swapping to EL34's- what is the safe range to look for ?

[cheameup]

so finally getting around to swapping out some 6l6's to try out EL34s in my dual


so have a local dealer with a good selection of matched quads but I see online I need to make sure they are the right range for a dual recto


can anyone tell me what this right range is and what to look for ?

I replaced my 6l6s 2 years ago and just bought a JJ quad and chucked em in and they were fine. maybe I was lucky ?

 

[bendo]

As long as they are matched, you can stick pretty much anything in there. Mesa's use a fixed bias, and on the Rectifiers, they are biased on the cool side.

Any matched quad will work fine. Just make sure to flip the bias switch before power on.

 

[domct203]

While I won't echo bendo's "plug and play" approach, most "average distortion" ratings will work, like any Groove Tubes rated 4-6.

I recommend you invest in a bias probe if you want to be 100% certain of the idle current (bias).

At the very least be sure there is not any red-plating.

Dom

 

[Hardy]

While I won't echo bendo's "plug and play" approach, most "average distortion" ratings will work, like any Groove Tubes rated 4-6.

I recommend you invest in a bias probe if you want to be 100% certain of the idle current (bias).

At the very least be sure there is not any red-plating.

Dom

Howdy guys,

3rd post but have been a long time lurker....seems like I know a lot of the characters that post here from reading over the forums for the last few years.....but you know little of me and hope to change that. I have a Roadster and Mark V heads and I am having the same thoughts of protecting my amps.

After reading tube recommendations (mainly for V1 position) I bought a few Tungspols 12ax7's form the tubestore in Canada. I'm from Perth Australia and its a fair bit cheaper than driving to the store to pick up some tubes than buying online including shipping costs so...we get bitch whipped here!!

While I was ordering the tube pre's I thought I might as well get a matched quad of winged C EL34's (to brighten up the Roadster which funnily enough the tungsol in V1 was all that was needed!) and got click happy and didnt add a description to what amp I was using so I was sent the EL34's with a reading of 40ma. I got back in contact with the owner and he said it should be ok but place the amps back to you while playing at gig volume to see if they red plate and if so swap them out and use them as paper weights ....the quad is still sitting in my practice room in there boxes because I'm too **** scared of putting them incase they toast the amp.

Dom a quick question for you as you seem switched on (I say that respectfully) do you think I am being over cautious....I have been told from other sources that they will just burn out quicker than normal and another said (EM7 on PRS forums) said not to do it as it can cook the amp.

Anyway sorry for the long post.....got a bit of spare time here in the oriface!!

Take it easy fella's

Rich

 

[domct203]

While I won't echo bendo's "plug and play" approach, most "average distortion" ratings will work, like any Groove Tubes rated 4-6.

I recommend you invest in a bias probe if you want to be 100% certain of the idle current (bias).

At the very least be sure there is not any red-plating.

Dom

Howdy guys,

3rd post but have been a long time lurker....seems like I know a lot of the characters that post here from reading over the forums for the last few years.....but you know little of me and hope to change that. I have a Roadster and Mark V heads and I am having the same thoughts of protecting my amps.

After reading tube recommendations (mainly for V1 position) I bought a few Tungspols 12ax7's form the tubestore in Canada. I'm from Perth Australia and its a fair bit cheaper than driving to the store to pick up some tubes than buying online including shipping costs so...we get bitch whipped here!!

While I was ordering the tube pre's I thought I might as well get a matched quad of winged C EL34's (to brighten up the Roadster which funnily enough the tungsol in V1 was all that was needed!) and got click happy and didnt add a description to what amp I was using so I was sent the EL34's with a reading of 40ma. I got back in contact with the owner and he said it should be ok but place the amps back to you while playing at gig volume to see if they red plate and if so swap them out and use them as paper weights ....the quad is still sitting in my practice room in there boxes because I'm too sh!t scared of putting them incase they toast the amp.

Dom a quick question for you as you seem switched on (I say that respectfully) do you think I am being over cautious....I have been told from other sources that they will just burn out quicker than normal and another said (EM7 on PRS forums) said not to do it as it can cook the amp.

