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Author Topic: blown tubes  (Read 6209 times)

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MikeB

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blown tubes
« on: Time Format »

Had a strange thing happen when i recently changed tubes on my mp1 (stock).  Rnolan had some spares that i put in and after a couple of minutes, one of them had blown. Luckily, he had three so we swapped out the bad one and all was good.  Fast forward a couple of months and when setting up for a jam, the volume and tone disappeared after about a minute.  It went very quiet and the tone was thin.  I tried a few things and when i swapped the tubes around, the tone improved but then volume was way down.  Even with everything cranked to the max i still needed to be miked up to be heard in the mix.  So it looks like another  tube has blown.  Richard has spoken to a techie mate of his who reckons it is the tube sockets.  Has anyone else had similar problems?  Any other theories?

If it is indeed the sockets, i have been thinking of just putting in one of mjmp's new tube boards. However, they are all modded.  There are no stock replacements. If i went with the one that has the gain mod, would that introduce a lot of noise?  Would that noise be eliminated with the noise mod? Does the gain mod have an impact on clean tones?

Any input would be gratefully received
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rnolan

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Re: blown tubes
« Reply #1 on: Time Format »

Ok some history (if it helps), this is one of the first MP1s to come into Australia (has line/inst level switch).  I changed out the Chinese tubes around 1996 with Boogies STRs (JJs most likely), I palyed a zillion gigs with it..... and sold it to Mike so I could buy MP2.  Mike went to the UK for quite a bit so it was in storage (in case that matters (other post from SC elsewhere here)).  So Mike and I did a tube change (again Boogie STRs), worked fine for 10 mins or so then went very quiet WTF...  We swapped the 2 new tubes and nothing, swapped back and very quite again.  New tube (again Boogie STR) in V1 (I'm assuming V1 is the closer to the front) and all was fine.  So blown tube (was it a dud, ??). Mike played it at a few jams here and a bit at home all working well.  Go to the jam with the band Last Saturday (lots of fun BTW), Mike dials up his sound all good, go to play and  duh, all gone quiet again (but still signal, just not much).  Swap tubes locations V1 <> V2 (no spares down there) and no sound, swap back very quiet (tone is ok though) so I mic it up and crank in the PA so we all still had fun  :thumb-up:   So another tube blown (but doesn't happen instantly and can sometimes be ok for quite a while).  Thus we are thinking maybe tube socket ? also stress other components (resitors).  So the simple fix would seem to be a new MJMP tube board.
My reading of MJMPs site re new tube boards is they are a direct replacement (not a gain mod or anything) but with much better new modern components.
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MarshallJMP

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Re: blown tubes
« Reply #2 on: Time Format »

The SS mod (super stock) is actually a orignal tubeboard,but with a lower noise/hum level and it has the original sound.I can make you one which has the same gain as the original,no problem.
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rnolan

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Re: blown tubes
« Reply #3 on: Time Format »

Hey MJMP, does our diagnosis sound correct ?, a new tube board should fix it ?

Cheers R
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Systematic Chaos

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Re: blown tubes
« Reply #4 on: Time Format »

I remember from a few years back (old forum) that the issue of blowing tubes occurred in (old/stock) MP-1s especially with the TungSol Reissue 12AX7........
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MarshallJMP

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Re: blown tubes
« Reply #5 on: Time Format »

I remember from a few years back (old forum) that the issue of blowing tubes occurred in (old/stock) MP-1s especially with the TungSol Reissue 12AX7........

Weren't these the Electro Harmonics tubes?Altough this was with the 3TM.
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MarshallJMP

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Re: blown tubes
« Reply #6 on: Time Format »

Hey MJMP, does our diagnosis sound correct ?, a new tube board should fix it ?

Cheers R

Well i hope so,hard to tell without seeing the unit.
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rnolan

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Re: blown tubes
« Reply #7 on: Time Format »

Hey MJMP, Can you think of any other scenarios given the description of the problem ?  We (Mike and I) talked about sending it to you for repair, we figured it's most likely the tube board (well something(s) on it) and cheaper to just change out the board, but what do you think ?
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Systematic Chaos

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Re: blown tubes
« Reply #8 on: Time Format »

IIRC it was indeed the TungSol Reissues and changing a certain resistor and diode on the tube board did the trick.....
These were also known to easily blow in HV cathode follower positions....
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rnolan

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Re: blown tubes
« Reply #9 on: Time Format »

But in this case we have just swapped out an old set of Boggie STRs with a new set (allegedly very tested JJs), burnt a tube in 10 ish mins, replaced it, it lasted a few months.... now another blown Boogie STR tube. I don't think it's the tubes ??
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MikeB

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Re: blown tubes
« Reply #10 on: Time Format »

New tube board on the way.  Unfortunately, I won't know if it has fixed the problem until i get a couple of years out of my next set of tubes.  I'm doing the noise mod at the same time so hopefully it will sound great and work properly.  <insert picture of banana with crossed fingers>
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