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Mad idea, Use VHS video-head ferrite chips on an N1700 drum.  

 
Alastair
(@alastair)
Reputable V-Ratter Registered

Always up for some experimentation I plan on Trying to use a set of VHS Head-chips in a Philips N1500.

Now--My 1500 is modded to half speed anyway and uses 1700 heads with good results. Both 1700 and 1500 heads are unobtainium these days, so to conserve the life of the two sets of good heads I have, I plan some experiments. I have a number of cheapo 'Matsui' VHS new heads, and I plan on murdering one of them. I'm guessing no-one will be wanting a head drum for a VX1000 or VX1100 anytime ever. :qq1

Obviously, There will be NO compatability with either N1500 or N1700 formats as the VHS heads are a narrower track at summit like 50uM while the 1700 is 80uM as I recall, and probably the azimuth angles are different too.
Not worried about any compatability, I would just like to run the machine and not worry about how much life Ive got left in it, to conserve the heads I have. A modded dead head-drum, of which I currently have 3, is my idea.

I see many obstacles and problems, not least in harvesting the ferrite pole-pieces from the VHS drum, as these are stuck with epoxy to a brass insert thats bolted to the drum.
--There's no room to fit this brass part holding the head to a Philips drum, as the head amp and side of the lower-drum would be in the way, so only way is to pull the chip itself, or do serious machining to the Philips lower drum and the head-amp, which I havent the facilities to do, and could also make the lower drum unusable for correct Philips format heads.

There was an article in 'Television' many years ago about re-using Philips heads, taking one good one from one drum and fitting it to another.
My plan is similar, but replacing both heads. Through research Ive found that the head needs to protrude from the edge of the drum by approx 1.5 thousandth of an inch. I'm thinking that I can with reasonable accuracy make that distance happen using a spacer of 1.5"" and a large Jubillee clip... :bbeard

Head dihedral position adjustment will be rather more vague and hence no compatability with anything--even another similarly modded drum--Not at all worried by that.
Head height will be governed by the accurate machined face where the head sits on the drum just as it did originally with the Philips head chip.

I'm guessing the makers used extremely high power microscopes to see the position of the head-gap and special optics to observe both heads at the same time, and some kind of reference marks, maybe even lasers were used Ive no idea.

I have no such technology--only a basic USB microscope.
Using this, I plan on marking the position as accurately as I can the current gap position before old head removal, and then using this mark, to line up the approx position of the new head gap. (Which I cant see with a VHS head, but just visible for a Philips head)

Line the new chip up, ensuring its square and up against the spaced jubillee clip, then stick the thing on with super-glue, leave for an hour then re-inforce with some epoxy, its then a simple job to re-connect the head leads to the Philips drum.

IF it should somehow work, I'll be writing 50uM slant-azimuth tracks but will also have a 30uM guard-band, basically as thats the constraints of the tape-speed for a 1500 running at half-speed--Maybe I could even slow the tape-speed even more....

All good fun!

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Topic starter Posted : 30/01/2015 4:46 pm
Refugee
(@refugee)
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Lining up the heads on mono reel to reel machines the manufacturers used to sell a stereo microscope that had to be bolted to the deck.

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Posted : 30/01/2015 4:59 pm
boyblue
(@boyblue)
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Maybe not so mad Alistair, some years ago I was given a low speed 96 hr. VCR that had done huge hours. The heads were very worn. I replaced the original magnetic parts with ones from a brand new Aiwa drum. I didnt line them up very carefully as I wasnt confident of good results. After a bit of fiddling, great results. Zero compatibility with other machines though. Go for it !

Peter

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Posted : 30/01/2015 5:30 pm
Anonymous
(@anonymous)
Illustrious V-Ratter Deactivated Account

Lining up the heads on mono reel to reel machines the manufacturers used to sell a stereo microscope that had to be bolted to the deck.

Done that in 1977. Once.
Unless the heads are premounted on a drum top half, it's pretty much needed.

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Posted : 30/01/2015 7:14 pm
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator

As you say, it's a mad idea, but what have you got to lose?

Have you ever considered loading a Philips VCR cassette with tape 'harvested' from a VHS cassette - it does actually work quite well, but the VHS tape is thinner (I'm led to believe) than the VCR stuff, but you can extend the life of a VCR cassette that way, and can increase the available 'run-time' for the shortest tapes.