Anyway sorry for the long post.....got a bit of spare time here in the oriface!!

Take it easy fella's

Rich

Welcome to the forum.

If a tube should red-plate and short you will most likely destroy the screen grid resistor(s) on those sockets. While it is not a big repair (time or $$), it is downtime none the less.

I don't know what the seller has based that 40mA rating on. If it is 40mA at 460V (the approx plate voltage of your amps) that means the tube will be at 74% of it's max plate dissipation (MPD) when at idle (very "hot-bias"). That is red-plate territory, especially in the Mark V.

If the rating is based on 300V then 40mA of idle current would put you at a safe (and "cool-bias") 48% MPD, but now were talking a theoretical reading.

These are chances I prefer not to take with a $2000 (US) amp.

Your best friend here is a bias probe. Something like these: http://www.eurotubes.com/eurotubes-Bias-Probe-Pro-One-current-watts-voltage.htm

While you might not be able to adjust your bias (Mesa uses non-adjustable fixed bias) you can confirm that the tubes in your amp are operating at safe and/or ideal conditions. I think this is better than watching your amp red-plate and blow a fuse.

BTW- Even with my Roadster modded for adjustable bias, I still find I like it best at "cool" to "moderate" bias (55-60% MPD)

My $0.02, YMMV.

Dom

 

[Hardy]

Thanks for the reply and welcome Dom.... I just had a look at the =C= EL34's and it doesn't actually say 40mA just 40. I'll have to go through my emails from the Tubestore but from memory I think he said that the highest rating they had successfully used and sounded great was 37 or 33. I'll troll through the emails to find the response from the store. But you certainly know your shiznit I might give the matched quad to my band member who has a JCM 800 for a couple of beers as its looking like I won't be able to use them.

I've been pretty lucky with tubes and never had the experience of tubes red plating..... What happens when it happens and what does it look like? I suppose the tube internals go red

Anyway this place is wealth of knowledge to douches like my self. Thanks again.

Rich

P.s. just for ships and giggles I bought my roadster new for $4300 Aus just giving an example of how we down under get shafted. I picked up the MKV on this very forum for a steal...(well for Aus pricing stand point) even though I had to pay an extra $1k to get it over plus the import taxs it's still a heap cheaper....consider your self lucky

 

[bendo]

[/quote]
Welcome to the forum.

If a tube should red-plate and short you will most likely destroy the screen grid resistor(s) on those sockets. While it is not a big repair (time or $$), it is downtime none the less.

I don't know what the seller has based that 40mA rating on. If it is 40mA at 460V (the approx plate voltage of your amps) that means the tube will be at 74% of it's max plate dissipation (MPD) when at idle (very "hot-bias"). That is red-plate territory, especially in the Mark V.

If the rating is based on 300V then 40mA of idle current would put you at a safe (and "cool-bias") 48% MPD, but now were talking a theoretical reading.

These are chances I prefer not to take with a $2000 (US) amp.

Your best friend here is a bias probe. Something like these: http://www.eurotubes.com/eurotubes-Bias-Probe-Pro-One-current-watts-voltage.htm

While you might not be able to adjust your bias (Mesa uses non-adjustable fixed bias) you can confirm that the tubes in your amp are operating at safe and/or ideal conditions. I think this is better than watching your amp red-plate and blow a fuse.

BTW- Even with my Roadster modded for adjustable bias, I still find I like it best at "cool" to "moderate" bias (55-60% MPD)

My $0.02, YMMV.

Dom[/quote]

I agree here a bias probe is a good idea. I guess I should've been a little more clear on my first response.

OP, even though our amps have a fixed bias, it's still a very good idea to ensure whatever tubes you pop in a operating within spec. To give you an example, I don't generally run Rectifiers any more as I prefer the pre-amp in the Dual Caliber. In my DC3 it runs EVERYTHING way too ******* hot. This is normal for these. Along with bias mods, I use a bias probe to test the bias of any set of EL84 quads I run. The first time I changed tubes after buying this amp was a set of Mesa EL84s. They red-plated fast and took out my screen grid resistors.

