The Sinclair QL Forum

I suppose it's a matter of microdrive speed and/or design.

Yes, I agree.
You seem skillful with your multimeter, can you try measuring the coils, to see what values you get on Iss#5,6 heads?

I will also mount my last r/w head here on one of Iss#5, so we could compare results then.

Tom

tcat wrote:You seem skillful with your multimeter

Maybe I seem but I'm not so skillful
There are some contacts behind the head:
https://www.dropbox.com/s/bpnjs2pdf88m9 ... A.jpg?dl=0
could you tell me where exactly should I put the test leads please?

EDIT Upper, lower, and erase coils. Tom

Thank you once again Tom.
Here are the measurements (multimeter selector placed at 200 ohm).

For straight-edged microdrives, respectively mdv1 and mdv2

Upper coil: 15 - 15
Lower coil: 16 - 15
Erase coil: 93 - 93

For "standard" microdrives, respectively mdv1 and mdv2

Upper coil: 15 - 15
Lower coil: 15 - 15.5
Erase coil: 97 - 99

Two more "standard" microdrives in my possess, respectively mdv1 and mdv2

Upper coil: 15 - 15.4
Lower coil: 14.6 - 15.3
Erase coil: 92.6 - 98

It is more correct to measure not only resistance, but inductance too. After measuring resistance using simple multimeter, don't forget to degauss measured heads.

Byteman wrote: After measuring resistance using simple multimeter, don't forget to degauss measured heads.

how should I degauss? Damage risk?

Cristian wrote:

Byteman wrote: After measuring resistance using simple multimeter, don't forget to degauss measured heads.

how should I degauss? Damage risk?

When you measure head resistance with simple multimeter, DC current comes through head and magnetizes it. Head will work, but after each tape pass across head, tape will be slightly degaussed (particularly on high frequencies). This will lead to data errors, the longer you use tape in this drive, then more data will be damaged. You can use any head demagnetizer for reel-to-reel tape recorders.

And about correct inductivity measurement: you can use something like LCR-T4 chinese tester based on atmega328. Cheap and accurate solution.

Hi Byteman

May I ask - even if not first measuring the tape-head resistance using a MM - could the head become degaussed simply over time and normal use?

Is there cause to attempt to demagnetise anyway, from time to time?

Byteman wrote:This will lead to data errors, the longer you use tape in this drive, then more data will be damaged.

Byteman wrote:And about correct inductivity measurement: you can use something like LCR-T4 chinese tester based on atmega328. Cheap and accurate solution.

Thank you very much for your information

could the head become degaussed simply over time and normal use

I am no audio expert, but I think an ordinary audio head must incur some residual magnetic just by regular use.

I wonder what happens during erase operation (write/format), as the erase coil is fed with VIN voltage. If it were AC (alternating current) that would demagnetise head itself, if it were DC (direct current), then it must magnetise it each time we write or format the tape?

Searching Google, there were long discussions about head demagnetization among Hi-Fi audio hobbyists, with unsure influence on playback quality, audible only by someone.

I have also read about a DIY demagnetise (degauss) solution, is to take a 12V relay, remove its coil core, place a soft iron core in place (ordinary thick nail), connect ordinary 12 VAC (alternating!) supply, put some soft protection not to scratch the head face, and apply for a few seconds.

But it sounds a bit silly to me, as I somehow feel unnecessary, but I stand to be corrected here by someone with sound knowledge in this area

Tom