6C33C SE-OTL Project

What people are working on at the moment
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#151 Re: 6C33C SE-OTL Project

Post by Ray P »

This amplifier has been 'off-line' for a while (I've been using my SissySIT amplifier) but I've been thinking about re-purposing it...

I will eventully put together my Pass SLOB speaker build and have the option of some 8ohm Aurel Bryan drive units that are about 95dB efficient and I've been putting together a bandwidth limited power buffer to drive them sans crossover - it rolls-off, 2nd order, below about 150Hz.

Ialso have the option, influenced by Nick's positive results with his acrylic Quasars, of using Lowther speakers for the full-range drivers in the SLOBs. These are more efficient than the Aurels and are also 15ohm so a reasonable match for the 6C33C amplifier to drive well enough in my domestic environment. Anyway, I've been wondering about modifying this amp to also be bandwidth limited like the power buffer. Here's the schematic of the amplifier:

Image

I would like the check my understanding of the modifications to achieve a 2nd order roll-off below 150Hz so comments/feedback are welcome. Apologies but the parts aren't numbered in the schematic.

THe 1uF cap and the grid resistor form one pole of the filter so I susbstitute a cap of about 21nF in lieu of the 1uF, retaining the 50K grid resistor,

The second pole is formed from the ouput cap and the speaker load (15ohms) so an output cap of around 70uF will be required.

Does that stack up?

A derived benefit of changing the output cap is that a plastic film cap is then possible, possibly sounding better than the elextrolytic currently used but also with enabling a DC voltage rating of 250V or more, which is higher than the DC that could result from a 6C33C failure.

Cheers.
Sorry, I couldn't resist!
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#152 Re: 6C33C SE-OTL Project

Post by Ray P »

I'll take that as a yes then.
Sorry, I couldn't resist!
User avatar
Nick
Site Admin
Posts: 15706
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#153 Re: 6C33C SE-OTL Project

Post by Nick »

My only concern would be the feedback. I would simulate it and see what happens.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#154 Re: 6C33C SE-OTL Project

Post by Ray P »

Nick wrote: Sun Aug 07, 2022 10:29 am My only concern would be the feedback. I would simulate it and see what happens.
Cheers Nick. I've not done simulations before but I guess learning to do it is kind of inevitable. I guess installing LT Spice is the starting point.
Last edited by Ray P on Sun Aug 07, 2022 9:21 pm, edited 1 time in total.
Sorry, I couldn't resist!
User avatar
izzy wizzy
Old Hand
Posts: 1496
Joined: Fri Nov 02, 2007 7:02 pm
Location: Auckland NZ
Contact:

#155 Re: 6C33C SE-OTL Project

Post by izzy wizzy »

The sim section on intact audio and Stephie's drop down models and model files make it super easy to use. Most valve types are there already.

Take a few working sims from there or I can give you some and you shouldn't have a fight on your hands.
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#156 Re: 6C33C SE-OTL Project

Post by Ray P »

Installed LTspice and started to watch the tutorials...
Sorry, I couldn't resist!
Post Reply