Remember These?

[Wolfgang]

How did you get to these results? Only by calculation or did you actually look at the output signal (scope, DMM) with an 8R dummy load connected?
Did you add already NFB?
I was playing already in my mind with ideas about this tube for OTL use.

[Nick]

or the CCS chip

You could add a series resistor to reduce the CCS dissipation.

[Cressy Snr]

I've got it going on a pair of sacrificial speakers; just drivers not even cabs, added some feedback 4k7 and it goes very loud indeed without distorting and that's no lie
Fly in the ointment at the moment is the dreaded hummmmm.

I'm going to try it on the main speakers to see what the bass is like. I should be able to tell, what's what despite the hum.

Until I can get to the bottom of the hum issue and eliminate it, there is not a lot of point in any sig gen squarewaves or scopery.

Watch this space, because what little I heard on the sacrificial speakers is damned impressive.

[Cressy Snr]

Tried it on the main speakers with a few snippets of stuff I know and......Oh my giddy Aunt! ..utterly, utterly stunning and any other superlative I can think of......WOW! And this despite needing realistic concert hall levels to drown out the hum. Nice bass too, maybe a little more feedback just to tighten it up a smidge.

Get that sorted and it'll be great. But that's for much later. Got to get the room remodelling finished before Christmas or my name will be mud.
The concept definitely works and I wouldn't hesitate to recommend Wolfgang, that you have a go with the 13E1. I can't see you being disappointed.

[Ray P]

Don't be deflated Steve, IMO this has the potential to be a very fine sounding amplifier and your starting point of using what you have to hand is very sensible. See how it goes before writing it off.

See...

[Ant]

Heater hum?

[Cressy Snr]

Sorted it
The CRC supply to the driver stage is complete shite as is. Because it is a voltage doubler I seem to have conspicuously failed to take into account the much greater amount of ripple they generate compared to a "normal" one. Clip leading a 10H choke between the two 100uF caps instead of a resistor has reduced the hum to barely audible levels. More filtration is an obvious direction to take, or even (horrors) a nice little tube regulation scheme. Did I mention that breadboards were fun?

So to get near silence, the input/driver stage supply needs improving. At least I now know what's required to get it right.

This could be a long listening session

[Cressy Snr]

Complete bloody madness if you ask me!
Nothing's caught fire yet. It seems stable and runs sweet as a nut.

[Ray P]

Steve, I have a picture of you sitting and listening with a big cheesy grin.

My 300B SE-OTLs are essentially silent; if that's possible with a DHT it ought to be possible with these indirect heated valves?

[Ray P]

On my 6C33C project I will be using a Neurochrome Maida regulator for the driver stage.

[Ray P]

or maybe you could try a Salas HV Shunt Regulator;

http://www.kandkaudio.com/other-kits/

[Cressy Snr]

Cheers Ray,
I'll have a look at the regs you suggest. I'll see what happens in the meantime with better filtration to the driver PSU.
As you've probably sussed, this will be absolutely going in a proper chassis in the new year. It leaves everything else I've had looking somewhat lacking.

This thing is a top class music maker and the Epcos electrolytic output caps aren't even bypassed yet, neither are the feedback resistors, but they are not yet fixed in stone.

[Mike H]

Sorted it
The CRC supply to the driver stage is complete shite as is. Because it is a voltage doubler I seem to have conspicuously failed to take into account the much greater amount of ripple they generate compared to a "normal" one.

Oh yes. 50 Hz peaks instead of 100 Hz.

[Ray P]

Try Elna Silmic RFS caps on the output (bypassed, I use Mundorf ZNs), they made a good improvement over the Nichicons I was using before.

To be honest you've now set the cat amongst the pigeons with my own project. I have an option on a pair of 13E1s at a good price and I'm thinking my 6C33C project might become a 13E1 project. The good thing is just about everything I have for the 6C33C build could be repurposed. My reasoning is that the 6C33Cs have a bit of a reputation for running very hot, being variable and tempermental plus the little more power on offer with the 13E1 wouldn't be a bad thing. I would optimise for my 15ohm Lowthers too.

[Cressy Snr]

Try Elna Silmic RFS caps on the output (bypassed, I use Mundorf ZNs), they made a good improvement over the Nichicons I was using before.

To be honest you've now set the cat amongst the pigeons with my own project. I have an option on a pair of 13E1s at a good price and I'm thinking my 6C33C project might become a 13E1 project. The good thing is just about everything I have for the 6C33C build could be repurposed. My reasoning is that the 6C33Cs have a bit of a reputation for running very hot, being variable and tempermental plus the little more power on offer with the 13E1 wouldn't be a bad thing. I would optimise for my 15ohm Lowthers too.

Thanks for the cap suggestion Ray.
Didn't mean to set the proverbial amongst the pigeons, but the 13E1s in the breadboard certainly don't seem stressed. They are pretty hot, but nowhere near the furnaces I was expecting. They are running about 150V a-k with just over half an amp going through them, so 75W dissipation each, which is well within the 95W limit in triode mode. I don't see any need, with my 98dB speakers to push them any harder, and running into 15 Ohms they should be very nice indeed.