5881 Replacement for 6L6?

[Bry Carling]

> Is it correct that the 5881 is shorter, more physically rugged,
> and more electrically rugged than the 6L6?

Not really no. There are MANY varieties and many brands of both 
that are all different.

So many other variants too, like 8417 etc.
 
> Is it OK to sub the 5881 for the 6L6 in the modulator circuit
> of a Multi-Elmac AF-67?

Probably, although I can tell you from experience from 
exchanging 5881s and 6L6es in guitar aos some years ago, 
it is possible to get a very different sound.

The characteristics and the bias needed are NOT necessarily 
the same. It depends a lot on which circuit is in use.
 
> Since it is a mobile-portable rig a more rugged tube makes
> sense.  Is there a "gotcha" here that I am missing?

A more rugged tube would be the 6L6 WGB or other variants 
with a W in the designator. 6L6GC by RCA is a great tube
IF you can find them still...
 
> I found this descriptive Tungsol text from 1950:
> 
> "The 5881 carries ratings similar to the 6L6, except that the allowable 
> screen dissipation is 3.0 watts instead of 2.5 watts while the maximum 
> plate dissipation is 23 watts instead of 19 watts for the 6L6. The tube 
> has a low loss micanol base."

There CAN be more to it than that.

http://firebottle.com/ampage/td/vtd5881.html
http://www.r-type.org/exhib/aaa0451.htm
http://www.wps.com/archives/tube-datasheets/Datasheets/CBS-PA-
5/4.JPG
http://www.mif.pg.gda.pl/homepages/frank/sheets/127/5/5881.pdf
http://oldradio.qrz.ru/tubes/foreign/01/5881.gif
http://firebottle.com/ampage/td/

I hope that hepls, but you may find some more anecdotes
around the web. Chances are that your 6L6es would do fine 
mobile anyway!

When will you be on 75m or 40m mobile ? We can try for a QSO!

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