Failing Marshall 8080

RowdyRock · 6th October 2011, 01:54 AM

Have a 20yo Marshall 8080 been fine but plugged my fender strat and lost all power from the Boost Channel. Can finly hear the amp sound, but very little. The amp squeeled for a second after plugging in and then this. I presuem that means the tubes in the pwoer Amp have blown? Had similar happen a couple of years ago when I first bought the amp. Is it possible that the cable was faulty? Foudn an old cable that came with the Strat and havent used in years. Is it easy to chnage the tubes? last time cost me $400 and the amp woudlnt be woth that much anymore.

Gilgy · 6th October 2011, 03:45 AM

I hate to break it to you but the Marshall 8080 doesn't use tubes in the power amp section. It hasa single 12AX7 (ECC83) in the preamp and a solid state power amp.

A bit of googling tells me that the 8080 only uses the preamp tube in the boost circuit ...

Marshall Amps :: The Secret Life Of Valves

... so if you're getting the squeal on all channels then it's not an issue with the preamp tube.

Gilgy · 6th October 2011, 03:47 AM

Just re-reading your post, if someone charged you $400 to change the tubes then you need to find a better repair guy.

Gilgy · 6th October 2011, 03:48 AM

ok, re-reading your post again you're getting a problem on the boost channel so yes, it could well be a problem with the preamp tube

costis_n · 6th October 2011, 11:11 AM

400 to "change the tubes", considering there is only one chinese ECC83 in there? I am in the wrong business.

kevinkr · 6th October 2011, 04:16 PM

Per FORUM policy I am moving this thread to I&A

Enzo · 6th October 2011, 11:35 PM

It could easily be tube related. If the clean channel works OK, then the power amp must be OK.

The tube itself could have failed, or one of its power supplies. Are the heaters in the tube glowing? And there is a small high voltage supply just for the tube, make sure a resistor in it has not opened and that there is B+ on the tube plates.

Otherwise, apply a signal at the input and just trace it stage by stage through the bad channel.

nigelwright7557 · 7th October 2011, 01:14 AM

ECC83 are very cheap I pay £3-50 for mine at RS components so its worth buying one to replace the possibly faulty one to try it.

basreflex · 15th October 2011, 06:00 PM

I'm currently working on a valvestate 8080 right now. It apparently fell on its nose, as most of the pots were open or intermittent. tubeampdoctor has them in stock.

Nigel Goodwin · 17th October 2011, 08:29 AM

Quote:

Originally Posted by basreflex

I'm currently working on a valvestate 8080 right now. It apparently fell on its nose, as most of the pots were open or intermittent. tubeampdoctor has them in stock.

I repaired a mixer for a lady singer, it had a large number of broken pot's - with the ones in the middle broken the worst. Once I'd found all the broken ones, it was obvious that it had been hit by a football - it was a perfect circular pattern, with the very centre ones damaged most.

It turned out she kept it in her conservatory, and has a young son who likes to play football

6th October 2011, 01:54 AM	#1
RowdyRock diyAudio Member Join Date: Oct 2011	Failing Marshall 8080 Have a 20yo Marshall 8080 been fine but plugged my fender strat and lost all power from the Boost Channel. Can finly hear the amp sound, but very little. The amp squeeled for a second after plugging in and then this. I presuem that means the tubes in the pwoer Amp have blown? Had similar happen a couple of years ago when I first bought the amp. Is it possible that the cable was faulty? Foudn an old cable that came with the Strat and havent used in years. Is it easy to chnage the tubes? last time cost me $400 and the amp woudlnt be woth that much anymore.

6th October 2011, 04:16 PM	#6
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Per FORUM policy I am moving this thread to I&A __________________ "Extraordinary claims require extraordinary evidence." - Carl Sagan

7th October 2011, 01:14 AM	#8
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	ECC83 are very cheap I pay £3-50 for mine at RS components so its worth buying one to replace the possibly faulty one to try it. __________________ http://www.murtonpikesystems.co.uk PCBCAD50 pcb design software.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Marshall Valvestate 8080	kdawg	Instruments and Amps	10	1st May 2012 12:08 AM
Guitar amp problem (marshall 8080 valvestate)	Palmu85	Instruments and Amps	3	26th September 2011 09:33 PM
Marshall 8080-Channel select button problem	tommy12	Instruments and Amps	2	10th November 2010 10:10 AM
marshall valvestate 8080 hiss raw/growl	meta11icafreak	Instruments and Amps	7	7th April 2010 02:26 PM
marshall valvestate 8080 repair tips needed	skid	Instruments and Amps	4	25th April 2006 01:01 PM


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

6th October 2011, 03:45 AM	#2
Gilgy diyAudio Member Join Date: Oct 2009	I hate to break it to you but the Marshall 8080 doesn't use tubes in the power amp section. It hasa single 12AX7 (ECC83) in the preamp and a solid state power amp. A bit of googling tells me that the 8080 only uses the preamp tube in the boost circuit ... Marshall Amps :: The Secret Life Of Valves ... so if you're getting the squeal on all channels then it's not an issue with the preamp tube.

6th October 2011, 03:47 AM	#3
Gilgy diyAudio Member Join Date: Oct 2009	Just re-reading your post, if someone charged you $400 to change the tubes then you need to find a better repair guy.

6th October 2011, 03:48 AM	#4
Gilgy diyAudio Member Join Date: Oct 2009	ok, re-reading your post again you're getting a problem on the boost channel so yes, it could well be a problem with the preamp tube

6th October 2011, 11:11 AM	#5
costis_n diyAudio Member Join Date: Aug 2008	400 to "change the tubes", considering there is only one chinese ECC83 in there? I am in the wrong business.

6th October 2011, 11:35 PM	#7
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	It could easily be tube related. If the clean channel works OK, then the power amp must be OK. The tube itself could have failed, or one of its power supplies. Are the heaters in the tube glowing? And there is a small high voltage supply just for the tube, make sure a resistor in it has not opened and that there is B+ on the tube plates. Otherwise, apply a signal at the input and just trace it stage by stage through the bad channel.

15th October 2011, 06:00 PM	#9
basreflex diyAudio Member Join Date: Oct 2007	I'm currently working on a valvestate 8080 right now. It apparently fell on its nose, as most of the pots were open or intermittent. tubeampdoctor has them in stock.

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read