807s replacing 6L6GCs

[Pyre]

I was looking at the tube data sheet for the 6L6gc and it states that the 807 shares the same curves and voltages but has a different pin out. I have an AR ST-70-C3 that takes 6L6gc’s and has individual tube biasing. Would it be possible without too much component changing to just wire in some 807 sockets and caps? Do you think there would be much more then that involved since all the voltages appear the same?

I traded my 6L6gc RCA clear tops for a nice set of Mullard EL34’s for an other amp and only have some crappy Russian tubes to run the C3 on and would like to hear some different tubes run on it. On a side note the guy I traded the clear tops to, on the first day he had them in his guitar amp he was pushing it on stage and the wheels hit something and the amp fell over destroying 2 of the tubes. R.I.P RCA Clear tops.

[SY]

If you're going to rewire the sockets anyway, by all means use the "super" 6BG6 from SND. They're like $6-7 each and will be more rugged than the 807s. I've used them in a couple of amps and they've performed very well. Tubelab.com has had a similar experience.

[Pyre]

I checked that out and they are about 20 bucks a matched set. Not bad at all. What do you think of the adapters for 10 bucks? Is it worth it or just wire up some caps?

[SY]

Just rewire the sockets and get some top caps. And order plenty of spares at these prices.

[nhuwar]

What is this place ,snd?

Nick

[Pyre]

http://www.vacuumtubes.com/6BG6.html

Good deal

[nhuwar]

Thanks

[Johan Potgieter]

Just a little more on the original question;

The 807 internal structure is exactly the same as the 6L6, but the latter has been ruggedised over the years, and the 6L6GC is now a 30W tube compared to the 807's 25W. Internal mounting has also raised the allowed maximum Vg2 to 450V (500V in case of UL) instead of the 270V (under correction) for the 807.

You mention "trading" 6L6GCs for EL34s, so it is a done deal. Still, for general interest I would mention that the two are not really inter-replacable, apart from ratings. Re ratings the EL34 can take 800V anode, but is only Pa = 25W compared to 6L6GC of 30W, also with almost double the heater current. Not asked, but I would venture to say that I found the 6L6(GC) a little more tolerant design-wise than the EL34. (Difference between beam tube v s. pentode and all that.)

[JohnAtwood]

One of the main improvements of the 6L6GC over the earlier 6L6's (6L6, 6L6G, 6L6GA, 6L6GB) as well as the 807 and 6BG6G/GA (which are essentially 6L6's with plate caps and higher plate voltage ratings) is that the 6L6GC uses a special 5-layer plate material that has copper in the core, so that the heat is spread out. This helps keep the plate from glowing orange right in the center, the way the old tubes would if they were overloaded.

One other difference when comparing the 807 and 6L6GC is the different rating systems each tube uses. The 807 uses the "Absolute Maximum" rating system, where the max ratings should never be exceeded. The 6L6GC uses the "Design Maximum" rating system, which for an average tube, should not be exceeded. This is about 10% more conservative than the absolute maximum system. The older 6L6s use the "Design Center" rating system, which is the maximum for an average tube under average operating conditions. This is about 10% more conservative than design-maximum ratings, or about 20% more conservative than absolute maximum ratings.

So, lets compare plate dissipation specs:
6L6 - 19 watts (design-center)
6L6GC - 30 watts (design-maximum)
807 - 25 watts (absolute maximum)

Now to compare apples with apples, lets normalize the wattage to all be absolute maximum ratings (multiply the design maximum by 110% and design center by 120%):

6L6 - 22.8 watts
6L6GC - 33 watts
807 - 25 watts

So, normalized to the same rating system, the 6L6 isn't that much wimpier than the 807, but the 6L6GC is quite a bit more rugged than the 807.

These rating systems are nicely described in the front section of the GE Essential Characteristics manual.

- John Atwood

[SY]

John, terrifically useful info; many thanks.