Can I put 2 JJ KT-88s in my 50 watt Marshall?

[RacerX]

...without damaging stuff?

Help, amp novice here. Amp is my old Marshall 4210 1x12 JCM800 combo. Has been my main amp since 1985, and was modded with an extra 12ax7 for gain around 1991. Last summer, no sound, I believed that the 2 Groove Tube 6550s had finally died (have not ever changed the tubes, IIRC these were the tubes that have been in the amp since 1985 (or possibly 1990).
OK. I just bought a matched pair of JJ KT88 tubes. Was planning on putting them in there and getting the amp rebiased...BUT...I just read in the other KT88 thread that 2 of em equal 100 watts. Give me the straight dope, amp experts! [img]/images/graemlins/grin.gif[/img]

Thanks

[Soloist1]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

Yeah they will probably fry the transformer Ron. The 6550 puts out less output wattage than the KT88's do. You should stick with 6550's just to be safe. Just out of curiousity though, are those the stock tubes that amp is supposed to use? I would have expected two EL34's for that amp. If they aren't stock the 6550's may have killed your transformer by being a bit to much.

[RacerX]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

Crap. What about this info?

http://acapella.harmony-central.com/...hreadid=843579

[Soloist1]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

They are two different tubes. The specs for each aren't exactly the same. They lump them together because a quartet of these tubes will yeild over 100 watts.

[LRGman]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

Its not uncommon to see JCM 800's with 6550's stock. A friends combo came with them. I read an interview with jim marshall and at one point the ran out of el34's or had a problem with supply or something and they shipped a bunch to the US with 6550's. Also is a common mod that was done to JCM in the late 80's early 90's. I had it done to mine at the time.

[Shawn Lutz]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

The 6550's may be the original tubes, they were on my 83 JCM 800 2203.

Yes you can use KT-88's in that amp (most 6550 amps too) without any problems.

Either way you go Ron I would re-bias so if you can't do that yourself take it in. Don't believe everything that you read on internt forums [img]/images/graemlins/smile.gif[/img] call Eurotubes and ask him PHONE 503-659-7401

Alos from what I heard was the the US amps were requested with 6550s from marshall because the el34's at the time were considered unreliable tubes...

[Twisteramps]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

If it came with 6550s, then no problem, you can run KT88s. Just have it rebiased.

Pete

[Final Sacrifice]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

How do you like the amp? I've been looking at them, but there's nowhere I can play one. How heavy can it go on its own? And how loud can it get? Thanks.

[RacerX]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

Thanks guys for all your help. A fellow JCFer is gonna bias everything for me. Final Sac, I love this amp, it really kicks butt, the gain mod really woke it up. I don't think I ever put the master over 4. I like a scooped sound. Here are some pics:

[zeegler]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

All the writing is upside down. [img]/images/graemlins/laugh.gif[/img]

[Final Sacrifice]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

What is a fair price for one of these? They seem to all be around $800 on ebay.

[kmanick]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

who did the gain mod?
I've been looking at a 2 12 version of this amp right now.

[Deneb]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

OKay, a fair WARNING about the KT88s. I had them in an old 800, 100 watter. I did it because Billy Corgan did, and I like him.

They are harder to distort, like for power amp distortion. They have a lot more head room (IMHO) and have a great clean sound. I think you'll like them, but they are NOT 6550s.

[Ace]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

Also check your speaker rating(in watts). You should get quite a bit more power, so you don't want to fry your one speaker.

[speed monkey]

Re: Can I put 2 JJ KT-88s in my 50 watt Marshall?

My Splawn modded 1987x 50 watter had KT88's in it.

Sounded simply freaking awesome. I think he needed to change out some resistors though - you might call and / or email him to ask what needs to be done, he's cool.

Steve E