A few resistors (including lowering the bias resistor), a full set of tubes, and she rocks like a dream. You should not have to do this with your recto as they are biased towards the colder side, but @4300.00 !!! AUS for you roadster, a couple hundred bucks on a bias probe to be sure will go a long way.

When a power tube redplates, it will be pretty obvious. The plate structure in the tube will start to glow light red from the center of the plates out. Looks just like the metal is getting to hot (which it is).

 

[JonCurcio]

Thanks for the reply and welcome Dom.... I just had a look at the =C= EL34's and it doesn't actually say 40mA just 40. I'll have to go through my emails from the Tubestore but from memory I think he said that the highest rating they had successfully used and sounded great was 37 or 33. I'll troll through the emails to find the response from the store. But you certainly know your shiznit I might give the matched quad to my band member who has a JCM 800 for a couple of beers as its looking like I won't be able to use them.

I've been pretty lucky with tubes and never had the experience of tubes red plating..... What happens when it happens and what does it look like? I suppose the tube internals go red

Anyway this place is wealth of knowledge to douches like my self. Thanks again.

Rich

P.s. just for ships and giggles I bought my roadster new for $4300 Aus just giving an example of how we down under get shafted. I picked up the MKV on this very forum for a steal...(well for Aus pricing stand point) even though I had to pay an extra $1k to get it over plus the import taxs it's still a heap cheaper....consider your self lucky

I use =C= 37s in my Single Rec at 35ma.

 

[cheameup]

While I won't echo bendo's "plug and play" approach, most "average distortion" ratings will work, like any Groove Tubes rated 4-6.

I recommend you invest in a bias probe if you want to be 100% certain of the idle current (bias).

At the very least be sure there is not any red-plating.

Dom

Howdy guys,

3rd post but have been a long time lurker....seems like I know a lot of the characters that post here from reading over the forums for the last few years.....but you know little of me and hope to change that. I have a Roadster and Mark V heads and I am having the same thoughts of protecting my amps.

After reading tube recommendations (mainly for V1 position) I bought a few Tungspols 12ax7's form the tubestore in Canada. I'm from Perth Australia and its a fair bit cheaper than driving to the store to pick up some tubes than buying online including shipping costs so...we get bitch whipped here!!

While I was ordering the tube pre's I thought I might as well get a matched quad of winged C EL34's (to brighten up the Roadster which funnily enough the tungsol in V1 was all that was needed!) and got click happy and didnt add a description to what amp I was using so I was sent the EL34's with a reading of 40ma. I got back in contact with the owner and he said it should be ok but place the amps back to you while playing at gig volume to see if they red plate and if so swap them out and use them as paper weights ....the quad is still sitting in my practice room in there boxes because I'm too sh!t scared of putting them incase they toast the amp.

Dom a quick question for you as you seem switched on (I say that respectfully) do you think I am being over cautious....I have been told from other sources that they will just burn out quicker than normal and another said (EM7 on PRS forums) said not to do it as it can cook the amp.

Anyway sorry for the long post.....got a bit of spare time here in the oriface!!

Take it easy fella's

Rich

Hey man

for what it worth if your looking for an aussie seller I just got a set from lucas miles audio in melbourne . asked him if he can supply a good power tube set for a dual recto and he could . he got back to me in 10 minutes of emailing and i bought the set half hour later

prices were good especially considering express post was only $15 and i got it the day after ordering

 

[Hardy]

Cheers mate, I'll give him a call tomorrow. Also my apologies for hijacking your thread.

What did power tubes did you get?

Rich

Edit: just had a look at the site, great prices! Thanks for the link

 

[cheameup]

Cheers mate, I'll give him a call tomorrow. Also my apologies for hijacking your thread.

What did power tubes did you get?

Rich

Edit: just had a look at the site, great prices! Thanks for the link

no worries

I ended up sticking the 6l6's in the end, got some winged C's.sound really good

I ended up being a bit dodgey on what the 34's would do to the clean channel which I use allot . got some gigs and recording the next month so didnt want to risk it and experiment . I'll grab some 34's to try at tax time when I have some cash to blow