[Joeztech]

Ron;

No, when I saw that they used the descriptive term Dynaco 470 transformer and I included the Dynaco Stereo-70 A470 transformer in my initial request that they would understand what I was inquiring about. I never expected to have to tell them that the primary had to have a center tap, two screen grid taps and two plate leads and that it was an ultra-linear design. They should know that if they purport to offer a replacement for it. Unfortunately they provide no photographs of their transformer nor do they show a schematic of their offering.

If I had been ordering a transformer for an antique radio I would have gone to more trouble describing what I wanted. If they do not truly duplicate the Dynaco A470 transformer, they should provide more details of the construction on their website.

This result came after the initial contact with them by e-mail left me believing that I was to receive an off-the-shelf item. Instead they had to manufacture the unit they sent me. That caused additional delays in receiving the part.

I do hope that they will be willing to credit me back for an item I can not use. I will still be out the expense of shipping it back to them.

Joe

[Ron Ramirez]

Agreed, if they advertise the product, then it should be the correct one.

[Arran]

The output transformer primary connections you describe sound like an ordinary push-pull type output transformer primary, like they have had around since the late 1920s at least. I thought that Williamson type output transformers also had extra windings, or taps, for feedback? Maybe whomever posted the item on their website got the Dynaco model numbers mixed up because there is no mistaking an ultra linear output transformer with a regular push-pull type. Hammond, and Edcore both sell ones with feedback windings. You would think that with all the computer age aids to assist there would be fewer goof ups but if anything there seems to be more of this going on.
Regards
Arran

[Joeztech]

Arran;

Yes, I concur. If the situation does not allow me to return for credit, I could find a use for the transformer some time in the future. I have two other output transformers of somewhat lesser output wattage ratings that have 4, 8, 16 and 70.7V output windings. I could put together a stereo output amp or make a single channel output amp to use for various purposes. Any such project would be far down the pike though.

Joe

[Joeztech]

Ron;

No, I did not specify screen grid taps when I ordered, but did identify it as being needed for a Dynakit Stereo-70. Today I received a response back from an engineer with Heyboer and he understood the problem. He did some checking and determined that the order was handled by a relatively new employee. They do indeed provide output transformers for Dynaco/Dynakit amplifiers made the correct way. He said that the one which was shipped to me is a similar unit made for guitar amplifier manufacturers and was on the shelf. He apologized and asked if a refund check would be OK. I told him yes. He said to just keep the wrong transformer. So everything is working out OK for me. It was just an unfortunate human mistake.

In the meantime, I ordered a new transformer from DynakitParts.com along with the new stainless steel chassis plus a hardware kit of screws and nuts for the amplifier. Those are in shipment by UPS as I write this. The new parts will likely arrive later this week.

Joe

[Joeztech]

Dynaco A470 Xfmr Autopsy

I decided to dig into the Dynaco A470 output transformer that tested almost twice the DC resistance measured plate to plate as the good transformer. I had nothing to loose.

I began by removing the end bells from the transformer. This exposes the interior assembly.

I removed the E and I leaves one by one until I had them all out. There were 130 E leaves and 128 I leaves.

I carefully removed some outer layers of wax impregnated paper and a Mylar tape wrap (1 turn). An extra layer of paper tape and some slender 3/8in. wide black tape was removed to reveal the primary winding terminations. Here is what I noted at this point. The magnet wire used appears to be one of the following kind: 34AWG if single insulating film; 35AWG if heavy film insulated; 36AWG if triple film insulated.

The two plate leads have two wires going to them. The two screen grid leads have four wires going to them. The center tap has four leads attached to it.

I found one wire to a blue/white lead that was broken in two about 3/8in. from were it came out of the wire bobbin. I decided it was worth trying to reattach the wire. I carefully un-soldered the rest of that wire from the end of the blue cloth covered wire. Then I tinned it and the free end of wire coming out of the transformer winding and bobbin with solder near where it had broken. Once I had a good solder take to the inner copper (the solder heat burns away the insulation), I tack soldered it to the free end coming out of the transformer winding and bobbin. I slid a very small OD Teflon sleeve over that repaired area, then used some clear flexible plastic hobby glue and some 3M electrical tape to hold it in place so that it would not move. I re-wrapped the free end of the wire previously un-soldered from the blue wire and soldered it there.

I took time out to use my ohm meter and compared the DC resistances of the repaired transformer to the good one. Both transformers now read the same DC resistance plate to plate. Checks from center tap to screens and plates of both transformers now match within a few ohms of each other – well within expected tolerances.

Next time was spent securing each primary wire to the end of the winding assembly/bobbin and making sure that they were all held tightly. Then each E leave and I leave was carefully placed back around the bobbin and winding. The last item to go back in place there was two wooden shims that help hold the winding and bobbin tightly against the E & I leave stack-up. The end bells, screws and nuts were put back on and tightened.

This took about 6 hours all together.

I now have two good transformers that could be used. I have a new one on order and intend to install it. This repaired transformer will be held in reserve as a potential replacement if the other transformer happens to fail.

