The Newton 300B

[Thermionic Idler]

as I want to give the thermal compound on the cathode bias resistor a chance to dry off

Why? Just asking if you have a reference to that being required.

I don't want to accidentally brush it with my fingers whilst it's still wet, it's bloody horrible goopy stuff. No better reason than that! And if the cat jumps onto the desk (which she does frequently) I don't want it getting on her, either.

[Nick]

Ok, was just wondering. You only need to put very little on anyway.

[Thermionic Idler]

Ok, was just wondering. You only need to put very little on anyway.

Yeah, I put way too much on. Not once, but twice.

[Thermionic Idler]

Further progress today - standoffs and hum bucker pot fitted, along with some of the rear panel-mounted elements including two of the motor run caps. These are what I can put on without blocking access to the transformer mounting holes and covers etc. I've done this on both chassis but from now on I'm concentrating on the left channel amplifier only.

Next up, heater wiring and input transformer.

[Cressy Snr]

Looking good so far Dave.

[Ray P]

Nice work Mr. Idler

[Ali Tait]

Shoddy!

[Thermionic Idler]

Today, I focussed on this bit of the circuit - specifically the input transformer and its load resistors as recommended in the Lundahl documentation:



Here's the transformer in place and configured 2:1+1, note also the test leads from the Analog Discovery. Takman carbon film resistors and Jensen PIO:



The LL1684 has some pretty impressive measurements. This is the 1kHz square wave response, both phases



And the response / phase shift at 50kHz

[Thermionic Idler]

Progress in the last couple of days - the signal circuitry and heater wiring for the input and driver stage is now done.

[Ant]

Fast work there dave!

[Ray P]

Excellent shoddiness Dave.

[Thermionic Idler]

Some more progress. The signal path wiring is basically all done, and yesterday I also tested and set the CCS's to the 29mA value required for the 6V6's. Next thing is the heater wiring on the 300B's and the power supplies.

Sadly it looks like my target of getting both amps built by the end of this week might be missed...

[Cressy Snr]

Ohmite Audio Gold are nice sounding resistors.
Not too costly either.

[Thermionic Idler]

Ohmite Audio Gold are nice sounding resistors.
Not too costly either.

That's good, it's the first time I've used them. Usually I opt for Mills but it starts getting horribly expensive if you use them everywhere, and I already had a lot of parts budget in the eight Jensen PIO coupling caps I needed. This time I just used Mills on the 12SN7 and 6V6 cathodes.

Did I mention this amp weighs as much as a boat anchor? Thank heavens I didn't include an interstage transformer, seriously if I had I don't think I could have physically lifted the final build. And that's for one monoblock.

I'm probably jinxing myself here, but I think if I get up early and go at it solidly, I may get it finished tomorrow. I tidied up the secondary wiring on the two main transformers today and got those done, also the heater wiring via the humbucker pot for the 300B's is now in place. Part of the issue with using off the shelf transformers is capping off and finding somewhere to secure all that unused wiring so that it doesn't get in the way.

[Thermionic Idler]

Finished - and it works perfectly! Voltages pretty much on the button with my Spice model predictions. It sounded a little edgy and congested at first, but bedded in nicely after an hour or two.

Does it improve on the Beasts? Actually, we think it does, but final judgement will be reserved for when the other one is built and we can hear them as a stereo pair. It's quite a close call but there is no mistaking the transparency, clarity and sheer musicality of DHT's done right. It really does sound quite glorious.

More later.