Realistically, how long should a pair of Winged C's last??

welshboyo

Got the symptoms of worn power valves I think - lack of volume, no clean headroom etc. Going to spend the day faffing around with the pre's to see if something is amiss there but I'm suspecting the EL 34's - now these were only replaced 12 months ago, have done a fair few gigs and amp gets used daily at home. It's my Shiva which inherently runs hot with high mA's - is it quite normal for the new Winged C EL34 to only last this long? I've had other amps which have done 2-3 years on a set of valves? (Mesa MK III and IV)

welshboyo

Sorry for lack of tabs etc, posting from archaic IPad!!!

ICBM

Mesas run the valves much more conservatively. (Apart from their cathode-biased models, which are the other way round!)

Modern power valves don't really last very long, they could well be worn out if they've been run hot.

welshboyo

Hmm ok @ICBM that's interesting, it's designed to run hot and Bogner advise only Winged C's due to the high plate voltages.

Got the back off now and one of the EL34's has a distinct blue tinge to it whereas the other seems to be the usual Orange glow.

The amp is also well down on power - I can run it at almost full whack on the clean channel which normally gives you eye watering levels of spank but it's nowhere near that..

New EL34's tomorrow then, hopefully Karltone can give me similar specs to these so I can possibly get away without a rebias , however, failing that I'm going to get a bias probe as well as this thing eats valves by the looks of it...

Drew_TNBD

Nothing wrong with a bit of blue tinge.

ICBM

welshboyo said:

Hmm ok @ICBM that's interesting, it's designed to run hot and Bogner advise only Winged C's due to the high plate voltages.

Winged C's don't hold up better than any other modern valves and possibly less well than JJs.

welshboyo said:

Got the back off now and one of the EL34's has a distinct blue tinge to it whereas the other seems to be the usual Orange glow.

The amp is also well down on power - I can run it at almost full whack on the clean channel which normally gives you eye watering levels of spank but it's nowhere near that..

It could be the one that *isn't* glowing blue…

Contrary to common but totally wrong popular myth which still seems to persist, blue glow is *not* a sign of a faulty valve - it's almost always a sign of a good valve working properly. You should see at least some blue glow, either on the inside of the glass or a slightly 'greener' blue inside the plate structure, which can be hard to see unless you look at just the right angle. But none at all means the valve is probably not working.

If that's the case you will get low volume - only around 1/4 of the amp's normal maximum power - and an oddly distorted sound because the waveform is being almost chopped in half.

welshboyo said:

New EL34's tomorrow then, hopefully Karltone can give me similar specs to these so I can possibly get away without a rebias , however, failing that I'm going to get a bias probe as well as this thing eats valves by the looks of it…

You really need to be able to do that. It's also not a great idea to run the valves that hot, again contrary to popular myth it doesn't usually improve the sound, and it does kill the valves. If you don't want to do the bias, I would get Karl to supply the *coolest* valves he can - combined with the amp being set too hot they will then probably be in the right range for sensible operation.

welshboyo

Cheers @ICBM

The plate voltage on the Shiva is 550 and it's getting approx 80 watts out of a pair of EL34's which mathematically doesn't work!! - 25 + 25 = 50!!!

The Bogner recommended idle bias is 29-31 so I'm going to go for a new set of valves and bias it to 30ish which if MY maths are correct is about 70% diss at idle

And just to confirm, bias with no load (guitar/signal)?

ICBM

welshboyo said:

The plate voltage on the Shiva is 550 and it's getting approx 80 watts out of a pair of EL34's which mathematically doesn't work!! - 25 + 25 = 50!!!

Remember that 25W is the max plate dissipation per valve and not the possible output power. If you run a pair of EL34s at 800V in Class B you can get 100W out of them without exceeding the ratings - the theoretical limit is four times the maximum plate dissipation per valve, not twice, because power is proportional to voltage-squared and it's the voltage swing that matters, not the power dissipated in the valves. It has to be Class B though, where each valve actually reaches cutoff, hence is not used for audio because of the crossover distortion. Class AB is always less efficient because the voltage swing must be less in order to allow the overlap that eliminates the distortion. (And is why you get *some* clean signal at low volume even with only one power valve working.)

welshboyo said:

The Bogner recommended idle bias is 29-31 so I'm going to go for a new set of valves and bias it to 30ish which if MY maths are correct is about 70% diss at idle

I'd probably go a bit lower. Old Marshall 100-watters with that sort of plate voltage usually sound best at around 55-60%.

welshboyo said:

And just to confirm, bias with no load (guitar/signal)?

No! Not no load - no input signal. Which may be what you meant . You must always connect a load (speaker or dummy).

Don't bias with no load even with no signal, just in case the amp is unstable with no load - a few are. At best this will give you wildly wrong readings and at worst might blow something.

welshboyo

Haha sorry yeah, no input signal!!

jpfamps

welshboyo said:

Cheers @ICBM

The plate voltage on the Shiva is 550 and it's getting approx 80 watts out of a pair of EL34's which mathematically doesn't work!! - 25 + 25 = 50!!!

The Bogner recommended idle bias is 29-31 so I'm going to go for a new set of valves and bias it to 30ish which if MY maths are correct is about 70% diss at idle

And just to confirm, bias with no load (guitar/signal)?

The higher the HT the more towards class B the amp needs to be biased to prevent the valves over dissipating.

The 70% "rule of thumb" was a maximum recommend by Randall Aiken for "average" guitar amps, and is based on his calculations of anode dissipation.

http://www.aikenamps.com/index.php/idle-current-biasing-why-70-percent

He does on to say that this rule doesn't work so well for amps with higher plate voltages.

Using 550 VDC on the plate with modern EL34s is not a great idea in my opinion and you will get through valves quicker.

If I wanted to design an 80W using only 2 valves I would either employ 6550s or KT88s.

I like the sound of =C= EL34s, however recent experiences have found these not to be as reliable as JJ EL34s. I've had problems both electrically and mechanically with them.

Furthermore, from what I understand =C= valves are not longer in production, so it might be wise to look for some alternatives.

fastboy

If you find yourself needing new valves due to the lack of decent NOS =C= being in circulation now (been reading a lot lately that what seems to be left is low quality) Bogner are now recommending the Ruby EL34 BHT as the replacement for their EL34 amps. 

It's designed to run 600V on the plates. I had a set in my current Shiva and they do sound good as well but being a complete gear whore I had to throw in a very strong pair of Mullard XF4's which I'm almost debating might have too much bottom end for the Shiva so am considering going back to the Ruby's...

welshboyo

oddly enough @fastboy I've just had a mail from Bogner advising the Ruby's!!!

fastboy

welshboyo said:

oddly enough @fastboy I've just had a mail from Bogner advising the Ruby's!!!

Ha ha

They do sound good so I wouldn't fret that =C='s are not readily available any more. 

welshboyo

bit of a shit to get hold of though..outside of Ebay...

fastboy

welshboyo said:

bit of a shit to get hold of though..outside of Ebay...

They are pretty rare in the UK but here's one place: 

http://www.tauntonavservices.co.uk/sales/leads-accessories-and-spares/valves/ruby-tubes-2-x-el34bht-matched-pair