The Sovtek 5881 WXT/6L6 WGC Tube Guide II

Cracking the Sovtek Tube Code: Part Two                                          

My Sovtek 5881 WXT/WGC Tube Guide has been immensely popular, and I thank everyone for the many emails I received as well as the countless links that have been posted to it all over the web. 

Please read the Sovtek 5881 WXT/6L6 WGC Tube Guide if you haven’t already as this article is an expansion of that one, and assumes you are familiar with the material discussed in it. This addendum is to answer the most common questions I have received on it.

5881 WXT & 5881/6L6 WGC Differences

As I said in the original article, they are the same tube (6Π3C-E) with different bases. Some readers found this unclear. So, I tossed some arrows on their press photos for clarification. The base is the black plastic part the the pins stick out of on the bottom of the tube. The bases pointed to in the pictures to the right are the only things that differ between the two tubes. You only need to spend the extra cash on the WXT if your tubes both:

Hang Upside Down (Glass side points to floor like in most combo amps) and

Are held solely from the base by little clips (called Bear Trap Retainers)

If your tubes stand on their bases or are held by the glass part by a holder and springs (kind of like a playground swing), you can save your money and get the WGCs.

WATTAGE AND Classification

Remember the Sovtek 5881 WXT and 5881/6L6 WGC tubes are Russian 6Π3C-E tubes and do not fit neatly into the U.S. tube classifications. It is nearly impossible to find data on the tubes’ output in class AB operation (which is what we are concerned with for guitar amps). However, if we extrapolate from what info is out there we come up with these approximate wattages:

Usage in Guitar Amplifiers:

At about 23 watts the Sovtek 6L6GB should be treated as a direct replacement for a 23 watt 6L6GB or 5881. Don’t stick these in an amp requiring 6L6GCs!

However, despite its lower output, we treat the Sovtek 5881 WXT and 5881/6L6 WGC tubes as direct replacements for a 30 watt 6L6GC!

The reason this works is that guitar amps are not designed to run their tubes at %100 of their rated output. If they did, the tubes would die a quick death. Instead, guitar amp power tubes are usually run at ~%50 to a maximum of ~%70 of their rated output. Because of their rugged military design, they can be run closer to their maximum output without killing them, and we can safely treat them as 6L6GCs.

Sovtek 5881 WXT 5881/6L6 WGC Biasing in Guitar Amplifiers

With no math, charts, or Java Applets!

This can be a whole lot of stress. If your amp doesn’t have a way to adjust the bias (e.g. Mesa-Boogies and Silver Face Fenders), or if your amp is already biased for tubes that have a Groove Tube rating or manufacturer color code, consider yourself lucky and skip ahead to the next section.

If you can measure and set the bias (with test points built either into the amp or with one of the various bias probes available online) I offer the following advice:

Forget the wacky formulas on the vacuum tube sites!

If you know how to check and set the bias on your amp, set it to the bias specified on the schematic or in the owner’s manual. It’s that simple. If you have neither the manual nor the schematic, a search on any search engine should reveal sites where you can download a free PDF version. It may take a good 20 minutes to locate it on the schematic (do yourself a favor and rotate the page in your PDF reader so you can read it more easily) but it’s there, and it’s usually marked with a footnote or asterisk.

Shouldn’t I, like, bias it really hot for maximum tone, dude?

Read the above section. You are already biasing them hotter. If running the tubes to the point of death was the best way to get a good sound out of your amp, the amplifiers designer would have indicated that on the schematic or in the manual. Many amp manuals do actually specify a range. My Fender “Evil Twin” has built in bias test points and the manual offers three bias settings: a hotter one for tone, a conservative one for max tube life and a medium setting in between them. In which case pick the one that sounds best.

With Math and Charts:

If you have a gig to play, rehearsal to go to, chords to practice, or pretty much anything productive to do in your life etc. feel free to skip this companion article:

The Sovtek 5881 WXT/6L6 WGC Tube Guide III

 (Ok, you can skip to it as soon as I've finished writing it. Until then, you can read on.)

What Groove Tubes/ Fender/ Mesa/ Sovtek “distortion” rating should I get?

First, let’s clarify what we are actually buying as the tube Manufacturers use different ratings. The Groove Tube rating is the de facto standard, as they invented the whole rating idea to begin with. FYI: Fender recently acquired Groove Tubes but is maintaining both systems. Note that color codes are very confusing. For example, Fender red and Mesa/Boogie red are very different and are not interchangeable without rebiasing.

Tube Rating Conversion Chart

If your amp is biased for, tubes with a specific tube rating use the chart above to find a replacement and don’t sweat the rebiasing. Just make sure to get a matched pair (for 40-50 watt amps) or quad (for 85-100 watt amps).

If you are setting the bias yourself or your amp has no adjustment (and unrated tubes), buy Sovtek Mediums or equivalent.  Why? Here’s the ugly truth:

In the Groove Tube rating system, they set GT 5 to “spec”. That’s what manufacturers are trying to make when they make each and every tube. The closer we approach the GT 1 and GT 10 ratings, the more the tubes’ electrical characteristics deviate from the norm. While GT 4 and GT 6 are close enough to be considered normal, as you deviate from the medium ratings you are, in a very real sense, buying a defective tube.

Will it have shorter life span or other problems? I really don’t know. Just understand that the tube manufacturer was trying to produce a GT 5 rated tube every time they made a tube. Make your own decision from there. 

To simply things:

Need Tubes? What To Do If...

Note: The Sovtek 5881 WXT and 5881/6l6 WGC have traditionally been very consistent, and close to spec. I received some reader feedback that the piece-to-piece consistency has dropped since the factory was bought by New Sensor, but I have not experienced this with any I have purchased.

You don’t Have to buy Tubes from Corporations

If you prefer to buy from independent tube dealers go ahead. You can specify the rating you want in any of the above rating schemes.

Suitability for hi fi Audio tube amplifiers

I honestly have no idea. I have edited the original text to clarify that all my points were referring to guitar amplifiers. If anyone has had definitive success or failure with these in Hi Fi amps, let me know and I will include that information in this section.

The Sovtek Blue Glow

 The blue glow inside of Sovtek tubes is normal and is not a sign of a defective or worn out tube. It is simply a byproduct of trace mineral elements in the materials Sovtek coats the internals with.