EL34 to 6L6 and vice versa

[fretburner]

Hi All!

Some dude is selling a JTM30 2x10 but changed the power tubes to 6L6. Can I change it back to the original EL34s without having to modify anything?

Thanks!

P.S. The guy was bull****ting me that the amp came with 6L6 stock. Never heard of a marshall with stock 6L6 or at least the JTM 30/60 series.

 

[cream123]

Re: EL34 to 6L6 and vice versa

you'll have to rebias it i believe that would be it.

 

[Gunny47]

Re: EL34 to 6L6 and vice versa

You can get THD Yellow Jackets and turn it into an EL84 amp if that helps...

 

[ErikH]

Re: EL34 to 6L6 and vice versa

The very first marshalls came with 5881's (electrical equivilant of 6L6's). The original JTM45 is based off the Fender Bassman. Little known tidbit you probably didn't know. So yes, some Marshalls come with 6L6's.

The JTM30 came stock with 5881's but 6L6's can be used as well since they are essentially the same tube. He wasn't BS'ing you at all.

If the circuit is wired to allow EL34's, then yes, you can put them in and rebias the amp. However, some amps require additional resistors and a few other changes to allow for swap because their pinouts are not the same.

 

[cream123]

Re: EL34 to 6L6 and vice versa

The very first marshalls came with 5881's (electrical equivilant of 6L6's). The original JTM45 is based off the Fender Bassman. Little known tidbit you probably didn't know. So yes, some Marshalls come with 6L6's.

life lessons form erikh!

 

[fretburner]

Re: EL34 to 6L6 and vice versa

The very first marshalls came with 5881's (electrical equivilant of 6L6's). The original JTM45 is based off the Fender Bassman. Little known tidbit you probably didn't know. So yes, some Marshalls come with 6L6's.

The JTM30 came stock with 5881's but 6L6's can be used as well since they are essentially the same tube. He wasn't BS'ing you at all.

If the circuit is wired to allow EL34's, then yes, you can put them in and rebias the amp. However, some amps require additional resistors and a few other changes to allow for swap because their pinouts are not the same.

i know the first ever marshall was based on the bassman, but i thought those were modified with kt66.

anyway, the manuals in the marshall website was saying they came with EL34s.

 

[ErikH]

Re: EL34 to 6L6 and vice versa

i know the first ever marshall was based on the bassman, but i thought those were modified with kt66.

anyway, the manuals in the marshall website was saying they came with EL34s.

A KT66 has the same pinout as a 5881 and 6L6, just more headroom in that tube.

From the Tone Lounge:
The very first Marshall amplifiers actually used American 5881 output tubes. When these tubes became prohibitively expensive, a switch was made to the inexpensive British tube KT66, followed by the EL34. The rest is history.

Did you read this manual? No mention of EL34's or any tube type for that matter.
http://www.marshallamps.com/downloads/files/JTM hbk Eng.pdf

 

[Stevo]

Re: EL34 to 6L6 and vice versa

I converted my 2204 to run with EL34s - got a kit from Torres Engineering. I added a resistor and rebiased the amp.

Some Marshalls sent to the USA did not have EL34s, even though they had EL34s when they were sold in England and other countries. That was due to QC issues with shipping I think.

 

[ErikH]

Re: EL34 to 6L6 and vice versa

Some Marshalls sent to the USA did not have EL34s, even though they had EL34s when they were sold in England and other countries. That was due to QC issues with shipping I think.

Exactly. The tubes weren't making the trip so they shipped them with the more rugged 6550's to the States at first.

 

[wixedmords]

Re: EL34 to 6L6 and vice versa

Edited: The JTM30 did come with 5881's, I remember seeing them with 5881's.

Ask what the plate voltage is and what he amp was biased at on the last tube change.

EDIT2: BTW, +1 on Erik's advise of it needing a resistor to bias correctly when changing to EL34's. There is a small chance it may not, but it likely will.

 

[fretburner]

Re: EL34 to 6L6 and vice versa

A KT66 has the same pinout as a 5881 and 6L6, just more headroom in that tube.

From the Tone Lounge:
The very first Marshall amplifiers actually used American 5881 output tubes. When these tubes became prohibitively expensive, a switch was made to the inexpensive British tube KT66, followed by the EL34. The rest is history.

Did you read this manual? No mention of EL34's or any tube type for that matter.
http://www.marshallamps.com/downloads/files/JTM hbk Eng.pdf

i stand corrected. must have been some other like blamepro. thanks man!

nwy, it seems that i won't be changing em (if ever i'm getting em) to EL34s. i guess i don't want more headroom if i want a better dirty sound? or is this a totally different thing, i.e. not related to having more headroom?

thanks again!

