Repair transformers

Hello everyone! 

It has been a while since we've posted! COVID-19 lands us in a really bad condition. Crippled operation. Stunted supply chain. Work from home. Movement restrictions. Anything that you can think of, can happen. Anyhow, life goes on!

Today, we want to share a lesson learnt from a customer of ours to you about transformer repairs. Hope that you do not land in the same situation when you want to repair your transformers, be it transformers for tube amp or transformers for solid state amp.

Customer has a faulty preamp output transformer. He heard of us, and approached us for a quotation. Our price seemed too high for him and he turned down our service to repair his preamp output transformer. 

After a month or so, I can't really remember, he came back, confirming that he would want us to repair the preamp output transformer for him, and he will be sending a pair, including the OK output transformer.

We told him - we only need 1 piece, the damaged one. We can and will reverse engineer it if it is not too badly burnt, and rebuild it according to the original design/methods.  

He said, he insisted that he needed to send us both the OK and NOK units. I asked, why? He sent the damaged transformer to another person for repair and it came back still damage - producing distorted sound. Now he needs to send it to us for another round of repair. And since the damaged unit had been tempered and may no longer follow the original design, we have to have the OK unit as a reference to rebuild the damaged preamp output transformer 

Ah ha!!! 

Now do you see the problem? Now we have to dismantle the OK preamp output transformer in order to know the design and rebuild TWO preamp output transformers now. Repair charge is DOUBLED now since we have to work on two units unfortunately.

Moral of the story - pay for quality, do it right the 1st time. In the long run, it may save you more money - for not resending it for another round of repair, for not paying for 2-3rd time of repair, for longevity of the transformer, for getting back the original sound, for peace of mind!

Only send to reputable repair center for your beloved transformers - J&K Audio Design, your faithful repair guy next door. We may charge higher for the repair because we really, really reverse engineer your transformers, and rebuild them based on the original design, use good quality wires, and original materials when available. In addition, most importantly, you get peace of mind that it is in safe hands and you will get it back to be as close as original.

We've repaired tonnes of super high end transformers that cost as much as a car. We've repaired transformers from 1940's to 2000's. We know almost all the designs. We know what we are done. 

Thank you and that's all for this time! Stay tuned folks!

Take care and stay safe! 

J&K Audio Design

28/11/2020

  

Voicing of output transformers

Howdy everyone! 

After repairing and measuring sooooooo... many vintage and modern output transformers from no-name to legendary brands, we've had a good grasp on how they voice the output transformers, from the materials used, winding techniques, etc... to the sizing of cores.

If you're going after a certain tone, you can let us know and we can wind towards that. Else, we will do the best for each level (Level 0 to Level 3) of grading for our transformers, using the wide bandwidth winding method, with sufficient dynamic headroom for all sorts of music, including faithful 20Hz reproductions. 

Our Level 2-3 output transformers are usually specified to ~10Hz @ -3dB region (or lower if required or paid for), and therefore anything at 20Hz is of no issues at all. We're not that worried on the high frequency response side as that's something easily manageable and easily achievable. We'd tend to just limit it at ~60k-75kHz to avoid unnecessary side effects but if one still want 100kHz, just let us know. 

Just a refresher to all perhaps, we do offer OCC Cu, OCC Ag magnet wire transformers now, that we previously do not (maybe 2 years ago), due to the wire price, amount of orders and scarcity of such materials. Now, we can say that they're pretty common. 

On the other hand, we have to keep the transformer repair price to at least U$200/pc and above. The amount of work involved are just too labor intensive and charging below that is just PAYING YOU TO REPAIR FOR YOU.  

Each transformer requires around 1 week to complete. Say if we pay a technician to do so, at U$15/hour for 5 days, that would be whopping U$600 labor charge slapped onto the repair price. You see what we mean now? 

Anyhow, we'd like to thank everyone that supported us so far to lead us till today. You're such a gem! 

And, apologies for those that had hiccups in their projects. We will keep on improving ourselves and keep on serving you guys better.

J&K Audio Design
8/9/2019. 

Audio Transformer Repair

Audio Transformer Repair

If there's something strange in your neighborhood.
Who you gonna call? Ghostbusters!

If there's trannies burnt in your neighborhood
Who you gonna call? J&K! 

Nothing beats getting back the original sound, original look, and original material for your beloved audio gears collection! We repair any audio transformers - be it input, output, interstage, power transformers or chokes. We do not repair SMPS chokes though - get a new SMPS for Pete's sake!

4pc of damaged vintage input transformers were sent to us for repair recently. It was cleaned up and rewinded with traditional Kraft paper with old-school technology, following the generation when it was manufactured. It is fully restored back to the older days glory! 

The in/out wires are following the original color coding as well!

If your transformers, be it power, input, output, interstage, or anything at all, are damaged, don't forget to drop us an email to have them restored! A close to original vintage gear, at anytime, has much higher value than those with damaged or non-original components on it. 

Spend now and you will be rewarded financially, or in terms of audio enjoyment.


