For my own I would like to say :
1) About « stereo » heads :
The ONLY advantage to use this type of heads is to wire them like Roland did on his RE (tape) models. On the RE ’s Roland, this wiring is the same that the one used on the guitar humbuckers pickups. The two coils are (seem to be) « out of phase » for the "external hum" and in phase for the record/playback signal.
Hope it’s clear ?
So and through this kind of wiring (done on these stereo heads) the external (magnetic and electrostatic) hum (for exemple from the main transformer) is mainly reduce…
It’s the UNIQUE advantage…
Otherwise, and for doing a clone of a SEP : FORGET these stereo heads…
2) Now and about the impedance of these (mono
) heads :On the tube Echomatic Meazzi, the heads used, came from an Italian firm: Photovox.
It’s EXACTLY the same heads which are used (recently) on the ESE models.
For this Photovox heads there was two possible types for the inductance (impedance):
120mH low impedance for the transistors electronics and
600mH (by memory ?!) high impedance for the tube electronics.
It’s EASY to know the type ! by just taking a look on the rear side of the heads:
If the rear side is light grey, the inductance is 600mH (like the one found on an Echomatic or an an ESE)
And if the rear side is dark grey the inductance is 100mH.
So :
For cloning an SEP using a tube electronics you HAVE TO CHOOSE the whole heads with an inductance (near of) 600mH.
Remark:
On a tube Binson, the inductance of the record head is a little bit less than 600mH. May be only 400 or something like that ?
But, and as to day it’s difficult to find this kind of heads, a set of light grey bottom Photovox heads is (very) fine…(!)
3) About the « cassette heads » same remark than for the stereo 1/4' models : FORGET them.
For two reasons:
its (working…) width of only 1/16 inch
its too low inductance (impedance) to work correctly with a tube electronics…
4) Now !
About the model «J» and the Vox Echo SEP models:
If on the SEP/ Vox Echo the four delays are 100, 200, 280 and 360ms for the three main delays heard in Apache or Theme from Giant with the J model (or F model…) the 3 delays are 123, 430 and 600ms.
You can remark that if the original apparent speed of the drum and the position of the heads are « calculated » (first) for obtaining the 3 delays 123, 430 and 600ms, if you are now able to reduced this (apparent) speed of (around) 18%, the 123ms delay becomes : 100ms, and the (other) original 430 becomes: 360ms…
So I think that:
If you want (or try to want) to obtain, Ecca, on a SAME machine (same mechanical frame) the right delays found : on the SEP model J or/and on the SEP/Vox Echo, the BEST and « simple » way is to be able to change (by mean of a new DC motor) the apparent speed of the drum.
And in addition to this trick you can see that you have to use only five playback head + a record one…
Nevertheless !
For instance, and on my two Binson PE 603 T (converted in SEP/Vox Echo) and because (and on the both) the motor used is the AC original one, I have, for instance, no possibility to do that !
In addition....
The other « problem » on a Binson, is to keep in mind the mechanical possibility (due to the « volume » of permanent erase magnets + the rubber Wheel) for adding « somewhere » (!) a playback head which generates a 600ms delay…
Sure that and by lowering the speed it’s always possible to acheive a 600ms delay. But this corresponding speed does not to be too low for keeping the original dynamic… (Like a tape recorder switched between an original speed of 15inch per sec to a reduced 7’ 1/2 or less... It's the same but it's different !)
Hope this help Ecca
And sorry for my english mistakes !
Best regards
Patrice