McCurdy CH-12

[FreaK]

So after a little back and forth with myself I decided to start a dedicated thread. I recently acquired one of these ‘tables as a motor unit after being pretty struck by the overall elegance of the approach.

They’re a funny case because they are like a slightly more agricultural cousin of ROKs more specifically the Rondine/B12 H, they seem to fetch a little bit more money despite that. The top plate for instance is sheet aluminium. The platter as well. The bearing design is similar but uses the drop out circlip thrust pad solution in a 2” diameter alu cylinder, rather than the closed end cast (iron?) Rek O Kut style.

This uses the 1/100hp Ashland D80KBU, whereas it seems the ROKs typically use the 1/200 variant, though ROK was apparently known for having loads of running changes as well. To that end I’ve seen at least three motor mounting schemes on these.

Currently planning on a plinth build not too dissimilar in format to the attached. The swivelling armboards in my case to be to the Micro Seiki equivalent fitment. I’m hoping to set myself up well for experimenting with different arm lengths and styles. I’ve started off by sourcing a Fidelity Research FR-24. Stretch goals include homebrew Schroeder or Supatrack. Love to try linear tracking but so many of the designs are ungainly.


Anyway, this will be the official spot for updates on this project as it moves along.
Hopefully I don’t blow up the value of these tables in the process, i think the going rate is about spot on for what they offer relative to what they demand, though sonics will be the final arbiter of that.

 

[gadget73]

Whats the spindle to thrust plate interface like, ball bearing like an ROK or is it a pointy spindle that runs right on the plate?

 

[FreaK]

It’s like this:
There is an upper and a lower bushing in the bearing case.The ball bearing is actually crimped in place. Never seen that anywhere else. Looks like a 3/32”.

 

[gadget73]

well thats interesting. When you said thrust plate held in with a circlip I was picturing just a flat polished steel plate, not an aluminum slug with a ball bearing captive in it.

 

[adnick]

Very nice table, thanks for sharing your project and knowledge

Had a very early Rondine Deluxe with 1/100 hp motor but otherwise ROK used that 1/100 motor on TR models….

The Captured ball reminds me of some Russco’s, although it’s in a grub screw.

Keep us updated….


Andy

 

[FreaK]

well thats interesting. When you said thrust plate held in with a circlip I was picturing just a flat polished steel plate, not an aluminum slug with a ball bearing captive in it.

TBF that’s what I thought I was gonna see when I popped the circlip too.

So speaking of the 1/100… I was able to open her up and it looks nice and clean, but ideally I’d like to be able inspect the fan and thrust bearing but the rotor appears to be captive?? There’s like a 1/4” of axial play with the top of the can open but with a hard stop.
I was able to disassemble the top bearing and make sure I had only clean new appropriate oil, but the oil I piped into the bottom bearing to make sure it wasn’t running dry(before I got some Zoom* turbine oil) is not meant for such applications

 

[gadget73]

Cover on the back with a fan under it? That would keep it in there

 

[frankhertz]

Hello,
I had one of these for about 10 years. I passed it on about 5 years ago when I wanted an automatic or semi-automatic turntable as I aged and got rid of all my manual turntables. Mine was bought from a gentleman who said it had come from The CBC studios here in Canada and was brought home by a former tech who worked there. The tech bought it home when the company was getting rid of them and built a large, heavy box-like plinth for it. It had a long Shure(?) tonearm. I made new armboards for the different tonearms I tried. It was surprisingly quiet for a turntable with the reputation for having a rumble problem. I did clean it and re-oiled where I could. The major problem was that it ran very warm. After a few plays, the records would actually feel quite warm. So I never played more than about 3 lps at a time. If I had been more adventurous, I would have taken apart the motor, cleaned and re-lubricated it. That was a step too far for me.
Enjoy the adventure. I hope it provides you with much pleasure.
Harry

 

[FreaK]

The two Ashland variants are known for running hot. This version with the fan is marked as 30 deg temperature rise. The fanless version seems to usually be marked 50deg.

