Did I destroy my tubes.....?

[Jaded Faith]

I have a sinking feeling on this one, but here it goes.

On Monday, a tube failure light lit up for an EL34L in my RT2/50 that was only a week old. Replaced the fuse, kept playing. All seemed well. Then it failed again. I checked the bias and the tube that failed was way off. Like 11mA.
I had suspicions that my multimeter was "off", so I bought a new one from work.

The tube in question wouldn't bias any higher than that and the JJ logo turned from red to black....sounds fried right?

Then I had a look of horror and though about my KT88's that I had biased with the old meter...and two pairs of 6L6GC's....... :shock:

So I now have 3 pairs of tubes that bias "strangely". All have the same issue. It appears the previously matched pairs are far off. Say I set test point 1 to 40mA. I'll go to check test point 2 and it will read around 79-90! I'll bias that test point down to 40, but then point 1 has dropped to around 20. All three sets seem to now have this 20-27mA mismatch. Does this mean they are now junk?

FWIW, I checked the old meter against the new one and it was about a mile off. I think I may have bias these 3 pairs so hot I reduced their life from 6-12 months to 7 days. Thoughts?

I did place 2 new sets of 6L6GC's in tonight and they bias right on and are within 0-3mA apart. Sounds like the amp is ok and the tubes are toast.

 

[jmgman70]

From what you are saying,the new ones bias up correctly and I would tend to believe the old tubes are now bacon!

 

[Dallas Marlow]

Well, it sounds like you just fried the **** out of the tubes. From what I understand once a tube red plates, its gone, there is no going back and it can and will generally take out it's other tube pair if you don't catch it fast enough.

It sounds like you red plated a tube to me if it turned the JJ logo black.

I'd say just scrap all the tubes in question rather than trying to salvage them, if they are damaged they could potentially throw anything else you pair them up with way out of wack too.

The good thing about a tube amp is 99% of the time the problem is the tubes, so it sounds like your amp is ok! Just be thankful for that and toss the toasted tubes!

Dallas

 

[Mailman1971]

Doesnt the Fuse blow first before the tube blows? That happend to me the tube started to get REALLY bright, but the fuse blew. Took me a few times to learn to Bias, but now after several tries and SEVERAL fuses, and learning to read that DARN Mulitimeter with all the Settings.....I can do it effortlessly in the middle of practice. That RM100 is the BEST!!!!!!!
No more dropping off at the Music shop to do a 5 minute job!

 

[khingpynn]

Red platimg can mean death to a tube but not allways. Sometimes Tubes red plate and if caught early can be biased and do well.

This happened to me. My Koch multitone started humming... the humming was getting louder... turn off amp right now... as I'm turning off the amp I take a peek and one tube is cherry red... did not blow a fuse.

After cool down I pulled the chassis and got set up for a bias... Randall has the test points on the backplate of the MTS... why doesn't everyone do this??? Since I'm a die hard no modifications guy I'll leave it... anyways I did a bias and the tube was out for whatever reason something changed inside the tube and values changed with it. I have been running the same tubes for a year now with no other problems and the tone is just excellent on the Multitone.

Another incident I had was with a set of 5881's in my Soldano. I'm happily playing along and bam... lightning storm inside one of the tubes... crackle can be heard from the speakers... turn amp off... no blown fuse... cool down and pull chassis... set up for bias test... everything biased normally... operate amp again with no problems but am concerned that blue lightning inside a tube may cause damage to the tranny... pull tubes and throw away.

Craig

 

[Dallas Marlow]

Your correct when you say red plating may not ALWAYS mean a tube is totally done for, however; just to save him time and headache I'd say toss them on the chance that he really did fry one theres no point in risking trying to test it to blow up another in a pair. That's all I was getting at you know?

Sometimes blue inside tubes is normal for their operation depending on brand etc. However; I recall reading something that once a tube really becomes blue inside it's because some failure inside of it... it's not the vacuum being lost I don't think because that causes total failure. I can't recall what it is exactly.

 

[hotlicks2go]

They may work but are no longer matched. Thus dont bias very close. I highly recomend replacing with a matched set and rebiased for best sound quality and better life expectancy.

 

[Jaded Faith]

Thanks for the replies guys. I wound up tossing the suspect tubes. Two pairs of 6L6GC's, a pair of KT88's and one EL34L. I only lost out on about $90, since several of these came with the amps from previous owners. On the upside, the amps are now set up with good sets of tubes and biased with the trusty new meter and sound great. Not as AMAZING as they did when biased 70mA too hot, but still pretty good! :wink:

I have 5 new pairs of power tubes on the way for Monday delivery. Two pairs of JJ EL34L's, a pair of Tung Sol EL34B's, a pair of Tung Sol 5881's and a pair of EH KT88's. Liked the JJ EL34L's, but the rest are all first time buys for me. I have heard good things about the Tung Sol 5881's and I think Maximus swears by the EH KT88's, so I look forward to hearing them. Anyone have opinions on these? Specifically the EH KT88's compared to the JJ's? Loved the JJ's, but I hear a lot of great things about the EH's and they are much cheaper.

