Presto 8dg refurb. (Lathe porn)

[Simon]

Hi guys,

I put my lathe down for a few year and am looking to finish it this year

I posted the video on YouTube with the rare variable pitch unit.

Presto were know to make test/sample models and put them out in the field for testing.

https://youtu.be/g4E6ysveYpg. Here is the link.

I am still trying to build the relay element for the third motor as mine was missing.

I would like to know if I can just swap out the 78 motor for a later 45 one if I can find one for sale .

[sameal]

I am still trying to build the relay element for the third motor as mine was missing.

I would like to know if I can just swap out the 78 motor for a later 45 one if I can find one for sale .

I drew out a schematic of the 45rpm adapter plate, was that you?

I think switching one side of the transmission box to 45 would require at the very least a 45rpm worm gear as well for inside the transmission. I could be wrong.

[sameal]

For anybody else needing that information, and can decifer my hyroglyphs, here it is according to my machine

[Simon]

thanks that’s what I needed

[Simon]

I see the type 50 ohm res

But what is the type and value of the other ?

Also you show two solinoids on the the diagram .

One on the mount arm that throw arm for the puck and another next to the 40uf 240v cap.

Looks like a black selenium rectifier, any numbers or values - I think I can see EDI PRS

I think you replaced the cap and added a blue one instead, you may have an idea of what you replaced it with


Thanks

[sameal]

I see the type 50 ohm res

But what is the type and value of the other ?

Also you show two solinoids on the the diagram .

One on the mount arm that throw arm for the puck and another next to the 40uf 240v cap.

Looks like a black selenium rectifier, any numbers or values - I think I can see EDI PRS

I think you replaced the cap and added a blue one instead, you may have an idea of what you replaced it with


Thanks

Here's a close up of the plate electronics. I'll get the resistor value asap.

I believe those resistors are ceramic. I'd really like someone to confirm that they are ceramic and not wire wound.

The selenium numbers are clear in that photo. Im not sure which numbers are needed. If your building from scratch i would ditch the selenium and go with a modern rectification solution, and then share that solution here.

From what im told those seleniums emit toxins when they go. I don't know the severity of that situation, however id just skip the whole affair and get something modern in there. Also any seleniums you find would probably be NOS as opposed to new manufacture.

Their is only one solenoid in the plate. The drawing by the motor cap is my artists rendition of the motor.

I did replace the original electrolytic capacitor with that blue one you see. I went value for value on that i believe. 40uf @ 250v

[Simon]

It looks like a

EDI E3

PRS 250

I think the resistors are wire wound ones.

I will start hunting for a modern alternative

[Simon]

No the same make, but I just found this cool old catalogues

http://www.tubebooks.org/books/srhbst.pdf

http://www.vacuumtubeera.net/SeleniumRectifierCatalogs.pdf


I think it is a 130v 250ma


I found a nice vid showing how to replace the SR with a diode and a resistor

https://youtu.be/EVOaKQXCu64

[Simon]

So I have purchased the following

1 x motor start 40 - 50uf 240/250 volts

To replace SF
1 x 20w 100ohm ceramic resistor
1 x 1N5404 Diodes 3 Amp 400 Volt


Now to get a bit more information on the two other black wire wound resistors.

RES 50 ohm ??w tapped resistor, this is for adjustment - any other writing on it ?

Make sure the power is off!

Are you able to measure the resistance of the tapped resistor? End to end should be 50 ohm. Then the from the connected tap to the centre tap measure resistance. I think this will still work while in line....then I can buy one with similar value as yours without the tap

?? Ohm Type AB 10w resistor - any other writing on it ?

[sameal]

Im gonna try and get those measurements soon.

[Simon]

No problem. Thanks again for all your help

[sameal]

No problem. Thanks again for all your help

So the 3 terminal resistor is 50 ohm at the connected terminals. Taking a measurement on the third disconnected terminal gave me 100ohm. So they are using it as a 50ohm.

The second resistor gave me .4ohms no matter how i placed my leads. That doesn't sound correct, so it may need to be lifted from the circuit for accurate measurement. I did finally see the print on it. " IRC "

[sameal]

I wedged myself back there and got some better photo's. Looks like the second IRC resistor is 500 ohm

[sameal]

And i made v2 of the air chuck. Much better.
I cored a guitar knob out to fit the spindle of the platter and a small copper tube. Works much better. I kept the set screw and leave it close but not touching the spindle. Now i can feel the vacume pull the lacquer.

I also added fans and a controller to the vacume box. Which is actually pretty quiet. But heat still rises to past 100°, but slower now.

[Simon]

Thanks so much for the new picture. I will start putting mine together and post some pics

[piaptk]

Dang. A cored out guitar knob is a great idea for a record clamp!!! Never even considered it! Perfect for anyone with a k8, 8dg, 75a, etc. just ordered a few knobs!

[sameal]

Dang. A cored out guitar knob is a great idea for a record clamp!!! Never even considered it! Perfect for anyone with a k8, 8dg, 75a, etc. just ordered a few knobs!

At first i was trying to reinvent the wheel which almost worked. But i saw some photo's of a few chucks that looked like a guitar knob too me just kinda held by gravity.

I think i took a little too much out of mine but it still works. I might try again.

[sameal]

Tonight to combat the wow and flutter i was getting i cut my own prestoflex filter disc joints out of rubber i got from a cut your own gasket hardware store kit.

And it worked!

Thanks to mr. Kris d for the tip on the wow and flutter source issue.

[rsimms3]

I'd recommend a hole punch set, super handy when making your own neoprene slip mats and in cases like this.

[sameal]

I'd recommend a hole punch set, super handy when making your own neoprene slip mats and in cases like this.

Awesome. Im watching a set now.

The "make your own gasket kit" has enough sheet to make maybe 2-3 full sets. Might make a few more with those punches.

I think it pretty succesfully removed the weird wow and flutter type stuff i was getting on playback. Not bad for 6 bux.