Lynch box problem HELP!!!!!

[guitarteck]

I thought this amp was the coolest until last night.
I turned it on at soundcheck and it lasted about 5 minutes till it lost power and gain. then it came back middle of the 1st set it went out again and i shut it off and turned it on and it seemed fine for the rest of the night. I think it may be tubes but what pisses me off is these tubes have 3-3hour shows on them. they are basically new and i need some input before i get new tubes or just get rid of it for a more dependable amp like my singe rectifier combo.

 

[crankyrayhanky]

is it loaded with el34s? If so, there is a real bad batch out there- grab something else

 

[guitarteck]

yes they are el34s i got the amp new last september and have gigged it 3 times. Is there a way to tell if it came from a bad batch? kinda sucks that an amp of that price and Randall would stick the people who bought their poduct if there is a problem with the tubes

 

[crankyrayhanky]

It seems to be a lot of amps- many of the big names- have had these issues and are starting to switch out their 34s for alternatives...i just hope you didn't damage your amp in this mess, it really is a great amp, the tube quality control may be to blame..regardless, it should be covered??

I've been running 6L6s...I thought about hearing some other types but I'm not going anywhere near 34 for at least a year, it's not worth the risk

Good Luck

 

[gtr31]

sometimes it is impossible to know . they test fine and blow a week later .
EL34's are just VERY unreliable right now
The fact that your single recto had 6l6's and never let you down ,I would recommend getting 6l6's into the LB

 

[gtr31]

I hear ya Ray the sound great but its scary .
I remember reading that post from Jeff(Egnater) saying of all the amps that have had to have boards replace . the EL34 was the tube that did it EVERYTIME

 

[jmgman70]

yes they are el34s i got the amp new last september and have gigged it 3 times. Is there a way to tell if it came from a bad batch? kinda sucks that an amp of that price and Randall would stick the people who bought their poduct if there is a problem with the tubes

It's not just Randall,it's the tubes!Peter Diezel is starting to use 6550s be cause of the EL34s being crappy.And then the Amp manufacture gets a bad rap for the tube failure and his amp gets shot down when in fact it's usually a tube and lately EL34s.

 

[Julia]

1. assume the tubes are bad. There is no way to tell which batch it is because JJ doesn't put the lot number on the tubes.

2. change the fuses (you need Littlefuse 400 ma Fast-blo fuses and you will need to order them online -- get a couple packs)

3. turn the bias trim a bit counterclockwise but not too much.

4. replace ONLY the bad tubes with spares if you have them

5. turn on the amp and take it off standby -- only the speaker load, do not play the amp -- and watch it closely for about 20 minutes. This is to check to see if you took out a screen grid. Yes? take it to an amp tech. No? go onto step 6.

6. Replace the entire quad with a new quad, and bias the tubes right dead center. I've learned biasing cold is bad. Biasing hot is bad. Really you need both a multimeter and oscilloscope to do it right, but since i have no oscilloscope to double check things I have to trust my multimeter.

Useful tip: Never gig without a backup.

This can mean a spare head (I have a 5150 II that will come in with me) or have a POD XTL you can plug into the mixing board and use through the PA. If you have an endorsement from an amp company you just put the other head on the floor behind your speaker cab. Most people in the crowd won't notice the difference anyway.

 

[guitarteck]

any chance on it being a preamp tube or should i just start with all new tubes from the ground up?

 

[Julia]

You know you could be having intermittent redplating of the power tubes. I actually have had the exact same symptoms on other amps. The volume drops for a while then comes back. Then it drops again. If I hit standby and turn them back on it comes back for a while again.

I'll put money it's a bad quad. Replace the quad. The Randall videos say you can replace the bad tube if this happens in a gig if you have a spare tube or duet, and the fuses (always carry these items). But in the manual they advise replacing the quad or duet with new tubes regardless of if the other tubes work. Chances are that the remaining functioning tubes aren't going to last long. It's best to get them ordered as soon as you can after a tube failure.

So replace the quad, and while you're at it sure, get three preamp tubes. It's good to have spares. If it does this with a new quad, start testing the preamp tubes by replacing them one at a time until you find the bad one.

I've had these same symptoms with Fenders and Marshalls. Fenders are pretty **** reliable.

It's bad enough that I'm going to remove the front panel of my tube amps so I can see the tubes if something strange starts happening. I'm going to see if Randall can get me the screen type front panel that's on the standard RM100. I'll find out how to do this tomorrow.

 

[nixerx]

Snag some Winged C or Svetlana EL34's. You'll never go back to JJ's .... ever.

Keep a backup set of Sovteks or EH's around too. No need to have any thing too pricey as they are backup.

 

[guitarteck]

All tubes tested good but im gonna get new ones anyway and just retube the whole thing. should i just go with 6l6s or take a chance and use a new set of 34s?

 

[Julia]

If you go with EL34's get the SED =C= EL34 from a Magic Parts dealer (Ruby) or from Groove Tubes (Fender still gets them but their staff has been replaced by contractors so I'd rather use Ruby). Doug's Tubes carries Ruby.

Svetlana's are New Sensor or a variety of Sovtek. SED's are made in St. Petersburg and are the stock Marshall tubes.

If you go 6L6 also go with Ruby. I got impatient today and grabbed a quad of Groove Tubes

Make sure you have a good multimeter. They're about $40 for a digital readout. Or get a biasing kit from Ted Weber.

 

[guitarteck]

Thanks for the help i put JJ 6l6s in at and rebiased it and it is sounding pretty good we will see what the future shows hold for dependability