For some applications, it should work fine, but I decided to give it a pass. On the other hand, of the options this is the one that seems most obviously different from the originals. probably a good thing now that signal levels tend to bigger these days than they used to be. On the one hand, it has a +20 dBu max input signal rating at 20Hz instead of the +15 or +16 dBu of the originals, so would have more headroom.

Jensen also has a simple schematic showing how to adapt the LA-2A circuit for this transformer. Although it is a 10K-10K bridging transformer, rather than the 600R - 50K of the original, many people have reported good results using it as an input transformer in LA-2As. The first option was to use the Jensen transformers JT-11-P-1. So, the hunt was on for a suitable boutique-grade modern production alternative. Authentic copies of this transformer in good condition seem to be pretty damn hard to source as well. Overall, its specs look fairly close to the HA-100X, except that it had secondary wound for 50K ohms. The other input transformer in the originals, and which was evidently more widely used, was the UTC A-10. This transformer has a good reputation, but for all intents and purposes it's now unobtanium.

50 Ohm, 150 Ohm, 250 Ohm 333 Ohm and 500 (600) Ohm were all possible, although pretty much everyone, I assume, just wired it for a standard 600 Ohms. The first was the UTC HA-100X, which has a fairly complex series of primary windings, which you can jumper in a variety of ways to get different impedances. The originals at different times in the production run had two different input transformers. I did a LOT of thinking about these choices, only a few of which I describe here. However, there are two audio transformers, and these almost certainly will make a noticeable contribution to the tone. Running down the list of usual suspects, it looked to me like the Hammond 269JX would do the job perfectly. So there appear to be lots of good alternatives. Frankly, there's not much mojo to be had in the PT - this is not like some guitar amps where the voltage sag of a poorly regulated transformer actually contributes to the sound. The center tap on the 6.3V isn't even really necessary, since I plan on using DC elevation of the heaters to reduce hum, and will be implementing an artificial centre tap in any case. The one in the LA-2A is pretty much a bog standard PT - the schematic specifies a 250V-0-250V (500V CT) delivering 40mA, and 6.3V CT.

Thing continue to develop on the LA-2A component acquisition front.

La2a schematic