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Tuesday, December 11, 2018

Restoring a Harmon Kardon T40 turntable

A good friend recently spotted this turntable, being sold on ebay, buy it now at a reasonable price , and very close to where I live. We had both commented  in the past that the Harmon Kardon T40 was a nice looking deck, with it's deep platter and champagne colour, so it was impossible to resist. Not that well known in the UK, and advertised as not working, with a hinge missing and a burn on the lid. I bid, won and collected it from the seller, who was very helpful , and it was exactly as described.

Upon inspection the main problem with the deck not starting was due to the belt having petrified  and broken into small pieces. the motor worked as I lifted the arm across the platter and appeared to correctly eject the arm at the end of side position. The motor turned fine.

As well as the drive belt, the 4 rubber feet had also aged badly. As you can see from the picture ,all that remained was the 4 springs and parts of the rubber cup. I think there would have been a boot or castor on the end . These needed replacing or repairing as the deck sat very low, its baseboard resting on the surface. This deck is not a floating sub-chassis deck, it relies on the feet to decouple it from external vibration.

Fortunately the rubber motor mounts seems supple and worked well.

I unscrewed the four feet, and removed the screws securing the base board. You can see that the deck is well made with a wooden plinth, ply wood cross bracing and a very neat layout. The deck uses a DC motor, features speed pitch control and 'lock' and , also adjustable output capacitance for the chosen cartridge, quite unusual for a turntable, something more often found on more expensive phono preamps.

The auto functions of the arm use a combination of LED optical detectors to sense when the arm crosses the start of the LP - and activates the motor. At the end of the side the arm activates a micro switch, which both cuts the motor and ejects the arm using a small servo to trip the  raise/lower  piston.

As described the deck was missing a hinge, but I recognised the type as common across a range of turntables including the Linn LP12 and the NAD 5120. I had a spare hinge from a donor deck in my attic. You can get individual examples on ebay for around £10.

Exactly as described the lid had an ugly burn, the seller thought it was from acid, perhaps an old battery had dripped onto the lid while in storage. next job was to use some chrome polish to buff that out. With time and elbow grease it was almost impossible to see.

Other features included a removable headshell, here you can see the included Goldring cartridge. A small  plastic grube screw secures the headshell in place. It's a little delicate, and while this allows easy fitting of new cartridges, I dont think it is robust to support the kind of cartridge swapping associated with SME/Universal mounts.

Returning to the problem of the feet, I remembered I had some old turntable feet from an ancient abandoned project. Luckily the threaded brass rod from the rotted feet could be unscrewed and reattached to the rotel feet, using the original nut. So I was able to make new feet from both sets. The thread of the bolt is M6,  so  standard Technics SL1200 replacement feet, are also an option off the shelf. 

The replacement feet fitted well and because I had retained the screw, they can be used to level the deck. The deck no longer sat on its baseboard

The lid polishing slowly worked its magic. I used AUTOSOL brand metal polish, which is a very fine cutting paste. It took a while but slowly the mark vanished, to the point where only a reddish marke is visible.
In certain light a dimple can be seen where some of the surface has been rubbed away, but it's not too bad

I ordered and fitted the new belt  from William Thakker , reliable and cheap . 

It worked well. Initially I found that the speed was rather fast, and I needed to reduce the pitch control to get the strobe markings on the centre weight to remain stable. Later I found that I had left some debris on the motor pulley, from the old melted belt. I cleaned this off with a rag and some Isopropyl alcohol, till it was all gone, then the speed was correct and needed  no adjustment. the speed was also correct with the 'LOCK' function engaged. I'm not sure if this is a preset or actually monitors the speed of the motor, but it keeps the speed correct as per the strobe markings

The deck sounds very nice. The sound is engaging , a little lighter than my Thorens TD321. Actually the deck both sounds like, and  uses similar technology to the TD280, (see other blog entry).

I'm not familiar with the Goldring cartridge, and would tend toward getting a new stylus when you dont know the wear on the old one. The arm is very light so would suit a high compliance cartridge, for example the Ortofon OM-series should work well. It looks very smart indeed, and sounds great.