Directly Heated 1619 SET

[Paul Barker]

Using the 6V6 triode curves 18Watts total dissipation, I see the strange 2nd harmonic reduction found in A2 operation because the left most curves pich together similarly to the right mose curves. So into 4k7 we see 5 Watts SET at 5% 2nd. Condisering the EL84 only achieves 2 watts power out, that is an achievement.



Driven by a el84 cathode follower loaded by a choke bias for the output valve is -15 so a small negative supply appropriate to the dcr of the choke and the -15v at the cathode. When I know the choke dcr I’ll know the negative voltage I’ll supply.

[Nick]

I see the strange 2nd harmonic reduction found in A2 operation because the left most curves pich together similarly to the right mose curves

Yes, that's true, but what is going on is that you are getting more 3rd harmonic being generated. I found with the A2 211, that you needed a driver stage to generate more 2nd that you would normally aim for to prevent 2nd from being lower than 3rd, I sounded better that way. At least to me.

[Paul Barker]

I vaguely recall the E88CC calculated out with 8% so that may help. I’m prepaired to find its not as good as the EL34, plus that’s more powerful. Its all a surprise how it turns out sounding. The 6550 was more powerful but unemotional. EL34 is less powerful but tone full.

Reports about the beam valves such as 6v6 arent encouraging. But nothing ventured nothing found out for yourself.

Of course I’m on route to the GM70.

One small point getting 5 watts in a triode connected directly heated valve at 5 watts is knocking on the standard 300b’s door. So it’ll have to sound better than the 300b, which it may, I don’t know. But I do know the 300b has more 2nd distortion. I did a rough sketch in a hurry, I’ll find it and put it below in an edit. But I could only make 6 watts into 4K7, no more powerful than the EL34 but EL34 lower 2nd distortion than 300b go figure?



Below is the EL34 which I hurriedly penned for a paraellel EL34 amp, the charts for one valve but its into 4k because there will be two valves parallel and power out is therefore double what I calculated for one valve. I,e, 16 watts.

Aslong as my 2k transformers can work well at the current involved where that doubles, (the core is twice the weight of the R cores) so I expect so. a 16 what amp will make 300b look small, which it does anyway look a bit pathetic, and quite surprisingly distorted.




Not withstanding I could parallel the 1619 for 10 watts with the 2k transformers. But after reading some negative comments about beam valves in triode mode. Maybe that is why the all grid EL34 is so nice.

[Nick]

But I do know the 300b has more 2nd distortion. I did a rough sketch in a hurry, I’ll find it and put it below in an edit. But I could only make 6 watts into 4K7

Again, just my take on this, but IMHO, I think comparing or even considering what the distortion is at full swing is misleading and missing the point. As I have said before, I would only suggest using a 300b (or for that mater a PX25) if you need a lot less that 1W at most. If you need for than that, you have the wrong speakers and will miss the point of a valve like that (or for that matter any valve).

It much easier (and cheaper) to make a 95dB/W loudspeaker and a 2a3 amp that sounds good, than a 20W SET and a 89dB/W loudspeaker that won't sound any better. If you need more bass, use an active sub, may not sound as good as the best 15" high efficiency driver, but it will get 90% there for a lot less pain. And if you do have 89dB/W speakers and want 50W, get a good class D amp, or even better, two of the Neurochrome modules. If you feel the need, a source or preamp with a valve in to add that bit of 2nd. You can chase the power with a PP valve amp, but it will not sound any better than the alternative and cost you 10 times as much to build and run.

If you want the fun of building something, copy what Steve C does, he seems to have it down to an art. If that doesn't work, and you still want to build something, do what Colin does and make model airplanes (though not sure if he has flown any of them yet).

If you really want to spend the rest of your life fixing something, buy a Land Rover .

[simon]

I agree with a lot of that Nick, particularly the Land Rover . I've ended up with a 45SE direct coupled to 96dB widebands above 300Hz, a MoFo direct coupled to 18" 96dB bass drivers, and a class D amp with subs. Really works for me.

The crazy bit is the relative costs of the amps. It's difficult to put a cost to the 45SE - how do you value two WKZs? But for illustration let's say there's £1k of bits in the amp, maybe £2k. The MoFo has nearly £200 of bits. The class D amp cost £20 from Amazon on a special.