Joe

[Joeztech]

A further comment about the Krylon chrome paint - I discovered that it has a rather delicate surface and even fingers will smudge it days later. I think it might still be OK, but it needs to be oversprayed with clear lacquer overcoat for protection. This morning I took the end bells from the bad transformer and resprayed them with the Duplicolor Instant Chrome paint instead. I will see how it is after a full day of drying. We had 56 degrees F. this morning and I did the paint spraying at that temperature in the barn although the paint itself had been stored inside the house so it was at about 75 degrees F. After some initial dry time I brought the end bells back into the house to finish their drying time. I use some wire hooks through the holes in the feet to carry the pieces while they are still soft. I refrain from touching them in any way with my fingers.

I ordered a set of input jacks from DynakitParts.com this morning. I should have ordered them last week but just forgot. The old jacks could still be used but were quite corroded and I just did not trust them. These have gold plated contact surfaces and are color coded like many other jacks in the rest of my stereo system.

At some point I need to order a full jack set for my PAS-3X preamp input and output jack panel. They are still 1964 original and may have some carbon traces as the unit was struck by lightning a few years ago. I replaced the PC boards in the PAS-3X with some modern material boards and polypropylene capacitors plus metal film resistors.

The new chassis from Tubes4HiFi came in. It really looks nice and puts the old chassis to shame. I will post some new pictures once I get the unit back together.

Joe

[Joeztech]

The new Dynakit Parts A470 output transformer came in on Friday, so since then I have managed to install the PC board, bias controls, tube sockets and various other parts. I had to remove the transformer bells and repaint them using the Duplicolor Instant Chrome paint. The Krylon seemed to be very soft and easy to damage even after multiple days of curing. The Duplicolor paint seems much harder after just 24 hours. I put the bells back on the transformers and installed them on the new chassis that also came from Dynakit Parts. I still have new RCA input jacks on order. I plan to work on installing new electrolytics under the chassis while keeping the original can electrolytic. You can see the newest pictures at: http://s1213.photobucket.com/user/rubal1...t=6&page=1
The new chassis really makes a difference! Definitely eye candy!

Joe

[Joeztech]

Today I received the new RCA input jacks and installed them. I went ahead and wired the stereo/mono switch into the input circuit since the wires were still attached. I used new 470k ohm resistors and used green wires from the jacks to the PC board. Green wires were an industry standard for signal carrying wires. I installed the tubes and took some pictures that were added to those already on my website:
http://s1213.photobucket.com/user/rubal1...t=6&page=1
I still have a few resistors coming and will finish modifications to the power supply and take some more pictures, test and adjust output tube bias and put it into service.

Joe

[Ron Ramirez]

So, how is the Dupli-Color Instant Chrome? Is it any better than the Krylon chrome paint?

[Joeztech]

Ron;

Yes, the Duplicolor Instant Chrome is tougher than the Krylon product. It resists scuffing better. I think for the long term, either would need a clear overcoat of lacquer. I noticed that the new transformer I received from DynakitParts.com had a clear overspray on the black painted bells too. It might also help if the paint was baked on, but I did not do that. If I have to do a little maintenance on them over the years it will not be difficult. Having the bells chrome plated is expensive since it is a small job. I have seen a few that have been done that way, but I can't afford to spend that much on chrome plating.

Joe

[Joeztech]

See the last two a pictures of the unit after restoration was finished. I have been enjoying listening for hours and love the sound. It is in fact better sounding than a 100W per channel solid state power amp. that I have. The sound is more detailed and clear with instrument placement easy to determine. Brass, violins, piano and voices sound natural and not strained or harsh any more.

Joe

http://s1213.photobucket.com/user/rubal1...t=6&page=1

[Pillo69]

guauuuuuu, very good job.

If you have dealt with Duplicolor paint on the chassis, as has protected engravings letters. ??

A greeting.

[Joeztech]

I have not used Duplicolor paint on a chassis, just on the transformer bells. I did use some Krylon satin nickel on a Philco 40-201 I worked on last year. Ron recommended that paint and it has just the right color and finish to look very close to the type of plating that Philco and many other manufacturers used on their chassis. It is a pretty durable paint and I would not hesitate to use it on a Dynakit or other amplifier if I did not want to spend the money for a new chassis or for chrome plating. After a chassis goes beyond a certain point of corrosion and pitting there is not much point it attempting chrome plating as the metal would have to be sanded and buffed to the point there would not be much strength to what was left to go through the plating step process.

I ultimately made the decision to get the stainless steel new chassis from DynakitParts.com It is a beautiful duplicate of the original in looks, but being buffed stainless steel the finish will hold up much better over time.

The unit sounds great with the new A470 transformer from DynakitParts.com I cannot tell any difference from the one OEM unit that is still in the unit as far as how it sounds. DynakitParts.com says their transformers are made to the original Dynaco specifications as to how they are wound, just that new insulation materials are used which have better resistance to flash-over etc. I have spent numerous hours listening to FM radio, LPs and CDs on it so far and find it to be much more realistic in reproducing music than an Onkyo M282 power amp that it replaced. I don't think I will ever go back to solid state after this.

Joe

[Joeztech]

I failed to answer Pillo69's question about the engraved lettering on the transformer bells. Yes even after the painting the engraved or stamped lettering is still visible and readable. That was one reason I wanted to keep the original bell from the defective transformer and put it on the new one. Of course the new transformer has 4 through bolts while the OEM types only had two through bolts, but I don't fault DynakitParts.com for that as it may eliminate any possibility of vibration and noise. The OEM power transformer does use 4 through bolts to hole it together and the extended shaft also provides for securing the transformer to the underside of the chassis. The power transformer also has stamped or engraved lettering on it which is also visible after painting.

Joe