5881 vs. 6L6GC

Sam Cogley

Sam Cogley

Last of the Time Lords
Subscriber
I'm still fairly new to reading tube data sheets and making comparisons. As I understand it, the 5881 is a variant of the 6L6 family, using the same pinout as the other 6L6s. Will it cause a problem for either the amp or the tubes to use 6L6GCs in place of 5881s? I know the GCs are rated for higher voltages and currents, and I also know that sometimes components don't like being run well under their design specifications.

As it is, I have four GCs (two GE, two RCA) and zero 5881s.
 
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I just got a vintage set of used Tung-Sol 5881 tubes. From the research I have done they were designed to be a "heavy-duty" 6l6. Infact they are listed as the same as the 6L6WGB. This is a good article that tells all about the "new" 5881
 
I did notice that the 5881 specs were higher than the standard 6L6/G/GA/GB tubes. It's good to know that the GCs won't be hurt by or cause damage to a 5881 amp.

Interesting - I just looked at the advertising sheets for my 70A amp. Fisher advertised 25W of output from a PP pair of 5881s - which are only rated for 23W plate dissipation. It would seem that Fisher's reputation for pushing tubes hard started early. The GCs appear to be a better match for the amp from a tube life standpoint than the 5881s.
 
Sam Cogley said:
Interesting - I just looked at the advertising sheets for my 70A amp. Fisher advertised 25W of output from a PP pair of 5881s - which are only rated for 23W plate dissipation. It would seem that Fisher's reputation for pushing tubes hard started early. The GCs appear to be a better match for the amp from a tube life standpoint than the 5881s.
Click to expand...

That's 23 watts dissipation for EACH tube, not a push-pull pair running most likely in class AB1. If you scroll down the data sheet page you'll see typical ratings for different configurations. 25 watts for a PP pair seems quite reasonable, considering B+ at the anodes is probably close to 430 volts.

I think the Tung-Sol 5881's are a lot tougher than people realize. I'm pretty sure the first Heathkit W4 I bought has the original pair of working 5881's in it. Granted, they are tired; one has a cracked base and the other a broken guide pin, but they still work. Who knows how many hours these tubes have on them.

Jeff
 
Yup, you're typically fine with 6L6GC in an amp that originally specced 5881
You could also run NOS 7581A or probably even new production KT77
Enjoy!
WOT
 
sloober said:
I just got a vintage set of used Tung-Sol 5881 tubes. From the research I have done they were designed to be a "heavy-duty" 6l6. Infact they are listed as the same as the 6L6WGB. This is a good article that tells all about the "new" 5881
Click to expand...

Good article
 
If you want to see the original of that article see:

http://www.the-planet.org/pdf/ts5881s.pdf

The KT77 isn't really a direct substitute for a 5881 - it's really a EL34 congener. A KT66 is the closest relative in the GEC family.

6L6, 6L6G, 6L6GA, 6L6GB have the same ratings, but different bottles 19w plate diss, 375v plate vmax, 0.9A filament current
5881 = 6L6WGB uprated ~20% to 23w, 400v, 0.9A (original tube in Heath W2/W3/W4)
6L6GC was uprated to 30w, 500v, 0.9A
7581 uprated to 30w, 500v, 0.9A (6L6GC equiv) with low loss base (some original tubes had pink bases)
KT66 uprated to 30w, 550v, 1.3A (original tube in Heath W5)

As a "general" rule any of the above tubes further down the list can replace any higher up (but watch filament current with the KT66).

Other NOS types include:

1614 = "transmitter rated" 6L6 metal (original tube in Mcintosh Mc30)
350B = WE/NU equivalent (good luck finding any... 1.6A filament too)
7027A (slight pinout variant)
5932 military type which included a crazy variant with two structures in parallel.

