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Friday, January 25, 2019

J&K TVC User Feedback

Happy 2019! 

It has been a while folks! You know we've been busy! 

For those who'd like to have more updated news and discussions from us, please follow our Facebook page! 

Below are some very nice pre-amplifier pictures from a customer of ours in USA - using the OPTVC that we've built for him some time ago. He's looking for more transformers for upgrades, and that's why the pictures have measurement tape being shown instead of being a studio-like photos for publishing. 

Here are some details of his OPTVC: 
33 step OPTVC
Pri inductance ~150Hy
Pri DC 10mA 
Potted with turrets 
OFC wires 

Comments from customer:

"Last year I got a TVC from you for a preamp my friend Oliver built for me. I'm liking it a lot. Very nice sound. Very happy with it. "

"Here is a photo you requested of the TVC preamp Oliver built. It is an active preamp with combined volume and output TVC with 33 steps. The TVCOPT are in the back to the left. It uses a type 82 rectifier with 6AX4 TV damper warm up buffer. Shown are 01a preamp tubes. It can also use 112a, 31 or 71a DHT tubes."

Some may ask, what the h*ll is OPTVC? OPTVC = Output Transformer Volume Control - It is TVC that can tolerate primary DC and use as a load for a tube stage. Some details can be found here:


J&K Audio Design

Monday, December 24, 2018

Western Electric transformers

Hi guys,

Merry Christmas and Happy New Year! 

We've an important announcement to make.

Western Electric cores are running low on the market. We're working on a customer order and got a shock. A lot of these cores are swooped by some vendors and make them to sub-par transformers - what a waste. As a result, these Western Electric cores are no longer abundant and choices are very limited. 

If you intend to use Western Electric cores to make transformers, please be quick and order soon. In future, we may need to buy those sub-par ready made transformers to obtain those nice Western Electric cores for rewinding to something much better.

We've made some in the past, as you can see below:

There are still some original WE cores, untouched at decent price. Make a move quick before it is gone. The WE1048 that used previously are no longer available at our previous source. What a sad news! 

Apologies to break such a news at such time, but I think it is a good news that we discover it early. Else, it will be as rare as the 1950's - 1960's WE 300B tube. 

J&K Audio Design

Friday, December 21, 2018

Transformers repair

Repair transformers? Call us trans repair king! I think hundreds, if not thousands of transformers have gone through our hands over the years. 

We are very happy to hear that our customer's McIntosh amp are repaired. Well, this is just one of the message we get, there are many more that we're just too busy to post. 

We can learn the transformer winding method from others, and we help to restore the damage equipment - saving mother Earth from being overwhelmed with more electronics junk! 

Nobody (or very less, LOL) repairs transformers like us. We'll unwind EVERY unit received and record down all the data about the transformers so that we can rewind it back exactly, according to the original materials, if can be found. 

Your transformers will get a new lease of life for another few centuries as long as it is working in the original designed conditions. 

Repaired transformers get a 1 year warranty. Conditions apply, such as, as long as is not abused, or placed in a faulty amplifiers (well, that could be what caused it to burn initially, right?). 

Tips: it is very important to keep the original core of the transformers. Once it's gone, it's gone. That's the most important component in repairing transformers. We recommend to reuse the original core to get back the original sound signature of the transformer. 

Now, get your damaged transformers here! McIntosh, Marantz, Scott, Dynaco, AudioNote, any transformers, as long as they are not burnt to ashes, we can repair it. Satisfaction guaranteed! 

J&K Audio Design

Thursday, November 1, 2018

Alternative payment option

Dear all,

We've found a way to save customers expensive PP transaction fees of 4.5%-5%

Contact us and we shall inform you how to do so during purchase!

J&K Audio Design

Tuesday, October 16, 2018

50 Tube

Type 50 Tube

For those that plays with DHT (direct heated triode), type 50 tube tube should not be a stranger to them - either a love or hate situation. They love it for the tone and character, but hate it for the scarcity of getting NOS (new old stock) tubes. They are getting rarer everyday, and price is quite hefty for such a low power tube - definitely a collector's item. 

No doubt, it is an interesting tube though, with many variations of the type 50 tubes, that I can't even comprehend all. These are the main old types and there may be more: 450 globe, 350 globe, 250 globe, 50 ST19, and 50 ST16. It is said to have a type 50 globe with mesh plate that I have not seen of myself, with heavenly sound some claimed.  

There are some new type 50 being manufactured due to the popularity of such tubes, such as Shuguang SG-50, Shuguang SG-60, EML 50, ER 50, Psvane globe mesh 50, Psvanwe WR50 and some that I may not even be aware of. 

I would suggest new users to just go with new tubes. Old tubes are quite hard to match and those that comes within the same date code, matching Gm, matching gain, matching internal structure, are almost impossible to come by, unless one is willing to pay an arm + a leg for them. 

The Shuguang SG-50 will be cheap as a test rig and casual listening tube to own. The EML 50 is ~$750/pair, oops. The EML 50 does have higher plate dissipation at 28W and can be pumped up to 6W output with a 4.1K OPT. 

Below are some pictures of the type 50 tubes. 

Shuguang type 50 with mesh plate

Type 50 ST19 - old stock
If you look at the picture of the type 50 ST19 above, you will see that there is some darkened patch on top of the tube, quite near the vent to the filament/plate cavity. I've seen quite some type 50 tubes having the same black patches. Some say that it is some sign of use and/or abuse but I cannot confirm that yet. Maybe someone with more knowledge can enlighten all of us via comments tab below.  

