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6LW6 operating points

Hello, I recently got a pair of Sylvania 6LW6 off of Ebay. I have heard that it is possible to obtain 140+W from these tubes at around 700 plate volts. However, I have been unable to find more info on this claim, such as necessary load impedence, screen voltage, bias voltage, bias current, etc. I have also been unable to find suitable plate curves to determine these points myself. Can any of you provide any information on these operating points? Thanks in advance.
Matthew
P.S. This is for a guitar amp, so low distortion is definately not a requirement.
 
I am one of the people who have obtained 140 watts from a pair of 6LW6's. I did this at least 10 years ago and don't have the original information any more. I used a 6600 ohm OPT, but may have put the 8 ohm load on the 16 ohm tap, for a 3300 ohm load. Drive was conventional control grid drive, and it was a guitar amp. B+ was obtained from a bridge rectifier on a 600 volt industrial control transformer. The exact screen voltage remains unknown, but was probably in the 300 volt range.

More recently I have operated a pair in screen drive mode at 550 volts of B+ with a 2500 ohm load. Power output was in the 150 watt range. At least one other forum member has done this also.

There are several different versions of 6LW6's. All can handle 40 to 50 watts of dissipation with ease, but some versions can do far better. The best are the GE's that have two large heat radiating fins welded to the plate. They also have fins on the inside surface of the plate. My current cathode follower experiments using 6LW6's are using Sylvanias which can operate at 75 watts easilly and don't red plate until 90 watts.
 

Brett

Member
2002-01-07 6:02 pm
tubelab.com said:
I am one of the people who have obtained 140 watts from a pair of 6LW6's. I did this at least 10 years ago and don't have the original information any more. I used a 6600 ohm OPT, but may have put the 8 ohm load on the 16 ohm tap, for a 3300 ohm load. Drive was conventional control grid drive, and it was a guitar amp. B+ was obtained from a bridge rectifier on a 600 volt industrial control transformer. The exact screen voltage remains unknown, but was probably in the 300 volt range.

More recently I have operated a pair in screen drive mode at 550 volts of B+ with a 2500 ohm load. Power output was in the 150 watt range. At least one other forum member has done this also.

There are several different versions of 6LW6's. All can handle 40 to 50 watts of dissipation with ease, but some versions can do far better. The best are the GE's that have two large heat radiating fins welded to the plate. They also have fins on the inside surface of the plate. My current cathode follower experiments using 6LW6's are using Sylvanias which can operate at 75 watts easilly and don't red plate until 90 watts.
Thanks. I think I have some of these in storage and if 150W is obtainable, may make a good bass guitar amp with the right iron.
Edit: and 2 or 3 pairs in PPP.
 
Hi Tubelab
I have recently come across this tube and am considering it as a replacement for the el509 looking at the specs it seems it should be able to match the 509 for power output at present I am running the 509,s at 860 b+ and 175 volts on the screens they shift 255 ma just prior to clip..B+ drops to 790 volts at clip, would they perform in a similar manner they are cheaper and seem reasonably available, the no,s 509,s Mullard, tunscram etc are almost extinct and the 6lw6 seems to be the ideal replacement, after the base change of course.
 
The 6LW6 was never a real popular sweep tube since most TV's had switched to Compactron's or Novars or Magnovals. I don't know what the availability is in the UK or Europe. I got several back when they were $5 each on Ebay. That was a long time ago! There is a 26 and 36 volt version which are cheaper. I got about 30 of the 36 volt versions for $4 each just couple of years ago.

The EL509 is identical to the US 6KG6 and the 6KG6 can be used as a drop in replacement. There is a Russian equivalent too, but I don't know the number.

There are several 40 watt sweep tubes in Compactron (12 pin) and Novar (9 pin) bases that all work pretty much the same. The smallest of the 6LW6's is also similar, and is electrically the same as the 6LF6 and the 6MH6. Data on the 6LW6 is scarce but it works identically to the 6LF6. There are two bottle diameters 1.5 inch and 1.75 inch. The large ones may not fit your amp.

There are several different constructions. All were made by GE or Sylvania regardless of brand. I have tested several of each, and dissected several dead ones too. All are identical inside the plate. The small ones are identical to the 6LF6 too. Some of the small bottle versions have small heat radiating fins welded to the plate, as do some 6LF6's and 6LR6's. The tubes without added fins start to red plate in a dark room at about 50 watts. The ones with small fins can eat about 60 watts before showing color. There are three versions of large heat radiating fins in the large bottle tubes, two GE. and one Sylvania. These can eat between 75 and 90 watts without showing color.

I have not gone beyond 750 volts on any sweep tube, only because of power supply limitations. My experiments from 15 years ago (when I got the $5 tubes) used about 750 volts (no load) and a bit over 700 fully loaded. The intent was a big guitar amp unfortunately after setting one OPT on fire, and blowing up a second, I abandoned the project. The second amp lived for a few months. I was getting about 150 watts through an 80 watt OPT. Only basic distortion measurements were done, and I haven't been able to find my notes from that era. I wound up making the big amp with a separate KT88 based power amp for each 12 inch driver, a total of 8 simple amps, each using the same 80 watt OPT. It was very reliable....I retubed it once about 5 years ago.

I have done several sets of experiments on sweep tubes in the past few years. All were fed from a HP 6448B bench power supply that goes up to 650 volts and can source 1.7 amps. I have used a big 400 watt Plitron OPT that can be configured for 1250, 2500 or 5000 ohms. I have also used the same 80 watt OPT's configured for 6600 or 3300 ohms. I did not actually test the 6LW6 in these experiments since I did not want to risk a set of the few 6LW6's that I have left. The high powered testing was done with 35LR6's which are similar to the small 6LW6 with the heat radiator. They show pale red at 60 watts as do the small 6LW6's. I got 45 of them for $3 each at the Dayton hamfest a few years ago, so they are now my "test" tube of choice.

A pair of 35LR6's will produce 250 watts at the onset of red plate into a 2500 ohm load on 650 volts. 4 of them made 504 watts into a 1250 ohm load on 650 volts. So will ANY of these tubes work in your amp? Probably.....see which ones that you can get for a good price, and consider spares. None of these is being made any more.

I have a new project coming together, and I will try the 6LW6 and all other medium and large sweep tubes in conventional G1 and screen drive in the next few weeks. There will be a new thread to report the results.....and maybe even some video!
 
6LW6

Hey Tubelab
I finally got around to converting the el509 amp to 6lw6,not all 6lw6 are created equal!, mine have two different plate structures and are in the mid size bottle, two are branded as emerson and amperex respectively and have some large heat fins either side of the plate and look like they have been well hot rodded, the other two are GE, and don't look so fancy, got the amp up and running-25ma at idle, 5 ma more than the el509 can take, ran them in for a week doing 400 watts and gave them a good thrashing at full tilt for two hours last week, amp is driving 4xW cabs loaded with gauss 4580,s, lights off and to my surprise the amperex/emerson were red plating which I watched blossom with interest for 15 mins- entire house is shaking!, switched off, cooled down and re set at 20ma this pair now stable, these tubes do kick ***, when I can obtain more GE tubes I will swop these out and see how far they can be pushed, I may up the screen voltage to 200 volts for them, I do not believe that they will take much more at this plate voltage, must be something special about the GE tubes