Lots of 6L6 variants in other bases or filaments - 6BG6, 807, 1619, 1631, 1625 as a few examples
Also Russian variants including 6P3S, 6L6GT, 6L6WGT
 
I've got a bunch of those 1614s, but the metal bottle always turned me off. I wonder how they compare in sound though? I'll have to give them a try.
 
Just make sure that your amps don't use pin 1 of the 6L6 socket as a tie point. It's a n/c on all of the later 6L6 variants, but is tied to the metal can on a 6L6.

They're actually a nice sounding tube within their power limits. Just a bit "unattractive". They're just selected 6L6 metal tubes - if you look at the base they'll probably be stamped 6L6 just above the crimp.
 
I tried some of the 1614 tubes the other night. They worked OK, but look stupid. The good part is after warming them up, I put them in my jacket pocket. They make great hand warmers. I may just rig one up with a battery if this cold doesn't ease up soon.
 
I have a couple of metal-case 6L6s in a PA amp that's supposed to have GBs in it. I haven't fired it up, but I'll be sure to double-check that Pin 1 isn't live on those sockets.
 
I always understood that the metal case 6L6s had much lower power output than do the 6L6GCs.
 
goldear said:
I always understood that the metal case 6L6s had much lower power output than do the 6L6GCs.
Click to expand...

The 6L6 (Metal) 6L6G (Large ST bulb) 6L6GA (Small ST bulb) and 6L6GB (Tubular bulb) all have the same ratings - they just look different.

They have no difference in output than a 6L6GC in the same circuit. The 6L6GC can be used with greater plate dissipation and plate voltage - but if you plug a 6L6GC in a circuit designed for a 6L6 it will not yield any more output.

If you take an amplifier designed for 6L6's you can run any type (eg, the Mcintosh Mc30). If you take an amp like the Heatkit WM5 that was designed for KT66's or 6L6GC's (and runs them fairly hard) you had better not use 6L6/6L6G/6L6GA/6L6GB's as they certainly won't last long.
 
goldear said:
I always understood that the metal case 6L6s had much lower power output than do the 6L6GCs.
Click to expand...

That was sort of a diversion from the main topic. My Masco PA amp was designed for 6L6GBs, not GCs. The metal 6L6s are the same, as long as I don't get electrocuted by a live pin 1. The GCs are going in a Fisher 70A that was designed for 5881s and apparently pushed them fairly hard. Hopefully the 70A will have a mate someday...
 
Gary Kaufman said:
I

6L6, 6L6G, 6L6GA, 6L6GB have the same ratings, but different bottles 19w plate diss, 375v plate vmax, 0.9A filament current
5881 = 6L6WGB uprated ~20% to 23w, 400v, 0.9A (original tube in Heath W2/W3/W4)
6L6GC was uprated to 30w, 500v, 0.9A
7581 uprated to 30w, 500v, 0.9A (6L6GC equiv) with low loss base (some original tubes had pink bases)
KT66 uprated to 30w, 550v, 1.3A (original tube in Heath W5)
Click to expand...

Very exhaustive list, except for the omission of the 7581A, which was further upgraded to 35 watt plates... as seen here:

http://www.mif.pg.gda.pl/homepages/frank/sheets/127/7/7581A.pdf

http://www.mif.pg.gda.pl/homepages/frank/sheets/135/7/7581A.pdf

These 7581s and 7581As were oftentimes labeled as "7581/KT66", to indicate their suitability as substitutes for KT66 tubes in amps used in America and other non-European countries (you frequently see them- specifically, the GE 7581As, mostly- in the aforementioned Heath W5).

Regards,
Gordon.
 
jaymanaa said:
I've got a bunch of those 1614s, but the metal bottle always turned me off. I wonder how they compare in sound though? I'll have to give them a try.
Click to expand...

6L6Ys (which are very close to exactly the same as 1614s) sounded very good in a modded Magnavox-design amp (AMP175 design, voltages and transformers upped to run 6L6s). In fact, they sounded better than anything else I put into that amp, for whatever reason...

Regards,
Gordon.
 
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