Replacing EL34 valves

[esperowl]

Hi, please bear with me on this one, as I am about to ask some questions which will have some veteran hifi-ers rolling their eyes in disbelief at my numptynes.

Yesterday I looked at the valves in one of my mono power amps. One of the four valves was not glowing (hard to see clearly because the glass is dark blue). The top of the tube did not feel hot to the touch, whereas the base of the tube was.

Is the valve kaput? (I'm guessing yes)

How come the amp still works?

Can I get away with buying a single replacement or do I have to get a matched pair / quads?

Out of the 8 power valves, some are labelled EL34B and some EL34M. Does the difference matter?

Thanks in advance.

[NRG]

Whats the amplifier?

The output stage sound like it could be paralleled PP or SE...If the other EL34s are working OK then the heater has failed on the duff one. You could simply buy a single one or if paranoid buy two matched EL34s

Edit. I think the EL34M is a 'Mullard' re-issue from GrooveTubes.

http://www.hotroxuk.com/groove-tube-el34m-per-pair.html

[Rare Bird]

I think the 'B's is an high impedence version...

Those 'M's are probably a modern attempt at the vintage Dual Getter 'XF2'! not sure tho..

[esperowl]

Whats the amplifier?

The output stage sound like it could be paralleled PP or SE...If the other EL34s are working OK then the heater has failed on the duff one. You could simply buy a single one or if paranoid buy two matched EL34s

Edit. I think the EL34M is a 'Mullard' re-issue from GrooveTubes.

http://www.hotroxuk.com/groove-tube-el34m-per-pair.html

Bang on! They are Groove Tubes. The amp is push-pull.

[esperowl]

I think the 'B's is an high impedence version...

Those 'M's are probably a modern attempt at the vintage Dual Getter 'XF2'! not sure tho..

Thanks for the info. Is there a reason for using high impedance tubes?

[hifi_dave]

Groove Tubes did a range of blue tubes, which were fairly popular with Tube Technology amps, back in the early 90's. I have a new matched set of blue EL34's here if you need replacements.

[esperowl]

Groove Tubes did a range of blue tubes, which were fairly popular with Tube Technology amps, back in the early 90's. I have a new matched set of blue EL34's here if you need replacements.

Hi, cannot see a tube section in your website.

Re, Rare Bird's response above - does anyone know why high impedance tubes are used?

[hifi_dave]

Plenty of tubes on there - EAR, Icon and Croft.

You still haven't identified your amp..:scratch:

[esperowl]

Plenty of tubes on there - EAR, Icon and Croft.

You still haven't identified your amp..:scratch:

Art Audio Tempo monoblocs. I believe they are push pull & triode if that helps.

Looked at the Groove Tubes site; the EL34L looks tasty.

[The Grand Wazoo]

I had some of those for a bit - they were push-pull pentode, with a 'wired for triode' switch. Are yours permanently in triode mode Chang?

[NRG]

Not sure what was meant by a high impedance valve, the EL34 has a set of characteristics that will be broadly the same from manufacture to the next so the plate resistance and other characteristics will more or less be consistent as the valve is an "EL34"... The construction may vary but valve from one manufacturer should work in the same cct as one from another...

[esperowl]

I had some of those for a bit - they were push-pull pentode, with a 'wired for triode' switch. Are yours permanently in triode mode Chang?

I believe so. What was your experience when switching between the two modes? Are pentodes 'punchier' and 'triodes 'sweeter'?

[esperowl]

Not sure what was meant by a high impedance valve, the EL34 has a set of characteristics that will be broadly the same from manufacture to the next so the plate resistance and other characteristics will more or less be consistent as the valve is an "EL34"... The construction may vary but valve from one manufacturer should work in the same cct as one from another...

I've been looking at various tube sites and wow it's a minefield. Tesla, JJ and Winged Svetlana seem to be well regarded. I feel drawn to EL34L types; as I am new to valve amps, I'm looking for a compromise between the SS and valve sounds. Apparently the EL34L has good dynamics, so maybe they'll deliver the compromise I'm looking for. Not sure if my monos will take other types of tube.

[The Grand Wazoo]

That would sum it up pretty well.

Studded leather jacket vs zoot suit!

[The Grand Wazoo]

How much do you want to spend?
Most people who try them like vintage Mullard EL34's, but they're expensive.
There's also the 6CA7, which is the US version - functionally identical but some feel it has a bit more control top & bottom.
Not forgetting the KT77, which will almost certainly work in your Tempos.

[esperowl]

How much do you want to spend?
Most people who try them like vintage Mullard EL34's, but they're expensive.
There's also the 6CA7, which is the US version - functionally identical but some feel it has a bit more control top & bottom.
Not forgetting the KT77, which will almost certainly work in your Tempos.

Well, I'll spend whatever it takes so long as I get good vfm; don't want to spend on foo or anything that only brings barely noticeable changes in th overall sound.
I checked the price of the Groove Tube EL34M (because that is what was supplied with my monos) and they are more expensive than other well regarded EL34. So I'm not sure what to conclude; either -
(a) Groove Tube products are well known but tube rollers recommend better tubes that can be had for less money, or
(b) fewer people have heard Groove Tube valves and therefore they are less likely to be recommended :scratch:

[The Grand Wazoo]

If you go for Groove Tubes, be sure you get them from someone who knows what you want them for. Their main market is guitarists and they often want something that will go into distortion early. This is the opposite to what you want! Groove Tubes are graded from 1 to 10 (I think they go up to 10 anyway) you want a high number!

[esperowl]

If you go for Groove Tubes, be sure you get them from someone who knows what you want them for. Their main market is guitarists and they often want something that will go into distortion early. This is the opposite to what you want! Groove Tubes are graded from 1 to 10 (I think they go up to 10 anyway) you want a high number!

Thanks for the tip Chris. I noticed the distortion gradings on the GT website and they indicate that a medium grade is suitable for general listening. I'll double check.
BTW, since I only need a single EL34 replacement at the moment
- would it matter if I just bought a single valve or do I need to buy a matched pair*
- would it matter if the replacement is from a different manufacturer than the others I'm using
- where does biasing come into all of this?

*I intend to eventually buy a fully matched octet when funds allow.

[The Grand Wazoo]

Well, ideally, you should get all eight tested by someone to see what you need to do.
At the very least, I'd expect to be buying a pair.

I think that all Art Audio amps have an auto biasing arrangement - my Tempos certainly did, so you probably needn't bother yourself with all that!

[esperowl]

Last question (possibly)
I assumed EL34 and 6CA7 where directly interchangeable. A local guy is selling matched pairs of 6CA7's but he says they are tetrode tubes (my amp is triode).
- I thought tetrode / pentode / triode were terms that referred to the internal circuitry of an amp
- my monos hold 8 power tubes; would I cause damage if 2 of the tubes were 'tetrode tubes'?

[The Grand Wazoo]

You're both right.
Triode valves do exist.
The valves you need are pentodes. All EL34/6CA7 valves are pentodes.
Your amp has valve sockets which are wired in a triode configuration. This is a kind of kosher bodge.
The valves will be fine - they are exactly what you need.

[NRG]

Well they are electrically equivalent! The 6CA7 is the American version of the EL34 but its a beam tetrode not a pentode, they will sound subtlety different. I would stick to the same valve as the others you have.

[Ali Tait]

I had an EL34 amp for a while that came with cryo'd Shuguang valves. Sounded very good to me, and they are not silly money. I have four matched RFT valves I'd let go if you are interested, say £80 for the set.

[The Grand Wazoo]

......... but its a beam tetrode not a pentode,

Yes, apologies - I stand corrected - I knew that!