40K primary s not too high; the higher the better. A transformer doesn't have own impedance; it reflects the impedance of the load according to turn ratio. Winding resistance may be too high, or wire ampacity too low.
As I understand it though, "mis-loading" the secondary may result in some frequency response unpredictability and the need for some zobel-ing, but I get what you're saying.
Question: In selecting a transformer, how much DC Unbalance current should be accounted for?
Looking at some of these UTC transformers, in particular the A-15, has 8 ma rating for UNBAL. Others have 0. Is this an important thing to note in this particular circuit?
Question: In selecting a transformer, how much DC Unbalance current should be accounted for?
Looking at some of these UTC transformers, in particular the A-15, has 8 ma rating for UNBAL. Others have 0. Is this an important thing to note in this particular circuit?
"Misloading the secondary"
There is only one way of misloading: with too low an impedance. The result is low impedance load of the primary circuit, which would cause reduces gain and increased distortion. But the high impedance load on the secondary only improves transformer performance. Am interstage transformer works best with infinite secondary load.
If a transformer allows primary DC current, it has a gapped core. The frequency range is rated for the indicated current. If you use lower DC current, transformer performance will improve, specifically at low frequencies. For example, the A-15 with 4 mA DC primary current will have -2dB point not at 40 Hz, but at 20-30 Hz.
If the rated primary DC is zero mA, a transformer has a gapless core that will be saturated even at a very low DC current. Such transformers are primarily intended for parafeed applications. If it has center-tapped primary for PP application, the DC imbalance of primary halves must be very low, typically in the range of 0.1 - 0.2 mA. Due to tube bias drift, such good balance would be difficult to achieve practically without frequent re-adjustment f the balance.
There is only one way of misloading: with too low an impedance. The result is low impedance load of the primary circuit, which would cause reduces gain and increased distortion. But the high impedance load on the secondary only improves transformer performance. Am interstage transformer works best with infinite secondary load.
If a transformer allows primary DC current, it has a gapped core. The frequency range is rated for the indicated current. If you use lower DC current, transformer performance will improve, specifically at low frequencies. For example, the A-15 with 4 mA DC primary current will have -2dB point not at 40 Hz, but at 20-30 Hz.
If the rated primary DC is zero mA, a transformer has a gapless core that will be saturated even at a very low DC current. Such transformers are primarily intended for parafeed applications. If it has center-tapped primary for PP application, the DC imbalance of primary halves must be very low, typically in the range of 0.1 - 0.2 mA. Due to tube bias drift, such good balance would be difficult to achieve practically without frequent re-adjustment f the balance.