Plate voltage

Dave Meis · Post by **Dave Meis** » 22 Feb 2018 10:10 pm

I'm looking at a new quad of tubes for my Twin, and there's conflicting info on the plate voltage rating for the tubes . One place says they're rated 400dcv, and one says they're 550dcv. The plate voltage in the amp is 495/510 (actually measured) depending on bias. IF they are indeed rated 400dcv and I install them, should I expect shorter life (mine or the tubes)? Smoke? Unexpected oily discharge? TIA

David Gertschen · Post by **David Gertschen** » 23 Feb 2018 10:52 am

What brand/part number of tubes are you looking at? I haven't run across any 6L6GC tubes that wouldn't survive working in a Fender Twin...

Dave Meis · Post by **Dave Meis** » 23 Feb 2018 11:16 am

The ones I'm looking at are Shugang 6L6 WGC. I have a pair of them in a '65 Bandmaster, and they work really well! My Twin is the UL-135, and has a reputation for eating power tubes, but I've had good luck and long life from a variety of tubes over the years, and would like to try these (since they're $12 a shot!). I feel they have performed well in the BM, and I've run everything in it over the years, including NOS GE's, and these aren't better, but good (to my ears). Amplified Parts has them listed in the 'tube' section in the Q&A as 30w 550vdc, but in the 'tech corner' they list them as 25w 400vdc. so... I looked all over the internet, and found nothing to confirm or deny.. I called them, and they looked it over and said they could only say 400vdc because of 'lack of info'..
Pretty sure I'm gonna try 'em, but if someone could tell me 'Don't do it!'... I probably won't.
Guess the real question is: what's the worst that could happen?

Jim Sliff · Post by **Jim Sliff** » 23 Feb 2018 11:59 am

In my experience they'l handle 500V on the plates & 450 on the grids.

For a while. I won't install them nowadays because they're firecrackers at pretty much any voltage and sound....lame.

They're cheap for a reason - they're *cheap*, meaning built lightly and meant for volume sales. They are among the least robust of Chinese-made power tubes IMO.

IMO these particular tubes have nothing going for them except as cheap spares to keep on hand for an emergency. They have a "flat, clinical" sound to them with deeply scooped mids. This makes them problematic in many Fenders, which are already voiced with a "mid scoop".

And if you bias them towards the hotter side to try to get some warmth out of them you'll shorten the life even more. They also do not hold bias as well as better quality tubes. And the double-edged sword is that a colder bias to help tube life will make them sound even worse.

I would not waste my money on them. If the Twin is one of your primary gigging amps don't use cheap tubes to save money. the tone will suffer and it will cost you more money in the long run, as you'll go through tubes more quickly. If you are absolutely dead-set on them for some reason make sure the amp is up-to-date service wise (electrolytic filter caps no older than 15 years or so), have 2+ watt screen resistors installed, the driver circuit checked for balance, and the driver tube should be replaced any time new power tubes are needed in a Twin).

And if it's your ONLY amp there's no way I'd install cheap tubes. I think every gigging player should carry a backup amp, but for those that won't I recommend only NOS tubes AND JJ 6L6's as spares. For home players with one amp - well, a Twin is way too much amp to start with, but I would go with JJ 6L6's as good sounding tubes that don't strain the budget. (preamp tubes are an entirely different subject).

What tubes are you replacing - and why?

Dave Meis · Post by **Dave Meis** » 23 Feb 2018 12:39 pm

Thanks Jim..I appreciate your input. I'm currently running Tung Sol's, and I'm not planning to replace them right away. They've been in a couple of years and sound great. Just planning for the future.. As stated, these sound fine in the Band Master, but I seldom use that amp other than home. The Twin IS my go-to amp, and I keep it serviced. I'm not a fan of JJ's power tubes simply because I've had 2 failures with them..one drifted so far out of bias the amp would hum, and one shorted out and fried the fuse (bad heater?) Anyway, I like to try different things, and these seem to have thick micas, 8 contact points within the tube and dual halo getters. I can't speak to 'life', since I haven't been using them but a year, but I'm impressed enough to consider them for the Twin, but I was concerned about the voltage..which you answered (Thank you!). The other one that caught my interest was the Groove Tube 6L6GE-MP..any experience with those? I crank the mids on the Twin, so maybe that compensates?

