Quote:
Originally Posted by Boulevardier
In case it's useful in your search for replacement heads, these are the specifications for the heads given by HW Hellyer in his review of the Series 80 Truvox's -
“Head details are as follows: Record/Playback head inductance is 1.25mH (½-track) and 850mH on either section (¼-track). Impedances are 7.8K (½-track) and 5.5K (¼-track). Resistances: 1.1K (½-track)and 1.1K (¼-track). Erase head inductance is 1.4mH (½-track) and 80µH (¼-track). Record signal current is 70µA for the ½-track head and 50µA for the¼-track head, and the required bias voltages for these are 120V and 75V respectively. Bias and erase frequency is 55 Kc/s and erase voltage is 45V (½-track) and 12V (¼-track). The gap length is 0.00014in., and the crosstalk figure stated for the two-gapped head is better than 55dB.”
Mike
[EDIT - looking at these, I wonder if their proof-reader missed a few things - e.g -the inductances of the half-track and quarter-track playback windings seem wildly out of proportion - perhaps it should be 850µH.]
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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.