Transformer ratings & how to interpret them

Regarding the transformer output ratings, I need to clarify how to interpret them.  I use the manufacturer’s specifications in the description of various builds, but I don’t guarantee that you actually get that output in every instance.  For example, a 6V6GT in a single ended amp like the 5F1 Champster or 5F2A Prince will only have an output of 5.5 watts regardless of the output transformer used.  An 8 or 12 watt transformer will give you more headroom and a bump in volume over a 5 watt unit, but it’ll never exceed the ability of the tube itself.  When you get into the push-pull circuits like the 5E3 D-Lux, then the output of the two 6V6GTs can go up accordingly with some of the larger output transformers but still may not yield the rating of the output transformer.  

Likewise the 6L6GC in a single ended amp like the 5F1 Champster or 5F2A Prince the maximum output is 6.5 watts regardless of the output transformer used.  An 8 or 12 watt transformer will also give you more headroom and a bump in volume but once again it’ll never exceed the ability of the tube itself.  When you get into the push-pull circuits like the 5F4 SuperDawg, 5E5A ProDawg, 5F6A TopDawg, or 5E8A DoubleDawg then the output of the two 6L6GCs can go up accordingly with some of the larger output transformers and easily meet or possibly exceed the 40-50 watt rating of the output transformer.

On the other hand you can also lower the output of an amp by going with a smaller output transformer as well, and an example of that would be using a 25 watt OT in a 5F4 SuperDawg.  The added benefit of doing that besides the lower volume is that you can bias the amp for use with either 6V6GTs for the earlier break-up and smoky overtones, or 6L6GCs for the tight & bright chimey top end that they offer.  More on that later on.

4 thoughts on “Transformer ratings & how to interpret them

  1. In a 5E3 D-lux with Mercury magnetics Fat stack (ot FTDLX-O-FS and pt FTDP-E-FS) aparently a little oversized … May i put some different tubes to get more clean headroom?? Like a pair of 6V6 or GZ34/5AR4 or another rectifier??
    Or you need a bigger transformer??
    Regards from CHILE

    • Hi Jaime,
      The interactive controls are the best way to get more headroom out of the 5E3 circuit, and
      I’ll be posting some more info on them in just a bit. I also think that you have a good set of transformers already so there’s no need to worry about them.

      In the meantime let’s talk about the tubes and how you might be able to get the headroom with them. The traditional tube line up for the 5E3 would be a 5Y3GT, 6V6GT x 2, 12AX7, and a 12AY7. I’ve found that a lot of people use a pair of 12AX7’s in the pre-amp and while that would give more overdrive it wouldn’t be of much help for headroom. The 12AY7 is what sets the basic tone for the amp and one I do recommend using in the V1 position, but you can experiment with some other tubes in the V2 spot instead of the 12AX7. A good tube for more headroom would be the 12AU7 as it has less gain, and that means that it won’t overdrive the next stage as much which is the power tubes. So you end up with more headroom while still having a decent volume on tap. Some folks even go as far as a pair of 12AU7’s in the pre-amp to get even more headroom, so that’s a good place to start.

  2. I’ve seen a few builders claim their single ended 6L6 amps (most likely Champ or 5F2 A derivatives) run at 10 watts or more. Just 1 12ax7, maybe a tube rect. and a single 6L6; and the math just seems to disprove their claims.

    The sad thing is, an assuming amp buyer may think they are getting those watts when that simply ain’t gonna happen. Maybe a ploy with some small biz builders or ignorance; thanks for setting the record straight!

    • You’re correct in that there is some misinformation on the actual output possible with a single ended amp, and hopefully it’s not intentional. The benefit of a larger output transformer (OT) in single-ended amps can seem like a volume increase but you’re actually just getting the headroom, clarity, and detail which you wouldn’t have had with a smaller OT.

      When everything is said & done though the tube still can only put out so many watts regardless of how big the OT is that you’re using with it. I will say that an honest 5 watts of tube power thru an efficient speaker can sound much larger than it really is.

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