Copper Wire for FAIRCHILD 541 A Mono Cutterhead???

This is where record cutters raise questions about cutting, and trade wisdom and experiment results. We love Scully, Neumann, Presto, & Rek-O-Kut lathes and Wilcox-Gay Recordios (among others). We are excited by the various modern pro and semi-pro systems, too, in production and development. We use strange, extinct disc-based dictation machines. And other stuff, too.

Moderators: piaptk, Simon, mossboss, Aussie0zborn, tragwag, Steve E.

Copper Wire for FAIRCHILD 541 A Mono Cutterhead???

Unread postby Gus » Mon Feb 13, 2017 8:34 am

Hi,
I would like to rewound my FAIRCHILD 541 Mono Cutterhead from 500 Ohm to 8 Ohm i have available one reel of Enamelled Copper Magnet Wire of AWG 30 and one reel of AWG 32 what is better to use for rewound AWG30 or AWG32 and why?

Thanks in Advance!

Gus
User avatar
Gus
 
Posts: 198
Joined: Wed Jun 05, 2013 4:38 pm
Location: Athens


Re: Copper Wire for FAIRCHILD 541 A Mono Cutterhead???

Unread postby markrob » Mon Feb 13, 2017 11:20 am

Hi,

If you really want to wind to 8 ohms, you would have to measure the AC impedance at a specified frequency (e.g. 1 Khz). I don't think that is necessary, since most modern solid state amps can drive a pretty wide range of loads. The best bet would be to use the finer gauge wire and fill the bobbin(s). That will give you the largest length of wire in the magnetic field and therefore more force generated for a given current. Next measure the DC resistance and make a note of it. If its in the range of 3-7 ohms, you'll probably be able to drive it fine with your power amp. If its too high. Try winding the larger gauge and see where you land. If its too small, you would need to go a bit smaller in gauge. At the end of the day, the power handling is limited mostly by the I squared R loss in the winding. The current in the head also determines the force generated on the cutter stylus. So its a trade off. Once you get the winding in range, it would be good idea to determine the operating level in voltage drive a 1Khz that will produce a 5 cm/sec recorded velocity. Most heads are able to do that with a watt or so drive. So, at 8 ohms, you would be looking at 2.83 Vrms. That would be a good place to start. The actual power to your rewound head might not be exactly 1 watt at 2.83 V drive, but it will be in the ballpark.

Hope that helps.

Mark
markrob
 
Posts: 1086
Joined: Wed Nov 28, 2007 2:14 am
Location: Philadelphia Area

Re: Copper Wire for FAIRCHILD 541 A Mono Cutterhead???

Unread postby Gus » Thu Feb 16, 2017 3:25 pm

markrob wrote:Hi,

If you really want to wind to 8 ohms, you would have to measure the AC impedance at a specified frequency (e.g. 1 Khz). I don't think that is necessary, since most modern solid state amps can drive a pretty wide range of loads. The best bet would be to use the finer gauge wire and fill the bobbin(s). That will give you the largest length of wire in the magnetic field and therefore more force generated for a given current. Next measure the DC resistance and make a note of it. If its in the range of 3-7 ohms, you'll probably be able to drive it fine with your power amp. If its too high. Try winding the larger gauge and see where you land. If its too small, you would need to go a bit smaller in gauge. At the end of the day, the power handling is limited mostly by the I squared R loss in the winding. The current in the head also determines the force generated on the cutter stylus. So its a trade off. Once you get the winding in range, it would be good idea to determine the operating level in voltage drive a 1Khz that will produce a 5 cm/sec recorded velocity. Most heads are able to do that with a watt or so drive. So, at 8 ohms, you would be looking at 2.83 Vrms. That would be a good place to start. The actual power to your rewound head might not be exactly 1 watt at 2.83 V drive, but it will be in the ballpark.

Hope that helps.

Mark


Thank you Mark!
Thank you Mark!
Finally I re wound my Fairchild with AWG 32 my multi meter reads DC Resistance 5.2 ohm, also the magnet recharged,and i replaced the rubbers who are placed inside the tubes,cutterhead connected with 300 w power amp and it sounds very loud and crispy
i'm waiting to receive a new one sapphire to test it.

DSC_0521.JPG

User avatar
Gus
 
Posts: 198
Joined: Wed Jun 05, 2013 4:38 pm
Location: Athens

Re: Copper Wire for FAIRCHILD 541 A Mono Cutterhead???

Unread postby grooveguy » Sat Feb 25, 2017 2:09 pm

Hey, Gus,

Looks like you did an excellent job there! I used to have one of those heads; it cut a pretty decent-sounding groove. One comment: from what I see in your video, there appears to be a huge gap between the armature and pole pieces, at least as near as I can tell looking through the little glass window. When I rewound and rebuilt mine, I think I used two thicknesses of typing paper on either side of the wedge-shaped armature... much closer anyway. But you seem to be getting good action from the stylus with a low AC drive voltage.
grooveguy
 
Posts: 225
Joined: Thu Jun 22, 2006 5:49 pm
Location: Brea, California (a few miles from Disneyland)


Return to Secrets of the Lathe Trolls

Who is online

Users browsing this forum: aaron, Baidu [Spider], Ben, Google [Bot], Yahoo [Bot] and 21 guests