J&K Audio Design
2/19/2017

Repair Transformers

What have we signed up for this time?

According to the user, an input transformer from a Russian made tube audio compressor is damaged and needed our help to repair this transformer.

The matter of transformer repair is, sometimes, you do not know what you've got until you opened up the transformer case to see what is inside. This time, we had a headache reverse engineering the transformer (an input transformer for repair)! Words alone just can't explain how much work it has taken us on working with the delicate wires, and recording down every detail of the design, till rebuilding it to original form. (I actually regret taking on this transformer repair project! It is totally not worth the time spent versus our puny charges to repair them! Still, a commit is a commit, we will do our best and finish the job with the best effort put in.)

These are the pictures of the transformer being sent for repair. It is covered in wax and we've no idea what is inside yet.

Everything was still fine for the repair transformer job, until we see this:

The winding is such mess! I suspect maybe the poor winding method is what killed it at the first place. Cross-wiring will weaken the point where the cross happens and causing a short after use. Some parts of the wires look oxidized too, perhaps the vacuum impregnation was not done good enough to prevent it from damage. 

Anyhow, you can see that we've tags to indicate all the little details of the design to ensure no mistakes are made when we rebuild the transformer to ensure this transformer restoration job is done properly. (We're getting too old for input transformer repair job. Eyes are failing us. We might need to stop doing so one day.) 

These are the ultra thin wires we took out from the input transformer! Imagine the work involved to remove it without damaging it!

 

Till then, I need more Vitamin A or carrots to help with eyesight, and perhaps being more selective on what we repair, LOL. So, please do not take it personally if we reject your case as some transformers are not worth the repair. :P 

J&K Audio Design
1/24/2017

Wavac Amplifier Repair

Wavac Amplifier Repair

The interesting thing about being in this line is, you get to see a lot of amplifiers being sent to you for analysis for free, and the better thing is, they will pay you for it! 

Last week, a Wavac EC-300B amplifier were "causing" 300B tubes to have red plates. According to the owner, the tubes were checked and sent back to the tube manufacturer for replacement and it should not be the tube's problem. 

Well, okay, let's check the Wavac EC-300B amplifier then. It's a good opportunity to open a high end expensive amplifier like this, like what we did a while ago when we played with Wavac PRT-1. 

Before everything else, let's take a look at some pictures. 

EC-300B repaired!

Wavac EC-300B

Wavac EC-300B repair

Wavac EC-300B up close

EC-300B circuit

This unit is really well built, with ample over-sizing to ensure safe operation and long life. There aren't a lot of audiophile components on it, but it is decent enough. The mechanical design is very innovative as well with very solidly made top late. 

In order to debug the unit, we traced out the circuit as well from the input tube WE 435A, to driver tube 6L6 and finally the 300B. It does not use tube rectification though, which is something we like, but everything else are quite high in quality. 

WE 435A is direct coupled to 6L6 and Tango NC-20 is used as interstage to drive the 300B. There are no coupling capacitor at all in the design. That is the right thing to do. All the other transformers are Tango's and we've no complain on that, except to wish that it was made with our Level 3 NanoC transformers. LOL.

Visual inspection showed us nothing wrong. All components looks perfect with no leakage, burnt marks, or any abnormalities. A power test will need to be done, to check all the operating points of the tubes.

Upon measurement, we found that one side of the amplifier is showing DC on the grid, and that's causing the 300B to have red plates due to wrong biasing. We traced the DC further and found that it is actually having the same potential as the cathode! Now that's strange! 

For interstage coupled circuit, there shall not be any connection between the cathode and grid unless it is shorted. Therefore, we powered it off, and took it out for further measurement to see if it is the tube or the amplifier.

Well, let's have the picture to tell the story! It appears that the 300B tube was causing the short! The grid is shorted to the cathode! It was not the Wavac EC-300B's fault that it red-plates! 

300B short circuit

modern 300B quality issue?

We put on another pair of 300B, PSVANE 300B onto Wavac EC-300B to confirm if it is still working properly, and everything checked out OK. All the operating points are within the designed specifications and left/right matching are within reasonable tolerances.

That concludes our debugging! Time to send the 300B tubes for replacement! Wavac EC-300B works perfectly and no servicing required.

Thank you for sending us Wavac EC-300B for circuit tracing. We definitely learned something from looking at the design. 

J&K Audio Design
3/18/2016

Product Lists  
Level 0

Level 1: link 1, link 2, link 3

Level 2: link 1, link 2, link 3, link 4, link 5, link 6 

Level 3: depends on type, size and complexity. Email us for details.

Iso-trans: link 1, link 2

* Finished amplifiers, DACs, audio gadgets, upgrades and repairs - this is not our core business and we do it out of passion. We do not have fixed models, fixed price and we customize for each individuals. The sky is limit of creativity.  

* Our product lines are always improving and increasing. If you do not see what you want, contact us!  

* Please email for volume discounts, distributor and OEM pricing.