Marshall Artist 3203 bias mod

[mrkrausman]

This will be a practice amp that my brother handed to me. It has been idle for 10 years. I believe I have located the 56k bias resistor labelled R2. I hope this isn't a bonehead question but is this a 1/4 watt resistor, it measures 5mm long? I plan on replacing the electrolytic caps plus tubes and cleaning etc. A bias pot would be nice. Has anyone done this?
http://www.drtube.com/schematics/marshall/3203pwr.gif

[mrkrausman]

Apparently this has never been done before. Never mind I got this.

[danman]

1/2 watt is the normal rating for that position. Not a whole lot of current draw through it.

[mrkrausman]

1/2 watt is the normal rating for that position. Not a whole lot of current draw through it.

I agree 1/2 watt is normal in most instances but judging by the size of the carbon composite resistors contained in the 3203, they appear to be 1/4 watt. I replaced the 56k at R2 with a 22k pot and a 27k resistor and it works quite nicely. I now have an Artist head with adjustable bias.

[chrisom]

Since they first came out in the early '80's, I've owned a couple Artist heads and am currently on my 3rd or 4th Artist combo (not selling it this time). Looking at the schematic, it appears to be designed with the output section hardwired in the triode configuration like found on Marshall's Triode/Pentode switch (as found on Marshall Jubilee Series amps and their 9005 Series 50/50 power amps). That would explain part of how they are getting only 30 watts from a pair of EL-34's, aiding in a lower volume tube saturation.

I had a "cutting out" problem with several of my Artist's caused by a carbon build-up on the switching contacts of the Effects Send "Cliff" jacks (which I never used). It was cured by an internal jumper wire across the jacks solder terminals.

I never really loved the Artist's solid-state preamp that much. It seemed like it got you "almost there". Early on, to try and remedy this I used a Boss Super Overdrive for a boost/EQ curve, and then later on I just used to plug into a Mesa/Boogie Studio Preamp and run it's line out straight into the Artist's Effects Return (power amp In) with a Roland digital delay in-between.

But my favorite authentic classic Marshall sound with this amp is by plugging a Gibson straight into the amp, and running the output of the speaker jack into an 8-ohm THD Hotplate and engaging the Hotplate's Deep and Bright switches. It takes care of the solid state preamps EQ limitations and now sounds killer, gives me reduced volume ability, and also provides a line-out to a digital processor for Wet/Dry effects setup (or Wet/Dry/Wet if you want), allowing me to run the amp itself bone dry.
Thanks for sharing your mod with the rest of us Artist 3203 lovers!