 

[DesertRose]

Re: EL34 to 6L6 and vice versa

My JCM900 is fitted with 6L6, originally 5881s.
It still rocks.
The conversion will need a new tube socket, prolly some new caps and stuff and some rebiasing as some said earlier.

 

[Lake Placid Blues]

Re: EL34 to 6L6 and vice versa

The EL34 needs grid one and the cathode externally connected at the tube socket. The EL34 also needs a higher value grid resistor. A 6L6 tube goes right into a socket wired up for the EL34 no problem, because the 6L6 has an internal grid to cathode connection. However, an EL34 does not go right into a socket wired up excusively for a 6L6 (such as a Fender amp).

Marshall's tube sockets are traditionally wired up in the EL34 way regardless if the tube is 6L6 or EL34, so they can take either, as long the bias can be adjusted.

 

[fretburner]

Re: EL34 to 6L6 and vice versa

The EL34 needs grid one and the cathode externally connected at the tube socket. The EL34 also needs a higher value grid resistor. A 6L6 tube goes right into a socket wired up for the EL34 no problem, because the 6L6 has an internal grid to cathode connection. However, an EL34 does not go right into a socket wired up excusively for a 6L6 (such as a Fender amp).

Marshall's tube sockets are traditionally wired up in the EL34 way regardless if the tube is 6L6 or EL34, so they can take either, as long the bias can be adjusted.

that's a relief... hope i can find a qualified tech here though. i can't do it myself for sure.

thanks!

 

[BigDaddy]

Re: EL34 to 6L6 and vice versa

fretburner.....listen to me please. You seem to be cautious and that's good. Since you do not know who did the mods and what they did inside the amp if you decide to buy bring it to a good tech to have it checked out. That's something I always did no matter what, until I started building them myself. You would be surprised at the things people do to amps. that's one reason I build them now, I got tired of buying other people's hacked stuff.

From what I can remember about those amps they did have some problems in their design. I think they might have corrected them though. So there is probably a few different models internally, that might include changes to the power tubes, I think they all came with 5881's in those years but like I said that could have changed. here is a web site and they say those amps came with 5881's.

http://www.drtube.com/marshall.htm#JTM30

Anyway you look at it and even if the amp sounds great, get it checked by a good tech.

I got so disgusted with bad amp techs and hacked amps I learned to do it myself. If you have a back round in electronics it's not that hard. If you don't all it takes is some reading and trial and error. There are so many books and videos these days I am surprised more people don't fix and build their own amps. You just need some test equipment like a good VOM and a Webervst biasrite. There are loads of schematics and other information on the web.

 

[Lake Placid Blues]

Re: EL34 to 6L6 and vice versa

I agree that it's best to find a good, and honost tech if your unsure what to look for in the slightest. You need to make sure that pins 1 and 8 are externally connected.

 

[fretburner]

Re: EL34 to 6L6 and vice versa

thanks man. i really appreciate it.

 

[missionamps]

Re: EL34 to 6L6 and vice versa

The EL34 needs grid one and the cathode externally connected at the tube socket. The EL34 also needs a higher value grid resistor. A 6L6 tube goes right into a socket wired up for the EL34 no problem, because the 6L6 has an internal grid to cathode connection. However, an EL34 does not go right into a socket wired up excusively for a 6L6 (such as a Fender amp).

Marshall's tube sockets are traditionally wired up in the EL34 way regardless if the tube is 6L6 or EL34, so they can take either, as long the bias can be adjusted.

******************
A bit tired tonight but,
Adding to and detailing what was stated....

El34s are a real power pentode and 6L6s are a beam forming "power pentode" tube.
EL34s have a suppressor grid that is not connected internally, pin 1 and 6L6s (and the like) have a beam plate that is connected internally to pin 8.
The suppresor grid is not a signal "control grid" nor a high voltage screen grid and different in the 6L6, so don't be confused by this.
In EL34s, the suppressor grid lead is brought out of the tube through pin one and subsequently, lug 1 of the tube socket while 6L6s (and the like), have their beam plate "wire" internally connected to the cathode lead at lug 8.

If you wire the EL34 socket with lug 1 and 8 tied together, a 6L6 (and the like) will work in the same socket.

 

[Lake Placid Blues]

Re: EL34 to 6L6 and vice versa

I'm sure glad you chimed in with additional details and insight. I incorrectly stated that grid #1 was connected to pin 1, or internally the cathode on the 6L6, but it should be grid #3.

 

[fretburner]

Re: EL34 to 6L6 and vice versa

and the two posts above are alien to me.

nwy, if ever i buy that amp, i'll probably stick with the 6L6. and maybe, if i get bored with it, i'll play with it or have someone play with it and stick some EL34s in

rock on!