6C33C SE-OTL Project

[pre65]

Ray, there is a member on here, ACPEN, who did make several OTL amps using the 6C33 and a slightly smaller version of that valve, the number of which escapes me.

Might be worth sending him a message ?

[Ray P]

Might be worth sending him a message ?

There's lots of info out there already Phil?

So, are you thinking of building this amp?

[pre65]

Might be worth sending him a message ?

There's lots of info out there already Phil?

So, are you thinking of building this amp?

It's sort of been on my list for many a year, but there are things I want to do with existing amps first.

Like, finish the 833a amps, do something different with the GK71 amps (powerdrive maybe), do an 811a in A2, minor mods to the 832a push pull amp and finish the 50W Mosfet single ended amp superstructure.

[Ray P]

I'm shutting this project down and putting my eggs into the 13E1 SE-OTL basket.

Complete change of mind!

Having now heard the potential of the 13E1 SE-OTL I have to see (hear!) what the 6C33C can do in a similar situation. It'll be apples and pears though as, apart from using 6C33Cs the input/driver stage will be the 6SN7 Aikido cascade I already have assembled and I'll use a full house of Maida regulators, one for the input/driver stage and one per 6C33C. I'll use K&K Current Sinks on the 6C33C cathodes.

I have most of what I need already, fully assembled input/driver boards, the three Maida regs with a toroids, a couple of 120W 12V Mean Well SMPS I can use for the 6C33C filaments and most of the required metalwork.

Might be a bit of fun!

[pre65]

Might be a bit of fun!

Nowt wrong with a bit of fun Ray, bring it on.

[Ray P]

Had a bit of time free today and as I couldn't make any noise I started to assemble the 6C33C SE-OTL.

[SimonC]

You've probably answered this before, but where do yo get your sockets for the 6c33?
I've been through the usual run of trying to get the terminals to be reliable on the ceramic based ones and parked my 6c33 project because of this (and moving house...)

Cheers
Simon C

PS: looking good, and should keep you toasty warm in winter

[Paul Barker]

Put it away right attitude. Moving house not the time.

[SimonC]

Put it away right attitude. Moving house not the time.

I moved house over 6 years ago, its been in a box since then

[Ray P]

...where do yo get your sockets for the 6c33?

Hi Simon, I bought them from a guy on DIY Audio, original listing is here;

https://www.diyaudio.com/forums/swap-me ... ocate.html

They're not the cheapest you'll find but far superior to the normal 'pincer' sockets you see advertised for 6C33Cs. The ceramic is really substantal too. Here are a couple of close-up pictures so you can see what I mean.





I have his email address if you want to contact him - PM me and I can pass it to you. I'm pretty sure he still has a few left.

[Ray P]

I've been working on my second room heater project this morning - hooked up a couple of 120W Mean Well SMPS and powered up a pair of 6C33C filaments. I was actually a bit disappointed that I only measured a temperature of 126deg C - I was expecting higher based on the reputation of the 6C33C but then it is only the filaments generating heat at the moment. The SMPS are way over-spec'ed and barely get warm.

[Ray P]

Almost finished the power supply chassis for the 6C33C amp today.

[Ray P]

Productive few hours this morning assembling the 6C33C amp. Next up will be the HEATSINKS either side carrying the maida regs (for the 6C33Cs) and cathode current sinks.



Installed PCBs are regulated supplies for the 6SN7 filaments and a maida reg for the 350V B+ for the 6SN7 input/drive stage.

[Ray P]

Tested the Maida reg for the 6S7Ns (350VDC @ 20mA) this morning - OK.

Installed and tested first 6C33C maida reg (130VDC @ 480mA) - OK.



Nice big heatsink needed for the 6C33C regs. Nicely drilled, tapped and devices mounted on silicon insulation pads.

[Ray P]

Second 6C33C reg instaled and tested - OK.



Next up are the cathode current sinks.