Valve problem !

[Audio Al]

Typical :rolleyes:

Running my Quad 11 amps today , getting ready for the show on Sunday

Listening and all of a sudden the audio from the left hand 57 starts sounding bad :eek: I look at the amps and one KT66 valve is glowing a lot brighter than the others :doh:

Switched them off and let everything cool down , swap one valve for another KT66 different make

Switch on again , all seems ok ( fingers crossed )

Do valves just give up in this manner ? or do I have a underlying problem , they were looked at and had some new transistors fitted about 30 hours use ago

HELP :eek:

[synsei]

I'd say it is the valve Al, I've had the same happen to me with one going the same way from a matched quad of 6L6's, the others were absolutely fine...

[Tarzan]

l will be round in a minute- again.

[loo]

Typical :rolleyes:

Running my Quad 11 amps today , getting ready for the show on Sunday

Listening and all of a sudden the audio from the left hand 57 starts sounding bad :eek: I look at the amps and one KT66 valve is glowing a lot brighter than the others :doh:

Switched them off and let everything cool down , swap one valve for another KT66 different make

Switch on again , all seems ok ( fingers crossed )

Do valves just give up in this manner ? or do I have a underlying problem , they were looked at and had some new transistors fitted about 30 hours use ago

HELP :eek:

Hi Al,
new transistors? there are no transistors in a Quad II
also you really should be using matched pair KT66,s in them
but yes sounds like one has let go
Paul

[Audio Al]

Hi Al,
new transistors? there are no transistors in a Quad II
also you really should be using matched pair KT66,s in them
but yes sounds like one has let go
Paul


OK , so they may have been caps or resistors :o

Just ordered 8 new valves :eek:

[loo]

OK , so they may have been caps or resistors :o

Just ordered 8 new valves :eek:

what 8 kt66's, are you running 4 amps?
what brand have you gone for
Paul

[Audio Al]

l will be round in a minute- again.


No Need Mr aNDY

New valve on order

tHank yO'U

[Audio Al]

what 8 kt66's, are you running 4 amps?
what brand have you gone for
Paul

4 KT66 and 4 EF86

The ones recommended by Watford Valves , I hope they are £320 good :scratch:

[loo]

4 KT66 and 4 EF86

The ones recommended by Watford Valves , I hope they are £320 good :scratch:
I hope so too, Watford valves are pretty good so they should be ,
if you need a spare amp for the show let me know as I am local to you
Paul

[Tarzan]

No Need Mr aNDY

New valve on order

tHank yO'U


oKay MR aLLEN.

[Audio Al]

I hope so too, Watford valves are pretty good so they should be ,
if you need a spare amp for the show let me know as I am local to you
Paul


Thanks Loo , will see what happens when the new valves arrive and are fitted and tested , I do hope its not the amps :doh:

[loo]

Thanks Loo , will see what happens when the new valves arrive and are fitted and tested , I do hope its not the amps :doh:
Your welcome Al, I'm sure yours will be fine Quad II's are tough old lumps and if they have had new caps and resistors there's not a lot else to go wrong ,
cheers
Paul

[Audioflyer]

Have the capacitors C2-C3 (0.1uF) been change? These are the two large capacitor below the KT66 if not you should consider changing them for some polypropylene ones.

[Marco]

Thanks Loo , will see what happens when the new valves arrive and are fitted and tested , I do hope its not the amps :doh:

Worry not, daftee. I'm 95% certain it's a valve fault, not an amp fault. Even if it is the latter, it won't be anything major (possibly a resistor or capacitor issue). That's the beauty of such simple designs, like the Quads - there's not much to go wrong :)

Marco.

[Spectral Morn]

Typical :rolleyes:

Running my Quad 11 amps today , getting ready for the show on Sunday

Listening and all of a sudden the audio from the left hand 57 starts sounding bad :eek: I look at the amps and one KT66 valve is glowing a lot brighter than the others :doh:

Switched them off and let everything cool down , swap one valve for another KT66 different make

Switch on again , all seems ok ( fingers crossed )

Do valves just give up in this manner ? or do I have a underlying problem , they were looked at and had some new transistors fitted about 30 hours use ago

HELP :eek:

Yes and lucky you caught it as a failing valve can do all sorts of damage to an amp...

Never leave valve amps switched on and unattended, especially EL34 using ones......when those fail it can be quite spectacular


Regards Neil

[Spur07]

Have the capacitors C2-C3 (0.1uF) been change? These are the two large capacitor below the KT66 if not you should consider changing them for some polypropylene ones.

audioflyer is right - if these are still original they should be changed for modern equivalents - if they go they'll be no warning and the damage could be eye wateringly expensive.

[Audio Al]

A well known Quad repairer had these for 2 weeks , he did mention uprating something , so I assume its done

These were done as a private job in his leisure time so I dont feel at liberty to name said repairer ;)

[lurcher]

Do valves just give up in this manner ?

Just to answer this. Yes, they can. Often they will have been going down hill for some time, but the nature of push pull feedback amps is that they will hide the fact until they fall off the cliff.

[Firebottle]

Talking of EL34 amps, I am repairing one at the moment.
One of the valves is shot, it is drawing serious grid current. It may be just a coincidence but one of the output transformers is also shot, with short circuited windings. The reflected impedance with an 8 ohm load is only a couple of hundred ohms :eek:
So an expensive repair.

:cool: Alan