Amp question for Presto cutterhead 1B

[chuckthemovieguy]

I want to thank everyone for their help so far.
It has been a frustrating and exciting project so far.

If you assume I know nothing you would be 100 percent correct, just a guy with a dream and a jukebox in need of records of my choosing.

I have a Presto 1B cutterhead. on the back it says 500 OHMs.
However written on the cutter head in marker it says 65 OHMs.
When hooked up to a meter it reads around 67 OHMs.
I would assume it has been rewired in the past?

So the question is, what kind of an amp can I use and how much power should it have.
Also what would be the correct fuse to use for this?

Thanks,
-Chuck

[tragwag]

I have a basic knowledge of this stuff, so someone more experienced should chime in.
here's what I know:
getting a reading of 67 ohms means the coil is wound for 500 ohm. it's because of the difference between DC/AC resistance (don't quote me on that)
it has not been rewired, and is probably all original.

I use the Presto 1D cutterhead with the 92 series amp.
It has a 500 ohm output impedance, and I believe about 30W output power.

Your main issue will be finding an amp with 500 ohm output impedance.
You may be better off getting the cutter head rewound to modern 8 ohm impedance for a few reasons:
- it's old and probably doesn't function right anyway (dampening is hardened, magnet is weak)
- it's hard and expensive to find 500 ohm amps, modern 8 ohm amps are more abundant and cheaper

hope that makes some sense, again someone with more technical knowledge should chime in

[chuckthemovieguy]

I have several amps lying around, 2 of them are tube amps.
I don't know how to measure the amp to determine the ohm output impedance.
How do I do this?

[tragwag]

best way is to check the manual/specs for output rating.
it normally says "Output 50W at 8 ohm" or something similar.

[chuckthemovieguy]

Where can I send my cutterhead to get it rewound?

-Chuck

[mratx]

Frequently on older tube amps that have a 500 ohm output there are multiple speaker connections on the back labeled for different ohms, so it may be marked on the back. If there are not multiple connections on the back, I would suspect it's not 500 ohms unless it's some type of specialized amp (like one designed for a specific record cutter.)

I don't know of a simple way to check the impedance on the output if you don't know it, the methods I know require knowing something about the output transformer or disconnecting it for testing.

As someone else who got into cutting solely to populate my jukebox, I wish you luck!

Mark

[rsimms3]

Like this but with a 500ohm tap.

[powerstrip]

you may not want to send it in to be rewound.

Look at the amp above.

See where it says "25V"?

you may want to find an amp with the 25V/70V taps, those WILL drive 500 ohm cutterheads.

Trust me on this one, I searched and searched and searched, as I have several 500OHM heads; and finally discovered those 70V taps work for 500 OHM

[tragwag]

Where can I send my cutterhead to get it rewound?

-Chuck

this is a sort of toss up,
a few months ago there was a forum member "master scott" rewinding heads, not sure what his status is.
Len Horowitz has been known to rewind heads, not sure if he's accepting those sorts of jobs at the moment. http://www.hrsrecords.com/
Gib from West Tech used to wind heads, again I have no clue if he's currently taking work: http://www.west-techservices.com/

[Steve E.]

re: Masterscott1:

http://www.lathetrolls.com/viewtopic.php?f=2&t=5154

[Presto Repairs]

The ratings for watts and ohms for 70v + 100v outputs are as follows...

490 ohm @ 70v = 10 watts

500 ohm @ 100v = 20 watts

I dont have a chart for 25v lines so unfortunatly I cant help you there...

If you are interested in getting your 1B rewound - Send me a P.M and we can discuss your requirements...