The Repair Bench: Marshall Valvestate 8200 Amplifier Head

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21:39 Sunday.01 January 2012
Nice, informative article. I like that you mentioned running the amp over a period of time at operational temperature. I recently ha a similar experiene with the purchase of a solid state Hughs Ketnner that was too cheap to pass up. (S/S amps seemingly appear to be abundant , cheap and ez fixes)

I had a friend whom was in a bind, with no appreciable budget and needing a amp to immediately gig. Rather uncomfortable loaning my personal equipment I offered to help get this amp going for the price of a complimantary pair of darlington transitors for the output. Unfortunately in haste and somewhat of a noob myself we didn’t spend the extra time to be fully diligent enough to run extended dynamic testing. unfortunately this could have saved further frustrations for my friend with his gig. In our haste to get him outa the shop and to rehersal we overlooked fully tightening our components to the heatsink and one the transistors wasn’t making good thermal conductivity and would overheat and would drop off in power…. The extra time spent being diligent and testing on the work bench would have saved much face!
My question is what is your dummyload composed of and how much power can it continously dissipate? At what power levels do run your extended testing at?
How about a article on basic test gear, the practical application and how to build and acquire some the basics such as your signal generator and especially a inexpensive, simple down and dirty dummy load?

04:20 Friday.28 October 2011
Thanks for a clear and practical description of troubleshooting. Very helpful. While ancient Greeks might have said “caveat emptor”, it is in the Latin tongue. Alexander Haig brought “caveat” into English usage as a stand alone verb in the late 20th century.
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21:05 Saturday.17 March 2012
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04:53 Friday.28 October 2011

Thanks for the language factoid Ross. Always good to learn something new.

04:48 Wednesday.30 March 2011

Excellent start to finish trouble shooting guide. Very informative.

Will Smith
02:53 Wednesday.11 March 2015

I have the bi- chorus combo. I had experienced a power drop, so I replaced the tube. Much to my surprise that didn’t work. I read the above post and looked over the circuit board for anything that looked burnt out. I found nothing. I noticed that the reverb box had springs lying at the bottom of the amp. I unplugged the reverb cords (red and black) and put duct tape over the loose rc jacks. I put the amp back together. I still experience a fuzzy power drop. I tired turing the effects knob all the way down. Bingo- It worked!!!!! I hope this helps someone.

02:12 Saturday.16 November 2019

Hello I have this exact same amp and it means a lot to me since my father give it to me as a gift, I have the challenge to restore to a factory condition, could you please help me on recommend me with some one that could repair it, I live in Mexico City but I could send it to any part of the world just to get that factory condition

Jeff Bollettino
22:34 Saturday.17 August 2013

Dave, we are in Northern Virginia but not in the business of fixing customer amplifiers. Since you have an electronics degree, perhaps you could learn to troubleshoot the amp yourself. Do you have a digital multimeter? What are the amplifier symptoms?

John Simms
01:47 Friday.17 October 2014

Any idea what caused this damage? Anyway I’d love to own one of these amps.

Dennis L. Ellrod
03:14 Wednesday.29 January 2014
Can I get some suggestions on troubleshooting a B-52 LG100a solid state amp?

The amp has a very low sound output on the clean channel. The sound goes up and down with the volume pot but it doesn’t come close to the 100 watts of power. The distortion channel only makes low static noise.

One more request. Where can I find a good repair manual for Solid State amps? I have searched all over the inter-net and can’t find a repair manual that has detailed trouble shooting for a Solid State amp.
Thank You, excellent site, Dennis my e-mail

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