Why would an EL34 amp have to be modded....

[korovamilkdud]

To run the JJ EL34L ?

http://www.fjamods.com/XXX_JSX.html

At the bottom of the page he has a $125 mod to make a XXX or JSX EL34L friendly.

How would the JJ EL34L differ from JJ's EL34 ? ( I know the difference tonally, I just don't understand why an amp mod would be necessary).

 

[Van Noord]

Re: Why would an EL34 amp have to be modded....

E34L's require a higher screen grid resister value. Early XXX and JSX models came with SGR's valued at 100. Since late 2004 they come with ones rated at 700. E34L's should be able to use the 700, but a 1000 value is advised.

Something to remember is these amp were designed to use 6L6's and EL34's only. The JJ E34L is unique to JJ Electronics only and these amps were not made to cater to that specific tube in stock form.
Mods are also necessary for these amps to accept KT88's and 6550's, just like a lot of other amps would also need mods for those.

 

[korovamilkdud]

Re: Why would an EL34 amp have to be modded....

Thanks.

 

[Lake Placid Blues]

Re: Why would an EL34 amp have to be modded....

In my experience E34Ls bias up differently from EL34s too. Depending on the bias circuit and bias range of a particular amp, mods may be required to bias them as required.

 

[Nightburst]

Re: Why would an EL34 amp have to be modded....

Because JJ E34L's are weird tubes!
I ordered a 'cold' set and they wouldn't bias lower than 45-50mA. Normal levels in my amp (xtc) would be 32-37mA so I send them back and the guy that was selling them had to hand pick a 'very cold' set that would bias.
Those settled at 38mA with the bias pot trimmed all the way down!

I'm not shure if these tubes are ok to use but they sound spectacular! Hard to explain but I'd dare to say they fall inbetween the 6L6 and EL34 sound somewhere. Almost like they have the Low end of 6L6 and the top end of EL34. Great for glassy cleans and fat crunch tones, you name it they deliver. (soundclips soon)
Been using these tubes for 3 years now and this is my 2nd set.

So if you want to try those out just order a 'cold' set. That might do the trick for you.
Not shure if these tubes are safe to use in every amp! Maybe they need a high plate voltage to operate at full potential?

 

[metlking]

Re: Why would an EL34 amp have to be modded....

I used them in a Marshall 9100 poweramp with no issues getting them to bias correctly.......

 

[RealtyViking]

Re: Why would an EL34 amp have to be modded....

Any different from the Groove Tube EL34LS?

Got a new set of the GT EL34LS' for cheap and noticed bias bottomed at 38mV DC at test point.