[Nick]

Yes, I keep forgetting about the MoFo, a great and relativity simple power buffer that with the right speaker will sound exactly like whatever it is you put before it.

[simon]

I was surprised how close the MoFo sounded to the SET. The 45s have a bit more tone for me, triode love as Andrew L used to describe it, but the MoFo is nice and clean in the bass.

[Paul Barker]

Well I get the point, and I liked the mofo at Steve’s in Hull. But I prefered the 45 and its worth the cost.

Right, after looking at the 6SL7 it is woefully short of 2nd distortion. It has enough gain for a single stage though. But searching for luscious sound it came to mind carry on with the e88cc and increase the gain with 6em7 power stage. So I found it distorts 2h nicely at 8.69%.

Now Mark would be silently screaming 4P1L pentode first. The problem I have with that is we want rid of odd order distortion, not start with it aswell.

I still dont know how much of the out of phase distortion cancells same distortion in next stage. One would think gain plays a part. So maybe the 2nd of the ecc88 stage gies through to the output stage reduced by the lower gain of the 6em 7 output. Hence we need the 2nd from the start to arive at the finish.

So thats the plan. E88CC volt amp RC coupled and boosted with RC coupled 6em7 driving EL84 CF direct coupled to grid of 1619 floated at -15v with a resistive divider between b- and ground b- depending on my desire to make this element act as a GM70 driver aswell. Obs I should do that.

All the time Knowing the EL34 is already perfect for the Quad 57’s. Bolocks, this gives me a passion. Mofo doesnt. El34 is passionate. But I just want to know if the 1619 is aswell. Not woth doing agreed. But otherise I’ll get my attention on my wife’s journey along the dementia road. But no knowing how long that journey will leed since the fitting was so efficiently trying to put her lights out permanently last time 5days intubated in icu. Left her void of mos of her faculties. Next time if I were God I’d let it end there.

Under those surrounding conditions, this project is good for my mental health. That and going to the gym.

[simon]

Indeed Paul.

I wouldn't use MoFo over 45s if I had just one choice. But I use 45s for mid and treble, MoFo for bass and class D for sub. Seems to be the best of all worlds. So far.

[Paul Barker]

Unless youre happy with Quad 57’s which I am.

[Paul Barker]

Transformers







I also have a pair of these Black Potted transformers. But only good at 380mA for 5 minutes, then need 10 minutes rest.

So I wonder if you only demand a 1/3rd of the milliamp capability you can use them full time? 120mA. Not much use really?

Paybe I’ll strip out the double C core these are usually made of an wind a pair of chokes.

Also they look just as big and heavy as the pair of higher voltage transformers. 2920 centre tapped for 250mA each. i.e. 1460-0-1460 would provide 1200 b+ choke input. More appropriate for a GM70 .

[Paul Barker]

Meanwhile I found the glass audio b+ delay cirquit. But I prefer the dls.10 which sits quietly until its heated from cold before it allows a single sausage of b+. On a cold day can take 3 minutes. Patience is a virtue in this matter.

[Paul Barker]

I found the GM 70 build where a choke was involved achording to measurements unnecesary. States “its presence does not influence the measurements at all, but in listening you can clearly hear the difference- it sounds more crisp and clear with the choke.”

The 40H choke loads a 5687 cf driver together with a 5687 ccs.

Be that as it may. That part of the cirquit only drives a 300b which is LC coupled to the GM70 that has a 1k cathode resistor. Oops i.e a lot of ideas in the cirquit but nothing to allow grid current.

Maybe driving grids positive is barmy?

[simon]

Unless youre happy with Quad 57’s which I am.

Absolutely. DIY audio, particularly, is a deeply personal thing with lots of compromises.

[Paul Barker]

I always saved my wife from their dimensions in the living room. But now Ive got them I realise their worth whereas other electrostats are hard to drive. The 63’s were OK but not as good.

A whole group of people did a website that said the dimensions of the 57’s is where the better sound was. So it is also for the then single driver open baffle community. The Briggs dimensions were the key.