TIme for new tubes

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ido1957

ido1957

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Turned on my amp this afternoon and got the familiar "tubes are wearing out" crackling. Went away after a minute of warm up but it's off to the shop soon before it really starts to crap out.... :D
 
Whatcha gonna get? I've read about and had my own horror story with JCM900's and improper tube selection and bias straight from Marshall. Make sure whatever you get biases properly.
 
I'm getting ready to re-tube my main amp as well. I have to say, a few years ago, after having about the glories of new tubes, I was disappointed when I re-tubed my last amp. And the tubes were fine--I was purely going for a sound upgrade. $80 later, no difference to my ears.

This time, I have to--mine are crapping out as well. At least my expectations are tempered.
 
Greg_L said:
Whatcha gonna get? I've read about and had my own horror story with JCM900's and improper tube selection and bias straight from Marshall. Make sure whatever you get biases properly.
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I'm hoping the tech I brought it to before is still in business haha. He was referred by the local music store and his shop is in my end of town. I like the sound/tone/etc of the amp now - he did do some tweaks including bias, I think I only got one tube the last time. I have to call the music store tomorrow for his name/address as he is a one man shop and is never guaranteed to be there if you drop by. He has a typical shop full of crap being fixed - he's in demand. The music shop tech won't fix stuff if you didn't buy it there and it's not under warranty - or at least they wouldn't a couple years ago. It's usually a minimum 2 weeks in the shop though, due to backlog. That's a long time - but it's okay playing through my GK. I can't find my last work order so I can't remember if I use EL34's or KT66's I think EL34's.....
 
Finally got hold of the shop - same guy is still in business (no surprise considering the demand). I'm sneaking out at 3:00pm to go home and get my head and drop it off at the shop before he closes at 4:30. I'm still thinking it was EL34's installed in there... the other type possibility was 5881 from my research...
 
Yup, 5881s are common for those amps. Your tech will know which one's to use. Have you changed your preamp tubes lately?
 
The tech at the music store put a new pre-amp tube in 2007. The last tube was a power amp tube probably 3 years ago. I always ask them to test all the tubes while they have it in the shop.

Here's the repair from 2007 - The last guy rebiased the amp in 2009 (?) cause he said the bias was wrong and it would burn out tubes quicker. I think the setting was in the 40's but I'm not sure. I'll post the repair details when it's done - that way I have a track of it for futre reference like the one below.

Repair Details from 2007:
Replaced second preamp tube.
Replaced low voltage supply zener diodes and master volume switching opamp.
Replaced factory installed (in 1990) 56K bias resistor with 47K bias resistor as per 1994 schematic to lower increase the negative bias voltage from -50V to -38V to properly bias the EL34 tube configuration.
Resoldered misc components and organized wire layout to help with noise further.
Rtv’d misc components.
Test ok

Mesa Boogie 12AX7 preamp tube 13.95
YSL Marshal Part Valvestate IC M5201 5.95
YSL Part 1N5245B 15VO OW5 Z (2) .50
YSL Part 1/2W 47K5 T&R RES .25
Repair Labor (60) 65.40
Subtotal 86.05
GST 5.16
Total 91.21 (CDN)
 
Here's the post from 2009 when I last got a tube check up:
Tech checked the tubes on a tube tester and they all seemed okay. But tapping on the tube created a fluctuation and I guess the static. Replaced an EL34 tube and did a thorough cleaning and checkup of all the sockets, jacks and switches. I fired it up for 1/2 hour and seems okay - no static and tone is good. Seems a little louder and more sustain.
He also mentioned that he turned down the voltage from 42 to 35 as 42 is too hot and will burn out tubes faster. Maximum is like 43 or something and 42 is the setting recommended in the specs but that's if you buy Marshall original type tubes - the kind that came with the unit originally - which are long gone so no idea what brand/style. Doesn't seem to have any bad affects reducing the voltage. $204.......
 
Dropped it off at the shop - told him what he did last time as it's the same problem.We chatted about the bias and stuff and what the various settings will do to tone and tube life - interesting. Should get it back in a couple weeks maybe sooner....
 
