Deep Grooves Mastering - Now Offering Mono Coil Repair!

[opcode66]

I've been working on replacing the coil in an RCA cutterhead I purchased that was blown. This video demonstrates the rolling solution I've devised. I can now make really nice mono coils of any size or shape!

If you have a fried mono cutterhead, I can now repair them.

http://www.deepgroovesmastering.com

[emidisc]

Have you attempted Saddle Coils yet?

[45rpmdude]

what are saddle coils. are they the mc 41 ???

[emidisc]

image.jpg

Them coils are looking great....
BTW hopefully I have attached a picture of a saddle coil

[opcode66]

I've never attempted a saddle coil. And, since it really doesn't fit with all the projects I have going at the moment, I'm going to pass for now. Maybe in a year or so I'll have time to try to figure that out for you. It would require a different rig and different jig parts. And, you are the only person on the planet asking me about these. So, I can't book the time on that right now. But, the future possibly.

[markrob]

Hi,

Anybody who owns a Grampian with a blown coil would want this type of winding.

Mark

[opcode66]

Certainly is doable. I'm not saying no. Just a lack of people willing to pay me to sort it out at the moment.

[45rpmdude]

There isnt enought month at the end of the money.. ha ha

i made a joke.. Ok so i have to wait a while to get the head fixed. ok

i see what you mean.

[opcode66]

I think you misunderstand. That is more or less a call out to other Grampian users out there. Do you have a blown head that is needing repair? If I get more than one, I'll try it for sure. Otherwise, I feel it is more important to the community for me to continue work on my reasonably priced high quality stereo cutterhead. Cool?

[ROLANDJAYS]

is there no body who can fix a grampian head these days?

[opcode66]

Gib does I think. But, you know.

Not sure if Len does. I could ask him.

It seems to me like all I would need to do is make a 3d design of the form and print one. I could probably even make a kit. Imagine a 3d printed coilform that was made such that it had guides to make the winding easy and the hold the major loops of the saddle coil. The coilform would be made in such a way that it could be disassembled and removed later. You wind the coil with a proper length of wire of the proper gauge to get the desired dc resistance (and therefor ac impedance for this inductor). You apply resin. You let it dry. You break away the coilform. Add some shrink wrap and some leads and your done.

After getting the hang of it and working out the coilform with guides and break away parts, I could crank out like 30 or 50 in a day. But, it is a lot of time and effort to get the first correct one if you follow. You are asking with deep sincerity. So, I'm willing to check it out. Is that picture of a loose coil that you have? Is it blown? Can you send it to me? Do you know what DC Resistance it is supposed to be? I can sort out the gauge with my caliper and then run the math for the length.

If you want to send it to me and pay for at least a spool of proper enameled wire I will take a look between other projects. If I can make these then I could make a lot of them at once. I've never studied the inside of a grampian. The more information and pictures you can provide the better. What does that attach to? Do I need to clone other parts or just the coil?

I will always assist passionate cutters the best I can. You sound like this really matters to you.

[emidisc]

The saddle coil in the picture is one I have wound myself using a small winding jig I made it's a very simple set up that can likely be improved greatly but I could find nothing relating to saddle coil formers?
The coils I have made are for my BSR cutter heads but it would be interesting to see a saddle coil from a Grampian especially the 1D? With feedback? I can post few pics of the method I use if it's of interest? I am not currently in a position to make coils for other heads nor do I have enough knowledge on the subject but after sending my cutter head to Gib waiting 6 months then getting it sent back in bits with a note saying he could not repare it I had little option but have a go...........

[opcode66]

Ok. Well, I guess I'm confused now about what exactly you want me to do? You just read what my plan would be to solve this problem. Sounds similar to yours. I might try lining the jig parts with saran wrap. It should not adhere to epoxy. Maybe silicone sheet would work too.

In my opinion, you want a really accurate jig that can be removed from the finished coil without damaging or deforming the coil. Even after resin is applied and allowed to dry, you want to be able to remove it easily from the jig. So, lining the jig with something that wont get glued by the resin seems to be the tricky part. But, solvable. Then, its all about making you coilform. Which, in 3d, I think could be done really cleanly. Make a couple pieces that are removable, and be sure the coil is easily released from the rest of the jig, and there you have it. Print a bunch of coilform jigs, line them, roll a bunch of coils, resin them, leave them out to dry for a week, remove the removable coilform parts, gently release the coil from the lined coilform, melt the ends of the leads, hook up an ohmmeter, measure dc resistance, if all good, throw it in the good bin. Done and done. Beer time.

To anyone else reading this thread, the main thing to point out is that the approach to making this sort of coil would be very different from the one I documented in the video above. Entirely different to be specific. I wouldn't need my winding machine at all. This would be done by hand with what amounts to a mold. No magnification required.

[Stevie342000]

As an aside the documents which may give you all the information are (I think) in the reference section, there are full drawings and it may even tell you how many turns of wire and the gauge etc etc.

You will find them in the BBC documents around 1942-45, there are 3 of them I think which relate to the Grampian head. In addition there it includes an article to modify one of the Presto amps for use with the BBC (Grampian) feedback head.

[45rpmdude]

im not following,, is Presto a grampian or is grampian a presto ? M 41 Megnetic head.

Ive tried rewinding the coil, several times,, the coil deteriorated. i was winding it with a straightened paperclip...

It looks like the one on gibs page Cutter Head Repair.. its just ive sunk more then enough money into this and its just called a money pit. I dont feel like paying 65 dallars to have gib fix it. I sent it to him twice,, youd think if it was borken hed fix it..
Ive been stubborn for this long. Im thinking about hanging up the towel.. Its just not worth it anymore to me. Ive ruined many dvd''s. I jut wanted to make some custom mixed records and play them for haloween. This bites ??????

[Stevie342000]

Relatively simple really the Grampian head has saddle coils the documents can be found referenced in the BBC R & D archive, with full drawings, specifications.

The BBC had Presto cutters, 6N lathes and 88A amplifier (I think from memory), anyhow it had 4 807s, this was on lease/lend during WWII.

The BBC modified the 88A amplifiers so it could be used with the Grampian feedback cutter head they were developing. They compared the Grampian to the Presto Head used with the same amplifier you just put a link in to complete feedback loop rather than run it from the feedback coil from the Grampian.

Additionally the BBC modified the Presto 41A Limiter, its mentioned in the documents, if you want to know how to wind saddle back coils the information is there for the picking. Simples...

For your Information the BBC designed and built their own equipment or modified existing equipment to meet there needs and there specification which was usually at the cutting edge of technology. For example there are documents in 1946 from the BBC R & D department about the report on the Magnetophon tape machine and its importance. The BBC saw that it would cut costs and increase flexibility. EMI had one of the machines and from that they got the EMI BTR1 in 1947/48 (as an aside in the US Jack Mullin had one and worked with Ampex) tape machine. The BBC did a report on the BTR1 and feedback to EMI who in turn developed the BTR2 in 1952. This time the BBC bought into tape technology and the writing was on the wall for direct to disc recording which is what the BBC report stated in the 1946 report.

Take up of the new technology was faster in US than the UK even EMI who designed the machines did not really take them seriously until the advent of the BTR2. The BBC were still using the same BTR2s in the late 70s or early 80s. The transports were so well built that after 20 years of constant use they had no noticeable were however the electronics were dated, so the BBC designed new Solid State Electronics and converted them from Mono to Stereo Machines.....like I said simples.....you need to go look in the reference or circuits section or do a search on this site for the BBC and you will find the archived documents.