Every now and then I consider the UTC LS-51, HA-114, and A-26 for push-pull tube output stages. The LS and HA both mention 1 mA of unbalanced DC in the primaries, while the A does not mention DC at all. Has anyone built a PP circuit with these units, and did you use DC in the transformers, or did you use parallel feed? I cannot think of a single circuit I've ever seen using these pieces. The quoted 1 MA of imbalance would be fine with low current tubes, but seems like it could be problematic with something like 12AU7's or 6SN7's. Sometimes I think parallel feed may really be the only safe way to go with these, and I'm not inclined to see if I blow one up experimenting.
Can anyone address, from experience, the suitability of the various UTC LS, HA, and A series pieces for push pull use? Obviously UTC has some that are designed specifically for PP use (LS-12, LS-51, HA-101, HA-114, A-12, A-26), and others that are only mentioned in regards to single ended use that have split secondaries (LS-10, LS-50, HA-100, HA-113, A-10, A-26). Is this later group wound to less balanced tolerances, or are they perfectly suitable for PP use as well? I have certainly seen plenty of LS-10's on PP input stages. Has anyone tried paralleling windings for lower ratios, and looked for detrimental frequency effects due to the paralleling? Can anyone address the use of the PP types in single ended applications (input and parallel feed output), either at series or parallel connection? Say, like an LS-12 paralleled for single ended 30K secondary and an LS-51 paralleled for P.F. 7.5K primary?
In related thoughts, I see a lot of discussion here concerning the difficulty of winding good iron for push pull preamps like the Langevin AM-5116-B, AM-16, Altec 458A/459A, output of the Altec 428B, output of the RCA BA-21A, etc etc. If you look at the early transformer literature, you find lots of units that are specified for either SE or PP use, especially inputs. Are we to assume that they were not overly concerned with high frequency imbalance in those days, or that we are talking about a difference between 'usable colored sound' and 'modern lab grade' sound when discussing these winding difficulties?
I realize I'm asking for a small dictionary here. I'm mainly curious about folks real-world experiences with these pieces.
Best,
Can anyone address, from experience, the suitability of the various UTC LS, HA, and A series pieces for push pull use? Obviously UTC has some that are designed specifically for PP use (LS-12, LS-51, HA-101, HA-114, A-12, A-26), and others that are only mentioned in regards to single ended use that have split secondaries (LS-10, LS-50, HA-100, HA-113, A-10, A-26). Is this later group wound to less balanced tolerances, or are they perfectly suitable for PP use as well? I have certainly seen plenty of LS-10's on PP input stages. Has anyone tried paralleling windings for lower ratios, and looked for detrimental frequency effects due to the paralleling? Can anyone address the use of the PP types in single ended applications (input and parallel feed output), either at series or parallel connection? Say, like an LS-12 paralleled for single ended 30K secondary and an LS-51 paralleled for P.F. 7.5K primary?
In related thoughts, I see a lot of discussion here concerning the difficulty of winding good iron for push pull preamps like the Langevin AM-5116-B, AM-16, Altec 458A/459A, output of the Altec 428B, output of the RCA BA-21A, etc etc. If you look at the early transformer literature, you find lots of units that are specified for either SE or PP use, especially inputs. Are we to assume that they were not overly concerned with high frequency imbalance in those days, or that we are talking about a difference between 'usable colored sound' and 'modern lab grade' sound when discussing these winding difficulties?
I realize I'm asking for a small dictionary here. I'm mainly curious about folks real-world experiences with these pieces.
Best,