Tung-Sol 6550's - blown up (PIC)! Reliability thoughts?

[PM33AUD]

Hello,

I was on my second set of (properly biased) TS6550s when this happened:

When the amp freaked out I looked in the back and saw a hairline crack all the way around the glass. When I took the retainer off to remove the tube, the top fell off. lol. I like to think they just couldn't handle the insane playing

The first set was just making some scratchy noises every hour or so (very intermittent but still unacceptable in a recording/working amp) so I bought a second set. The first pair were only about 6 months old. I got about 2 hours of playing with no problems when ^^^ that happened. Never have seen this EVER in all the tube amps I've worked on/built/used/etc...

Anyone else had any issues with these? I am thinking I will stop using them 0/2 over 6 months isn't good odds!

Phil

 

[glpg80]

thin place in the glass + heat = cracking

pretty cool, thanks for sharing. odd to see it happen, you know every one of us have at some point wondered if it was possible

 

[glpg80]

According to most tube data sheets for 6550's, they can only handle 400 - 440 volts on the screens and 680 volts on the plates.

As with most power tubes the screens are the weakest link. In the NOS days many amps ran the screens higher than 400volts but those were NOS tubes which generally were conservatively rated. With current production tubes who knows what they really can take.

In most guitar amps that run these tubes, they can be in the area of 460v to 500v on the plates and the screens are usually only a few volts less.

NOS tubes usually could handle with no problems exceeding design specs and this was done quite a bit with tube amps in that era. But today's current production tubes are just not built as well and the data sheets on them are just re-prints of the old data sheets of the good tube days.

do you have a vacuum tube tester? it would be nice if someone could measure a few of the current running designs and figure out design spec's of today's lesser quality tubes.

 

[JTyson]

Not that this is relevant, but your amp blew the top out of that tube! THAT'S METAL
sorry.. Ive never seen that happen in 35+ years. Put some SED's in that thing, it will be fine

 

[glip22]

Only speculation so no offense. You may be biasing too hot. Regardless that these are rated at 35 watts, you can only use a max of 28 watts maximum plate dissipation when calculating a safe range to bias these at. Especially in amp where there is more than 450 on the screens. If your amp is putting 460v on the plates my bias would be no higher than 36 ma. If you bias up past 60% you're asking for failures with these and most new production 6550 tubes. The SED's are better as they can handle the current better than the Tung Sols. I ran a few quads of these at 460v on the screens and they held up fine.

 

[JerryP]

What amp are they in?
Are you running an attenuator?
Are you running a fuzz pedal or heavy distortion?
Is your impedance matched for the speaker you're using?
Jerry

 

[Jeff Hilligan]

If they were in your Avatar MOD 50 then the plate voltage is close to 500 volts. That's the max on Tungs.

 

[moltenmetalburn]

I had a dsl 100 when they first hit the market, number 49 to be exact. One day the amp sounded better than ever, it quickly began red plating ad the glass of the tube melted all over the socket and chassis!

 

[Rampage]

I had this happen to an Electro Harmonix 6550 in my 2203 a few weeks ago. Perfect cut around the glass.

 

[MrDan666]

Did the tube redplate before this happened?

I had a set of tubes redplate in an amp once years ago, and by the time i saw it happening the amp luckily blew the fuse. When i removed them, the glass was completely out of shape and had caved in at one side. In some cases, if it happens for long enough the glass will just break.

 

[killertone]

I had this happen to an Electro Harmonix 6550 in my 2203 a few weeks ago. Perfect cut around the glass.

Hmmm. EH and TS are made in the same factory...coincidence?

This is why I refuse to buy the New Sensor relabled reissue crap.

 

[Ventura]

I am somewhat behooved by this all.... I mean, that is a perfect, near surgical cut around the tube in the glass!?!?!?!?

I can understand inconsistencies resulting is breakage, or shattering, or spider-web cracking, or something more "chaotic", but this?? This is just uber funky to me!! Seriously, totally weird. I'm perplexed.

Mo

 

[PM33AUD]

Yea, normally I bias amps and calculate the dissipation and compare it to the datasheet however the mod50 is designed to not have to crack it open to bias for different tubes, I just followed the manual which states 35-45ma for 6550. The levels others with mod50's and the TS6550s have been reporting 45ma (on the high side).

