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Old 7th December 2011, 08:20 AM   #1
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Default marshall 9200

Hi looking for help in converting a marshall 9200 amp to run el34 valves any help will be appreciated .
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Old 7th December 2011, 09:22 AM   #2
Enzo is offline Enzo  United States
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What tubes were in it to start with? I would have guessed EL34s.

I see the screen resistors are 470 ohms, so perhaps 6L6s?

Ah, I googled it, it came in either EL34s or 5881s.

As with any amp:
Load the heater winding down either with all 8 EL34s or equivalent load to see if the power transformer can handle the increased heater draw.
check to see that pin 1 is connected to pin 8. I'd increase the screen resistors to 1k 5W myself.
verify the bias adjstment has enough range.
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Old 8th December 2011, 10:52 AM   #3
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Hi Enzo thanks for your reply , the amp has 5881s , so wanted to know what i had to change and check in order for the conversion ,was also wondering if it would be possible to adapt bias select as ive seen is a feature on some Messa Boogie amps , thank you again for your help regards Luther.
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Old 8th December 2011, 03:05 PM   #4
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Hi, I have 2 9200's, 1 9100, and a 20/20. The mentioned current draw of the heater current is one issue. The other issue is B+ current. The 5881's in my experience have an average Ip (Bias current) of 22 and the EL34's an average Ip of 26. So the El-34's will draw more B+ current. So the Bias supply circut will have to be modified to provide a higher Bias current aside from the Bias adjustments at the power tube circuts. The 9200 is a pretty reliable piece of equipment on 5881's , especially the WRT versions.
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Old 8th December 2011, 05:25 PM   #5
kevinkr is offline kevinkr  United States
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Moved this thread to I&A per forum directive.
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Old 9th December 2011, 12:44 AM   #6
Enzo is offline Enzo  United States
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Having pointed out these details, the amp has the same documentation for either version, so I tend to believe the power supply is up to either tube.
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