Interstage transformer ratio.

[pre65]

The interstage transformer I use on 833a has a primary of 5K, and two secondaries,200 and 600.

Is the ratio of the 200 and 400 simply by dividing in to 5K ?

So 5K/200 = 25

5K/600 = 8.33

The reason I ask is that, in the past, I've been using the 200 tap to drive the 833a grid, and looking online the preferred ratio seems to vary from 1-4 to 1-10.

PS I did try and look the ratio thing online, but I got confused.

[pre65]

I've been watching a video about 833a amps, and the chap was doing it similar to me using a 45 amp via a Lundahl LL2765 interstage at 5K - 600R, so perhaps that gives me an answer ?

[Paul Barker]

Well there are many ways to get a great sound out of the 833. The way of driving it from the output transformer of a already good sounding single ended triode amplifier is one I can verify that. Never however used any of the ratios you are talking of.

But the normal amplifier output transformer made for speaker impedances certainly nails it. This was how me and Darren first ever heard the 833 way back when, you could have knocked us down with a feather, wow is was such a great experience neither of us would deny that. We couldnt share it with anyone here. Next morning we rang Mark, but he had to go to work. Its a flipin shame it sounded so good.

But if I drive it again today, I would do what Im doing now for the gm70 with greater b+. You never know I have the heater transformer and the Tributes. Nothing stopping me. Depends on the other things going on in my life which are very bad and I never know when it will change again. All I can say is Im constantly waiting for the next move of Multiple Schlerosis toying with my wife like a cat toying with a shrew.

But beginning to play with valves and going to the gym when I can get away are keeping me going. I think the endorphins are greatest from the gym, this here hobby isnt the greatest it can go a bit like gambling where you are always chasing something you remember but cant quite find it again.

I think my priority is the gym. Meanwhile and in between my wife ‘s specific MS style of dementia is trying to ruin my life.

But I wish you well for youre searcg Phil. I think Id just stop at driving it with another amp on normal speaker ratios. You dont need the volume you just need easiest was to drive it. Job done. Its not as if its a competition. Youve never disgraced yourself with the 833, The only way you fail is the music you select and Im not a great fan of youre open baffle speakers. But open baffle can be really hard to please. Its not given to us on a plate, plenty of money has been spent in Barker Towers on chasing that goal. I have to confess Im poor at speakers.

[pre65]

Hi Paul, thanks for replying.

I feel for you in your struggle at home, and I think you are going the right way to make life better for yourself.

Regarding the amp, I only have the one OPT now, so the interstage will have to do. It seemed to work OK on the 200R tap last time it was used, so that's a fall back solution if the 600R tap proves to be sub optimum.

A few of us here came to DIY audio, and this forum because we needed to find alternatives to grief and sorrow, and, in the main, it's a good and happy place to inhabit.

Best wishes for a better 2024 for you, and anyone else with issues with themselves, or their loved ones.

[Mike H]

The interstage transformer I use on 833a has a primary of 5K, and two secondaries,200 and 600.

Is the ratio of the 200 and 400 simply by dividing in to 5K ?

So 5K/200 = 25

5K/600 = 8.33

Just an observation -
That's impedance ratio, not Voltage ratio, isn't it?

To convert to turns ratio or Voltage ratio (they're the same), use the square root.

Sqr of 8.33 = 2.88:1

Sqr of 25 = 5:1

I would say, try both and compare .....

[pre65]

Aha, so 5-1 would (I think) be better.

Perhaps that's why it was suggested ages ago (by Paul ?) that 200R was the way to go.

EDIT.

At the time, Paul suggested I try cathode drive, with the 600R tap. I did, and it worked, but I went back to 200R driving the grid. Funny how we can forget things we've done.

[Paul Barker]

Aha, so 5-1 would (I think) be better.

Perhaps that's why it was suggested ages ago (by Paul ?) that 200R was the way to go.

EDIT.

At the time, Paul suggested I try cathode drive, with the 600R tap. I did, and it worked, but I went back to 200R driving the grid. Funny how we can forget things we've done.

Funny how we can forget things we’ve said too. LOL. Sounds plausible.