Tried interstage with LL1692A in both 7119/46 and 46/300B positions, with disappointing results. For the Amity, I would lean towards the 1660S as it has the highest inductance, but the layered windings Lundahl uses in these transformers will likely all perform similarly with regards to stray capacitance and resonances. You are heading the wrong direction in my opinion; aim for a bifilar wound c-core and you will be richly rewarded.
For the OPT, tried the LL1620 and O-Netics. Lundahl won in this contest, though it was further bested by going with Monolith. If you are resolved to use Lundahl, I would probably lean toward the LL1620 with the XLS tube depending on how hard you want to drive things. It's generally a more flexible transformer for other potential projects as well. Then again, I predict if you go with a Lundahl interstage you will be distorting at the 300B grids well before you drive the output stage anywhere 5W.
For the OPT, tried the LL1620 and O-Netics. Lundahl won in this contest, though it was further bested by going with Monolith. If you are resolved to use Lundahl, I would probably lean toward the LL1620 with the XLS tube depending on how hard you want to drive things. It's generally a more flexible transformer for other potential projects as well. Then again, I predict if you go with a Lundahl interstage you will be distorting at the 300B grids well before you drive the output stage anywhere 5W.
I agree with zigzagflux regarding the interstage. The IT-02 is bifilar 100%:
http://www.monolithmagnetics.com/sites/default/files/ITA-02-interstage-transformer-final.pdf
It appears this is the only MM model in production right now for PP application.
For the input stage, my favourite is the Sowter 1475. This is one of the models still in regular production. It's 10K input and does not need any kind of secondary networks to get smooth frequency response when driven from source impedance in a rather wide range up to 10K.
https://www.sowter.co.uk/specs/1475.php
http://www.monolithmagnetics.com/sites/default/files/ITA-02-interstage-transformer-final.pdf
It appears this is the only MM model in production right now for PP application.
For the input stage, my favourite is the Sowter 1475. This is one of the models still in regular production. It's 10K input and does not need any kind of secondary networks to get smooth frequency response when driven from source impedance in a rather wide range up to 10K.
https://www.sowter.co.uk/specs/1475.php
Correct, IT-02 Summit series.
It's like there is no transformer at all, no measurable or sonic signature, no aberrant phase shifts or notches in the impedance. Just straightforward theoretical turns ratio behavior. Driver tube has no issues, just whatever grid capacitance the output stage presents. Will never go back to layered windings after this experience.
Only limitation I was presented with was the 300V DC winding/winding voltage rating. Looks like that has increased to 375V since I purchased. No big deal; a set of 0D3 regs and we are safe.
It's like there is no transformer at all, no measurable or sonic signature, no aberrant phase shifts or notches in the impedance. Just straightforward theoretical turns ratio behavior. Driver tube has no issues, just whatever grid capacitance the output stage presents. Will never go back to layered windings after this experience.
Only limitation I was presented with was the 300V DC winding/winding voltage rating. Looks like that has increased to 375V since I purchased. No big deal; a set of 0D3 regs and we are safe.
What about ITA-02 and ITX-02? Are all IT+02,
What about
What about ITA-02 and ITX-02? Are all IT-02, ITA-02 and ITX-02 bifilar winding?
Also, which monolith output transformer would you recommend for Amity with 320B-XLS?
Whether you feel the core material will make a difference with a bifilar winding technique is really up to you to decide. Is the money worth it? That was kind of my reason for stating how the transformer is so transparent with no phase shift anomalies; I see no reason for a higher grade core when performance is to the level it is. By their own specifications the three versions have the same bandwidth. Does distortion show up significantly differently with core when bifilar is used? You could ask Monolith; don't be surprised by the response 🙂
I used the Summit 6.6K version since that was where I wanted to operate the tubes. 5K or 8K are certainly options that would work with various watt output and distortion differences; higher transformer Z will be lower watts, lower distortion.
3.3K on a 300B is quite standard, Rp at 700-800 ohms.
If interested in spending extra money, I would invest it in amorphous OPT rather than the IT.
I used the Summit 6.6K version since that was where I wanted to operate the tubes. 5K or 8K are certainly options that would work with various watt output and distortion differences; higher transformer Z will be lower watts, lower distortion.
3.3K on a 300B is quite standard, Rp at 700-800 ohms.
If interested in spending extra money, I would invest it in amorphous OPT rather than the IT.