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Old 22nd October 2009, 05:45 PM   #1
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Default 6L6GC -Which Shuguang can take the Heat?

Hallo fellow Tube-beaters.

I enjoyed reading on these pages about how the Shuguang 6L6GC can take high voltage and heavy power handling, and still keep playing the gig.

So I bought some new Shuguang 6L6GCR. When I opened the box I was really surprised to find valves built very like the old Russian 6P3S (an old 6L6G-A /-B equivalent with 19W anode and 270V max screen voltage).

Sure enough, when I found the data sheet, it's rated as 19W/270V:

Shuguang 6L6GCR(6L6G) Vacuum Tube - Vacuum Tube Datasheets - HiFi Audio DIY Forum AnalogMetric Hi-Fi Audio DIYer Forum - Powered by Discuz!

These are built nothing like the Shuguang 5881A, which is constructed like a real 30W 6L6GC (30W, 450V screen max.)

So the question is - are these Shuguangs the real tubes folks have been running at 500V? Have I got the wrong part? If you run the screens at 500V in a guitar amp, don't they blow up at the first chord??
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Old 23rd October 2009, 12:50 AM   #2
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They look like the same GCR's I've used in my RA-100 amp,at ~640V B+..There hasn't been a failure with those tubes,yet. I should mention that they've only been run in that amp for a handful of hours,so far.
Pic 1
Pic 2

Last edited by DigitalJunkie; 23rd October 2009 at 12:56 AM.
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Old 23rd October 2009, 01:37 PM   #3
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Digital - thanks for the pics. What kind of architecture is the amp? Triode UL, or Pentode connected? I'm very interested in how much of that 640V is getting to the screen grids...

I guess it's biased fairly cold, too?
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Old 24th October 2009, 02:02 AM   #4
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It's UL,so it's all on the screen grids. IIRC,during intial testing it was running in the 45-55ma range(30+W!),and the tubes were getting fairly red.They appear to be able to take a fair amount of abuse,though I wouldn't condone it for long periods,but you can 'push' them a little bit. I think the point where they start to blush was about 25W.
There are some more pic's and videos there on my photobucket site.
Here's a pic of one running ~30W: Red plate

I think Tubelab (George) has punished these tubes a bit also,perhaps he can give some more data.
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Old 24th October 2009, 06:08 AM   #5
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I'm under the impression Tubelab's work with these has revolved around driving the hell out of G1, and keeping DC idle below the cherry-anode potential. Not sure, though. Are the G1 supports as big as the other grid/anode supports? Are there little square metal "flags" attached to them?

If so, I think MOSFET, cathode follower, or other current driver in front of G1 would allow A2/AB2 operation and thus more power.
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Old 24th October 2009, 11:09 AM   #6
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Default Shuguang tubes

still need to take care about their tubes despite they are a LG - Philips joint venture in Changsha, Hunan. We have done some evaluations about the tubes and manufacturing, not all was found ok. They promised improvements. They improved a lot the last years, but with the ongoing economic recession they are ander pressure as well. I am in China as electronic engineer since more than 11 years, watching , what happens and consulting manufacturers. The Shuguang 6L6 GC may not take the full plate voltage as stated unless they improve production / vacuum etc. Pls. remember, the workers salary there is around 150.....200US$ there / month or even less.
There , for example, it was normal, to write with a graphite pen on the insulating mica sheet, thus reducing, the creepage betwenn G1 and G2 / Plate, which was going to arc later in the (power) tubes. if the request / performance (and voltage is not too high, the Shuguang tubes are not so bad. ) They also tend to blacken faster at the glass from heater wire evaportion, or creating a brown coating inside the power tubes caused by lead in the glass close to the mica sheet.
The russian tubes ( EH, Sovtek, Svetlana, etc., regards to New sensor corp.) in average still are built much better than the chinese, this also applies to chinese NOS and Chinese army types.
We have them all here, and tested.
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Old 24th October 2009, 11:22 AM   #7
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Quote:
Originally Posted by DigitalJunkie View Post
There are some more pic's and videos there on my photobucket site.
Here's a pic of one running ~30W: Red plate

I think Tubelab (George) has punished these tubes a bit also,perhaps he can give some more data.
Great Pics! thanks for sharing them. So that's running the screens at 640V on a tube with 270V max rating! Is that the record for spec-busting?

M6tt, the grid mounting has the same single 'flag' radiator as the Russian 6P3S (old sort, not the -E) which is also a 19W valve. The others, including the shuguang 5881A have a pair of larger flags.

