audio-talk

Since my small push-pull amp has turned into a single-ended job, I’ve started a new thread. The PP amp is not dead.....yet, but it’d be daft to talk about it in a push pull amp thread. As usual I’ve got diverted.

I really like the sound of SE amps, built with regulator valves. For example, the recently built 13E1 SEOTL is, for me, a milestone project that sets a standard that this 6336A project is not going to reach, but I’d rather have more than one valve amp in my collection, for those times when I feel like swapping things around. And it’ll be something new for Owston 2020.

So....
6336A curves:


260 ish on the anodes and 90mA idle current at 80 ish Vk looks decent to me.

2K5 loadline.

Some working out (not mine, but why reinvent the wheel)



The blue line gives 26.1W plate dissipation per section, plus the 31.5W of heaters. This means having to shift 83.7W of heat from a bottle the size of a KT88
The green line at 23.5W per section is a little cooler at 78.5W to manage. The valve is designed to manage this heat, but it’s a bit warm to say the least. I’ll probably go for the green line, even though the max distortion is slightly higher at full power.

Driver needs to swing 160V pk-pk, so a simple 6SN7, or 12AU7 cascade will easily manage it on a shallow load line.

If I choose a 6SN7 cascade to drive the 6336A, I might even be able to adapt the pair of SEOTL driver PCBs, Ray sent me last year. It should work nicely with only a couple of component value changes.

Cressy Snr wrote: ↑Sat Jul 20, 2019 3:01 pm If I choose a 6SN7 cascade to drive the 6336A, I might even be able to adapt the pair of SEOTL driver PCBs, Ray sent me last year. It should work nicely with only a couple of component value changes.

Should you need a spare or two Steve I'm sure I've got a few more of the 6SN7 boards somewhere here.

Ray P wrote: ↑Sun Jul 21, 2019 1:27 pm

Cressy Snr wrote: ↑Sat Jul 20, 2019 3:01 pm If I choose a 6SN7 cascade to drive the 6336A, I might even be able to adapt the pair of SEOTL driver PCBs, Ray sent me last year. It should work nicely with only a couple of component value changes.

Should you need a spare or two Steve I'm sure I've got a few more of the 6SN7 boards somewhere here.

Cheers Ray. I may have to take you up on that, as I seem to have mislaid the 6SN7 boards.

I'll see if I can find them just in case then.

Ray

I've found the boards Steve, I have half a dozen of them should you need any.

Ray

Ray P wrote: ↑Mon Jul 22, 2019 10:20 pm I've found the boards Steve, I have half a dozen of them should you need any.

Ray

It’s OK Ray, I’ve found the blighters.

I've decided to resurrect this design after four years. Whether to use a pentode driver or a low mu triode cascade is one decision I have to make.
The 6336A gain is 2.7 and at least 140V Pk-Pk is required for full drive: 300B territory.

Nice ...
Maybe a pentode with a 5687 CF too as an option ?

Or a LTC6090

Now there’s a thing.
Trouble is, I wouldn’t have a clue how to apply it.

IslandPink wrote: ↑Fri Aug 04, 2023 2:43 pm Nice ...
Maybe a pentode with a 5687 CF too as an option ?

Thanks Mark, I’ve got one or two pentodes to choose from:

EF80
12GN7
D3a.

Wouldn’t mind looking at a HV solid state follower of some sort between the pentode and the output stage. It’s not the enemy any more. Breadboard might be the way to go in the first instance if I need to try these things out.

I’ve got a lash-up running.
It’s using the E88C as a driver at the moment, but I know that more welly is going to be required in that department. Nevertheless it shows great promise as is, so it’s a design worth pursuing. It’s clean and clear, which in my book is a decent place to start from.

The result of auditioning these tubes, is that they are absolute bass monsters and combined with the Hammond 1627SE OPTs, which are no slouches at the bottom end, it felt like I was being hit around the head with a sledgehammer! It all became too much for my lily-livered disposition.

Also, the heat this tube gives off is blistering; 31.5W of heaters and another 30W of max dissipation per anode. That’s 90 plus Watts to get rid of from a tube the size of a KT88. Ideally it needs a fan blowing air from underneath, otherwise it all just gets too hot. The poor old E88Cs were being roasted alive by the radiation.

I’ve shelved the project for now until I sort out some better heat management and a layout that isn’t going to fry the small signal tubes. It’s all a bit 6C33C at the moment.

I’ve downsized the power tube to the 6AS7G and the OPTs to Hammond 125FSE. The voltage requirements are lower, so I made use of a choke input supply to power the thing. The sound is more balanced and the bass is more in proportion which is infinitely preferable to being slapped around the head. At my age I want to relax and chill.

Tomorrow, I’ll continue this conversation in the ‘something stirs’ thread, where I’ll start planning a stronger gain structure.