 

[Mailman1971]

I was running Sovtek KT88 in my Lynch box and when I was playing alone at lower volumes, it was sounding so SWEEEET! When I got together with my band and played at loud levels, it was SOOO MUCH POWER that it was killing out all the other players! I ended up switching back to the EL34 but was thinking of KT 77's. Anyone here have these in there amp?

 

[Ugg]

Jaded, let us know how you get on with your new tubes, especially the KT88's.

I recently picked up some new JJ 6L6's, SED EL34's and TungSol 5881's for my RT2/50. Not liking the SED's so much but the JJ's and TungSol's are rockin'. The 5881 is an in-betweens sound that has some bass like the 6L6 and some mids like the EL34. IMO, for the RT2/50 I think I still prefer 6L6 and EL34 for more of a tonal difference between channels.

 

[Jaded Faith]

Tried several pairs last night. I am at work now but I'll try the rest tonight and give you a review. Some very interesting findings so far though!

 

[Jaded Faith]

Tried them all here's what I found:

JJ 6L6GC: Biased at 40mV. Awesome for cleans and adds a natural scoop to the tone for metal high gain rhythm tones. Lots of lows, scooped but present mids and good smooth top end.

JJ EL34L: Biased at 35mV. Perfect for the Marshall crunch tone. Mids are crunchy and smooth at the same time. Good low end and more in control than the 6L6GC, tighter if you will. My second favorite for lead tones. Passable on cleans, but not as good as the 6L6GC.

Tung-Sol 5881: Biased at 35mV. Similar to the 6L6GC, but some notable differences. The lows were tamed down, the mids more present (particularly the upper mids) and the highs were the most present of all the tubes. I found I rolled the Presence back a notch or two with these. They have an airy 3D quality to them. They didn't sing as well for leads as the EL34L's, but the mids were less compressed and better for solo work than the 6L6GC's. I think this is because they don't overdrive as quickly as the EL34L's.

Tung-Sol EL34B: Biased at 35mV. Almost twice the price of the EL34L, but wow what a tube! The biggest surprise out of the bunch. These tubes have the best Marshall crunch and singing mids for lead work out of any of these. Good lows, amazing mids and smooth highs. Really worth trying a pair.

EH KT88: Biased at 49mV. These tubes sound huge. They do the best job out of all the tubes mentioned of covering clean, mid-gain, high-gain and lead all in one. Lots of lows, present crunchy mids and smooth singing highs. I had a pair of the JJ KT88's and they were twice the price. These sound different, but as good with their own flavor. At half the price, I would buy 2 sets of these next time before buying 1 set of the JJ's. Great value.

I also tinkered with some preamp tubes. By far and away, I prefer JJ ECC803's on the chassis of both my RM4 and RM50. I tried EH 12AX7's and Tung-Sol 12AX7's. I will try the Tung-Sols again, but for now I have settled on JJ ECC803's Gold Pins in V1, JJ ECC803's in V2 and Balanced JJ ECC803's in V3. On most high gain modules I am running JJ ECC803's in V1 and Tung-Sol 12AX7's in V2. This pairing is great, with the Tung-Sol balancing the aggressive character of the JJ's perfectly. I use a JJ ECC81 in V1 on my Deluxe for less gain, but I can still get plenty of dirt if I dial it in.

I currently have the EH KT88's and Tung-Sol EL34B's in my RM2/50. I will probably try the 5881's in place of the KT88's though, maybe the 6L6GC's. Either pairing will be a great contrast for the switching feature of that amp. The RM50 will most likely run the KT88's, as they do the best job of covering all the tones well.

Hope this helps some of you and I would love to find out what you all have found to be the best bias points for these tube types. I love these amps. 8)

 

[RockManiac]

Thanks for the review. I use the TungSol 5881 in one channel of my RT2/50 and love it. The other channel runs with JJ E34L. I am also happy with this one for Marshall tones, but want to try the TungSol EL34 next.

I also love the JJ 803 in my M4, use it in V2 together with a Chinese 7025 in the Bassman module and in V2 together with a TungSol 12AX7 in the Vox module.

The more I play these amps, the more I love them.

 

[JKD]

Tung Sol are making some great tubes lately....here's hoping they prove reliable! I've lost 2/5 of the ECC803s gold pin tubes in a matter of weeks from new with one more looking far too burned out on the flashing for a new tube :-/

 

[khingpynn]

That was a great review. I'm interested in trying the Tung Sol El34B. Have not tried them yet but based on your description I'm betting I'll like them.

Craig