Members David Rabitor Posted October 19, 2008 Members Share Posted October 19, 2008 So a friend of mine has had his '86 (I think) JCM800 2204 sitting at my friends studio for the past 5 years without being played. After looking at it every time I would go to the studio for the longest time, he said I could borrow it for as long as I wanted because he doesn't play guitar anymore, but he isn't willing to sell it. So once i got it home I took off the back panel and it's a 50watt amp of course(2204), and I think it has the stock 6550's and also the stock Marshall 12ax7's. So here is what I'm wondering: 1. Can I just pop in some EL34's or 6L6's as long as I bias the amp? or do I have to change some of the components? And what two pins do I test to get the plate voltage? 2. Are there simple mods that can be done to increase the gain slightly? 3. Should the amp be serviced since it is 22 years old? Thanks - David Link to comment Share on other sites More sharing options...
Members Gary Cohn Posted October 19, 2008 Members Share Posted October 19, 2008 1. Can I just pop in some EL34's or 6L6's as long as I bias the amp? or do I have to change some of the components? And what two pins do I test to get the plate voltage? 2. Are there simple mods that can be done to increase the gain slightly? 3. Should the amp be serviced since it is 22 years old? Thanks - David 1. You can throw new tubes in it, But to go from 6550 back to el34, youll need to add one resistor back (as it was clipped to put the 6550 in). 2. sd-1. Im partial to the old 2204/2203's, I have a 2203. Youll notice with el34's youll get more saturation at lower volume. I hate seeing all these nice old amps getting chopped and modded. If you want an amp with more gain, get a different amp imo. Kinda like if you want a truck, dont buy a mint chevelle and add a truckbed to it. Get an el camino, or a truck. Makes it hard when your looking for a vintage amp and some jackass has gutted it all to nothing. Like I said, thats just my opinion. try it with el34's and a sd-1, if you need more, look at a splawn or something else. Leave the poor ol' fellow alone. 3. You might need to replace the caps, and/or power tubes. Seems you are doing one of the 2 already anyways. If the plug is a 2 prong (which it shouldnt) get a 3 prong and you should be alright. You might have some scratchy pots, etc. All in all, the 2204 is a trouble free tank. You should be good to go. Link to comment Share on other sites More sharing options...
Members cap'n'crunch Posted October 19, 2008 Members Share Posted October 19, 2008 Go to voodoo amps website www.voodooamps.com. He has instructions for converting from 6550 to EL34. Start with using some pedals (sd-1, bad monkey, EQ, etc.) to boost the gain a bit and/or add body. Also, these really sound there best with the volume up about halfway or more. Some people crank the master all the way up and use the pre-gain as a volume control. Link to comment Share on other sites More sharing options...
Members David Rabitor Posted October 19, 2008 Author Members Share Posted October 19, 2008 Thanks for the info guys! Link to comment Share on other sites More sharing options...
Members Gary Cohn Posted October 20, 2008 Members Share Posted October 20, 2008 Thanks for the info guys! Hey, NP! Let us know how it goes! Link to comment Share on other sites More sharing options...
Members Shask Posted October 20, 2008 Members Share Posted October 20, 2008 How can you mod it, if it isnt yours? But yes, try a few od pedals. It will kick it up a bunch... Link to comment Share on other sites More sharing options...
Members David Rabitor Posted October 20, 2008 Author Members Share Posted October 20, 2008 How can you mod it, if it isnt yours? But yes, try a few od pedals. It will kick it up a bunch... Well, if I did manage to buy it from him, I was wondering what my options were. Link to comment Share on other sites More sharing options...
Members David Rabitor Posted October 20, 2008 Author Members Share Posted October 20, 2008 OK, now I have a question about biasing. With the bias probe that I have, I need to find what the plate voltage is in an amp, and then use that to find the BBe (I think?) to set the correct value for the bias. But what I'm unsure if is what two pins do you take the plate voltage reading from? Now I know it can depend on what type of power tubes you're trying to bias, but does it also depending on the type of amp the power tubes are in? ....... I was told by someone that for 8 pin power tubes you should get the plate voltage from pins 1 and 3. Is this correct? Link to comment Share on other sites More sharing options...
Members Brick Posted October 20, 2008 Members Share Posted October 20, 2008 I had an '86 2204, absolutely smoked with EL-34's in it. Link to comment Share on other sites More sharing options...
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