I'm thinking here though, that using harvested tape could be a better alternative than trashing original tapes by running inaccurately placed heads and other potential unknowns.

As an aside, try shining a light through a VHS tape, and then the Philips stuff - notice which one allows the light to show through?

Marion

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Posted : 30/01/2015 9:02 pm
boyblue
(@boyblue)
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Yes Katie I like your economy! Many years ago when VHS tapes were expensive, I had the idea of reversing the tape end to end so that the worn start of the tape appeared at the end. Its not that easy to do as you cant just reverse the reels. Anyway my ruse worked but gave the initially puzzling symptom of old recordings appearing upside down! A little thought showed the reason, also the lack of sound. In spite of no sync the pictures were remarkably stable.

Peter

Who said it wouldnt work?

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Posted : 30/01/2015 9:23 pm
Refugee
(@refugee)
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And the video may also have been upside down.

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Posted : 30/01/2015 9:27 pm
Alastair
(@alastair)
Reputable V-Ratter Registered

Funny you should say that, Marion.....!

Been doing that for some time. I found that it takes 1.7 x 4 hour VHS Cassettes to make 1 LVC180 sorta equivalent. A tedious job to do, but worth it.
At my last job, I rescued around 30 4 hour TDK cassettes, so I'll be OK for a while!

A big bonus in doing this is the VHS tape surface seems somehow shinier/smoother than the Philips stuff and doesnt have that nasty matte black back-coating that seems to increase the backtension the Philips/BASF type tapes have, so maybe could increase the head life.

A lesser bonus is a greater RF signal from the higher remnance VHS tape., gives less drop-outs...

VHS tape seems to pass through the machine easier than the original tape, maybe its more flexible.....

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Topic starter Posted : 30/01/2015 9:46 pm
Alastair
(@alastair)
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Ah--So, Run into a couple of problems!

The first issue was I Thought I had a number of cheapo Matsui heads. It appears--as I vaguely remember--giving some away a good few years ago.
I did however find one head-drum fitted to the lower-drum and head-motor mounted on top, and was clearly unused.

I successfully removed the two heads from the drum and from the brass inserts using heat from a soldering-iron to soften the epoxy fixing. On one head the connecting leads unsoldered cleanly and threaded back out through the hole in the brass plate. The other, one lead broke near the soldered point, but still had about 3mm available.

The head chips however are very much shallower from front (tape contact face) to the back (Drum bearing side) so the mounting is only about 1mm wide taking into account the cut away area for the coils. They are about a third the depth of a 1700/Philips head.

I was able to mount the heads--in a similar way to described, but used clear sellotape tape rather than a metal Jubillee clip. The tape I measured at 1.5 thou thick, so one layer was applied to the Philips drum, then cut away at the point the head is mounted.

Another layer of tape was used on top of this, but not cut. It was surprisingly easy to locate the head-chip, as the sticky layer of the sellotape assisted in holding the chip lightly while it was lined up. When I was happy, I applied light pressure to the head-chip vertically to hold in position while I applied just a tiny amount of Super-Glue which due to capilliary attraction was 'sucked' under the head-chip. I held it for 1 minute, and did the same to the other.

I left the drum for an hour, then mixed a little epoxy up and applied to the top of the chip and the area behind the chip. The coil wires were partially covered in this glue--Big mistake!

The head-chip with the full length of coil wires soldered up fairly easily to some added 38 gauge tinned copper wire and connected to the mounting-posts on the drum. I checked the resistance of the head chip coil after disconnecting the rotary-transformer and found a 2.1 ohm resistance. Seemed reasonable so I coated these rather feeble thin connections with some UHU type adhesive.

The head chip with one short head coil lead however was a problem. Even though the iron was set pretty cool, the short wire from the coil seemed to just vanish. Dunno what happened to it. Maybe all the messing around had made it fragile and it just fell off--no idea.

So, Where we are now is with one apparently mechanically and electrically sound successful transplant and one broken head coil. I removed this dead head-chip, no point in leaving it on there, and no way to repair that broken lead, as it was under the epoxy and too close to the head face.

I may have another new basic VHS head-drum somewhere, so I'm stopping proceedings till it or another turns up.....

At That point, I'll have to determine whether its Righty-Slanty or Lefty-Slanty that needs to be fitted, as the coils are both yellow on these heads, with no ID on the original head-drum....

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Topic starter Posted : 02/02/2015 10:55 pm