5881 to EL34 - straight swap

[fretburner]

Hi All!

What happens to a JCM900 with 5881 if someone put EL34s in it straight up, i.e. NO re-bias, etc. etc.? Just pull out the 5881 and then put in the EL34s.

Thanks!

 

[Buckeyedog]

Re: 5881 to EL34 - straight swap

Don't know what would happen, but I wouldn't do it. 5881's are a 6L6 variant, so it may even have to be modded slightly to make EL34's work in there.

 

[fretburner]

Re: 5881 to EL34 - straight swap

Somebody did this and I thought it was the reason why there's no gain in the drive channel and the reverb is dead. Though I've always thought it's the preamp tubes that's giving you that crunch?

 

[jeremy]

Re: 5881 to EL34 - straight swap

the socket will need a little rewiring to use el34's
he shouldnt do it as he might hurt the amp

 

[fretburner]

Re: 5881 to EL34 - straight swap

he did it though... so was that the reason why the drive channel sounds like a broken speaker? it's like a clean channel turned all the way up. not high gain at all. could he have fried something up, which is why the reverb is dead?

 

[jeremy]

Re: 5881 to EL34 - straight swap

el34's pull much more heater current than a 6l6 type tube so the power tranny might cook, also it will rob current from other parts of the amp which could be the problem with the reverb, maybe even with the gain.

he should stop doing it immediatly. if he hasnt hurt the amp yet, he could. if he kills the power tranny, it wont be cheap to replace

 

[ErikH]

Re: 5881 to EL34 - straight swap

Oh boy, I don't believe I'm reading this. I hope for his sake the PT is ok. It was gonna cost me between 3 and 4 Franklins to get my Marshall fixed, and thats parts and labor. Mine went just from pure usage.

 

[ES350]

Re: 5881 to EL34 - straight swap

the pin configuration is different, the screen resistor is a different value, and it pulls more current---bad idea without a tech verifying that it's OK to swap...you could be lucky, maybe you only lost a screen resistor.

 

[fretburner]

Re: 5881 to EL34 - straight swap

how would i know if the PT is damaged or not? the clean channel seems to be OK though it doesn't stay as clean as my jtm60.

 

[i love everyone]

Re: 5881 to EL34 - straight swap

if the PT is fried, then you probably won't get anything out of the amp. like it might turn on, but nothing else will happen. also, you might start smelling something burning...

 

[ErikH]

Re: 5881 to EL34 - straight swap

If the PT is fried, the main fuse will pop and there will be no power anywhere. The only current left will be what's stored in the filter caps.

 

[fretburner]

Re: 5881 to EL34 - straight swap

there's power and the clean channel seems to be okay. so i guess the PT is still "alive". the gain channel sounds like a loud fart at best. it's like clean channel that just wouldn't clean up. i couldn't tell if the speakers are busted or something else fried.

is there hope in this amp? get it to a good condition for gigs?

 

[ErikH]

Re: 5881 to EL34 - straight swap

Yeah, get those EL34's outta there and put the 5881's back in. If he wants EL34's in it, it has to go to a tech to be "done right". There is no other option.

 

[jeremy]

Re: 5881 to EL34 - straight swap

i doubt the speakers are busted

 

[fretburner]

Re: 5881 to EL34 - straight swap

what about the reverb?

 

[jeremy]

Re: 5881 to EL34 - straight swap

hard to say

 

[fretburner]

Re: 5881 to EL34 - straight swap

how will a busted reverb ruin the tone from that amp?

if ever i get it, i will have it modded to go EL34s since i love El34s anyway. and the dude already messed it up anyway.

im just concerned that it wouldn't sound "right" coz the reverb is part of the circuit correct?

 

[ErikH]

Re: 5881 to EL34 - straight swap

If the reverb is busted, it'll be no different (with the correct tubes and bias done) than having the reverb knob on zero. The reverb tank in those is small anyway so don't expect Fender type reverb if it works.

 

[jeremy]

Re: 5881 to EL34 - straight swap

it might not be that messed up, has he tried to put the 5881 back in?

 

[fretburner]

Re: 5881 to EL34 - straight swap

he hasn't. i don't think he has some spare 5881's. if the old 5881's are put back in, would i get the high gain drive channel that it supposed to give me if he didn't put the EL34s in the first place?

i will ask him anyway and see if there's some noticeable differences. i'm very worried about frying up the entire circuitry that's why there's almost zero gain on that amp.

it's good to know though that it should work fine without the reverb. at least for the meantime i can use a pedal to cover for that.