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Old 6th January 2012, 06:46 PM   #1
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Default amp sounds bad- fatman itube 252

hi ' i'm new here . and don't know anything bout electronics.
my prob is ....... my valve amp sounds terrible after it's been on for an hour or so , especially if i turn the volume up loud .meaning , even when i turrn the vol back down quiet the same unpleasant gritty distortion is preasent in both speakers . . it's not the peamp tubes coz i got a spare set and and same thing happens with both sets.
there's pair of driver tubes( well i think that what they are , not sure tho ) one for each channel . don't think it's them coz i've had one of them microphonic b4 but the squealing was in one speaker/ channel only .

i got a quad of power tubes , stock ones from new 2 and a half years ago, i was wondering if all 4 power tubes can start dying at the same time or if one is failing can that effect both stereo channels . or do you think it's an internal problem . i read somwhere about filter cap thingees not holding a current for long that gives a similar amp problem . will i be waiting my money buying a new quad of power tubes ... please help ,,
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Old 6th January 2012, 07:34 PM   #2
DF96 is offline DF96  England
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There are some clever people on this forum, but few of us can do mind reading. Could you help us by giving a tiny clue about which amp you have?
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Old 6th January 2012, 07:41 PM   #3
sturmj is offline sturmj  United States
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Also how old is this amp? I'll put my vote in for a bad capacitor (electrolytic) some where causing this. They do go bad with age.
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Old 6th January 2012, 09:06 PM   #4
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sorry i didn't think the make of my amp would make any difference,don't they all work on the same basic principles ? ... it's a fatman itube 252 , push/pull type .. it's 2 and a half years old ... any advice would be great , thanks

btw , i've read a few posts on here and some of you sound so clever i wouldn't be suprised if you could read minds
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Old 6th January 2012, 09:30 PM   #5
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What kind of speakers? Has there always been a problem or is this a recient occourance?
Help us Help you. Do some research and find out more about this beast. Like what kind of tubes, who makes it, and best of all a schematic diagram. The statement about the electrolydic caps comes because that is a common problem but---- it would be a guess at best. No its not likely that multiple tubes went bad at the same time especally if they are in different channels. Does the problem exist with all audio sources? Do that test first. Also do you have extra speakers to try. Try a real carefull listening test. Fire it up from cold and play at the same level dont crank it just a modest level. Note the time it takes for the problem to start. Let it cool off for several hours and repeat the test. Is the problem related to heat? Its very possible, but try to nail it down. My quick poke around on the interweb dident reveal much but the usual reviews and sales pitches, but I will bet someone has looked into the beast. Write or e-mail the company and ask if the will let you have the schematics, then post them. We really need the schematics. Otherwise take it in
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Old 6th January 2012, 09:30 PM   #6
DF96 is offline DF96  England
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Which amp makes a huge difference. Even amps with similar topologies can have different common faults due to component selection etc.

My guess is gassy output valves - I assume Chinese ones, which don't always last very long. However, others on here might be familiar with that particular amp.

Maybe one of the mods could change the thread title to include the amp type? (see post 4)
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Old 6th January 2012, 09:33 PM   #7
SY is offline SY  United States
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Old 6th January 2012, 09:34 PM   #8
DF96 is offline DF96  England
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Thanks.

Note: this amp may have some similarities with the Chinese Dared MP 60. 'Designed in the UK' might not necessarily mean starting from a blank sheet of paper.

Last edited by DF96; 6th January 2012 at 10:00 PM. Reason: add note
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Old 6th January 2012, 10:14 PM   #9
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hey to remind not all the problem comes from "Chinese" < sometimes @@
But i'm sure that city like HONG KONG is really wet this will cause many problems e.g(some of the component will turn bad, or silver wire will turn black easily in some cases) As DF96 and SY said the capacitor might be the reason, and if the amp. is without using for long period this may cause capacitor down, in this case you should not use it as normal< you should open it in different time period e.g(1st time 20s, then off it for 5min then turn it on again for 40s, turn it off ......... each time period should increase due to the capacitor recover process)
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Old 6th January 2012, 10:26 PM   #10
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thanks for editing the title sy .. i've have run different sources through it and different speakers ,monitor audio 6 ohm 90 db ...and b&w, ( the speaker outputs on the amp are 8 ohm tho ) same result.. i could play it comfortable volume for about 3 hours or so before the mids become all gritty and nasty but if i crank the volume up to about 60% of max it just speeds the process up and once the distortion i there it stays there untill i switch it off for half hour .this problem has been gradualy increasing for a few months. i could live with it before when it only happened after pushing the volume to about 80% , i mean who needs go that loud everyday but it's getting to be a pain now ( spoiling my parties on saturday nights,, grrr)...
yes df69 they are " no name" generic chinese power tubes (el34) i got 2 "jj 12ax7 " pre amp tubes
and i got one EH 6sn7 driver tube and one "no name" chinese driver tube for the other channel in the belief that only power tubes need to be matched sets . have i made a mistake ? could that hae dameged something inside ?
firechief, thanks for advice about getting the schematics off the company . i will emeail them as soon as

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