Tag: 814

Goodbye 814SE Amp, it’s been a fantastic journey

After 2 years of listening pleasure, it’s time to retire the 814SE monster amp. With its breadboard nature and high voltages around, this is not safe to have around with my daughter now being 8 months old. Sad to see this amp go and I hope to listen to it some time in the future.

Filament bias and winter heating system
814SE Amp
814 output valve
814SE Amp and Lenco Turntable
+HT supply
6D22S rectifiers
HT power supplies

What is was really painful for my back was to lift this ton of iron up to the attic. It’s so heavy and not keen to move it for some time. This amp has been a fantastic learning experience for me, as well as a huge challenge. High voltages, A2 operation, DC-coupling and the mix of sand with plenty of iron here in a 100% DHT amp was the right mix to give me several headaches along the build and testing stages. However, it’s a beauty to listen to, in particular thanks to the 46 and 814 valves which are unique in my view for this circuit and also the optimal tuning of the operating points and the iron used.

Enough for now, however I’m still working on my safer 4P1L PSE amp, so watch this space 🙂

814 SE Amplifier: Custom Output Transformers

 Improving the 814 SE Amplifier

photo 3After more than a year listening to this fantastic amplifier, it was time to do the first significant improvement to it despite I resisted to modify it after so much work and effort put into the design and build. The evident upgrade was the output transformer. When frequency response was measured, it was evident to see that the HF response was lower than expected. This is the result of the transformer and its configuration in this circuit. The LL9202 is a better OT for higher impedances and in this circuit, it is used in the 6KΩ /8Ω mode.

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814 SE A2 Amplifier

Goodbye 4-65a SE, at least for now

IMG_1401After enjoying the 4-65a SE amplifier for many months, I couldn’t resist myself from upgrading the output stage to the 814s.  I just needed changing sockets and filament raw supply transformers to fit the requirements of this lovely transmitting valve. Needless to say, my recent tests on 814s were very encouraging. The 814 seemed to perform much better than the 4-65a in delivering 10W of class A2 sound at half the distortion levels. This to me, was only worth trying.

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A super-linear output valve and fireworks :)

Testing the 814 in triode mode

Worried about the G2 maximum voltage limit as per datasheet in class B, I decided to test the 814 carefully. So carefully that had a bit of smoke and fireworks (but not inside the valve)

Paul Leclercq suggested adding the grid resistors in G2 and G3 and do some baby steps whilst testing this lady.

Here is the test rig used:

The valve is astonishingly linear. At 600V anode voltage and 50mA quiescent current the valve only produced THD=0.01% at 15Vrms output!

Internal pannel meter wasn’t disconnected and apparently didn’t survive the 600V exposure so blew up and a domino effect provided some interesting fireworks inside my bench supply (series MOSFET regulator) 🙂

Evidently something went wrong with an unexpected short to ground, couldn’t be bothered with doing some proper root cause analysis so shut everything down and brewed myself a cup of tea….