Grid Choke

In the past, we've mentioned about two coil choke for power supply, now this round, let's talk about Grid Choke. 

Grid choke is a small-medium size, high inductance choke for tube amplifier use. The choke is built with a single coil, tapped at the center for various usages, for grid load (replacing resistor), for phase splitting, or for special grid bias scheme. Since it is for audio usage, it is wound with a special low capacitance coil winding methodology. 

Center Tap Grid Choke

Low capacitance coil winding methodology will be needed to the load is consistent across audio frequency spectrum. 

Grid choke is sensitive to pick-up of noises from the surround such as magnetic field emitting from surround transformers and therefore needs to be shielded or potted to prevent such events. Also, mount it further away from transformers to avoid hum pick up. 

We have the following standard 3 types for your considerations, and of course, low levels such as Level 1 and 2 are available too if Level 3 is over budget.


Level 3 Nanocrystalline Double C core choke, potted

- Low current, high inductance grid choke, U$690 per matched pair (ex: 5687, 12AU7, 12AX7, 13E1, 300B, 2A3, 45)

- Medium current, high inductance 304TL grid choke, U$690 per matched pair (211, 845, 212, 304TL, 805, 811)

- Universal grid choke, U$1290 per matched pair (for all tubes) 
- Others sizes, please email us

Specs: 600H - 1200H, 1mA - 20mA, DCR = depends on user requirements, size


One size does note fit all since there shall be varying grid current being drawn for different tubes. So, it is critical to select or use the correct grid choke for the accompanying tube to avoid saturation. 

For pre-driver stage, use smaller grid choke, for power stage, use bigger grid choke. Voltage swing is another consideration when using such chokes. Smaller choke will tolerate ~50Vpp, and bigger choke will tolerate more. When order, please specify to us so that we can ensure what you get fits what we build for you.

What's the benefit of using grid choke? 
* Better voltage swing (peak to peak) compared to grid resistor. 
* Better low frequency response compared to grid resistor. 
* Different tonality compared to grid resistor (User comments: more solid and stable imaging, 2D -> 3D).

If you do not see what you need on our website, please do not hesitate to contact us. We are expert in custom made transformers. Do note that our custom made department are always fully loaded with projects and therefore lead time is long. Please order early to avoid disappointment or long wait.

J&K Audio Design
2/28/2016

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.

211 Output Transformer

Greetings!

We’ve talked about 211 tube load line previously. Today, let’s look at 211 output transformer frequency results. We’ve made a 16K primary impedance output transformer for 211 use. The actual in-circuit measurement results are as follow:

211 Shuguang, class A, 1200V plate voltage, 60mA plate current, bias -70V grid.

Core – EI105 Z11.

* Primary impedance 16K, 
* Primary current 60mA
* Primary inductance 77H 
* Power: 40W (20Hz) 
* Level 3 design methodology

* Price – U$990 per matched pair of 211 output transformers (EI Z11)
* Price - U$1190 per matched pair of 211 output transformers (NanoC)

(Other Levels and primary impedance upon request)

Frequency response:

20Hz – 20kHz @ -0.5dB

7Hz – 40kHz @ -3dB

211 output transformer

 Note: very minor difference between pre and post impregnation

The specifications of the 16K primary impedance output transformer can still be tweaked to obtain different results, say better low or high frequency responses but not both. The above is the specification we feel optimal for 211 tube.

Nanocrystalline cores are usable but the results will not be as good due to electrical properties limitation. We can’t get the Nanocrystalline cores to have as high primary inductance as EI Z11 and therefore is not as good as EI Z11.  

Why do we always stress actual in-circuit measurement? We do so because we want to preset the ACTUAL performance our customers will see when they use our transformers at their machines. Measuring it at laboratory conditions, driven by signal generator at a no-load condition will generate over-optimistic results that do not represent the specifications of the said output transformer at all. Such false representation is something we do not do.

A similar 845 output transformer can be made too with very similar frequency response, with higher primary current and higher output current. We can achieve the following specifications of:

Core – EI114 Z11

20K primary impedance, 80mA primary current, Level 3

20Hz – 20kHz @ -0.7dB

Price – U$1090 per matched pair of 845 output transformer

(Other Levels and primary impedance upon request)

If you want the best results out of your 211 or 845 NOS tubes, you better give them what they deserve, and they will serve you well beyond what you can buy on the shelf. If you are looking for better damping, better linearity, higher power, and better sound, look no further. Order a pair now. You can’t go wrong with these transformers. 

J&K Audio Design

2/19/2016

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.

845 output transformer

We've received many emails with regards to 16K output transformer for 211 since the publication of the previous post. Quite a number of them asked about its' applicability on 845 tube too since it is often made interchangeable on commercial designs. 

Before we go further, take a look at Amperex's 845 tube datasheet! It actually calls out that a 16K load resistance for the 845 output transformer, and it has higher power output compared to 9K load resistance at the same 845 plate dissipation at 65W. I didn't invent that. It has been there for over 60-70 years. Take a look at a snippet of the Amperex 845 tube datasheet below.

Amperex 845 operating point

One thing that wasn't shown clearly is the distortion % for 845 tube at various load resistance. It states only 5%, but you all know that higher load resistance provides better linearity. So, let's do some drawing again to see for ourselves.

Amperex 845 Tube Curve

Green - 9000 at Amperex tube datasheet operating point
Red - 16,000 at Amperex tube datasheet operating point
Dark blue - 16,000 at higher plate dissipation
Light blue - 20,000 at higher plate dissipation 

Green: At 9000 load resistance for 845 output transformer, you can see that there are severe compression starting at -250V to -350V grid voltage. I wouldn't use this if I were designing my 845 tube amplifier. It would have premature distortion at very early stage. 

