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10-09-2018, 03:14 AM
Hi Guys
The fact is that there is NO specific match of a given tube type to a given OT primary impedance that one would assume and use universally; rather, as TUTs repeat, the range of OT impedances that all the common tube types can use is widely overlapped and that for the most common applications you can use ANY tube provided there is sufficient heater current and bias control range.
The TUT3 projects use _widely-available_ transformer types made by Hammond. At the time of writing, the 1750-series did not exist. That fact is actually immaterial inasmuch as the designs fall sort of into the "middle" of the operating range for the usual tube types: 6L6, EL-34, 6550, et al. The 1650K requires 292V peak at 343mA peak to achieve 100W peak output. With the usual 272JX PT, the unloaded Va is about 420V but will drop under load. Even if the supply stayed solidly at 420V, a single tube per side could easily drive the OT to 100W peak with only 25W peak dissipation over the audio cycle - which is about 18W continuous and well within the power ratings of all the tubes you mentioned.
Marshall used many surplus OTs and PTs in their production in the early years, so the "matching" is all over the map and supply regulation is not always stellar. In later years, cost still over-rode any other consideration.
Hammond's 1600-series OTs were designed for hifi applications but used in many guitar amps due to their good value-per-cost. As TUTs state, the bandwidth is narrower at higher than rated power levels, primarily as a loss of bass response and increase in distortion produced in the transformer itself. This is generally acceptable for MI, and thus you see the 1650T (120W rated, 1900aa) used in the Traynor Custom special at 160Wrms, and the 1650N (60W, 4k3aa) used in the 80W Bassmaster. (Traynor used simplified forms of the stock models). The OT in a 100W Twin reverb is about the equivalent of a 1600-series 45W model if one existed.
What OT primary you use depends on the power expected, the capability of the tube, and the voltage environment. There is no magic primary number for a given tube type. There is no single idle current for each tube type. You can use tubes to produce LESS power than their capability (most often the case). There is a lot more latitude in our way of thinking because we follow tube-safety-rules rather than tube-hifi-rules.
The fact is that there is NO specific match of a given tube type to a given OT primary impedance that one would assume and use universally; rather, as TUTs repeat, the range of OT impedances that all the common tube types can use is widely overlapped and that for the most common applications you can use ANY tube provided there is sufficient heater current and bias control range.
The TUT3 projects use _widely-available_ transformer types made by Hammond. At the time of writing, the 1750-series did not exist. That fact is actually immaterial inasmuch as the designs fall sort of into the "middle" of the operating range for the usual tube types: 6L6, EL-34, 6550, et al. The 1650K requires 292V peak at 343mA peak to achieve 100W peak output. With the usual 272JX PT, the unloaded Va is about 420V but will drop under load. Even if the supply stayed solidly at 420V, a single tube per side could easily drive the OT to 100W peak with only 25W peak dissipation over the audio cycle - which is about 18W continuous and well within the power ratings of all the tubes you mentioned.
Marshall used many surplus OTs and PTs in their production in the early years, so the "matching" is all over the map and supply regulation is not always stellar. In later years, cost still over-rode any other consideration.
Hammond's 1600-series OTs were designed for hifi applications but used in many guitar amps due to their good value-per-cost. As TUTs state, the bandwidth is narrower at higher than rated power levels, primarily as a loss of bass response and increase in distortion produced in the transformer itself. This is generally acceptable for MI, and thus you see the 1650T (120W rated, 1900aa) used in the Traynor Custom special at 160Wrms, and the 1650N (60W, 4k3aa) used in the 80W Bassmaster. (Traynor used simplified forms of the stock models). The OT in a 100W Twin reverb is about the equivalent of a 1600-series 45W model if one existed.
What OT primary you use depends on the power expected, the capability of the tube, and the voltage environment. There is no magic primary number for a given tube type. There is no single idle current for each tube type. You can use tubes to produce LESS power than their capability (most often the case). There is a lot more latitude in our way of thinking because we follow tube-safety-rules rather than tube-hifi-rules.
