Restoration of an Eko Viscount Reverb amplifier

Great work, thanks for this nice addition to my schematic collection !

You're wellcome! Thanks for the appreciation, I really hope it will be usefull for all those having troubles with Prince and Viscount. It helped me in trouble shooting a couple of issues this amp had when I found it. Well it had more at that time, but at least it was possible to hear some sound coming from the loudspeakers until it stopped playing

PART 2
Inductor
Another fast and easy job: some cleaning, light rust removal plus transparent and insulating paint to avoid future rust. The insulation of the two wires was broken in some points, I fixed it with heat-shrinkable tube.


Chassis
The case and the chassis restorations are the biggest jobs of this project. First of all I removed all the electronics from the chassis: components board, front panel jacks, potentiometers, transformers, inductor and the two big electrolytic capacitors. Here are some pictures of the naked chassis.




The chassis was slightly bent in some places, probably because of the heat coming from the power transformer and from the output tubes or because of some hits during transports. I straightened it and then I removed the rust, first mechanically (sand paper) and then chemically with a first bath in phosphoric acid, also useful for rust proofing.


Some weldings were needed to restore cut away parts and to fix the two wands between the front and the back sides.



The chassis is now almost ready for the final work. One electrolytic capacitor needs a larger hole to fit its pins and four more holes for the clamps’ screws of both capacitors. The original sockets are in such a bad condition that all need to be replaced: all retainers are missing and the silvered contacts have no more silver attached to them, only thick oxidation and rust. Sockets identical to the original ones (noval, bakelite, chassis mount with retainers) are not available anymore, there are only the ceramic ones. I chose the type with normal contacts, because the gold plated ones have too little gold on them and this causes more problems than those the plating is supposed to solve. The new sockets need larger holes because they are bigger than the original ones and, due to the different orientation of the pins, new holes for the screws need to be drilled.

I’m taking the chassis back to the blacksmith to complete this job. After the restyling for further rust removal & proofing the chassis will spend some more hours in a phosphoric acid bath and it will be ready for the final finishing.

Originally the cassis was lightly chromed, but now all the chrome has been detached from it because of rust, bends & cuts, weldings and holes enlargements. I think that the final look would have been horrible with the chrome back again and so the cost would not be justified. I painted it with a zinc based paint exactly as I’ve done with the power transformer and with the reverberation unit.


After the painting I started reinstalling the components: irons, two big electrolytic capacitors and tube sockets with retainers.




Ciao!

PART 3
Knobs
Originally there were two knobs missing, those of the vibrato controls, and one more is almost gone while disassembling the amplifier: although I tried very hard I was not able to unscrew its screw, so I had to take it out of the potentiometer in a “hard” way. Luckily I found three knobs on eBay in a more than excellent shape! I then cleaned all of them and enlarged the holes to be able to fit them on the new potentiometers.


Jacks and Pots
The potentiometers are all Alpha apart for one CTS for the vibrato speed control. I’m going to change the mains switch too because in the original one part of the chrome has gone away.

The jacks are all Switchcraft apart from the footswitch and the phones ones. You can foresee some add-ons I’ve already planned: this amp will have phones output and two jacks for the loudspeakers, obviously plugging the phones in will disable the loudspeakers, it’s a very little and super fast add-on that will make in home use more comfortable.


Tubes
It took me three hours of searching in my OOS (Old Old Stock) and testing using my AVO Mark III mutual conductance tube tester, but finally I have all the tubes for the amp tested and matched. The result is:
- three Telefunken ECC83 (one with long plates);
- one Siemens ECC83;
- one EK ECC83, it tested much stronger than the others and will be installed as the driver for the output stage;
- one unknown brand ECL86;
- four 6P14P/EL84M Reflector military Russian tubes.
The matching I’ve done for this amplifier, considering it is not audiophile/high end, is for me very satisfactory:
- ECC83 within +-3% for each section of each tube, +-5% between tubes;
- EL84 +- 5% between tubes.

A little note about tubes. I do not like brand new (chinese) tubes, they test and sound much worse then old ones, no matter if they are NOS or used but in good condition. Nowadays NOS tubes have terrible prices, so brand new ones are the only choice for projects that are not “cost no budget”. For my audio equipment I only use military grade Telefunken, Siemens, Mullard, Philips, Amperex and Tungsol tubes, in my opinion they are the very best; in the future I’ll give a try to Russian NOS tubes, so far I only tried their equivalent to 6SN7 but I didn’t like the result, red boxed low microphonic Tungsol are “miles away”.

Circuit board
It’s time to lay my hands on the electronic circuit board! While reverse engineering this amp I spent some time in testing all the resistors to place an order for all the electronic components. Apart from the “mustard” capacitors that will be tested with power applied to the amplifier, electrolytic capacitors, small capacitors (56pF, 100pF and 470pF), potentiometers, solid state diodes, shielded cables and out of tolerance resistors are all going to be replaced. Because of the increased filter capacitors value I decided to employ bigger diodes: BY255 rated 1300V 3A, stronger that the original BY127 rated 1250V 1A.
I decided also to replace the original coupling capacitors in the critical points: the reverberation unit driver and the output tubes. The others are not critical because, in case of leakage the maximum current flowing in the following tube is limited by both the anode and cathode resistors that have high values. If the coupling capacitor of the reverberation unit driver fails, the input stage of the reverberation unit would be blown away. On the other side if one of the coupling capacitors of the output tubes (those before the control grids) fails the current in two output tubes would raise dramatically leading to sure damage of the tubes and, in worst cases, of the output transformer too. These are definitely issues I want to avoid, so here we have brand new Audyn Cap capacitors waiting to be installed on the circuit board.