Question is - can the Russian 6P3S (old type, built with the same structure as the shug 6L6GCR) take high voltage as well? Would I dare put a pair in a 500V fender??
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Old 25th October 2009, 01:01 AM   #8
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Default Shuguang

the russians gave the chinese some technology, maybe even some tooling in the past. what they could not give them, was experience and accuracy. ( this is still the chinese problem today! ) So, for example, the vacuum was not so good in many tubes, too short pumping, etc., or sloppy assembly and adjustments were just normal in some factories. We have had EL34s arcing at 425V in 2007 after 100 hours working.
same construction does not mean same quality.

just recently, shuguang put a new, better vacuum pump into service.
inside china the chinese 6P3 types are sold for approx. 4 US$, and no one buys them...

so, if you want to know, try the shuguang at higher voltage. i recommend fast fuses for the plate and G2 to protect the output transformer.
ofcourse you will re-adjust the bias.
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Old 25th October 2009, 01:55 AM   #9
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Quote:
Great Pics! thanks for sharing them. So that's running the screens at 640V on a tube with 270V max rating! Is that the record for spec-busting?
The pics are a bit blurry,but you can get the idea.
I don't know if that's a record for spec-busting,but they are definitely being run quite far over specs,and haven't had a nuclear meltdown as of yet,It may be just around the corner though. I haven't used that amp in about 2 years now,with moving,and still needing to get a new bench setup and everything. Real Life gets in the way sometimes.
I plan to dig it out at some point in the future,and finish up a few tweaks,and put it into normal use.. I'll let ya know when that happens.
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Old 25th October 2009, 03:34 AM   #10
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Quote:
I think Tubelab (George) has punished these tubes a bit also,perhaps he can give some more data
Quote:
I'm under the impression Tubelab's work with these has revolved around driving the hell out of G1, and keeping DC idle below the cherry-anode potential.
I first found out about the Shuguang "Coke Bottle" shaped 6L6GC when Antique Electronics Supply was selling them for $7.95 each and claiming "we couldn't blow these up no matter how much we tried". That was 5 or 6 years ago. I bought a pair and found them to be pretty tough, and capable of handling 25+ watts of dissipation. They are still around here somewhere, but I think I did blow one of them up when I accidentally put about 500 volta on G1.

About a year later a friend brought me a Fender Bandmaster and wanted it retubed and rebiased. I pulled out a set of the same Shuguang coke bottle 6L6GC's that were branded "Ruby tubes". These tubes had seen about a year of use in a Bandmaster that was used 10 to 20 hours a week at nearly full volume.

They sat around my workbench until I needed some guinea pigs for the Simple SE development. During that time they were blasted hard and heavy at plate dissipations up to 45 watts! Yes that glow brightly at 45 watts. These well used tubes ate all of the abuse that I gave them for several months of continued operation in SE (triode and UL) at plate (and screen) voltages up to 500 volts (440 to 460 across the tube).

This same pair of tubes are STILL ALIVE and working well although the glass has darkened in some areas. They were recently used in my P-P AB2 experiments where they delivered 90+ watts without any distress. Yes, this test (and my AB2 driver) is designed to extract maximum power from a pair of tubes without abusing them, in contrast to some of my other experiments.

Back when I got the used tubes from the Bandmaster, I called AES looking to buy some more of them. They told me that they were no longer made. I called ESRC and got the same story. I bought 4 pairs of them on Ebay for $6 per pair knowing that they were likely factory seconds, but they all worked well, and are all still alive. They seem just as rugged as the old Rubies.

I got some of the 6L6GCR's about 3 years ago. Internally they look just like the old Coke bottles, but they dont like my abuse tests. They show signs of red plate at 24 to 28 watts and they are not all consistent. AES is now selling the "Coke Bottle" tubes again. I have not tried them but several users report possible issues with these too.

It seems that the Shuguang tubes are built in batches, and they may not be consistent from batch to batch. I bought the majority of my Shuguang tubes about 3 to 5 years ago. I have not had a failure in any of these tubes ( including a pair of 211's that see over 120 watts), but the current crop seems to be met with inconsistent reviews.

I tried some of the early Shuguang KT88's when they first appeared about 10 years ago. These tubes remind you that the Chinese invented fireworks, and I even had one spark out so violently that the glass shattered! They will all red plate at 25 watts or less. I still have about 25 of them, but I will only use them for "experiments".

I am attaching two pictures. The first is the old Rubies cranking along at 44 watts of dissipation. I doubt that they would live for long at this level. Notice that the entire finned section on both sides of the plate are evenly glowing. This is good. It indicated that the current density is evenly distributed throughout the tube. A tube that has hot spots or one side hotter than the other side is not well constructed. This means that a small area may be handling the majority of the current, leading to a short life if pushed hard.

I have not tested their 6L6GC's but I have been impressed with the new Electro Harmonix KT88. I have cranked 50 watts through them without glow.
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File Type: jpg FirstTest6L6GC.jpg (160.6 KB, 666 views)
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