Type 50 Globe - old stock
Tips: If you have (lucky you) and use a type 50 globe on your amp - consider lowering the actual operating voltage as compared to the datasheet to prolong the tube life. 

Below is the snippet of the type 50 operating conditions and characteristics. It's somewhere in between type 2A3 and 300B, with a maximum power of 4.6W when driven to the max. I wouldn't mind if I'm using some cheap type 50 clones, but definitely not for the NOS tubes. 

Somewhere at 400Vp with 55mA plate current would be something I'm more comfortable with or maybe even slightly lower at 400Vp and 50mA to get 20W plate dissipation, for longevity of the type 50 tubes. Hey, they are very rare, mind you! 
Type 50 tube datasheet

One of the very important application note of this type 50 tube is the grid leak resistance value. It must not exceed 10K Ohm. That leads to either grid choke, or interstage coupling, where latter is what would prefer for the uncompressed sound. A 10K grid leak resistor is possible too but that is rather a waste considering the price and rarity of the tube, blasphemy! 

Filament voltage is 7.5A 1.25A - for those that like AC heating, please stay away. For acceptable hum level, DC filament heating is a must to get it to acceptable level low enough for enjoyment. Exotic high frequency AC heating might work, but I've not tried that personally. 

I did not personally built a full set yet for this type 50 tube, but just a test rig, built on a piece of wood (LOL!) with a level 1 5K output transformer, powered with some parts that I dug out from my stash of components. The pre/driver tube was a 5687 RC coupled 5687, with some cheapo diode bridge rectification and some FT caps. B+ is 470Vdc with cathode bias and -70V of grid voltage. With the few variations of type 50 tubes I have on hand, all seem to fall to the bias quite closely on the very same circuit. 

Even with that, the body, harmonics and tonality stands out from all the other tubes I've built with. 

A fully built version will come soon, when I have more time on hand, or when there is a order for it being placed. Well, in actual fact, there is one set to be built for a local audiophile, but the build date has yet to be confirmed due to busy schedule.

Meanwhile, enjoy life, and then get back to work again! 
J&K Audio Design

Saturday, August 4, 2018

General transformer problems

General transformer problems?

Temperature is too high

- Short circuit in the winding, at primary or secondary. Once shorted, the current will be high and cause rise in temperature. If this continues, not only the insulation layers will be burnt, and the adjacent winding will be burnt due to high temperature, and the vicious circles continues, until the whole transformer is burnt. This high temperature happens whether it is loaded or unloaded. The only fix is to remove the bobbin and remove and replace the burnt winding(s), or all altogether.

- High temperature may happen at small transformers and goes un-noticed, where there are a lot of turns in a single winding. If the adjacent magnet wire got short-circuited, since the voltage is low, wires are long and thin, the temperature may not reach the exterior, but it will not work for long. 

Note: When there are shorts in the transformer, the no-load current will be higher than normal.

- Magnetic flux density (B) set too high - especially when using unknown transformer core/lamination. If B is set too high, causing the turns to be lesser than ideal. With reduced primary turns, the no load current will be too high, causing increase of transformer temperature. Even if secondary are unloaded, the transformer temperature will rise high. If you reduce the primary voltage up to a certain point, the temperature will be at normal temp, for such kind of transformers.

- Overloaded transformer - self explanatory

- Magnet wire is too thin - high DCR causing more power dissipated at the wires.

Electrocute feeling when touching the core

- If one touches the core and feels a slight tingle or eletrocute feeling, this is due to parasitic capacitance between the winding and core. You can measure a certain Vac value on the core with respect to ground. This may be resolved by adding grounding to the core or mount it at a grounded plate.

Magnetic flux leakage is high - causing noise

-When powered on, the field generated by the winding should follow the path formed by the core, and should have low magnetic path resistance, to enable a high efficiency transformer. Due to various reasons, if the path is not smooth, leakage form where magnetic flux to goes through the air instead (magnetic flux leakage). That could happen to uneven surface between the cores (gap), or cores not tighten enough with the E/I lamination, or the air-gap laminate is too thick, and various other reasons.

- If the transformer works alone, the impact is not much and may not be noticeable. If it is mounted in jam-packed equipment with lots of sensitive electronics, the magnet flux leakage will be detrimental, causing AC hum to the adjacent components (therefore, giving EI transformer a bad name). 

- To check for magnetic flux leakage, one can wind a 200-300 turns of wire on an iron nail, connecting it to a high impedance sensitive headphone, and move this to a powered transformer with magnetic flux leakage, and see if there are audible hum generated in the headphone. 

- To avoid this, the lamination must be even so that the interface is as close as possible. This is even more important when using refurbished cores. It has to be clean enough and polished to ensure the closest interface. OTOH, transformer designer should not design it close to the maximum magnetic flux density. Also, the copper band will come in handy to prevent such leakage from affecting the environment. Distance may help too since the density drops as it moves further away from the transformer. 

Noise when powered

- Ringing / hum when powered - this could be due to loose lamination. Lamination could get loose in many ways - abuse, drops, not tightened enough, and etc. Low grade core with un-eveness in the cores (not flat enough).

- Short circuit in the transformer, where there is high current flowing., causing the lamination to rattle, and heate up. 

- Misaligned lamination - you can see the un-eveness alignment of the lamination when the whole transformer is constructed. Such zig-zag lamination will cause noise. This should be easy to see externally. 

So, you have been empowered now with the knowledge to know the general transformer problems. Choose wisely. 

J&K Audio Design

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