New Production 6550 - any thoughts on reliability?

[Milkmansound]

I had two amps fail with Ruby 6550 this week, and had to talk two customers off of ledges. I think its time to try a different brand.

I know JJ and EH make them - anyone have experiences?

The Rubys are awesome until the envelope loses its seal.

[eddie25]

I wouldn't say the EH 6550 tubes are the most reliable either. I've had a few that didn't last long at all in a dual rail bass amp (running close to, but safely under max voltages). They are just about the only EH tubes I really like when they work though. I had a dud JJ KT88 as well recently, and it was a 24 hour burn in. That made me kinda sad since I was really looking forward to those tubes and it was the first set I ever tried.

What's the screen voltage in said amps?

[statorvane]

I've finished an SE amp with a 6550 around November time frame, and have been playing it exclusively since then. Probably 4 hours/week. It is cathode biased, plates at 325, screens at 275. No problems and it sounds really good. Much fuller than the EL34 that preceded it. It is a Tung-Sol RI 6550.

I am going to try a Sovtek 6550WE and another Tung-Sol. I intend to use the extra Tung-Sol in another amplifier build for my son. Basically - no complaints with the Tung-Sol RI. I haven't looked into any KT88s yet.

[Stevem]

Tung sol reissues and EH tubes are all Sovtec made, if I had to put money on how many rejected tubes out of say 100 from Sovtec and 100 from JJ, my money`s on the JJs having less poppers!
Also in regards to customers amps, once they leave your hands you have no control, they could send the amp bungee jumping, or strap in into a paint shaking machine and you would never know!!
Look at how offten reverb pan springs give up the ghost from vibration and that metal is far more hardy then the grid and screen wires in a tube!!

[mhartman]

I like the Tung Sol reissues. Also, for what it is worth, I believe that Brandon is using the Tung Sol 6550s in his Hi-Plains Drifters.

[rp]

strap in into a paint shaking machine

Hey, that's how I get my BIG vibrato!

[Milkmansound]

Thanks all. I guess I'll let him try the EH tubes

I always try and upsell to NOS - and this particular customer almost went for it. It's like driving your new Explorer on the Firestones using the new prod stuff.

Thankfully the amp techs of the world generally know their stuff and can reassure that it's not the amp being unreliable in any way, just the tubes.

[billyz]

I recently retubed a svt running 700+ vdc on the plates with 385vdc on the screens. Used a matched set of EH 6550. They were very well matched from New Sensor. Handled the voltage no problem. Sounded very good. It's been 3 months now and no issues. I'd put my money on the EH 6550.

[Firestorm]

I've killed some new production 6550s (I think they were actually SEDs). Very sensitive to grid resistance. I don't think I really had to go all the way down to 50K, but probably not above 100K for sure.

[billyz]

I've killed some new production 6550s (I think they were actually SEDs). Very sensitive to grid resistance. I don't think I really had to go all the way down to 50K, but probably not above 100K for sure.

I think the grid load depends on a few factors. I recently converted a VHT from el34 to eh kt88 and used the standard Marshall specs of 150k grid loads , biased as a 30w tube , 1k screen resistor , plate was around 495vdc. A real design engineer would know the primary impedance of the ot amoung other things. Anyway it has worked well , if you like that sort of thing (I prefer the el34) . But this was a preamp distortion rig.

[Leo_Gnardo]

I know JJ and EH make them - anyone have experiences? The Rubys are awesome until the envelope loses its seal.

Ruby/Magic Parts is a rebrander. Nothing wrong with that. They test batches of tubes & mate 'em up in pairs & quads. Also they're pretty good at culling bad tubes and not passing them along to customers. One of the things you can't much test for is - 'is the tube going to lose its vacuum sometime in the near future?' I'd have to chalk it up to rotten luck, to have two 6550's, of different brands, go "white inside" within a couple days of each other.

If you're within Ruby's warranty period I'd let 'em know what's up.

[Milkmansound]

I have a great relationship with Ruby - and yeah, they rebrand and offer an incredible warranty. I am not upset with them in any way - I think its just luck.

[matt h]

(deleted)

[talbany]

Thanks all. I guess I'll let him try the EH tubes

I always try and upsell to NOS - and this particular customer almost went for it. It's like driving your new Explorer on the Firestones using the new prod stuff.

Thankfully the amp techs of the world generally know their stuff and can reassure that it's not the amp being unreliable in any way, just the tubes.

How are you running the screens? and at what load?

' I'd have to chalk it up to rotten luck, to have two 6550's, of different brands, go "white inside" within a couple days of each other.

It is very easy to tell if you are exceeding the screen dissipation. Simply look in the holes in the plates and see if the screen grid is glowing (don't confuse it with the filament). Typically, the screen will glow a bit, and the glow will get brighter as you play harder. If the glow is bright orange or white at idle, or gets very bright when playing hard, you are definitely overdriving the screens. The solution is to lower the screen voltage, which is most easily done by raising the value of the screen dropping resistor. You can go as high as 2K or 2.5K, although higher values will change the tone a bit (but sometimes for the better. Over 300V on the screens is pushing it!

Tony

[Milkmansound]

Did the "white inside" follow with the same socket?

Having two lose vacuum, if it were in the same position, would lead me to believe atypical stress was being put on the tubes, possible (likely) at the pins. Heat and cooling, expansion contraction.

I'm not sure. They are different amp models.

I am pushing 300V on the screens for sure. Maybe my luck just ran out