silicon oil for Grampian and others...

[motorino]

Hi Trolls!

Different impressions when use different centistokes..

I recomend only use 100 and 200 centistokes, 500 centistokes are very hard, the trebles go down a lot!

But 500 centistokes (like SAE90 density oil or "valvoline transmision gear oil") its very good for the damper, more definited cut sound, add a damper in my system are one of the best improvements how i made

Cheers



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[markrob]

Hi Motorino,

Thanks for that info. I know emorrit uses 500cst. I recently broke down and bought a gallon (Yikes!) of 350cst oil. It was the smallest size I could find at the lowest price.

http://www.chemistrystore.com/product.cgi?group=88697&product=88698

Appearently 350cst is food grade and more readily available. Its several lifetimes supply of the stuff. Good to know I can use as damper fluid. I have not had a chance to give it a try as I'm swamped with work.

Mark

[motorino]

Hi Mark

Do you know the silicon spray for demoulding? Normally this sprays are very cheap and only have silicon oil and a propellent...

In the exterior (not inside your house ) make a small hole with a plier in the spray cupule joint (little little or empty all) and wait 2 days for evaporate all the propellent, and you have silicon oil about 200 centistokes for 3 bucks

Buy two diferent sprays, and compare the viscosity, 200 centistokes its like a oil car, 100 centistokes like a vegetable oil, 500 like a gear heavy oil

You can mix diferent silicon oil

Cheers

[emorritt]

I use 500 cst and have more high end than I'd like... Motorino I thought you were using Flo's preamp schematic like I am. Since I was getting too "bright" high end FLo suggested changing the 50pf cap on the input to a 30, but I haven't tried yet, just make highs adjustment with EQ. Is it possible your head has solidified buildup from other fluids used over the years that may be damping in the high range and keeping the recommended 500 cst from working properly? Just a thought...

[motorino]

Hey Emorrit, you knows very good the Grampian

My Grampian needs rebuild, now the drive coil have 6,7 ohmns, i remember when i buy it have 3,9 ohmns, the black colour denote burn... my valve amp burn a 18" 1000w rms sub too in a party, 6 x kt88..



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Do you know Westechservices?

[emorritt]

Yes, I've had Gib work on a couple of heads for me. I don't know if Len at HRS does Grampians - I know he doesn't repair single coil mono heads or crystal heads like Gib at West Tech does. Len does all the service work on my Westrex heads and amps.

Your coil looks pretty rough. The Grampian 'D' head is supposed to have a DC resistance of 3.7 ohms on the drive coil and 23 ohms on the feedback coil; plus your braid wires shouldn't be tangled like that. I don't know that my head has ever been rebuilt, but the braid wires are neatly coiled separately extending up to the terminal block. They're shellac insulated, but still shouldn't be kinked up and touching. You probably should contact Gib and ask about a rebuild. His website is http://www.west-techservices.com/

From the appearance of your coil I think your high end issues are coil related, not damping fluid related. Grampian used the silicon fluid for damping instead of using a plastic or rubber part like Presto (e.g. "Prestoflex") and other manufacturers did.

[emorritt]

Markrob - a GALLON?!?! Bet that set you back big $$$. I bought a 100 gram bottle of 500 cst from Spectrum Chemical (it's thinner than you might think); they have an online website where you can order. The item number is SI112-100GM 100 grams is enough to practically last a lifetime because you use so little. They also have 100 and 1,000 cst ratings available. Dow Corning has a wider range of cst ratings in their line of silicone fluids and they will send you a sample as well. However, I've used the recommended 500 centistoke fluid and had no issues. Like I mentioned to Motorino my high end is too "bright" IMO and Flo recommended changing a few components in the preamp which I haven't had time to do yet. Wanted to locate a breadboard to experiment with, then only make the changes to the unit I built once.

[markrob]

Hi emorrit,

It was not too bad at $38, but unless I find some other uses in the future, I've got a several lifetime supply of the stuff. I have a local supplier, who custom mixes silicone oil, but they also would not do less than a gallon and wanted almost $80! How much was a 100 gram bottle? If its not too expensive, I might get an assortment experiment with.

Mark

[emorritt]

It was $42; the 1 kg is $142. Makes me wonder now if silicone oil and silicone fluid are two different things since what you got was so much cheaper. I would think that just about any oily fluid could be used for damping a Grampian head. Before I located the source for the 500 cst fluid I was told to use 20 weight motor oil - which is roughly the same viscosity of the 500 cst fluid. Probably a '6 of one, half dozen of the other' thing...

[markrob]

Hi,

The place I got my oil indicates its Dow Corning 200.

http://www.chemistrystore.com/cart.cgi?group=88696&child=88697

That's the stuff specified in the Grampian doc's you sent me (Thanks again BTW!).

