Marshall 2203 REEEEEEEEEEE-work

[harddriver]

The IN5408's don't really produce clipping like a Zener diode does in a Jose. It mostly just gives the saturated chewy effect to the tone especially in a 2203 circuit. I thought you might want to incorporate it into your 2203 rebuild. I was told it was Dave F's early sat switch diode choice. I don't know what he is using now I think I heard MPSA06's which i guess are similar to 12V Zener clipping threshold.

Here's a good read for you....
https://www.rig-talk.com/forum/threads/ ... st-2496296

[PLX]

The IN5408's don't really produce clipping like a Zener diode does in a Jose. It mostly just gives the saturated chewy effect to the tone especially in a 2203 circuit. I thought you might want to incorporate it into your 2203 rebuild. I was told it was Dave F's early sat switch diode choice. I don't know what he is using now I think I heard MPSA06's which i guess are similar to 12V Zener clipping threshold.

My BE-50 clone has 1N4739 diodes and MPSA06 transistors on the ERA switch.

From what I gather talking with Nik, the ERA (SAT) switch is positioned between the cathode follower (V3B) output and the tone stack input. Along with some other components it has a pair of MPSA06 transistors, though they're only being used in the circuit as simple diodes. The circuit seeks to clamp & distort signals above a certain size to guarantee distortion (or a different flavor of distortion).

This type of clipping circuit is not unlike the method used in pedals to generate distortion. The benefit of using it in a tube amp is you can get a lot more (or more severe) distortion without adding a ton of noise to the amp.

The Saturation circuit in the amp doesn't do anything to alter the power supply. And despite the "Z_" references on the the schematic, those aren't zener diodes.

[PLX]

Turret board going back in.
New choke installed.
All new filter caps. New filtering scheme.
Heaters REEEEEEE-wired.
New matched quad of EH 6CA7's

[harddriver]

You'll be making noise in no time PLX!

[PLX]

JCM-800 clone REEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE-DONE

[harddriver]

Nice..............how does it sound?

[PLX]

Nice..............how does it sound?

This thing kicks more ass than a midget on crack.

[PLX]

Wall voltage (124VAC)

B+ 453 VDC
EL-34's biased @ 38.5mA
17.4 watts plate dissipation ( 70% )


on Variac @ 90 VAC

B+ 324 VDC
EL-34's baised @ 19mA


Variac @ 70VAC
B+ 250 VDC
bias 7.8mA

[harddriver]

Are the 1 ohm resistors reading correctly now at 124ACV wall voltage or are you using something else to get that ma reading?

I am assuming that crackly break up noise is gone now? Does it sound different from the last time you played it before the refresh?

[PLX]

Are the 1 ohm resistors reading correctly now at 124ACV wall voltage or are you using something else to get that ma reading?

I am assuming that crackly break up noise is gone now? Does it sound different from the last time you played it before the refresh?

I didn't change any components from yesterday. I just looked up some stuff and thought about that range of bias I was seeing, then realized I was pushing that down with the variac.

I went back and watched Jim's video where he shows his amp running on a variac at 68VAC, giving him a B+ of 233 VDC and heaters running at 3.5 VAC.

He's not re-biasing, so that was putting his bias at 4.7mA on EH-6CA7's (of which, he's pulling the two inner tubes out).

The amp sounds great ! I'm playing around with the lower variac settings and thinking about swapping the EL-34's for the new EH-6CA7's