valve problem

[philv]

I have a primaluna prologue two.

I have svetlan el34 winged c in it.

I was checking the functioning of a dac and turned the amp on for 10 seconds, turned it off and then a ew second turned it on again.

Within a few seconds lots of static/noise from one channel.
Some flashing from within the cage that even i could see from that channel-s side.

I turned off.

I connected up some cheaper speakers and it seemed fine for 20 seconds and then again static/noise from that channel.
Turned off.

Is one of the el34 buggered?
Probably by turning on of on too quickly?

Thanks

[philv]

The fluttering static noise is quite loud even at low volume.

[philv]

I have a set of gold lion kt88
and a set of primaluna kt88.
As well as the el34 in the amp.

Suggestions for what i should do next?

[bumpy]

Can you switch the valve from one channel to the other? and see if the noise moves with it

[philv]

i just swapped two fo the el34 with each other.

Now it is playing ok it seems for a couple o minutes.

bit confused

valves look to be glowing normally.

O have an adversion to anything electrical.

this really boosts my confidence! ulp

[philv]

Noise has gone.
Any ideas, before i reconnect the more expensive speakers!?

Sounds superb.
I have been burning a new dac.

The primaluna is gorgeous through both the ank and pageant 2.
I think the pageant 2 are getting delisted for sale!

[bumpy]

Noise has gone.
Any ideas, before i reconnect the more expensive speakers!?

Sounds superb.
I have been burning a new dac.

The primaluna is gorgeous through both the ank and pageant 2.
I think the pageant 2 are getting delisted for sale!

It might have been dirty contacts which self cleaned on removal and refitting. :)

[philv]

It might have been dirty contacts which self cleaned on removal and refitting. :)

Thanks.

I think the primaluna is relatively safe with the ability to adjust to different valves.
I think it can run with a power valve missing.
Not that i would like to try it.

[simon g]

What you’ve done is a no no in the world of valves. Never turn a valve amp off and then on again in quick succession. Always let the tubes cool down before switching on again; about 10-15 mins is usually OK. I would also avoid running it without the speakers connected.

[philv]

What you’ve done is a no no in the world of valves. Never turn a valve amp off and then on again in quick succession. Always let the tubes cool down before switching on again; about 10-15 mins is usually OK. I would also avoid running it without the speakers connected.

Ah ok......i’ll remember that.

Thanks.

[Jazid]

Hate to be a downer but if you saw flashing then 100% it isn't dirty contacts and it needs attention. This is more likely arcing in one of the power tubes and quite likely caused as you surmised by switching off and then on too quickly. If the valves survived then they may be compromised and need proper checking (a simple valve tester may not show up the effect, you'll need a curve tracer). Or you could buy new and wait till the opportunity presents to find which have survived. I don't know the amp or the protection it has but better safe than sorry.

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[philv]

Hate to be a downer but if you saw flashing then 100% it isn't dirty contacts and it needs attention. This is more likely arcing in one of the power tubes and quite likely caused as you surmised by switching off and then on too quickly. If the valves survived then they may be compromised and need proper checking (a simple valve tester may not show up the effect, you'll need a curve tracer). Or you could buy new and wait till the opportunity presents to find which have survived. I don't know the amp or the protection it has but better safe than sorry.

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According to tne amp spec-
Tube plate fuse Protects the amplifier output stage. Other amps may need a trip to the shop if a tube fails. Not this one. Just plug in a new tube and fuse, and go.

I do seem to have a habit of ballsing up.
The last time i put winged c svetlana el34 into an amp, audio innovations 700, i inserted one with the guide pin out of line (very worn sockets) and had to get it repaired.
John wood charged me 80 quid to fix and put in a set of good used 5881.

I have form!

[philv]

Should the plate fuse be adequate protection until i find someone to check them over?

[philv]

Is there anyone on these forums that has tne ability to test tubes thoroughly?
Or any reccomendations?

[Jazid]

There are people around with curve tracers which is what you need rather than a single operating point type of measurement like most valve testers produce. Henry (toprepairman on the old 'Wam) has one and I'd be surprised if Graeme at Amp Regen can't test them thoroughly as well.

Is the amp safe with the old power valves? Maybe, Primaluna claim not to run the valves hard, but the arcing is likely caused by too high anode voltage. I suspect it is also likely to have affected one power valve rather than all of them. So the valve might still behave OK, or could be flaky and dangerous, or it could work fine but just with a bit of added distortion/non-linearity. That's what the tests are for.

