G'day from Oz,
I've just about finished a resurrection job on a Fender Twin Reverb and now just need a new matched quad of 6L6GC to finish it off.
The problem is that they run 570V on the anodes and 550v on the screens. I replaced all the 470R 2W carbon film screen resistors with 1K 5W Wirewounds which should help a bit.
I'm currently leaning toward using Svetlana tubes.
BTW bias is -62V and its one of those Fender circuits with a Output Balance control ONLY.
Any advise gratefully received.
I've just about finished a resurrection job on a Fender Twin Reverb and now just need a new matched quad of 6L6GC to finish it off.
The problem is that they run 570V on the anodes and 550v on the screens. I replaced all the 470R 2W carbon film screen resistors with 1K 5W Wirewounds which should help a bit.
I'm currently leaning toward using Svetlana tubes.
BTW bias is -62V and its one of those Fender circuits with a Output Balance control ONLY.
Any advise gratefully received.
Sch3mat1c said:...Fred Nachbaur (RIP) had an amp running them at 600V or so with no problems. Ratings are recommendations only
Long as current is low enough, you can't get red plate... red plate is dissipation.
Tim
Tim,
Maybe no red plate....at first. These newfangled tubes are not so well outgassed as the good old ones 40 years ago. At high voltages all it takes is a cosmic ray to pass through the tube, or holding your mouth wrong to encourage the residual gas to cause grid current in these crappy tubes. With normal (highish) grid circuit resistances they will go into thermal runaway and hot plate as grid ion bombardment makes the bias go away. Operating these questionable tubes at lower plate voltages (under 400) helps prevent the problem.
This is my experience so far anyhow.
Bullet proof....?
Hallo everybodies....!
Looks like HOT topic : Bullet proof 6L6GC.....
Well, if you insist to use 6L6GC, seems like you'll get the red and hot tubes... Also shorter life of those 6L6GCs... and of course, no 6L6GC can stand that voltage (refers to tube data, please... They only have plate voltage 450V and 30W dissipations)
For today 6L6GC schematic, you may use 6L6WGC or 5881, SOVTEK or Electro Harmonix.... They have higher voltage plate ratings (approx 600V), that is suitable for your schematic...
Otherwise, rcavictim has gave the solutions...
Have a great day...!
Hallo everybodies....!
Looks like HOT topic : Bullet proof 6L6GC.....
Well, if you insist to use 6L6GC, seems like you'll get the red and hot tubes... Also shorter life of those 6L6GCs... and of course, no 6L6GC can stand that voltage (refers to tube data, please... They only have plate voltage 450V and 30W dissipations)
For today 6L6GC schematic, you may use 6L6WGC or 5881, SOVTEK or Electro Harmonix.... They have higher voltage plate ratings (approx 600V), that is suitable for your schematic...
Otherwise, rcavictim has gave the solutions...
Have a great day...!
Thanks Tom
I knew if I waited long enough someone would eventually address the question.
This amp is NOT as bad as first thought. Somehow I screwed up some voltage readings and so managed to misslead some folks - sorry. Anode Volts was ONLY 520 not 570. I checked heater voltage, which was high (6.7V AC) and so changed primary tap on the power transformer from 240V to 260V. Heaters now run at 6.25V AC and the Anode Voltage is 498V. I am much happier with that.
I had great success with JJ Tesla EL84 for a HiFi Amp I built so will give their 6L6 a try.
I knew if I waited long enough someone would eventually address the question.
This amp is NOT as bad as first thought. Somehow I screwed up some voltage readings and so managed to misslead some folks - sorry. Anode Volts was ONLY 520 not 570. I checked heater voltage, which was high (6.7V AC) and so changed primary tap on the power transformer from 240V to 260V. Heaters now run at 6.25V AC and the Anode Voltage is 498V. I am much happier with that.
I had great success with JJ Tesla EL84 for a HiFi Amp I built so will give their 6L6 a try.
Those numbers were overly high for a Fender. Even with the tubes out of it that would still be high. Glad you got a handle on the volts. You did have tubes in it for the measurements, I hope?
That bias control can be easily rewired as a level control rather than a balance control. With matched quads, the balance control becomes less valuable. Years ago they used random tubes and that control was the poor man's matcher.
Other tube numbers might work, but you do want it to still sound like a Fender, don't you?
Personally, I prefer the Svetlanas for most guitar 6L6 applications. I run them in my Fender amps, and unless otherwise directed, I put them in my customers' amps. Good sounding, sturdy tube. The JJ is also a very good choice.
I have nothing against the Sovtek tubes like the WXT+, but I generally don't buy them. I am no fan of the chinese tubes, but the Chinese Ruby 6L6GCSTR is a really nice tube - sounds good and it holds up. Plus I like doing business with the folks at Magic PArts.
Here in the USA you have to be careful when buying Svetlanas. The New Sensor folks bought the rights to market tubes under the Svetlana name. SInce New Sensor is the force behind SOvtek, they now sell relabelled Sovtek tubes under the Svetlana name. They all have the "S" logo.
But Svetalana still makes tubes, but here they are sold with the "winged C" logo. So look for the C if you want real Svets in the USA. I hope the rest of the world doesn't suffer so.
That bias control can be easily rewired as a level control rather than a balance control. With matched quads, the balance control becomes less valuable. Years ago they used random tubes and that control was the poor man's matcher.
Other tube numbers might work, but you do want it to still sound like a Fender, don't you?
Personally, I prefer the Svetlanas for most guitar 6L6 applications. I run them in my Fender amps, and unless otherwise directed, I put them in my customers' amps. Good sounding, sturdy tube. The JJ is also a very good choice.
I have nothing against the Sovtek tubes like the WXT+, but I generally don't buy them. I am no fan of the chinese tubes, but the Chinese Ruby 6L6GCSTR is a really nice tube - sounds good and it holds up. Plus I like doing business with the folks at Magic PArts.
Here in the USA you have to be careful when buying Svetlanas. The New Sensor folks bought the rights to market tubes under the Svetlana name. SInce New Sensor is the force behind SOvtek, they now sell relabelled Sovtek tubes under the Svetlana name. They all have the "S" logo.
But Svetalana still makes tubes, but here they are sold with the "winged C" logo. So look for the C if you want real Svets in the USA. I hope the rest of the world doesn't suffer so.
Thanks Enzo
Checked Aussie Import Agents
JJ Tesla 6L6GC supplied by Scott Thompson at Rarefaction A$50 each (about US$70)
Winged 'C' Svetlana 6L6GC suppied by Arthur at Evatco A$36 each (about US$50)
Aside: Arthur also offers NOS Blackplate RCA 6L6GC at US$100 ea
Given that will go with your RECOMMENDATION of the "real" Svetlana.
Thanks to everyone who offered advise.
Checked Aussie Import Agents
JJ Tesla 6L6GC supplied by Scott Thompson at Rarefaction A$50 each (about US$70)
Winged 'C' Svetlana 6L6GC suppied by Arthur at Evatco A$36 each (about US$50)
Aside: Arthur also offers NOS Blackplate RCA 6L6GC at US$100 ea
Given that will go with your RECOMMENDATION of the "real" Svetlana.
Thanks to everyone who offered advise.
Sch3mat1c said:
OK smartypants,
but what about self-biassing cathode resistor type circuits? They run away too and it is because of what I said. You have to dig into the amp and deliberately lower the grid leak R value to help solve the problem of crappy tubes, but that creates its own problems like messing with available drive and drive circuit LF response with the given coupling capacitor values etc.
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