Category: Gyrator PCB

EF86 – 300B XLS SE Amplifier build

Here is a very nice build from Dan Kercher on his contraption of the 300B amplifier with auto bias. The driver is an EF86 with SiC diode biasing, the topology is a hybrid mu-follower and a source follower drives the output stage. Filaments are DC with Rod Coleman’s board:

Dan Kercher’s EF86 – 300B XLS SE Amplifier build

More details can be found below:

Hi Ale, 

I wanted to thank you for all of your PCBs.  I just finished a project that uses your Gyrators, SiC bias boards, and SiC Source Followers.  I'm so happy with the results.  Details posted on Audio Asylum.  

https://www.audioasylum.com/forums/tubediy/messages/27/276814.html


Cheers, 

Dan 

300B SE Amp – here we go

A Brave New World

Surely you’re as tired as I’m with COVID-19. One of the best things I can do to distract my mind is to keep myself away from social media. Every stone you turn, there is COVID or a statement about it. I won’t moan as I have a job for now and a healthy family. Some members of my family were infected but nothing major. I can only say is that the world has change. And so my day to day life looking after the young family whilst working is a real challenge. Starting my fifth week of lockdown, I have to distract somehow my mind at times, otherwise will go mad.

A New Concept

Continue reading “300B SE Amp – here we go”

Mini Hybrid Mu-follower board test

 I had a  go first at a mini-gyrator board using SMD. Blimey, it’s hard work to get all these crammed into such a small footprint.
I did a quick test with a D3a and worked fine at 100V/10mA (low voltage of course). It was +35dB flat up until a couple of Mhz. Even the over-current LED works!
Footprint is as small as you can get: 45mm x 25mm 🙂
More to report later!

VT-25/801a/10Y DHT Preamp with SiC filament bias

For quite some time now I wanted to share one of the variations of the famous VT-25/10Y pre-amplifier. As usual due to work, business travel and family duties, I’ve struggled to find the time to update the blog.

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D3a driver w/ Rev08 board

A friend from Canada ordered a pair of boards and I used the opportunity to test the newly arrived hybrid mu-follower (aka as gyrator) Rev08 PCBs.  He will be using these boards in the 300B design posted here.

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45 SE Amplifier – revisited

A unique sound

If you have a small room and high-efficiency speakers, then keep reading. If not, you can still enjoy reading about probably the best sounding output valve in my view. The 45. I wrote about it few times and have to say, it’s still one of the best. Better than a 300B but unfortunately can do only 2W. You can use it in Push-Pull and is superb. Have a look at this.

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45 Push-Pull Amplifier

Chasing that sound

The 45 DHT is probably one of the best sounding valves out there. In fact, I have struggled to get a similar level of detail and timbre in a 300B or 4P1L output stage. Even my 814 SE Amplifier (which was class A2 and had thoriated-tungsten filaments) couldn’t replicate that sound. I posted time ago my incarnation of the 45 single-ended amplifier here.  The main challenge with this valve is that it can only put out there nearly 2W, not more. With its 10W anode dissipation, you will struggle to get more juice from it in class A at a low distortion level.

However, if we look at a push-pull amplifier with the 45, we can hopefully retain the timbre characteristic of the valve, despite it won’t  be a single-ended one. Well, I love good PP amps, so why not?

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Hybrid Mu-follower (aka Gyrator) Rev08 PCB Update

It’s been far too long since I last posted on this blog. With the limited spare time I’ve got these days, I concentrated in setting up the new workshop and system since we moved back to our place. I’m nearly there, so now it’s time to get back to work

I made some updates to the “gyrator” PCB. I’ll stop referencing it gyrator from now on, since the name is misleading. However, it got popular that way. Nevertheless, it’s a hybrid mu-follower circuit but if only if you take the output from the anode, it behaves like a “gyrator” from a frequency response perspective. If you’re interested in this circuit in more detail, please read the lecture I gave last year at ETF.18. You can download it from here.

Back to the board, here are the few changes made:

  1. Moved the trimpot P1 for easier fixing of the board with the M3 standoffs.
  2. Added a gate stopper resistor (R9) to avoid oscillation at low anode current (<10mA) when using high-gm MOSFETs in the lower position J4. This was evident with devices like BSH111BNK
  3. Added an LED (D4) indicator and a series resistor (R8) at the drain of M3. This enables indication of:
    1. Normal operation subject to  value of R8
    2. Source current into load (e.g. like in A2 operation) subject to value of R8.
    3. Short output to ground. Depending on duration and current limitation of power supply, this may prevent damaging M3 MOSFET. Not guaranteed, but in some scenarios will work.

Continue reading “Hybrid Mu-follower (aka Gyrator) Rev08 PCB Update”

ETF.18 DHT Preamps Lecture

ETF.18 has been an emotional journey. I moved house literarily when I got back from ETF so my life has been more than hectic over the past few weeks.

I promise I will do a write-up of this amazing experience. There’s a lot of people out there who would love to attend so is my duty to reflect and share as much as I can.

In the meantime, I wanted to share the lecture I gave at ETF on DHT preamps. It was a challenge on its own but went really well. This was my first ETF and without knowing the audience I had to guess the level of detail, entertainment and expectations of an unknown audience. I knew a fair bit of the ETF folks, but audience was big and wide.

I struggled to find the time to prepare this lecture I have to confess. Between moving house, house building works, my second daughter’s arrival , weekly work travel and everything else, I seemed not to find the time to get this done. Thank you Morgan Jones and Rod Coleman for proof-reading and making this an easier task.

I hope you enjoy it. There are some notes on the slides I put together for the people who didn’t attend ETF. Otherwise the slides aren’t of much use on their own.

I’m writing this blog entry whilst enjoying the lovely Bourbon that Pete Millett gave me on the way back. Thanks Pete!

ETF Lecture on DHT Preamps (with notes):

DHT-Preamps-ETF2018-final-notes

ETF Lecture on DHT Preamps (slides):

DHT-Preamps-ETF2018-final