PART 4
Hi all! It’s a very long time since I last wrote a post. Many things happened meanwhile. Keep on reading and you’ll discover some of them!
End of the boring job!
It took me many hours to refit the electronic board inside the chassis. It was not a mere “screw & weld”: I changed all the shielded wires rooted them as far away as possible from high voltages and from the AC heaters supply, then I fastened them with cable ties, I also finished their terminations with a heat shrinkable tubing. Not a very “vintage” solution but good for safety and trouble free operation. I again had some troubles with the “new” PIO and teflon capacitors: because of the diameter some of them were a little bit too “high” and it would have been difficult, if not almost impossible, to refit the chassis inside the cabinet, so I had to reposition other components in order to gather some space to correctly position them on the board. At the end I sprayed PCB insulating paint on both faces of the board. I have to admit that from time to time I stopped working to admire the job: I really like it!
In the internet, thanks to an extremely kind guy (thanks a lot Andrea!) that patiently answered my requests I had the opportunity to view pictures of an Eko Prince Reverb and to check the components values of the vibrato circuit. My suppositions were almost all correct apart from the intensity control that is a 50K linear potentiometer and the resistor in series with the frequency (VELOCITA’) control that is 56K. I’ve updated the previously posted diagrams.
I still have to refit the front panel bulb and the voltage selector because I first have to complete the job on the front panel badge… do you remember that nice hole?
Front panel badge
This would have not been a tough work if that horrible hole would have not been drilled in to this badge.
Anyway, after a couple of nightmares I came to a solution. First of all I took the faded black paint back to its original black color. I used a thin polishing compound, in the next picture you can see the difference between the untreated (left) and the treated (right) paint.
Now it’s time to fix the hole. I cut a round piece of aluminum sheet of the exact measure and shape of the hole, with a hammer I fixed it in the hole then I finished the job with some resin. I chose this solution because there was no way to weld a sheet without damaging the paint and the writings around the hole. Here is the result, still to be painted.
Black paint…
… some artwork and transparent paint and the job is done!
Output transformers - 2
Some time ago I wrote that it was an easy job… until I powered the amplifier. I realized that these transformers had problems because I could not get anything more than a mere 9W out of the amp!!! I tried first changing the power tubes, I swapped 2 new couples but I could still get 9W. Everything seemed fine, but it wasn’t. After 30 minutes of measurements I decided to retest the transformers and I found that one of the primary windings (there are four in each transformer) was interrupted in both transformers. I fixed them but when I powered the amp again another primary winding blew up. Too bad!!! Probably in all these years of far from perfect storage the insulating paint got damaged and the wires oxidized in some points, it was not possible to try to fix them again. I bought a new couple from an artisan here in Milan specialized in transformers. By the way, I searched for the original part and it seems to be a Philips PK 508 12 (15W output power, 7 Ohm secondary, 8 KOhm plate to plate). I think it might be useful to post the winding specifications of the original output transformer because it should be common to all Eko production of the late sixties (Zodiac, Valet, Duke, Herald, Prince and of course Viscount) employing a push-pull of EL84 in the output stage. Here is a JPEG with all the specs, I hope I did not mistakes counting turns
After 8 months finally the electronics are finished.
Some tests
It’s time to connect the amplifier to the instruments and take a look at the performances. A couple of shots at the first signs of saturation (25W/4 Ohm)…
… and at approximately 10% THD giving 30W/4Ohm, I consider this its maximum power output.
Cabinet
Now that the work on the electronics is finished it’s time to take care of the outside. The tolex was beyond restoration, there was no way to get it in a comparable shape of what will be inside. Here is how the front looked like…
… and this is the back side.
First step is to remove the old tolex without damaging it in order to have cutting guidelines for the new pieces.
The old pieces…
… and the new ones.
