Restoring a ST-35 & EFBâ„¢

[Dynaco_WJW]

I was lucky to obtain a Dynaco ST-35. Here in the Netherlands you have to find these objects with a lamp! (Dutch saying). I had to drive about 100 miles for this beauty. It was clear to me that it had to be restored. For a extra $15,- I also bought two PAT-4's.



Under the hood are the famous Z565 output transformers



The cadmered chassis at the inside is in a good condition. The outside is unfortunately corroded. This corrosion could be removed mostly with silver polish



The circuit board is very dirty. These boards will be replaced by new boards from Audioregenesis http://audioregenesis.com



Next step is to completely dismantle the amplifier.

Update in my next posting.

[Dynaco_WJW]

Update:

Meanwhile all the components are removed.



As can be seen there is some corrosion on the cadmered chassis. If you want to clean corrosion of a cadmered chassis you can use Rust Stripper van Rust-Oleum. Unfortunately it is not for sale in Europe so I had to use something different..... (for the results with Rust Stripper see http://www.youtube.com/watch?v=-n8-vY7OBaQ



......I used some kind of silver polish. I had to make a foam and I treated the surface with this foam and got this result. Some deep corrosion points can still be seen. These I have to polish.



The bottom plate contains text. This may not be lost of course. There is a possibilty to bring it on again with silkscreening but I don't have any experience with this. For your understanding. The cadmere process is prohibited (only allowed for aviation products. When I should nickel or chrome plate it, it will not be original anymore and I try to keep the appearance as it was originally. On the next picture you see what the acid on your fingers do with the metal. Thats why I wear thin gloves when I have to replace a amplifier like this.



Finaly it looks like this. I guess I have to be satisfied with this result.




Next step is to clean all the components and polish the screws.

Update will follow soon.

[WA4SWJ]

Really, really nice! Good job so far. Good luck with the reassembly. Keep the pictures coming please.

Regards,

[dcgillespie]

WJW -- Very nice work indeed! The original ST35 is getting to be a fairly rare bird over here as well. It looks like your drive was well worth the effort!

Dave

[EWBrown]

That is very nice! This should give me some encouragement to re-start an ST35 restoration project which I let slip off my "radar" over the past few years.

I have three ST35 "carcasses" (chassis and metal top cage) with no PC boards, and they have all the original PA774 and Z565 traisformers.
The chromated chassis all have that scuzzy yellow chromate, correction: cadmium haze, but not too much actual rust.

Two of these have those obnoxious "tar dipped" PA-774s They tested out OK, but they are definitely not very attractive, no, just plain ugly...

Maybe Dynaco had a problem with "buzzy" power trannies in the early days

I bought six of the fiberglass ST35 replacement boards, scrounged up all the small components, and assembled them, but then I got no fiurther than that... NOS 7247s and 12DW7s are somewhat expensive, but J/J has an equivalent, the ECC832, so I bought a bunch of them.

These would definitely be good candidates for Dave's EFB modification, and better PSU boards (found three on e-bay) and a C354 choke in place of the 50 ohm 5W resistor. The can cap was just enough to do the job, the PSU boards, (which mount on the empty space on top of the chassis, as well as does the choke) offer a LOT more capacitance for the B+.

I also have a fourth ST35 which I built from a NOS / NIB kit, which I built back in 2003 (and which led me to find this website back then). I almost ended up just listing it on e-bay, could have made some nice $$$ but then, look at all the fun I would have missed over the past eight years
This one had the yellow "scuzz" on the NOS chassis, but it cleaned up very easily, and there was no rust or other corrosion.

I use this working original ST35 as "standard" with which to compare the newer designs (Like Shannon's ST35 boards) , which have better power supplies, and other circuit upgrades modifications.

/ed B in NC

[Dynaco_WJW]

@ed -- It would be nice if you also start to restore a ST-35. Maybe we can change some expierences during the restoring. I want to built in the EFB concept of Dave Gillespie in it but I don't know exactly how to do that. I have some ideas but I'm not sure about that yet.

You said you don't like the 'tar dipped' transformers. My power transformer is also 'tar dipped' and I must say that I like that. It is made like this about 40 years ago, so it belongs to this amplifier. And remember, nowadays, if you have a matte black painted car you would have a cool car. The new expensive cars are like this

About the chassis, I think it is not chromated but cadmered. Chrome has a bit of a blue colour, nickel plated is a bit yellow and cadmered chassis are a bit grey/yellow. To cadmere metal is forbidden right now.

I also bought the JJ-832 tubes. I bought boards from http://audioregenesis.com These boards are fantastic. I used these already in two SCA-35 amplifiers. These boards have their components already. You are lucky to have so many ST-35. Indeed they are worth a lot of $$$.
What can you tell us about the comparison between the ST-35's?

My next post will be some progress pictures.

[Dynaco_WJW]

Update restoring ST-35

I'm am cleaning the parts. The paint of the transformers was a bit weathered. I cleaned this with Commandant Cleaner nr.4. This has a fine structure and is suitable for synthetic bath-tubs, so the paint will not become scratchy. Naturally the letters Z565 may not be polished off!



The screws were rusty. I polished these with a Dremel and polishing paste. These brushes wear away quickly, I already placed a new one.



The new boards of Audioregenesis wil replace the old boards.



The parts for EFB™ are received now, also new wires. I wonder if the ST-35 was wired with different colours like is shown on the drawing. Who knows anything about that?



