what specifically do you not like about the Iso tangos?
Let's look at the XE-20S, which is often pushed as a great transformer for use with 300Bs at the $1000 price point.
https://tango-trans.com/wp-content/uploads/catalog/XE-20S.pdfIn the 3.5K configuration, the 18H of primary inductance means the transformer holds up to about 35Hz, then kinda dies below that (both rolled-off response and rising distortion). In the 3.5K:8 ohm configuration, there's a ton of unused copper on the secondary winding which reduces the performance of the transformer (poor coupling/treble issues). This issue is really bad in the 5K:8 configuration where very little of the secondary winding is used.
Perhaps the most irksome thing about the XE-20S is the "20W" rating. I've seen measurements of this transformer at 3.5W at 30Hz when used as a 5K unit, which gets you about 5W/30Hz when used as a 3.5K unit.
Now if we compare that to the Monolith S-9:
https://monolithmagnetics.com/sites/default/files/datasheets/Single-ended-output-transformers/datasheet%20S-9%20300B%20single%20ended%20output%20transformer%20prelim.pdfThere's about double the primary inductance, and this output transformer will stay well composed to 16Hz. Notice that they give a power rating that is power
with frequency, so the 10W at 17Hz is about 6 times the power handling of the XE-20S. This transformer is also flat to about 100kHz being driven by a 300B. All of this performance comes at a price tag that's around $700.
The Lundahl LL2785C gives 30H of primary inductance with about the same DCR as the Monolith and the Tango with slightly poorer high frequency response and a 16W/30Hz power rating. These are $600...
These comparisons become even more obvious when you compare the weight of these pieces of iron, as the Tango is 2kG, the Monolith is 5kG, and the Lundhahl is 2.5kG with no steel case.
In the Kaiju iron, there's even more primary inductance in the plate choke (40H), and the power handling of the output transformer is quite high (PJ might remember where that landed, I wouldn't be surprised to see 20W/30Hz), though we don't push as hard to extend the highs beyond what's considered audible. The issues associated with unused copper on the secondary windings are mitigated by having two tapped windings that can be put in series or parallel to get different step-down ratios rather than having a single secondary winding.
The FC-40-3.5S is a little bit better, but now you're spending $1500 to get a transformer that's still not as good as the European units that are less than half the price.
