marshall 9200

blackarab · 7th December 2011, 07:20 AM

Hi looking for help in converting a marshall 9200 amp to run el34 valves any help will be appreciated .

Enzo · 7th December 2011, 08:22 AM

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.

blackarab · 8th December 2011, 09:52 AM

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.

speakerfritz · 8th December 2011, 02:05 PM

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.

kevinkr · 8th December 2011, 04:25 PM

Moved this thread to I&A per forum directive.

Enzo · 8th December 2011, 11:44 PM

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.

7th December 2011, 07:20 AM	#1
blackarab diyAudio Member Join Date: Dec 2011	marshall 9200 Hi looking for help in converting a marshall 9200 amp to run el34 valves any help will be appreciated .

8th December 2011, 04:25 PM	#5
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Moved this thread to I&A per forum directive. __________________ www.kta-hifi.net

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7th December 2011, 08:22 AM	#2
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	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.

8th December 2011, 09:52 AM	#3
blackarab diyAudio Member Join Date: Dec 2011	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.

8th December 2011, 02:05 PM	#4
speakerfritz diyAudio Member Join Date: Jul 2008	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.

8th December 2011, 11:44 PM	#6
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	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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