J&K Audio Design: March 2016

Friday, March 18, 2016

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.

Saturday, March 12, 2016

Toroid Isolation Transformer Prices

Toroid Isolation Transformer

Power conditioning is a critical component of a complete HIFI system. One would never realize the full potential of their HIFI system until proper power source is supplied to their equipment.

Nowadays, the incoming mains are filled with all sorts of noise riding on them. Lots of these rubbish are entering the HIFI chain and causing all sorts of issues like humming, noise, heating, harshness, sibilance, noisy background and all sorts of other negative factors.

There are many types of power conditioning, and isolation transformer is one of the most effective method of conditioning. Isolation transformers have been used in hospitals, factories, R&D laboratories and many other facilities with sensitive electronics.

Now, these isolation are quite common in home audio due to the effectiveness of such devices.

J&K isolation transformer capacity - up to 3KVA (maximum size for grade A1 made in Japan toroid core)
- 3KVA unit is U$790 for isolation transformer only
- built unit vary in prices due to accompanying accessories and components

Options

soft start, must for toroid transformer above 500VA (not sold separately due to limited stock)
DC filter, must for toroid transformer to prevent DC saturation/hum
EMI/RFI filters, clean up incoming and outgoing EMI/RFI
single or dual display (input / output)
different grades of audiophile IEC output sockets
balanced or single ended output
potting, must for lower noise operation and shielding
electrostatic shield

Notes:

other toroid core grades are available but not recommended due to less ideal electrical properties, higher loss, higher operating temperature
we would recommend separate individual isolation for each individual equipment than a big toroid transformer with everything connected (shared) to it (audio gears generate noises themselves and cross-pollute each other)

Fully built audiophile balance power isolation transformers (with chassis, sockets, meters and etc) using Grade A1 toroid (highest grade toroid core, extremely low loss, high permeability, low operating temp, potted, made in Japan)
- 2.0KVA U$1220
- 2.5KVA U$1370
- 3.0KVA U$1472
- 3.5KVA U$1620 (max size for grade A1 core, other cores available)

Fully built audiophile balance power EI Z9-Z11 Standard Isolation Transformer (with chassis, sockets, meters and etc, using 0.27-0.35mm SiFe Grain Oriented (Hi-B), made in Japan)
- 1.0KVA U$1190
- 1.5KVA U$1740
- 2.0KVA U$2040
- 3.0KVA U$2390
- 4.0KVA U$2690

Audiophile balance power ULTRA Isolation Transformer (SiFe Grain Oriented (Hi-B), made in Japan)
- 500VA - U$390
- 750VA - U$540
- 1000VA - U$690
- 1500VA - U$1240
- 2000VA - U$1540
- 3000VA - U$1890

Note:

EI balance power isolation is best for HIFI / Stereo use, projectors, tube amplifiers, front end (source, pre-amp) - warmer and quieter
Toroid is better for AV amplifiers, high power systems - dynamic and fast
Professional grade equipment case are available for international shipment

Soft-start and EMI/RFI filter

Audiophile IEC sockets

Dual Display - input and output voltage

Potted toroid transformer, industrial grade power distributor

Testing for shorts

Potted 2.5KVA isolation transformer

Some previous postings for your reference:

Toroid Isolation Transformer
Isolation Transformer
Isolation Transformer Review

J&K Audio Design
3/12/2016

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

* 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.

Monday, March 7, 2016

211 Push Pull Output Transformer

Level 3 Custom Made Output Transformer – 211 Parallel Push Pull OPT

10K-PP, or 5K SE, is a very unique primary impedance. Such OPTs are usually very universal since a lot of tubes in the market can actually work with 5K primary impedance. Here goes another high end OPT made for 211 PPP, or 212 PP tube amplifier.

This OPT is made slightly different compared to the 212 PPP output transformer, where we do not need to have that much air-gap (notice the highish primary inductance) in comparison to manage the medium high output power compared to the very high output power of 212 PPP tube amplifier.