Red: At 16,000 load resistance for 845 output transformer, things are much better than 9000 load resistance where severe compression starts only after -300V grid voltage. Still, from -350V to -450V, you can see that the V-swing narrows significantly.

Dark blue: still at 16,000 load resistance for 845, the operating current is raised higher. Things started to look better now. Severe compression starts only after -350V grid voltage. This is something I would consider doing. 

Light blue: if I can design a 20,000 primary impedance output transformer for 845 tube that still have considerable bandwidth compared to a 16,000 primary impedance output transformer, I would definitely use a 20K output transformer. Same theory applies. I would try a 20K primary one day, when we have more free time. It would be something worth looking forward to. 

As a conclusion, the magic number -> 16,000 Ohm primary impedance for 845 tube output transformer is still recommended. 9K, 10K, or 12K are still not ideal although 845 tube Rp is much lower compared to 211.

Don't follow blindly on the recommended loadline or load impedance for your tube. Think and look at the datasheet before you choose the output transformer for your design. Your design or your amplifier could be under-performing (lower power, higher distortion, worse sounding that it is supposed to be!) due to this and deserves better!

Till then.

Postscripts:
- We can make very decent 10K, 12K, 15K (sample 1, sample 2)/ 16K / 20K OPTs for pre or power output.
- Due to the large grid swing and grid current needed, 211 drive 845 or 211 drive 211 might be needed to fully utilize the high primary impedance. Ordinary drivers will not be able to manage such swings.

J&K Audio Design
2/15/2015

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.

211 tube loadline

开工大吉!

Born of 16K primary output transformer for 211 / 845 use! 

In Chinese believe, the 1st day to start work for the Lunar year has significant impact on the following days in the year. 5th day of Lunar 2016 is supposed to be an auspicious day to work and here we are, our 1st post of Monkey year! 

What could be better than to talk about tubes, or tube amplifiers? In this auspicious day, we would like to share with you some insights we have on tube amplifier design. Although title says that it is about 211 tube loadline, it can be applied to many other tubes as well, especially for tubes that are capable to go to class A2 operation, where the grid can work at positive voltage versus cathode. 

Common sense says that the higher the load impedance, the better the linearity, and the lower the output power. This is generally true for other tubes but it does not apply for all tubes.  The most commonly used example are for 300B tubes, between 3.5K and 2.5K load. The output power variations are not much though in this case. 

Let's look at 211 as an example. Before we start, take a look at the 2 figures below:

Figure 1: 211 with 10K load

Figure 2: 211 with 16K load

Figure 1 shows 10K load for 211, and figure 2 shows 16K load for 211. The load line for 10K load is much steeper and for those sharp eyes readers, they will notice that the LINEARITY for steep curve is lesser compared to the 16K load line with less steeper slope. 

On figure 2 with 16K load, you can see that the grid can actually swing more negative & positive compared to figure 1 with 10K load, and that translate to more power, on top of better linearity. For 10K load on 211, significant compression starts at -120V grid, and would be very noticeable when measured or listened too.

Let's do some calculation here, with both tubes at same plate dissipation, with operating point adjusted & optimized for both cases.

For 10K load,

• Class A1 output power = 13.8W
• Class A2 output power = 22.8W

 For 16K load,

• Class A1 output power = 14.3W
• Class A2 output power = 31.3W 

Not only 16K primary yield higher output power in pure class A1, in class A2, the increase of power is significant! Imagine what additional 10W of reserve can do for your power hungry speakers. 

Therefore, for better sound and higher output power, 16K load line for 211 is the only way to go. One can go for 20K but the return will be lesser due to diminishing returns or tube characteristics limitations. 

211 PSE at 8K primary perhaps? Ya, but for purist design and best sonic results, single is better than parallel. NOS 211 are not cheap nowadays, and replicas are expensive, not to mention matching issues (more expensive, limited and not dynamic matching, ages differently with use and many cons, etc) Why waste on precious NOS tubes? Output transformers last forever! Invest in good OPTs and prolong your NOS tube enjoyment.

If 16K is that wonderful as 211 load, why aren't there many 16K output transformers in the market? It should have been a hot-cake, right? Although 16K is good for 211, not all output transformers are built the same. The worst enemy for 16K output transformer is the high frequency response! To achieve such high primary impedance, much more primary winding/turns are needed, and therefore the additional capacitance will bring the high frequency response down. 

Try searching for them, and find out their frequency response, with the -3dB point listed, if it is ever stated in the datasheet or site. I tried Googling for it, so far I've seen none. The best so far is none other than ours ->  

J&K 801A output transformer (Z11)
Audible bandwidth 20Hz (-0.26dB) – 1kHz(0dB) – 20kHz(-0.5dB)  
Full bandwidth 10Hz (-0.5dB)   – 1kHz(0dB)  – 55kHz(-3dB)
 
J&K Western Electric Output transformer (WE 1038A) 
Full bandwidth:7Hz – 60kHz at -3dB 
Audible bandwidth: 20Hz (-0.76dB) — 1 KHz (0db) — 20 KHz (-0.41dB)


, with -1dB and -3dB measured, in-circuit instead of in laboratory environment with unreal conditions using signal generator as source, and not in a real working conditions.

So, if you want to build the absolute best 801, 211, 845 or any other high Rp (plate impedance) vacuum tubes, you know who to look for, for high impedance output transformers. 

Postscripts:
- We can make very decent 10K, 12K, 15K (sample 1, sample 2)/ 16K / 20K OPTs for pre or power output.
- Due to the large grid swing and grid current needed, 211 drive 845 or 211 drive 211 might be needed to fully utilize the high primary impedance. Ordinary drivers will not be able to manage such swings. 

Happy Lunar New Year! 
J&K Audio Design
2/12/2016

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

* 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.