While we are on the subject, do you ever flush out the old oil or is is lost to the environment over time? How often do you add new oil?

On the preamp front, awhile back I ran some circuit simulations of the Jamaika pre from Flo. I found that there is a small bump in the 5Khz range of about +2db. Not a big deal. I played around with the circuit elements and came up with a version that uses standard value parts and seems to tame the peak. Here are two screen shots of my simulator with the changes.

First, the original:

http://home.comcast.net/~markrob1066/pwpimages/Jamaika_original.JPG

and the modified:

http://home.comcast.net/~markrob1066/pwpimages/Jamaika_mod.JPG

I haven't built this to verify, but it should be correct. To simulate, I cascade the preamp circuit with an ideal RIAA playback transfer function block to show the response from cutting to playback (which should be flat).

Mark

[motorino]

Hey Emorrit, a comercial men from Repsol explain me the viscosities looking the diferent drops running in a pirex, well i believe isnt an engineer but knows her work, i know this men few years ago.. and i look the demostration

I look 500 centistokes like sae 90 oil, sae 90 oil at 30º centigrades have "same" viscosity, multigrade car oil like 10w40 at 30º its like 200 centistokes, its my impresion.... i dont know this silicon oil origin but isnt it Dow Corning

Mark i go to tray your examples, now im working in a new scheme, with the jamaican in mind but in passive, with tech help, with 5687 valve and input transformer, adding the filters in small pcb for selecting in the preamp, half speed too, and feedback preamp with "bus" posibilities, and a good bipolar amp, no valve for the amp. I speak about this proyect with some people and i have the help! I need some weekends..

When i finish... you knows

Cheers

[markrob]

Hi,

Sounds like a cool project. Look forward to seeing the results. I have something similar in the works. I pickuped up some old Heathkit tube phono preamps and am modding them to use the passive IRIAA from Flo. They will interface directly to my Dynaco Mark III tube amp.

I've seen the comaprison of SAE motor oil to viscosity. The problem with motor oil is that the viscosity changes so much with temperature. The advantage of the Silcone oil it that its temperature dependence is much lower.

Mark

[Kris D]

Hi,

Anyone tried warming up the head like this:

The trick was to put it down onto acetate and make it sound the way the public wanted to hear it at the sound system dances. Thats why I went out to these dances so that I could "capture" the sound the way they wanted to hear it. The disc cutter was a fixed pitch Neumann lathe with a Grampian MQY mono cutter driven by a Gotham amp. I happened to meet George Piros, the master cutter at Fine Recording Studios in NYC. He advised me to warm up the cutting head by feeding straight tone into it for about 5 minutes...."Get them coils and armature loosened up, man"...and purge the damping fluid that Grampian supplied, replace it with high quality brake fluid, administered with a special hypodermic needle cut to size so that the fluid would actually get down to the armature instead of bopping around the magnets.

From SH forums interview with Graham Goodhall aka Goody of Federal Recorders Jamaica

Thanks - Kris

[markrob]

Hi kris,

Very interesting post. I can see the advantage of doing some pre-heating to get the head near a stable operating temperature. The question would be what power level should be used? I would think the best bet would be to try and aproximate the RMS of the track to be cut. I guess a good way to do this would be to just play the track back once or twice without actually cutting.

The brake fluid coment was also very interesting. Not knowing anything about brake fluid, I did some searching and discovered that some fluid is actually silcone based. Looks like DOT5 is the correct stuff. I assume he was targeting that type.

http://www.imperialclub.com/Repair/Brakes/brakefluid.htm

It makes sense to try to get the fluid where it would do the most good.

Not sure how to purge the head of older fluid. Any suggestions?

Mark

[ameise]

Hi,

Len once told me to not use any damping oil with Grampian Type D.

Although i got myself some silcone oil with the correct specs
from Dr. Tillwich (i tried V250 and V50)
http://www.dr-tillwich.com/
i found it also better to notch out or electronically damp the resonance frequency (use Match-EQ from Logic for example, to get an impression
on how the curve could look)

but of course the oil might also be good to transport the heat of the
drive coil system...(but i never had problems with that when cutting dubs)

greetings
mart/ameise

[motorino]

Hi friends

Brake oils (dot 3-4) have some metal aditives like zinc, cadmiun and others like sulfur (sulfur its the "best" and cheap lubricant for all packet in oils)

The oil base can be silicon but the 90% of all oils have a aditive packet (only oils for planes or jets are single syntetic oil very expensive)

This metal parts can conditioning the cutterhead normal functionment?
Ferrofluid can be a best option? I think I'll try ferrofluid on my old rca MI cutterhead

Cheers

[motorino]

For cooling my grampian i use the out of my kitchen freezer compressor, this compressor i use like vacuum for my lathe little noisy and powerfull suction

Cheers