I’ve heard with fancy motor controllers you can get some of the electrically induced vibration down and run the motor at a lower power setting meaning less is lost to heat too.

The one I’ve got my eye on is the HiFi HAT

H.A.T. CPS-2 - Thorens TD124 - H.A.T Hanze Hifi webshop

De jongste telg van het H.A.T. geslacht is de CPS-2 (Clean Power Supply 2). Het is een apparaat dat in staat is om de vervuilde netspanning op te schonen.

shop.hanzehifi.nl

Though the asking price is more than my Linn is worth. Probably not worth doing that kind of step till I’ve got the mechanicals are fully sorted.

 

[gadget73]

Also possible you can reduce the heat some in a pretty low-tech way, simply use a bucking transformer or even a light bulb in series with the motor to knock the input voltage down a bit.

 

[FreaK]

There is already a lightbulb that turns on with the speed switch. I’ll check to see if it’s in series or parallel with the motor.

 

[adnick]

There is already a lightbulb that turns on with the speed switch. I’ll check to see if it’s in series or parallel with the motor.

Don’t think You’re understanding Gadget’s suggestion, it will take a fairly large (wattage) bulb to power the table with the idler engaged. Lowering the voltage may reduce motor noise some, but I’m not understanding the desire to reduce motor heat, those Ashland motors are designed to run hot….

Andy

 

[gadget73]

probably in parallel.

The light bulb thing came out of a discussion in another thread. I think it originated with the Garrard 301 as a speed reducer thing but there were some thoughts that it may reduce motor noise a bit as well. Also might be useful depending on the motor's rating and your actual line voltage to drop 5-10 volts. High line voltage tends to make more heat.

one of these days I'll chuck together a dim bulb tester and see if it does anything for motor noise on my ROK. Maybe if I'm feeling ambitious I'll compare it to the variac at the same voltage just to see if I can tell any difference.

 

[FreaK]

Reminds me of some of the early diy Pass builds. I remember one with 4 or 6 like 40w standard lamps as part if the circuit. Made it look like a tube amp. I forget what the logic was in that design exactly but I assume it was to absorb a certain excess somewhere and act in the same way a tube buffer does in more recent designs.

 

[FreaK]

Side note: weird brainwave, has anyone made a plinth using fibrocement? I’ve seen concrete builds, some factory, and the companies who do fibrocement boards suggest you can treat it essentially like plywood. And since I’m planning, at least for the first pass, to do the classic stacked birch ply with pretty hardwood cheeks i was at the local home reno box store to see if they happened to have the good ply (they didn’t I’d have to order it in). While i was there I was doing the knuckle test on stacks of sheets and the fibro cement was remarkably inert.

 

[FreaK]

I do have one puzzler that I really don’t know what to do with. I have the platter sat on the bearing while I do various other things and as you can see the spindle sticks out like 10mm or so from the bearing. You don’t see this when it’s mounted as the clearance from the top plate to platter at the rim is correct.

 

[gadget73]

that may just be normal. I had a fair bit of that on my ROK when I had the platter just stuck in the bearing with it not mounted.

 

[FreaK]

Seems a little weird IMHO. Anyway, that’s a back burner question for the moment.
I’ve spent the last little while working out the cutout patterns. Hopefully I can upload some PDFs of them eventually for anyone else with one of these.
But I do have one near-ish term question.
My motor grommets are still soft but not in great shape. How can I tell what ones to replace them with? The markings look kind of ambiguous.

 

[adnick]

Those look exactly like the ones used on ROK tables

 

[Blackdog61]

Seems a little weird IMHO. Anyway, that’s a back burner question for the moment.
I’ve spent the last little while working out the cutout patterns. Hopefully I can upload some PDFs of them eventually for anyone else with one of these.
But I do have one near-ish term question.
My motor grommets are still soft but not in great shape. How can I tell what ones to replace them with? The markings look kind of ambiguous.

Look like these.

3 PACK ~ PARKER LORD RUBBER GROMMET ISOLATOR J2927-4-1 / J292741 | eBay

These are new and unused.

www.ebay.com