Let’s take a look at the original circuit board. It’s very well engineered and constructed, the layout is neat, especially the ground paths have no loops at all, not only considering the board itself, but also the shielded cables to and from the reverberation unit, to and from the front panel jacks (inputs and footswitch), to and from the controls (volume and tones), moreover the grounding is done at the output of the circuit, as it should be. There are tons of articles about grounding schemes to be used in audio equipment (CD players, amplifiers, etc.). An in depth look at this 1967 amplifier tells you all. Great school!
Front side…

… and back side.

As you can see while disassembling the amplifier I put some stickers on all the cables I detached from the transformers and from the tube sockets: this will be of great help when I’ll put everything back together because I will not have to continuously check the schematic diagram.
Here all the replacements.


After some time with the soldering iron in (and on!) my hands here is the result.


Ciao!

telefunken diamond are bestin this amp

Hi lokrian,
thanks for your suggestion. In my extremely messy lab I still have some places where to look for other ECC83s. Last time I've been at my father's place I didn't have much time to both look everywhere and to test&match all tubes. When I read your reply I recalled I have some other tubes I didn't find while searching for all replacements. Somewhere I have some 50 russian 6SN7 (6H8C) I wrote about that I did not see, this means that I did not search in every place. Awful mess !
I know for sure that somewhere there are also the original Telefunken EL84 that I used in a vacuum tube integrated amp I made some 10 years ago. I know they are there, I never throw away tubes!

During the Christmas holidays we took our nephew to a big musical instruments store where he had the opportunity to test... well let's say play with a lot of acoustic and electric guitars. He really liked a Gibson, I don't remember the model, only its golden color and its tag price... 2500€ After playing with a couple of Marshall, one Fender and one Pevey amps I connected the guitar to a Vox AC30. Astonishing! We all really loved that sound. The difference in sound dynamics and richness was dramatic... of course only in my/our opinion.

Lokrian, by the way, can you please tell us a little bit of this amp? How does it sound like?

Have a nice day!

Hi Stefano, We have had email contact about the eko valet amp thath I recently obtained, and you have really helped me out by sending the drawings and advice about the transformer... I'm putting this link of my dutch thread here, about the eko valet. It's in dutch, but maybe it can be of use for others to come. I'll also put the links to photobucket, wher I've put a lot of pictures of the Eko Valet amp:

http://www.gitaarnet.nl/forum/(...)19132

http://s277.photobucket.com/al(...)2002/

http://s277.photobucket.com/al(...)alet/

Bye, Piet.

Hi Piet,
thanks for your appreciation. From tyime to time I take a look at your thread. Don't give up, you'll dominate your amp!!!

Ciao
Stefano

What was wrong with the electronics
Some jobs I’ve done to the electronics were more preventive than actually fixing. As I’ve told you the substitution of the electrolytic capacitors is a good habit when you deal with vintage electronics and high voltages. I found some resistors out of tolerance (>15%) and three were interrupted. Both the resistors of the reverberation unit driver had greater values leading to a lower gain and higher output impedance of this amplification stage; one resistor of the phase inverter of the power amplifier was interrupted so only a half of the output stage worked and the distortion was high. The most interesting thing was the interrupted 4.7M resistor of the neon driver of the vibrato effect: this prevented the circuit from working. This failure probably convinced the previous owner to internally install another circuit of which the only clue was the two different potentiometers installed in the chassis.
Other issues came from the potentiometers. Although they were not interrupted and had a good mechanical movement their values were all out of specs. The 1M ones (volume and bass+mids) were between 800K and 1.3M and the 500K (treble) were about 800K, this would have prevented a good performance of the tone control network. Front panel jacks and tube sockets were far beyond any possible recycling, new ones were a must!
All these issues may look like a disaster and in fact it almost is, but let’s not forget where I found this amp (junk yard) and where it has been stored for 18 years: in a loft, humid, cold in winter and awfully hot in summer, definitely not a proper place for electronic equipment!
A picture of all the scrapped components.

