasheet.
Im not sure you really want 80/100 watt output section.
For a live band running full tilt usually you want the classic 40 watt pair.
EL34 are used for quicker breakup.
And even then it is massive loud.
Mesa Boogie rather notorious for using rather small spongy transformer that saturate easy.
So any after market transformer is a upgrade.
Refer to RCA datasheet.
Im not sure you really want 80/100 watt output section.
For a live band running full tilt usually you want the classic 40 watt pair.
EL34 are used for quicker breakup.
And even then it is massive loud.
Mesa Boogie rather notorious for using rather small spongy transformer that saturate easy.
So any after market transformer is a upgrade.
I used this site for calculate. Is It right? https://www.py2bbs.qsl.br/calc_transf_audio.php#gsc.tab=0
Through the voltage of the primary and secondary I can calculate the transformer. I used 4000R for impedancia of valvula to calculate. Is the voltage of 447v in the primary and 14v in the secondary correct? For 100w just multiply the current of the primary and secondary.
At a first glance calculation looks plausible to me.
More than 2000turns of thin magnetic wire on the primary
requiring good insulation - is a challenge anyway.
More than 2000turns of thin magnetic wire on the primary
requiring good insulation - is a challenge anyway.
The Simulclass OT is special, using different primary impedances for inner and outer pair.
To understand the principle you might want to read this article:
https://www.ampbooks.com/mobile/classic-circuits/extended-a/
The Mark II doesn't use Simulclass.
To understand the principle you might want to read this article:
https://www.ampbooks.com/mobile/classic-circuits/extended-a/
The Mark II doesn't use Simulclass.
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Winding an OPT for a tube HiFi amp is possible but challenging to get right. Winding an OPT for a guitar amp requires a lot more attention to insulation than the typical HiFi amp that rarely sees clipping.
A guitar amp will be driven into clipping, often hard enough that the output tubes begin to operate like switches. The resonant impedance peak of a guitar speaker is often INSIDE the frequency range of a guitar. Here that "8 ohm load" can be 20 ohms or more. This can lead to some rather rapid voltage pulses across the OPT as the tubes transition from OFF to ON and back to OFF. I have measured 2.4 KILOVOLTS on the plates of an EL34 in a guitar amp that runs at a B+ voltage of 430 volts and was driven into hard clipping.
In my particular case I was finding that the old black phenolic tube sockets were breaking down and an arc would strike from pin 3 (plate) to pin 2 (heater) inside the socket. This was partly caused by the heat and humidity of Miami Florida, so all of my builds used ceramic sockets. The insulation in an OPT must be able to deal with heat, humidity, and high voltage or it will not last long.
That reminds me of a repair episode with an 50W Marshall decades ago. It took less than a minute of hard percussive playing of the owner to burn both EL34 in a short and intense flash. Had some headache to cut these peaks down.
The transformer had a primary resonance near 5kHz and luckily survived.
I wound some power supply transformers and they work fine. I didn't know output transformers were so different.
I made the transformer I'm using in the Mark II's power supply myself and it works perfectly. I tested the preamp and it sounds really cool. But it's missing the output transformer and EQ inductors. I've just realized that it's not as easy to make the output transformer as it is to make the power supply transformer.