audio-talk

Cathode current sinks installed;

Not havng power supplies with big caps and inductors leaves plenty of room in the chassis.

Onwards with the 6C33C project - tested and pre-configured the cathode current sinks - heatsinks can now be assembled onto the chassis and power supply hook-up completed.



B+ on this project is fully regulated at 130VDC. Cathode current set to 0.475mA so 6C33C dissipation is at 62W so around 20% below the max.

I got the first of the input/driver PCBs installed today. Just waiting on some 6.3mm spade connectors and I can hook up the switches, connect power and see what happens!

Everything is done and has been checked several times - except for the AC wiring, which is still waiting on the spade connectors for the switch connections.

Anyway, three Maida regulated supplies, one per 6C33C and the other shared by the input/driver stages. Mosfet based cathode current sinks.

Just have to be patient now.

That looks nice!

Cressy Snr wrote: ↑Mon Jul 13, 2020 3:57 pm That looks nice!

When anyone says "that's nice" it reminds me of Mrs Brown.

I don't comment on every photo that's posted, but you are doing well Ray.

Cressy Snr wrote: ↑Mon Jul 13, 2020 3:57 pm That looks nice!

It's amazing how much room there is when you don't have a lorry load of iron to accomodate!

Couldn't resist turning it over and plugging in the valves to see what it'll look like.

Yep, it’s something you just have to do, isn’t it.

It's alive!

Just tested each channel with my portable player and sacrificial speaker.



For some reason I felt really nervous before powering it up so, for once, I followed the advice of 'check twice, cut once'; I had hooked up the transformer secondaries, 0-105VAC and 0-310VAC, the wrong way round! Phew! Pretty sure that would have resulted in some magic smoke.

Anyway, music comes out of the speaker, not pretty but good enough to tell that there don't seem to be any problems. Now I have to pluck up the courage to put it in the system where the 13E1 is currently sat.

One that Steve will appreciate...

Trifling.

Looks good Ray. I remember the first time I fired up an 833a (GU48) filament (10V @ 10A) and left it on for an hour to prepare the innards for proper use.

Are you doing a heat soak test with the "warts" ?

I've just had a quick listen to the amp plugged into the main system; my Lowther horn speakers and a Buffalo 3SE DAC as source.

First impressions are very positive, this is one very fine amplifier - in the very limited context in which it is usable - it has less output than even the 13E1!

It's going to be very interesting to do a proper comparison with the 13E1 down the line but my immediate impression is that it sits somewhere between the 13E1 and the 300Bs - it has more of the sweetness of the 300Bs but with the weight of the 13E1, but a little quieter! At one point I was listening to Christine Collister's 'Hallelujah' (Leonard Cohen) thinking 'this is amazing' - the presentation and detail of the voice and piano really portrayed the emotion of the performance.

It was just 30mins of jumping between various tracks but I've heard enough to know it's worth spending the time finishing the build off and to look forward to a shoot-out at some point.

Given the reputation of the 6C33C valves I was expecting it to run hotter but after half an hour the chassis/heatsinks were only warm. The septal sockets for the 6C33Cs seem to be excellent with a secure contact with the pins around their circumference - people seem to have a lot of trouble with heat, especially the filament connections, when using the cheap pincer type sockets that are commonly sold for these valves.

The main work to finish off is to make a proper umbilical cable to connect the power supply chassis to the amp chassis as it's currently just connected with terminal blocks.

Chore time now.

Nice work, and nice pictures !