Hmmm, now looking back, that's a pretty wide range. The Mod50 has test points on the back but for current only so w/o knowing the plate voltage, your pretty much in the dark. Oh well, that's what I get for being lazy. The tubes didn't redplate, but I typically keep the amp facing with the front towards me

Anyway, anybody have recommendations on a decent sounding RUGGED tube? I am looking at only EL34s or 6550s for this amp. I really can't have tubes failing on me and, yes, bias was likely on the high side but the tube still should have held in there for longer than 2 hours. At 80 bucks a pair, they aren't the cheapest either.

I have the chassis removed so I'll measure plate voltages on this amp just so I know for the next set )

Phil

 

[glip22]

Yea, normally I bias amps and calculate the dissipation and compare it to the datasheet however the mod50 is designed to not have to crack it open to bias for different tubes, I just followed the manual which states 35-45ma for 6550. The levels others with mod50's and the TS6550s have been reporting 45ma (on the high side).

Hmmm, now looking back, that's a pretty wide range. The Mod50 has test points on the back but for current only so w/o knowing the plate voltage, your pretty much in the dark. Oh well, that's what I get for being lazy. The tubes didn't redplate, but I typically keep the amp facing with the front towards me

Anyway, anybody have recommendations on a decent sounding RUGGED tube? I am looking at only EL34s or 6550s for this amp. I really can't have tubes failing on me and, yes, bias was likely on the high side but the tube still should have held in there for longer than 2 hours. At 80 bucks a pair, they aren't the cheapest either.

I have the chassis removed so I'll measure plate voltages on this amp just so I know for the next set )

Phil

Yeah Phil, At 490 on the plates the Tung Sols are not the best choice. My bias would have been 33-34 ma on the hottest tube. No higher. I am one who is now carefull after taking out two OT's in amps. The fuse doesn't always do it's job.

 

[JTyson]

Yea, normally I bias amps and calculate the dissipation and compare it to the datasheet however the mod50 is designed to not have to crack it open to bias for different tubes, I just followed the manual which states 35-45ma for 6550. The levels others with mod50's and the TS6550s have been reporting 45ma (on the high side).

Hmmm, now looking back, that's a pretty wide range. The Mod50 has test points on the back but for current only so w/o knowing the plate voltage, your pretty much in the dark. Oh well, that's what I get for being lazy. The tubes didn't redplate, but I typically keep the amp facing with the front towards me

Anyway, anybody have recommendations on a decent sounding RUGGED tube? I am looking at only EL34s or 6550s for this amp. I really can't have tubes failing on me and, yes, bias was likely on the high side but the tube still should have held in there for longer than 2 hours. At 80 bucks a pair, they aren't the cheapest either.

I have the chassis removed so I'll measure plate voltages on this amp just so I know for the next set )

Phil

SED's =C=
They run at 495V in my modded Metro Plexi, had the same set in there for over a year doing 6 hour sessions every couple of weeks
No problems yet, best sounding EL34 I've heard

 

[PM33AUD]

Do you like KT88's?

Never tried em!

 

[killertone]

Never ever had a problem with any SED 6550s. They sound killer in the Evil Pumpkin and also work awesome in my 77 JMP with 480 volts on the plates. The most rugged 6550 and best sounding, too.

 

[Nigel Tufnel]

I've noticed that the glass bulbs on some of the big bottle New Sensor tubes have this kind of spun look to them. It looks like little horizontal lines in the glass from however they make them. That might be why it was such a clean break. If the springs on your tube retainers feel super tight you can stretch them out a bit to try and lessen the strain on the glass, do it a little bit at a time to make sure you don't go too floppy. Just to be clear I'm no New Sensor apologist, it could very well be a flawed tube, don't even get me started on that.

 

[parntz145]

I have used them in many of my Marshall's and never had a problem. I really love the tone of the Tung-Sol 6550. I just ordered a matched quad of them for my 83 JCM 800 and the PV is 468. Is am going to set the bias a 52. You guys have me nervouse now. think they will be ok?

 

[PM33AUD]

I have used them in many of my Marshall's and never had a problem. I really love the tone of the Tung-Sol 6550. I just ordered a matched quad of them for my 83 JCM 800 and the PV is 468. Is am going to set the bias a 52. You guys have me nervouse now. think they will be ok?

If our plates are about similar, then NO! I was only biasing them around 45ma and went through 2 sets in 6mo. They do sound good, but I'm sure there's more stuff out there I haven't tried that may sound even better and are more robust.