Then it is the cabinet turn: I removed the old glue and filled all voids caused by use, cigarettes (!) and water with a wood filler, then I smoothened the surfaces with sand paper. The same for any other irregularity in the surface or edges, such as small gaps in box joints. The top of the cabinet was slightly bent, this is how I got it almost straight again.
The result just before applying glue and tolex.
Some black paint inside before the “sticky job”.
And here is the final result after replacing the logo badge, handle and feet.
Here is an interesting link about tolex application, unfortunately the original WEB site is no longer available, it links to a thread where there is the original text but not the pictures:
http://steelguitarforum.com/Fo(...).html
I had also to rebuild the back side cover because it was missing. Here you can see the pieces…
… and the final result.
Having new transformers with 4-8-16 Ohm outputs that paralleled give the possibility of connecting 2-4-8 Ohm loudpeakers I decided to have a connector for phones (connected to the 2 Ohm output) and two jacks for loudspeakers connected to an impedance selector (4-8 Ohm).I installed everything on a panel to be screwed in the rear side.
Another facility I added is the IEC connector. Not vintage at all, but safer and more comfortable than the original fixed cable. Moreover, I used one with a mains filter inside to have a cleaner supply.
The final result!
Loudspeakers
After 8 months of searches finally an ad came up: on sale a 2x12 Eko cabinet of the late sixties. I contacted the seller asking for photographs. Oh yes, it is the original one!!! It has only one loudspeaker and not original, it’s a Jensen C12K. Well, not too bad, I already have two cones of the sixties waiting to be installed in a cabinet. Here it is when I received it.
I removed the Jensen loudspeaker and installed mine. After a couple of days spent on restoring the tolex using some pieces cut from the one of the amplifier, new screws on the rear side, a new handle and here is the final result.
In the meantime something else happened. One day while parking my car near the office I saw a P.A. speaker case (only the cabinet, no cones nor the crossover network in it) laying on the ground. After 10 seconds it was in the trunk of my car. It was all painted with some sort of red paint that never dried and there was a rectangular hole on the top. Ugly indeed! Anyway, I took it home and began working on it. I removed all the corner protections, the handle and the jack plug. It took me a long time to remove the paint from the cabinet and from all the parts. The tolex was almost perfect, great! I only had to fix the hole and to cover it with some tolex. After three hours of work the cabinet was almost like new! During 2009 summer holidays a neighbor decided to clean up the cellar and gave me a pair of loudspeakers with a broken woofer. I didn’t need the woofer, because it was too small (20 cm - 8”), but I used the crossover and the tweeter (a very nice one with aluminum horn). I drilled a hole for the bass reflex tube, I recovered the damping material from the loudspeakers and carefully fitted and fixed inside the cabinet, then I installed the crossover, the Jensen C12K woofer and the tweeter with its level control. I used a grill to protect the woofer. Here is the speaker for voice and/or acoustic guitar that cost me… €12,90 of paint thinner!
The complete system
All comments are welcome!
Was it worth the effort?
That’s a question I asked myself several times. When I decided to begin this project I thought that in about six months I would have finished everything. During this period I had some issues with the electronics (original schematic, output transformers, some components were difficult to find, etc.) that slowed me down. Then I decided to have the complete system almost as sold back in 1967, more searches to be performed that added to other things I had to do. At the end it took me almost two years to finish. So it’s really difficult to answer the question. I have no idea of what should be the current quotation. I’ve seen some ads for the Prince Reverb ranging from €450 to €550, not restored, in a “as is” condition but anyway well kept. The Viscount with it’s 2x12 loudspeaker was the top of the line in 1967 catalog, although not completely original (loudspeakers) and with the effects foot control still missing
I do not want to think at the money spent, but let me tell you that considering all the hours spent on this system… well I wouldn’t do it again for anybody. For me it has been a pleasure doing it for my nephew and sharing this experience and information with anybody who is reading these notes. I hope they will be useful for anyone having troubles with this or other similar amplifiers.
Ciao!
