Pentode Differential Pair (Hybrid Mu-follower)

Pentode drivers are very interesting. You can get excellent results out of them. Here is my version of a differential pair using pentodes. I want to try them out in the 45 PP design I wrote previously Continue reading “Pentode Differential Pair (Hybrid Mu-follower)”

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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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

PL84 triode

TV-Roehre-PL84-Telefunken-m--Raute-ID1497-1497

The PL84 pentode is very well known out there. I’m not going to write about it as there is plenty of information about the use of this pentode in push-pull amps, etc as well as comparisons with the EL84, EL86 and Russian equivalents such as 6P14P, 6P15P and 6P43P. I recommend you to check Klau’s work here.

I have a nice set of Telefunken PL84 which I may be using in triode mode as part of a Spud project I’ve been working on the design for some time. I’m interested in triode-strapped curves but also will be looking at tracing the Schade-feedback curves when I get the time to do so.

I quickly found a sample valve that was close to the pentode specs at 90%. Good enough for my purpose so I proceed to trace the triode curves quickly in uTracer.

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Merry Christmas!

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It is so great to have another Christmas. It gives us an opportunity to wind down and spend proper time with our loves ones. The ones who are physically with us, and remember the ones who are no longer here, but still very present in our memories.

In fact, we all look forward to the holiday period to crack on with our projects. We all have a pile of endless projects and ideas and no better time than Christmas to start working on them.

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Custom Transformer Supplier in Europe

Custom transformer supplier

Custom OT

Given I had several emails asking about the output transformers I used in the recent upgrade of the 814 SE Amp, I asked Mr. Vincenzo to kindly provide an email address so you can reach directly to him. You can send your request via the form below which protects his email address from internet SPAM :).

Alternatively, if you don’t want to use the form below you can browse his website (in italian only sorry).

 

 

Fixed bias regulator

 Testing the Rod Coleman Fixed Regulator

As part of my 300B SE project design, I looked into various fixed bias arrangements and regulators. Rod Coleman has developed another fantastic circuit after the success of his DHT filament regulator which is now the preferred filament supply kit within the DIY audio community. After many years of refining the DC filament regulator, Rod came up with a clever design for fixed bias using the same concept: a gyrator and a temperature-compensated CCS. Instead of feeding a current through the DHT filaments, in this case the current is used to generate a clean bias voltage across a “bias resistor”. The bias resistor is bypassed by a capacitor as the high impedance loop formed by the regulator and the bias resistor is sensitive to pick up HF noise which could be amplified by our system.

The kit is of the same quality you would expect from Rod’s boards and very easy to build. It takes less than an hour to build the boards:

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4P1L Push-pull Amplifier

Shiny Eyes by Radu C. Tarta

This is a fantastic 4P1L push pull incarnation done by Radu. I hope you enjoy reading this post as much as I did. Cheers, Ale

Introduction

“Shiny Eyes” Push-Pull tube amplifier is the result of 6 months of research, experimentation and lots of music listening. It started in the summer of 2012 when life opportunity re-opened the door of an old passion: electron tubes. However, this time my goals were directed towards audio. I understood from the beginning that after 30 years of interruption I have to dedicate a great amount of time and energy to catch up with technology and ideas. I want to thank my wife Paula for her emotional support and understanding. I am also grateful to the fanatics from the DIYaudio community for their contribution to the world of tube audio experimentation. Personal thanks to Kevin Carter of K&K Audio for his advises and help, to Ale Moglia of Bartola Valves for his inspiring work and to Rod Coleman for his excellent filament regulators.

Initial tests

radu1Here are few images taken during design, experimentation and final building: Early stages…

radu2
Initial breadboard
radu3
Layout design stage

Continue reading “4P1L Push-pull Amplifier”