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801a DHT Triode Spice Model
My friend Bela, who is an experienced DHT user and very fond of the 801a, asked me if I could help in developing an LTSpice model for the venerable 801a. I have several 10/10Y but unfortunately no 801a...
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Sweep buffer
I’ve been using my sound card and Pete Millett’s interface for testing. However, the limitation on high frequency response is due to the sound card. A cheap, but yet effective option, is to use the...
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Russian PSE in steroids (4P1L into 4P1L)
Introduction: DHT madness I’m not going to dwell on DHT sound. I’d rather say that if you’re looking for a stellar DHT candidate, the 4P1L beats them all. It’s dirty cheap, reliable and sounds amazing....
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Russian PSE in Steroids (6E5P into 4P1L) – Part II
Well, it was obvious I couldn’t leave last post as it was. There is an option to change the driver for a different valve. You can use a C3m (low gain in triode mode which is ideal here), a C3g,...
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Russian PSE in Steroids (01a into 4P1L) – Part III
From Russia with Love East-West Divide, Copyright by Justmeans The interesting combination to explore from our previous designs is to mix some western valves like 01a into the Russian parade. The...
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Russian PSE in Steroids (01a into 4P1L) – Part IV
More power Our previous west meets east circuit can be improve further. In fact, a compromise made with the filament bias design is that coupling between driver (FET follower) and the output stage...
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Rolling valves
I’m not a big fan of rolling valves. Perhaps it’s likely to do with the fact that I don’t have too much free time these days. However, I do look into burning in the valves. A noticeable change found...
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Teflon sockets
I have used Jakeband teflon sockets for over 3 years. They are very well made and of high quality. Luciano from Jakeband can provide you with any custom socket you may need. This time, I requested a...
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Gyrator PCB: using the J310 jFET
A minor update that is worth mentioning to everyone here. After some abuse on the J310 JFET in the gyrator board for using in a 20-30mA stage (e.g. 4P1L) I managed to kill it after a full turn-on (via...
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Differential buffer and preamp
As part of improving my bench test gear to do sweep tests and impedance measurements, I ended up building a great preamp and buffer gig based on the SSM2019 device as described previously here. Here is...
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CX371a / 71a DHT Preamp
71a DHT Preamp (2012) More than 4 years ago I ran a lovely 71a preamp which sounded amazing. I used it for some time and enjoy its sound up until I continued with my exploration around DHT preamps....
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27 Preamp
An IHT preamp, oh yes! I always loved the 27 valve. It was one of the first line stages I built many years ago before adventuring in the DHT world. I still have a large collection of them and I was...
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Alpair 10M / FT96H speakers
It’s been a long time since I haven’t tweaked my speakers. After more than 9 years I decided to change the drivers after falling in love with the Alpair 10M from Mark Audio. I listened to my friend...
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4P1L Preamp
4P1L gyrator test mule It’s always great to come back and revisit a great design. The 4P1L preamp performs flawlessly so I tweaked the gyrator board to see how it worked with the BF862 FET. The result...
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Filament Bias: a practical example with 3A5 DHT
Introduction Recently I was asked about whether I could write on my blog about how to design a filament bias stage. My immediate answer was around 1) I don’t have much time these days am afraid and 2)...
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RL12P35 German Transmitting Pentodes
It was pure lust and love at first sight. I found the RL12P35 german transmitting pentodes and couldn’t resist in buying them. A very nice set of NOS Telefunken and Valvo valves with also NOS sockets....
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2P29L – Preamp and driver for 4P1L PSE Amp
A very interesting Russian directly-heated pentode related to 4P1L is the 2P29L. It has a similar mu (μ=9), much higher anode resistance 2.8-3KΩ and transconductance of 3mA/V when triode-strapped. The...
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2P29L/4P1L PSE Amp
Looking for more Well, ok. You want more power from previous 4P1L PSE amp? Here is an alternative approach: 2P29L into 3x4P1L PSE You can get 5W at 2% THD maximum. I’d rather avoid filament bias at the...
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45 SE Amplifier
Introduction More than 5 years ago, I built a fantastic single-ended amp with the unique 45. The 45 has a distinguished tone and personality despite its mere 2W of output power. If you have high...
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DvB (IN1166) input transformer test
IN1166 DUT This is a long overdue post, as I have carried out these tests time ago but never got around to publish the results. Dorin from DvB transformers sent me a pair of his transformers for...
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