I could have stopped at this point but it would not have been good enough for me. The original tubes were in still good shape but I decided to change them with selected and matched ones, all apart from the ECL86. At this point my aim to have almost perfect electronics took control of my mind. Those 40 years old coupling capacitors made me think a lot, I was worried that sooner or later a failure would have been experienced. I have looked for some time for capacitors of the same brand, the so called “Mullard mustard”, but I could only find used or NOS ones at high prices. In my opinion NOS is fine but it depends what we are referring to. It is for tubes, transformers, knobs, etc. but when we talk about passive components such as resistors and capacitors the scenario changes… dramatically! The characteristics of this type of components are not static, they change as time goes by. This is due to use, storage, humidity, temperature and age. The degree of such changes also depends on the quality of the components, meaning for example if they were produced according to standard specifications or to military ones. A NOS capacitor that has been properly stored, after many years might be like new. Unfortunately nobody can guarantee the “proper storage”. A NOS capacitor that for example has been stored in a humid place with big temperature variations, might have capacitance out of tolerance, current leakings because the internal structure oxidized or it might fail after a few hours of use. Keeping all this in mind I decided to change the remaining capacitors too. I decided to install components with sonic characteristics similar to the original ones. The usual metallised film (MKP, MKT and so on) are of course out of the game; no NOS Mullard mustards stored in a nice “nobody knows where”… so what else? The answer is quite simple: military grade PIO russian capacitors, but only aluminium foil, no metallised paper, so I chose the K40Y-9 (aluminium-paper-oil) and the K72P-6 (aluminium-teflon) types, probably among the best capacitors for sonic performance.

And here is their internal structure (thanks to Dmitriy of Radio-Spare).

They are NOS… so what about what I’ve just written??? Well, first of all they are all military specs; they are air tight because glass sealed, so no air can go inside; they come from military surplus so there are many many many more chances that they have been properly stored than for those “found in the shop of an old TV technician that passed away” and, last but not least, the ones I bought have been made in the late ‘80s or early ‘90s, not 20 or 30 years earlier. This, in my honest opinion, is a huge difference and a good guarantee of many years of trouble free service. The only 220nF MKT Audyn Cap are the coupling capacitor of the reverberation unit and the one in the negative feedback loop.
Before refitting the electronic board in the chassis I’m going to replace all the shielded wires… this for me is really boring.
I hope to be back soon.

Ciao!

8O

Solen got good poly cap, also, not quiet as "Vintage" as your russian alu-paper-oil, but good nice stuff too.

Hi, thanks for the suggestion. By the way I'm still looking for a replacement of the 2200pF (0.0022uF) caps, I only found the K72P-6 aluminium-teflon capacitors rated 1600V They are huge and I cannot properly fit them on the board Another choice is ERO KP1832 or KP1838 but I couldn't find any of the correct value. At the moment the last four "survivers" can stay there, they are not in critical places, but as soon as I'll find a good replacement they will go
I have plenty of time for searching, the cabinet is still untouched and it needs a lot of work

good work stef' !

WHAT DO TOU THINK ABOUT THIS?

Hi everybody!
my main interests are old cars and electronics applied to hi end audio, I don’t play any instrument, apart form oscilloscopes, distortion analyzers and audio oscillators. I’m 42 years old and I started playing with electronic components when I was an 8 years old kid, long time ago! At the age of 21 I moved my interests to hi end audio gear and ended up designing my own equipment because the “off the shelf” products were definitely too expensive. I really like tube equipment and my projects are all tube based. As you can imagine I’ve been playing with high quality components for quite a while and in these years I had the opportunity of testing many of them. I used to purchase them at fairs where I was allways able to find a supplier with good prices, NOS components of excellent quality. I suppose that fairs are still the best place where to make good deals, but now I have little spare time so I have to rely on the internet sources. As far as I know the 12AX7/ECC83 (and any special quality or industrial/military grade variant) is not of high interest for hi end because there are many other tubes much better performing in terms of both completeness of reproduction (soundstage, micro and macro dynamic contrast, image focalization, tone aberrations, etc.) and electrical characteristics (transconductance, capacitances, plate resistance and output impedance). You can check this with fast search in just a couple of forums. Because of its low noise and high amplification factor it has been used in most equipments through the past four decades. Although I have no experience with guitar amps, but anyway they are electronic circuits and I understand a little bit of electronics, I begun this project to have a present for my nephew that started playing guitar last year. In the last few months I’ve been searching the internet for spare parts to be used in this restoration project: on-line shops, ads, forums and obviously eBay. We all know the last one and indeed sometimes it is a good place where to make good deals. Sometimes… but actually I should say “seldom” especially when looking for collectibles or vintage stuff. Given all I have so far written (please excuse the length) and the fact that NOS tubes usually perform technically & musically better than some new ones, I have to understand the reason for such prices, I think you are the best candidates for the answer
ECC803S – I know it’s a SQ type, but always an ECC83
450£ one piece

1,299US$ two pieces

1,333.33€ four pieces, affordable!

There is no good reason for these silly prices, apart from the growing rarefaction of NOS tubes.
I mainly use NOS tubes, and you can find good ones for a way better price.
Added to that : the more sought after NOS tubes are not the best to use in a guitar amp imho (Mullar and TFK give pretty tiny lows).
Least : ECC803S JJ (NOT a real ECC803, but an actual LP) or Sovtek 12AX7LPS are great guitar-amp tubes.
I am a 12AY7 user too, and i can assure you that the EH modern one is 99,5% as good as my 1953 one (speaking of tone, as for the relaibilty, i don't know yet, but who care's if a 15$ tube does not last 20 tears ?).

Thanks a lot!
Probably tonight I will be able to power it up after such a long time and work! I'm looking forward to see if everything works fine.