Although the 212 PPP OPT outshines this 211 PPP OPT in terms of power, still, it packs a lot of power at hand to drive most speakers in the world.

P/s: This 211 push pull output transformer looked exactly the same like 212 pparallel push pull output transformer, therefore we skip the pictures for this post.

Technical Parameters
Tubes:               211 PPP, 212 PP, 211 PP (class A2)
Power:               200W at 20Hz
Core:                 Nanocrystalline / Amorphous Cut Core

Measured in circuit response
                          20Hz (-0.06dB) —1K Hz (0db) —20 KHz (-0.38dB) (8 Ohm, 1W)
                Further results next to the FFT graph
Primary:            10 KΩ PP
Secondary:       0-4-8Ω
Primary DCR:    210.5Ω, 210.3, P-P，11℃
Secondary DCR:
                           0-4Ω, 0.18Ω
                           0-8Ω, 0.26Ω
Primary inductance:
                           206H, 212H, 20Hz, 5Vrms
Primary current: 290mA (maximum)
Efficiency:           0-4Ω >93%, 0-8Ω >94%。

Note: P1 and 8Ω are in phase.

In circuit measurement, testing conditions:
•    211 PP, 70mA per tube (4K Rp)
•    ~5Hz – 55 kHz -3dB

• 211 PP, parallel with 4K per tube to mimic 211 PPP, 70mA per tube/resistor (2K Rp)
• ~3Hz – 70 kHz -3dB

We can't wait for the 212 PPP and 211 PPP owners to complete the amplifier and send us their creation pictures!

Till then, have fun and build more amplifiers!

J&K Audio Design
3/7/2016

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

* 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.

Friday, March 4, 2016

J&K Power Transformer Customer Review

Thanks to Alexei for the feedback on our Level 3 power transformers.

Link to customer feedback / review on our blog (scroll to bottom). A screen capture is posted below for your ease of reference.

We are very glad that it is well received.

J&K Customer Service
3/4/2016

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

* 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.

Tuesday, March 1, 2016

212 Push Pull Output Transformer

We are pleased to announce the arrival of the giant: 212 PPP OPT - 212 parallel push pull output transformer!

Level 3 Nanocrystalline Double C Core Output Transformer for 212 Parallel Push Pull

Parameters

Output power: 350W (@20Hz)
Measured in circuit response: (8 Ohm, 1W)

* 20Hz (-0.17dB)—1 kHz (0db)—20 kHz (-0.18dB)

* ~5Hz – 100 kHz -3dB

Primary impedance: 5KΩ PP

Secondary impedance: 0-4-6-8Ω
Core material: Custom made Nanocrystalline SiFe cut core

Primary DCR: 62.2Ω (62.1 Ω) (P-P, 6℃)

Secondary DCR: 0-4Ω: 0.18Ω; 0-6Ω: 0.22Ω; 0-8Ω: 0.25Ω

Primary inductance: 58.5H (59.1H), at 20Hz, 5Vrms

Max primary current: 600mA
Efficiency: 0-4 (>93%), 0-6 (>93%), 0-8 (>94%)
Weight: ~20KG/pc

Note: P1 & 8Ω are in phase

P/S(3/4/2016)
212 PPP OPT was designed with 350W at 20Hz. Actual power rating at 30Hz is over 500W. In order to increase the core's Bmax, magnetization saturation (maximum flux density), a calculated precise air-gap is inserted into the core to sustain such power output at 20-30Hz.

The low frequency response of this output transformer is not limited by the primary inductance, but by the core's Bmax, magnetization saturation (maximum flux density), to sustain the flux density at such power level. We lowered the primary inductance knowingly to counter such effects.

The in circuit measurement below has proven our theory and the low frequency response is as good as with high primary inductance, and yet, our output transformer can perform as good as small signal results at full power, as required by the user's demand.

This is done here, as well as in our ALIS-5SE Ultimate OPT for 300B or 2A3 to improve the performance and power handling, yet retain the low frequency response, where primary inductance of18H result is as good as 28 or 34H at actual circuit.