That all sounds right. Many Of those 900s need a resistor changed to run EL34s properly. My first 900 was way cold when I got it. It was biased it at 16 or so. I kicked it up to 36 and it sounded way better. It depends on your plate voltage and the tubes but 30-39 is a good range for EL34s in a 900 IMO.
 
Man, I gotta retube my whole twin (something like 12 tubes total), the power tubes in my Dr. Z and Orange.

I need a part time job for a month to get these going.

Also, most amps come biased pretty cold from the shops. I don't know what most techs will do, but I like to get them pretty hot. They wear out faster (supposedly, I haven't noticed since I haven't done a comparison), but the sound is usually significantly more "tubey" with a hotter bias.
 
I have new power tubes for my Super Reverb on order. New tubes are like a fresh shave or a haircut; kind of a PITA maintenance to deal with, but you feel so much better once it's done.
 
With all these new tubes on the way, this would be a good place to post some tones.
Just sayin' ;)
 
Telegram Sam said:
With all these new tubes on the way, this would be a good place to post some tones.
Just sayin' ;)
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When I receive them and get them biased, I'll post some. Maybe I'll post some of the old ones for comparison, too.
 
IMG.webp
Amp is ready - picking it up after work. I'll try and post what he did when I get the invoice listing. He did a lot of things trying to recreate the crackle - but I don't think he ever did get it.

He did get a hum eventually (wonder what he did to create a hum which wasn't there orignally lol... and saw a power tube getting fireworks (as he called it) thus replaced it and it's match (Electroharmonix EL34).

The holder for one of the pre amp tubes busted taking out the tube so he had to fix that. Thorough cleaning, resoldering circuit board, two new power tubes. Said the bias has moved up from 35 to 38 so he moved it back to 32 for now.

Since I don't gig anymore I think it might have made sense to let the thing get worse before bringing it to him so it would be easier to find the issue. I still say it's always tube related when it starts to crackle like it did.

$224 including tax. I think that's about the same as last time with one more tube added.
 
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So I played it for a for a few minutes and it's back to normal... Have to find that picture of my amp settings I posted. It sounds good but just want to make sure...

rayc - I can't find my settings picture - do you still have a copy? Can you post it here or email me if you do ?
 
So what tubes did you get? I can't read that chickenscratch handwriting. :D
 
I don't think "crackling" is necessarily always a sign that it's "time to put in new tubes".

During the summer/humid months, you can get oxidation and a little condensation at the pins/sockets.
I've dealt with it many times. You can have the same thing happen with microphone XLR pins.

Pull out the tubes and apply a little deoxit on the tube pins, work 'em in/out a couple of times...done. Apply some also to your jacks, and pay attention to jacks that have a grounding spring/contacts, since they can weaken/bend with use, and if that grounding is not connecting/disconnecting cleanly with the insertion/removal of a plug...you can get ground noises, etc. If there are dual/quad input jacks, check them all, not just the one you use mostly.

If the tube pins look a bit crusty...a brass wire brush first, then the deoxit...but the amp would need to be in a real bad area, like near the ocean where you get the humidity + salty air.

Anyway...next time before you drop $225...try that first. :)

Some folks get crazy and swap tubes like guitar strings, but there's really no need to, and sometimes the amp sounds different/worse than before, depending on the tubes. :(
 
Greg - he put in a matched set of Electroharmonix EL34's . He said one of them was running at 17mv so it was really low. The other one was okay but he figured a matched set was the way to go. I'm not a tech and I don't mind paying for him to spend two days bench testing this thing, cleaning, soldering etc etc. I'm contributing to the economy/small business and I know he does a good job. :D
 
ido1957 said:
Greg - he put in a matched set of Electroharmonix EL34's . He said one of them was running at 17mv so it was really low. The other one was okay but he figured a matched set was the way to go. I'm not a tech and I don't mind paying for him to spend two days bench testing this thing, cleaning, soldering etc etc. I'm contributing to the economy/small business and I know he does a good job. :D
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Those are good powertubes. 17ma is way cold for your amp. I bet you notice a difference on the good side.
 
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