tapes whether vhs, audio or betamax are all mechanical devices and are subject to wear a used tape has usually worn best trying to use new media for new recordings old ones sometimes have drop-outs etc

Indeed, tapes do wear out after a while, but they can usually be re-used a few times. Certainly for broadcasting I'd use a new tape for something high quality like classical music, but for speech a tape that wasn't too heavily used would suffice. Also, record at the highest possible tape speed; 15ips for high quality, at the very least no less than 7½ips. Full track mono or half track for stereo. And a decent machine like a Revox B77.

Yeah for anything important I would probably opt for a new or NOS tape (or record digitally) but for most of my recordings, which are music mixes dubbed from digital or vinyl, I'll reuse tapes until they get worn enough enough to have significant drop outs. Sometimes if the drop outs are close to the ends of the tape I'll just cut out the damaged portion and resplice the remaining tape to the leader before reusing.

I've never used a reel to reel machine so for cassettes, I'll use a type II for anything important, if not then I'll just use a type I. Would love to have something like a Revox B77, I got a pile of 1/4" reel tapes (mostly new) that I could make use of.

I've never used a reel to reel machine so for cassettes, I'll use a type II for anything important, if not then I'll just use a type I. Would love to have something like a Revox B77, I got a pile of 1/4" reel tapes (mostly new) that I could make use of.

The Revox B77 is a beautiful machine, we had three in the studio, one in each of the 2 control rooms and one rack mounted in the equipment room which was used for playing in pre-recorded programmes when the station was unattended. Sadly they are hard to come by now, and when they are they cost upwards of a couple of thousand pounds, so we won't be getting one any time soon 

I wonder if I can use a preheat ballast as a degausser, connecting it to direct mains and operating it by short pulses not to overheat it.

I wonder if I can use a preheat ballast as a degausser, connecting it to direct mains and operating it by short pulses not to overheat it.

You need to make sure the magnetic field decays slowly compare to the AC period. Otherwise the tape ends up magnetized, so very noisy. So never use switch to deactivate the field close to the tapes, move them away first.
And for the demagnetization you would need way stronger field than common around ballasts.

You need to make sure the magnetic field decays slowly compare to the AC period. Otherwise the tape ends up magnetized, so very noisy. So never use switch to deactivate the field close to the tapes, move them away first.
And for the demagnetization you would need way stronger field than common around ballasts.

I just ran a 40W ballast and tried to demagnetize a neon screwdriver and it kind of worked; the ballast could run for quite some minutes before getting a bit warm. But the magnetic field leaking out of the ballast can do at best nothing, I would need to remove the iron sheets but that's impossible without destroying the windings. Unless I use the leaking magnetic field from a 1kw induction motor I could do a bit over nothing without tearing things apart. Seems like the best way would be to wind my own coil.

In my opinion the best way to create a strong enough magnetic field that is powerful enough to clear the tapes is with a powerful magnet. 
Not trying to create one by running a ballast.

In my opinion the best way to create a strong enough magnetic field that is powerful enough to clear the tapes is with a powerful magnet. 
Not trying to create one by running a ballast.

Powerfull magnet does erase the recorded signal, but leaves the tape magnetized. And because the tape is a grainy thing, when magnetized the grains irregularities cause the field to become irregular along them, hence the noise.
If you want to eliminate tge noise, you need to demagnetize it completely and for that you need a slowly decaying AC field.

The erase head does that to some extend (to the depth of normal recording), provided it is a proper AC erase/bias system (usually operating at few 10's kHz) and not the cheepeese permanent magnet and DC bias recorder.
But it does not demagnetize all the material in the full depth, so the noise from the deeper layers remains, once it was magnetized (e.g. by the typical "whole cassette" permanent magnet eraser; those are intended to destroy the recordings, not that much to clean the tape for new use).

I still believe that the electromagnet I showed earlier is the best way, it is what we used in the radio station I volunteered at, although mainly for reel-to-reel tapes rather than cassettes. Put the tape on the top of the device, switch on and slowly rotate the tape a few times, then while still powered, very slowly move the tape away before switching off. Worked every time.