Guys, I have some questions about the Presto K8.
With new tubes, what would be the best frequency response of the cuts?
Can it be adapted for 33 and 45 rpm? How?
Can it cut 12 inch blanks?
Is the amplifier relatively easy to rebuild? I would think any K8 would have to have the amp rebuilt and the caps replaced, right?
Any help is appreciated.
Retro
Presto K8
Moderators: piaptk, tragwag, Steve E., Aussie0zborn
Hi,
I'd expect response to about 6-8Khz. I would not replace the tubes as a first step in restoration unless you can see the tube is damaged. Re-capping is a must with old equipment. As a bare minimum, the power supply electrolytics should be done and any interstage coupling caps should be replaced. Normally, any mica or ceramic caps can be left alone. Typically, the paper foil caps will have high dc leakage which will upset the bias of the tube stages. The two most critical parts are the two coupling caps from the phase inverter to the push-pull power stage. If these are too leaky, you can cause the failure of the output transformer.
You will also need to do a mechanical overhall as well. Old lubrication tends to get gummy and causes all sorts of issues. The idler wheels might need attention if they are dried, cracked, or have flat spots.
I don't know the K8 that well, but you can probably get the 45 speed by making a sleeve to slip over the part of the motor shaft the drives the 78 speed idler. By making this diameter larger, you slow down the turntable speed. This may require some other changes in the mechanics. If that's not possible, you could cobble a motor speed control using a AC inverter. The inverter creates an AC supply at a lower frequency that the normal 50 or 60Hz. That will make the motor run slower. This approach is much more costly, so I'd look at mechanical methods first.
Hope that is of some help.
Mark
I'd expect response to about 6-8Khz. I would not replace the tubes as a first step in restoration unless you can see the tube is damaged. Re-capping is a must with old equipment. As a bare minimum, the power supply electrolytics should be done and any interstage coupling caps should be replaced. Normally, any mica or ceramic caps can be left alone. Typically, the paper foil caps will have high dc leakage which will upset the bias of the tube stages. The two most critical parts are the two coupling caps from the phase inverter to the push-pull power stage. If these are too leaky, you can cause the failure of the output transformer.
You will also need to do a mechanical overhall as well. Old lubrication tends to get gummy and causes all sorts of issues. The idler wheels might need attention if they are dried, cracked, or have flat spots.
I don't know the K8 that well, but you can probably get the 45 speed by making a sleeve to slip over the part of the motor shaft the drives the 78 speed idler. By making this diameter larger, you slow down the turntable speed. This may require some other changes in the mechanics. If that's not possible, you could cobble a motor speed control using a AC inverter. The inverter creates an AC supply at a lower frequency that the normal 50 or 60Hz. That will make the motor run slower. This approach is much more costly, so I'd look at mechanical methods first.
Hope that is of some help.
Mark
Get a copy of http://audacity.sourceforge.net/
There is an option to play at 45 rpm to 33 rpm
So when you play back the disc - it will play at 45 rpm
There is an option to play at 45 rpm to 33 rpm
So when you play back the disc - it will play at 45 rpm
Happy to learn something new.
Wanted: Stylus for Presto, Mono heads Grampian, Fairchild, Presto, Fairchild 740 lathes, Presto 8n, 8d 8dg lathes or parts or Presto or wot ever recording Amps, PM me what you have for sale.
Wanted: Stylus for Presto, Mono heads Grampian, Fairchild, Presto, Fairchild 740 lathes, Presto 8n, 8d 8dg lathes or parts or Presto or wot ever recording Amps, PM me what you have for sale.
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retrosonic
- Posts: 10
- Joined: Wed Jan 06, 2010 12:24 am
Thanks!
Hey guys, thank you both for your replys.
Retro
Retro