I think I've got a valve going down in my Fender DRRI . . . but I don't know which one ! !

maw4neu

As above . . . Its fine for around 30 mins . . . then I get a little "white noise" at low volume but the guitar volume through the amp rises a little . . . it stops after a minute or so then its fine  . . . ! ! I'm pretty sure its not the rectifier as amp hasn't blown a fuse or crapped out completely . . I've got a JJ 5751 in V1 for first gain stage on Normal, I have a Mullard 12AT7 in V2 as first stage gain for the Vib channel V3 is also a Mullard 12AT7 for the Reverb and Ive heard no pops or splashes there so I'd have thought that one was OK, V4 and V5 are both 12AX7's ( Harma Cryo's) V6 is yet another Mullard 12AT7 . . . The Power Tubes are Groove Tubes and so is the Rectifier . . Ive got some spares but not sure which one, or pair could be the most likely suspect . .  

ICBM

Sounds like a preamp valve. Does it do it if one channel volume is turned down to zero? That will only eliminate one side of V1 or V2 but it’s a start...

maw4neu

ICBM said:

Sounds like a preamp valve. Does it do it if one channel volume is turned down to zero? That will only eliminate one side of V1 or V2 but it’s a start...

It does funnily enough . . . . I always have the Normal channel Volume at Zero whilst I'm using the Vibrato Channel and vice versa . . . ( In truth I rarely use the Normal Channel ) It happened last night and one night last week and both times I was using the Vibrato Channel . . . . I could SWAP around the 5751 in V1 for the 12AT7 in V2 . . . ? ? ? 

ICBM

maw4neu said:

It does funnily enough . . . . I always have the Normal channel Volume at Zero whilst I'm using the Vibrato Channel and vice versa . . . ( In truth I rarely use the Normal Channel ) It happened last night and one night last week and both times I was using the Vibrato Channel . . . . I could SWAP around the 5751 in V1 for the 12AT7 in V2 . . . ? ? ? 

It won't do any harm to try it.

maw4neu

I had a rather nice Harma Cryo 12AX7 in my box of goodies so its now in V1 & I put the 5751 in V2 . . . Not heard the white noise since but then in fairness I've only played for around 20 mins tonight as the Football is on in 5 mins  . . .   

maw4neu

I spoke to soon . . . White noise and an intermittent rise in volume for less than a minute after about 30 mins ???

Normal channel on ZERO . . Using Vibrato Channel . . . Could it be V4 ???  Calling @ICBM ; :-)

ICBM

It could still be V1 or V2 - the second half of each is after the volume control. It’s just that if turning one volume down fully stopped it, you would know it was definitely that preamp valve.

It could still be any of the others except V5 - even V3, noise from the reverb driver can get back into the signal path. The best thing to do is swap out each one in turn.

maw4neu

ICBM said:

It could still be V1 or V2 - the second half of each is after the volume control. It’s just that if turning one volume down fully stopped it, you would know it was definitely that preamp valve.

It could still be any of the others except V5 - even V3, noise from the reverb driver can get back into the signal path. The best thing to do is swap out each one in turn.

Massively appreciated . . . I'll get on it tomorrow after work . . . early start in the morning so time for bed :-)

maw4neu

Swapped V1 & V2 for a pair of Tungsol 12AX7's . . . . So far, so good . . . fingers crossed . . ! !

maw4neu

Hmm . . .  this is not going away and I think it "may" need the attention of a good Amp Technician  / Engineer . . I swapped out each of the Pre Amp Tubes with some of my good spares I have . . and, while I had my SJB Ant, I was able to double check each tube by trying it in my "Spare Amp" . . . . None of the pre-amp tubes were faulty . . So I moved on . . I then changed the Rectifier and the Power Tubes  . . . but evey now and again I get what I can only describe as a Static / White Noise burst for a minute or so that peters outs to nothing . . then its back to its beautiful and sweet normal self ??? The white noise continues at the same volume level even if I turn the volume down and take out the jack plug ??

One chap I spoke to suggested it could be the CAPS ( the ones in the little tin bath thingy ) as apparently thay are cheap quality ???

Any ideas anyone ??? @ICBM may I trouble you yet again :-)

ICBM

It is possible, yes. But at this point you will need a tech to look at it, since you’ve eliminated a valve issue.

EioPago

On a DRRI check the 2 power grid resistors. They very often fail, it happened to me twice.

maw4neu

EioPago said:

On a DRRI check the 2 power grid resistors. They very often fail, it happened to me twice.

Cheers @EioPago . . . . Does the power grid resistor fault case an intermittant white noise/static sound ??? 

EioPago

maw4neu said:

EioPago said:

On a DRRI check the 2 power grid resistors. They very often fail, it happened to me twice.

Cheers @EioPago . . . . Does the power grid resistor fault case an intermittant white noise/static sound ??? 

That's one of the symptoms, another is the sound curring out, it's a fairly common problem in DRRIs.

Usually what happens is that one of the power tubes dies and it takes its power grid resistor with it (there is one resistor per power tube). Sometimes the resistors fail just for heavy overheating.
It's worth taking a look.

maw4neu

EioPago said:

maw4neu said:

EioPago said:

On a DRRI check the 2 power grid resistors. They very often fail, it happened to me twice.

Cheers @EioPago . . . . Does the power grid resistor fault case an intermittant white noise/static sound ??? 

That's one of the symptoms, another is the sound curring out, it's a fairly common problem in DRRIs.

Usually what happens is that one of the power tubes dies and it takes its power grid resistor with it (there is one resistor per power tube). Sometimes the resistors fail just for heavy overheating.
It's worth taking a look.

Im dropping it off next week . . . hopefully it wont be an expensive fix . . . . !

Fingers crossed :-(