EFB™ stands for Enhanced Fixed Bias. This leads to more power and less distortion. Maybe the biggest change for this design of amplifier (ST-35 and SCA-35) since this amplifier is on the market. Dave Gillespie did 'invent' this EFB™. But you all know about this already...so no use explaining more. For one of my SCA-35 it worked out fantastic!!

A link to the article:
http://audioregenesis.com/efb/EFB-Technical-Description.pdf

Next step is cleaning the RCA audio input connection. I have a nice solution for this! Will be continued...

[Dynaco_WJW]

Update restoring a ST-35

I cleaned the RCA connector first with a brass brush and then polished it with polishing paste. I did the job fith a Dremel. On the next picture you can see the oxidation.

BE CAREFULL ALWAYS WEAR SAFETY GLASSES The pieces of brass fly off, so now and then I felt these pieces against my face!



After polishing, this is the result:



The screws where a little bit rusty. Also these had to undergo a brass and polishing treatment.




Now the assembling can start ...

The new circuit boards and speaker connections are in there place. I follow the original manual so nothing can't (almost) go wrong. I also have to pay attention to the EFB™ now. These parts need to have there place in the chassis. For removing old solder I use desoldering Litze. (blue roller on the photo)




Most of the wiring is done. The extra components for EFB are placed except the voltage regulator. My plan is to put this on a small piece of board together with a piece of copper. This copper has to be attached under a nut of the power transformer. Thus I don't have to drill in the chassis and the heat is brought to the chassis trough the piece of copper.



The 'new' resistors for EFB. I realized I had to use 'spare' connections of the tube socket...hmm...have to change that.....



Here is the drawing. The components in red should give the enormous upgrade :) (drawing thanks to D.Gillespie/Audioregenesis)



This is my idea to cool the regulator trough the piece of copper to the chassis. I'm looking for small test sockets for measuring the voltage but I can't find them anywhere here in the Netherlands.



Update after holidays...

[dcgillespie]

Wim -- to the best of my knowledge, Dynaco supplied either solid red (eariler), OR solid black (later) wire for the complete construction of their MK II, MK III, MK IV, and Stereo 70 kits -- I've seen both colors used in different units, but never both at the same time in a single unit.

With the SCA/ST35 amplifiers, things changed considerably. They initially introduced green and used all three colors: black for ground and AC power, green for Left channel wiring, and red for Right channel and B+ wiring. Later, on at least factory units, they introduced brown and white into the mix, so that the black, red and green colors remained for their existing functions, while now brown/white powered Right channel heaters, and green/white powered left channel heaters. All of this was presumably to minimize construction errors.

Search back through the original thread where I introduced the EFB(TM) concept on this site. There were a couple of fellows who installed the EFB modification in an ST35 -- clone, and original. One (who goes by "paart"), did a superior job of implimenting it into his original Dynaco ST35, and did quite a write up on it in my section of the Tronola web site (Dave's Lab). I think it appears here in the ST35 section as well. That might be of great help as you install EFB into your own ST35. With the quality of work you have shown, I'm sure you will have no problems installing it successfully.

As usual, your work looks superb! Should be stunning when it's all finished!

Dave

[EWBrown]

You're right, I should have said cadmium-treated (or cadmered), chromate can have variious colors, from a bluish tint to a golden-yellow color, but they never look like the"yellow mold" on the ST35 chassis.

I did lousy in Chemistry class, except when the prof taught us about making various gunpowder and pyrotechnic mixtures and other fun stuff

/ed B

[paart]

A product that I have found to work well for cleaning up the both the Dynaco cadmium chassis, and whatever finish that they used on the PAS preamps is common automotive polish and/or cleaner. I like "Turtle Wax" brand "Scratch and Swirl Remover". It comes in a tall, easy spill, dark green bottle with a red cap. I've found if you rub a small section at a time, let it dry and then rub hard with a soft cloth to remove all the polish, it will leave an "almost new" finish. It will not however, remove deep scratches or heavy corrosion, which is a difficult problem.

The ST-35 pictured in the article on the Tronola website, to which Dave referred (above) is a "factory built" unit, with original wiring, except the rectifiers, which I replaced. Most of the wiring is red or black, however, the assembler "livened it up" with splashes of green here and there, but obviously not to denote the left channel!

[EWBrown]

With at least one of my future ST-35 restorations, I plan on wiring it up for a quad of 6GK6 power tubes, instead of 6BQ5/EL84s, and using individual 390 ohm, 2W cathode resistors, bypassed with 330 uF / 35V caps (because I have LOTS of this particular value).

This approach would make using Dave's wonderful EFB design a lot more difficult, if not outright impractical, but finding a "matched quad" of 6GK6s might take a lot of culling through a large quantity, in order to find four which are close enough to run with a single shared RK.

The way the ST35 / SCA-35 PC boards are designed, this "conversion" to 6GK6s would be a very easy "modification", as the output tube sockets have to be hand-wired, anyway, so no PC etch cutting would be required.

6GK6 is equivalent to 6BQ5 / EL84, but with a somewhat different pinout.
As far as I know, there are no European or Russian 6GK6 substitutes, this seems to be a USA-only (and perhaps Japanese) tube production, possibly these could have also been produced in Canada (only "Geek" would know the answer this

These tubes are still reasonably cheap, so it's worth trying the alternate approach. Plus it should be no big problem wo wre-ire it back for EL84s if desired at a later time. There are cheaper 10V, 16V and 29V filament versions, but that would become a technical problem of its own, when using the PA-774 power transformer.

/ed B