I have a 1996 jcm 900 4102 just back from voodoo modification. In addition to their circuit modification they put in new caps / 6L6 tubes. They do a break in process on new tubes and I also played it gently for first 2 sessions. Took it up to 6-8 volume day 2 for brief periods and then left the room...when I came back the room smelled like electrical fire. Sent the chassis back to Voodoo and they told me all the tubes were fried! They said they'd never seen that before...nothing wrong with the amp itself that they could find. Interestingly the fuses did not blow. BTW they claim the tubes are not under their warrenty of course
Burned marshmellow usually means a transformer. Can you confirm the OT is still good? That would take out the tubes. As would a bad solder point that lifted in the bias supply. Tubes can go bad but seldom take out all 4 tubes. IMHO somebody over looked something during the mod or you forgot to give the amp a load and took out the back end of the amp. Are the speakers ok in the cabinet?
Forget the mess, look what a badass can do! That restoration is amazing!
Like wiping doo off your shoe.
That Voodoo guy told me he couldn't drill extra holes because he'd split a plexi panel when I called for an artist inquiring about one of his secret mods, so I hung up and had someone basically do that same thing with a new board. Amp sounds amazing now.
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
I don't know what quality of work Voodoo does but the tubes may be at fault. Tubes aren't all that great at being shipped around the US by careless UPS/Fedex guys. If the OT is good (I hope the Voodoo guys checked this) then you might have just gotten a bad set. It happens..
Also I've worked on one of these amps and was not impressed with the build quality. The amp came in because it wasn't getting heater voltage. A few minutes of probing led me to a wire where the manufacturer missed the crimp by an 1/8th of an inch. I looked for signs of stress from tugging but saw none. I'm surprised the amp ever worked, you could feel where the wire was missing going into the crimp.
Reeltarded wrote:Forget the mess, look what a badass can do! That restoration is amazing!
Like wiping doo off your shoe.
Yeah, like I said, Rich is 100% old school. I'd guess he's close to 70 by now. He used an old belt driven dental hand piece to remove much of the goo. It must have taken time and patience. Amazing is an understatement.
I don't mean to defend Trace (I once had to do exactly what Rich described to a Plexi -- a PLEXI!!! -- that Voodoo had worked its magic on). But they have apparently sworn off gooping and there is a whole list of iconic amps they will no longer even mod. Sinners can find redemption.
As to the OPs situation, infant mortality in a whole quad of tubes seems sort of improbable. It sounds like a catastrophic bias failure. The fuses on the tube cathodes in the JCM 900 only blow above 500mA, so they're really only protective in the case of an outright short.
Virbrations of shipping and then louder playing may have joggled something loose. My bandmate's JCM900 can be a serious PIA in that respect, lots of intermittent problems that I attribute to spotty connections somewhere in the amp, just not consistent enough to catch and fix when it's acting up.
I attributre the gooped circuits to a time when intellectual property wasn't safe with blossoming use of the internet, and every guitarist with a solder iron was searching for the magic schematic that would make them the next amp guru. The gooping phase probably passed once it no longer served a purpose (kinda like Jimmy Page's plaid pants). I feel that the custom amp business is now matured to the point where most people understand it's not just the schematic that's all important, but the actual builder has a substantial effect on the finished product.
FWIW, my main and favorite amp for the last 8 years is a 50-watt Voodoo Hex with the now defunct OEI output transformer. Yes, it's gooped, but I don't really care. It sounds amazing, and has never once let me down. Through my own personal experiences with Trace over the years, I seriously doubt he would steer you wrong or cover up any mistake on their part.
I have a 1996 jcm 900 4102 just back from voodoo modification. In addition to their circuit modification they put in new caps / 6L6 tubes. They do a break in process on new tubes and I also played it gently for first 2 sessions. Took it up to 6-8 volume day 2 for brief periods and then left the room...when I came back the room smelled like electrical fire. Sent the chassis back to Voodoo and they told me all the tubes were fried! They said they'd never seen that before...nothing wrong with the amp itself that they could find. Interestingly the fuses did not blow. BTW they claim the tubes are not under their warrenty of course
Any of you experts with ideas?
Thanks for your help
Stoma
Maybe an oscillation, I can understand 2 cooking but 4 is a stretch
I think we forgot to ask... are the tubes Chinese? I stopped using off shore tubes after a 40% failure rate. coupled with brittle tone and short life. I found to some degree you get what you pay for.
Remember Ruby offers a 90-day/6 month warranty on dud tubes, it's how they make cheap tubes safe to use.
LOL Funny Shit !
Funny enough I worked for Time Electronics some 35 years ago ! Rich is an interesting guy but his heart is totally in to it. He has been around the block many times ! Good guy.
