Quote:
Originally Posted by barrymagrec
All those figures seem wildly low to me. 80mH is a fairly normal medium impedance replay head for transistor amplifiers, a suitable head for valve amplifiers without a transformer would be much higher.
Similarly a record head would be typically much higher than your figures especially with such a relatively low bias frequency.
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I agree that there’s something weird about Hellyer’s specs, Barry. Out of interest and for comparison, I looked up the specs for the Bogen UK202B R/P heads, which seem to work well with both valve and IC input stages (that is, until they go o/c!). These specs also come from Hellyer, although the inductance agrees with that given in JR Stuart’s WW articles on his “High-quality Tape Recorder” (though Stuart mysteriously gives the head’s inductance as “120mH
at 1KHz” [ - eh..?!]) --
(From: “Tape Recorder” magazine,
September 1967, article ‘Tape
Recorder Service’, HW Hellyer)
Recording head UK202, 2/2 track
Inductance – 120mH
Impedance at 1kHz – 780Ω
DC resistance – 75Ω
Bias at 100kHz – 23V at 1mA
Recording current (3-75 ips) - 120μA
Output at 2kHz (3.75 ips) – 2.4mV
Bogen did make a separate Playback head with different characterisitics, but Stuart specified the UK202 for both R and P.
Mike