Thanks again...

Dave Meis · Post by **Dave Meis** » 23 Feb 2018 7:43 pm

So..after thinking about it all day, and considering the info I can get (thanks Jim!), I'm gonna pass on the Shugangs. If they can't tell me the plate voltage, chances are not good I'll be satisfied in the long run. If they're rated 400 on the plates, I'll probably never get them biased to my liking...so, the search continues!

Being on Social Security, $600+ for a quad of NOS is outta reach (they ARE consumable, after all), so opinions on current production tubes are welcome. So far, JJ's have 1 vote! I gig most weekends, so longevity counts! Thanks to all!

J Fletcher · Post by **J Fletcher** » 25 Feb 2018 9:12 am

About 25 years ago, I put a quad of Sovtek 5881's in my bass amp , which had a 500 volt plate supply. These lasted many years , and finally one tube went south . Don't know if these tubes are still available from New Sensor. When they first became available a few decades ago , they were the only current production 6L6 type tube that could withstand those high voltages . Can't remember anybody really raving about the tone , but they suited me fine.

Karl Nutt · Post by **Karl Nutt** » 25 Feb 2018 10:27 am

Dave, I've been seriously considering TUNG SOL 7581A tubes for my 135 watt Twin. I haven't tried them in anything yet, but the reviews I've been reading about them are quite favorable. These are brand new "reissue" tubes. The price seems to be around $20-$25 apiece in a matched quad.

Dave Meis · Post by **Dave Meis** » 25 Feb 2018 11:20 am

Karl, I ran a quad of those when they first came out. They did a fine job for about a month, then one drifted, and the amp hummed. I called the supplier and they sent me another based on my order, I sent the suspect tube back. After that, I couldn't get the amp to run quietly. I don't know..maybe I should have insisted on a new quad. Maybe what I was seeing as bias was something else wrong in another tube. Anyway, I ordered a new set of the TS STRs, and have been satisfied with them..very quiet at idle, and sound good to my ears. I haven't given up on the 7581As, and may yet try to make 'em work..possibly by getting a new matched pair to split between the others. I check the bias of all 4, then I arrange them in pairs so the TOTAL of each pair is as close as I can get them, since the leg balance pot has been replaced in mine with a bias pot. I put the bias pot in the same position as the balance pot, so it's accessible without removing the chassis. Does yours still have the balance pot?
Whatever tubes I use, I re-bias them within a few months, and sometimes that includes re-arranging the tubes. My amp is on for hours a day..lots of hours!

. I don't think a 24 hour burn in is going to tell the story.
I don't know if this has been helpful. It really is the luck of the draw!

Dave Meis · Post by **Dave Meis** » 25 Feb 2018 11:31 am

J Fletcher, I haven't considered the 5881s because they list as 23 watts, but the 500+ plate voltage in the UL 135s has been a consideration, for sure! 23 may be enough, since there's 4 of 'em! Thanks for the info!

Karl Nutt · Post by **Karl Nutt** » 25 Feb 2018 12:12 pm

Dave, I really appreciate the helpful info! My Twin is still stock. I've had it "benched" for several years! I'm hoping to get it back up and running real soon, hence my search for decent tubes that it won't eat. When I last had it in use, it burned up one of me Winged C 6L6's from the bias being gone from that particular tube. I've started installing ceramic sockets, but have been sidelined by work, etc. I want to install the adjustable bias while I'm in there. The Tung Sol 6L6 STR tube you mention look promising as well.

Dave Meis · Post by **Dave Meis** » 26 Feb 2018 10:49 am

Karl, you might check around with some techs..I've seen setups that give you both the bias AND the balance.. might be worth looking at.