To SPUD or not to SPUD

Why not? Less is more and if well achieved the task, you will end up with an amazing result. To do this you will need a good quality OPT and the valve which can do this task. It will need high mu where possible and linear. There are just a handful of DHT that could do the job (like EML20/30) or you can look for the high gm pentodes (e.g. E55L, E810F, etc.) which are very expensive generally or Russian valves like my beloved 6e5p which is cheap as chips (still).

Depending on the step down ratio of your OPT you will need likely a step up input transformer to drive the 6e5p to full tilt. Here is what I experimented with many years ago. Unfortunately I didn’t take any distortion measurements but it sounded really nice.

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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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DHT Folded Cascode Experiments

Here we are on holidays and surprisingly I struggle to find any free time in which I can sit down in front of a tablet and write this blog entry. This is actually quite good as it’s a sign of me being disconnected and looking after my daughters. Life is good.

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Iron and Sand

Over the last few months life has been very hectic for me. Between work travel and family, I’ve struggled to find time to work on any audio related stuff. You probably noticed this as have reduced significantly the amount of posts over the last 4-6 months.

This is sad, as have many things piled up for sharing. Either way, my focus has diverted slightly over the last few months. I decided to get back to music performance after so many years. This is a great decision, which I’m very happy about. When I thought about which instrument to play again, I immediately looked into my tenor saxophone – which I played for so many years. Unfortunately due to family commitments, I can only play during night time, so saxophone was ruled out. So, what should I do? Of course, my mind then got stuck on to my next big instrument preference: the Chapman Stick. When I was at university, I discovered this amazing instrument. I believe it was Tony Levin from King Crimson the first one I heard playing it. Anyhow, as I couldn’t either afford one and also there were probably none available in Argentina at that time, I decided I would build one myself. Luckily my dad was very experienced in woodworking and crafts in general. With his help we designed and build one, which sounded really good.

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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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EML20A driving EML45B

I’ve got asked the question on how an EML20 (or EML30) can drive an EML45B. Answer is straight forward and hopefully this brief blog entry can shed some light to this request.

I recently looked back again on the EML20A. With a gain of 20, it’s a good candidate but it hasn’t got just enough gain to drive the output stage to full power:

EML45B with 5K OPT

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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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