EMT 140 Tube reverb restoration tips?

[mrclunk]

A friendly London studio, with help from a member here, donated an mono EMT 140 to my mates place and i've been tasked with getting it operational. 

I'm going  to work out what needs doing later this week and was hoping to, please,  draw on your combined genius!

When we moved it i had a look inside and the plate its-self looked fine, had all the clips attached and bubble around parts of the frame to stop it clanging around.

The tube driver / amp needs lots of work. Psu's been tinkered with and couple of the tubes were broken/missing. 

However i'm not really worried about the driver / amp,  its the pickups and driver magnet (coil?) that is the unknown for me..

There's a box of bits which i think contain the driver mount, some old coils and a conical shaped bit of metal which is the driver?? I'll take some pictures when there.

Anyway if anyone can think of stuff i should be checking, i'll be indebted to you!
thanks
paul

 

[Rob Flinn]

By coincidence I am having exactly the same model plate delivered here tomorrow morning so can take some pics if you need more detail.

I have worked on a few of these in the past.

The conical shaped bit sounds like the driver coil & is riveted to the centre of the plate & is Brass I seem to remember.  It has a coil wound on it.  The magnet, which is like the magnet on a speaker fits over this.

One of the best upgrades for this is to do the peizo pickup upgrade it drops the noise floor 10 or 20dB.  It is a big improvement.     

If you are messing with the amp, be careful with the wires.  On the valve version they are insulated by wrapped thread.  If you have to disconnect them the thread has a habit of unravelling, which can be a royal pita to sort out

 

[mrclunk]

Thanks Rob, going up to look at it tomorrow so I'll report back. I don't remember seeing the magnet when we picked it up...
Peizo pickups sound well worth it. Control rooms a long distance so it'll need all the help it can get.

 

[Rob Flinn]

Because the peizo pickup is much higher Z than the standard pickups the mod requires 2 or 3 component changes, from memory, maybe 2 resistors & a cap or vice versa, but I'm not sure which or what values.  However, my friend who I performed the mod for thinks he still has the documentation, & is hopefully going to dig it out.    The peizo pickups are just the standard roughly 1" diameter disc variety that are quite cheap. The process was to polish the area where you plan to glue the pickup with wire wool. The pickup is then glued in place with the type of glue that is used to stick a rear view mirror to a windscreen if I recall correctly.

 

[mrclunk]

If your mate could dig out the piezo circuit changes that would be great!
However i may just build a ss driver and pickup amp.. The tube electronics are in really poor shape, lots of rust, missing  tubes etc..
Also it would be nice to have two piezo pickups for stereo.

Good news is that the driver cone and coil is still attached and  measures 13 ohms. Plus the driver magnet was in the box of bits from the techs at its last home.
I'll need to clean up the magnet as its quite corroded . Bit of Brasso and some wet and dry should do the job!

Question for you, there's what looks like a removable casing on the back of the driver magnet. Should i be able to separate that from the magnet assembly? Its fused on with corrosion by the looks of things...
Anyway off to do some more research.

 

[Rob Flinn]

I would look at the echo plate driver amp & pick up amp.  I used to have an Ecoplate II that was great.  Brighter sounding than the EMT because of the stainless steel plate.  The electronics uses pretty easy to find parts & you could build it on veroboard quite simply (if you don't shun the stuff).  It sounds fine too.  I think the sound is more in the mechanics than the electronics.  The diagrams are pretty easy to find but if you get stuck I could mail 'em to you.  If you decide to ditch the original amp I could be interested in restoring it to make mine stereo.

You shouldn't need to take that plate off the magnet.  Thing to don is use some isopropyl in the gap to get rid of any metal particles which might abrade against the coil.

Best

Rob

 

[radardoug]

For the driver amp, buy a 20 watt  Chinese kit amp off Ebay, cheap as chips. The original valve EMT amp is underpowered.

 

[gyraf]

some of the sound I like is in the driving underpowering..

 

[mrclunk]

I had a quick read about the echo plate electronics, thanks. Looks simple enough.
There's a few old power amps knocking around, could use one of them and possibly just run a piezo pickup into a DI + mic amp for now, while i figure out the tube stuff. 
I need to research the eq thats applied to the driver signal. 
I don't think the owner will want to let go of original driver/amp i'm afraid Rob...
I've loads of posts bookmarked to read through here at the weekend.
Thanks guys!