To my mind it seems unwise to leave the amp exposed to possible damage for the cost of a bunch of relatively cheap cooking tubes to tide you over whilst you get the valves checked...

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[Haselsh1]

Not too sure about the amp in question but my Prima Luna has an LED in front of each power tube that indicates a fault with its associated valve. Even with this in mind though I had a problem when I borrowed a set of KT88's and tried them. Every time I switched the amp off there would be a cracking sound out of each speaker. Not so with the bog standard EL34's.

[AD Audio]

There are people around with curve tracers which is what you need rather than a single operating point type of measurement like most valve testers produce. Henry (toprepairman on the old 'Wam) has one and I'd be surprised if Graeme at Amp Regen can't test them thoroughly as well.

Is the amp safe with the old power valves? Maybe, Primaluna claim not to run the valves hard, but the arcing is likely caused by too high anode voltage. I suspect it is also likely to have affected one power valve rather than all of them. So the valve might still behave OK, or could be flaky and dangerous, or it could work fine but just with a bit of added distortion/non-linearity. That's what the tests are for.

To my mind it seems unwise to leave the amp exposed to possible damage for the cost of a bunch of relatively cheap cooking tubes to tide you over whilst you get the valves checked...

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IME valves that flash over like this will often continue working and will also test fine on a curve tracer, before eventually failing prematurely (or not). If I'm at all dubious of an amp's protection I replace. The best protection systems are electronic but few manufacturers even of expensive amps fit them because of cost and also the fact that fuses will protect in quite a high percentage of cases. Bare in mind many fuses used in even expensive amps are rated at 250v ac and are used at much higher DC voltages. Used at higher voltages the fuse can 'blow' leaving enough molten metal plating the glass cylinder to still allow conduction. My Mastersound Monoblocks use such 250v rated fuses to 'protect' the 1.2kv HT but are probably as much use as a chocolate teacup. Fuses also affect sound quality when placed in HT lines. A better place to put them is in the HT ac feed, where they won't affect sound quality, and where the volts will be AC and nearer the fuses rating, but need to be specced for the switch on capacitor charge surge. Which brings us back to properly implemented electronic protection as the best system.But having given those scare stories I've never had an output valve blow a transformer when failing as Ive generally been in the room and get to that off button pretty quickly!

[philv]

I did contact several companies/people about this.
I was told by one very knowledgable chap that it was impossible to tell if they werr compromisef. He told me to visually inspect for debris, pitting, colourations, etc. If all apieared fine and after a few hours all was well, then chancs are i'd gotten away with it.

Primaluna told me not to worry as there is a plate fuse. They make a big deal of this in their sales blur.
They said keep an eye out for 20 to 30 hours and replace if it flashes again.
If valve goes thrn simply replace fuse.

So far all ok after a coiple of half hour listens.

Can anyone be sure thr nos or used valves they have bought have never flashed in similar circustances? Probably not.

I will kerp an eye out or an ear out for the tell tale flutter noise, but not going to worry about it top much.

I will of course wear rubber wellies at all times.

[AD Audio]

:lol:

[hermit]

What you’ve done is a no no in the world of valves. Never turn a valve amp off and then on again in quick succession. Always let the tubes cool down before switching on again; about 10-15 mins is usually OK. I would also avoid running it without the speakers connected.

Is this also the case for valve phono stages?

[AD Audio]

Yes, but it's less likely to cause problems.

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[Jazid]

Most amps are safe enough, it's those with solid state rectifiers that you tend to have the problems with. I personally enjoy the sound of s/s rectifiers but switching off and on rapidly is going to risk these issues, especially in power amps where the amp is designed to run close to the valves limiting voltages.

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[hermit]

Yes, but it's less likely to cause problems.

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Thanks. Good to know.

[philv]

Well 3 months of light use later and 1 or 2 started their little firework display.

So they’re in the bin, and some very nice kt88 are in situ.

[Audio Al]

:scratch: Humm , I was told never turn a valve amp on without speakers connected :hmm:

[jandl100]

Well 3 months of light use later and 1 or 2 started their little firework display.

So they’re in the bin, and some very nice kt88 are in situ.

In my opinion, the best place for el34 valves is in the bin.
- not a valve that I have ever much liked the sound of, except when I have problems with insomnia. ;)
Much better off with kt88. Or anything else.
That's the joy of Primaluna amps, you can swap and change the toob types.

[Jazid]

:scratch: Humm , I was told never turn a valve amp on without speakers connected :hmm:That's my understanding too

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[philv]

That's my understanding too

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Not guilty.
My crime was turning it off and on again too quickly.
We live and learn.