FLEA PPP, all ecc99

[tinitus]

I would like to ask if this can be made work
am I on track, or complete wrong

its 3x eccc99 in total
output ecc99 have each half in paralel

😕

 

[aardvarkash10]

I don't think it will as drawn. You appear to have the output pairs wired to oppose each other...
For what I think you want you need to apply a bias voltage to the interstages and have both outputs on either phase connected to the same end of each interstage.

Bah - i'll draw it - it'll be quicker and clearer!

Crap drawing I know - inside the hatched area is an inverted repeat of the image shown...

 

[djn]

It sort of looks like an OTL. If you are going to use that many tubes, you might want to look at Tim Mellow's 25W OTL.

 

[tinitus]

It sort of looks like an OTL. If you are going to use that many tubes, you might want to look at Tim Mellow's 25W OTL.

hey, its only 3 tubes in total
you might call it ecc99 driving ecc99, PPP 😀

Im trying to understand how it works
it may show that I dont 😛

addvarkash
yeah, I think I made a mistake with interstage PP to PP
the two "out" to grids should be to PP output stage, and not to two paralel output
will try to redraw

 

[aardvarkash10]

you could simplify further. The ltp front end is superfluous. Both ITs can be driven from the same single anode as long as their secondary winding directions are opposed.

The cathode resistors in the outputs are also superfluous - bias should be set by applying a voltage to the IT secondary windings.

 

[planet10]

Could you not make it simplier yet by using a single interstage with a centre tap to feed the bias into?

dave

 

[aardvarkash10]

shure kould! I just figured the op was working with stuff they have...

 

[tinitus]

great info

Dave, I suppose it actually works the way you suggest, I just didnt know how to show ground connect
it is one single interstage trafo, PP to PP
but it could aslo be ordered SE to PP

http://www.lundahl.se/pdfs/datash/1660s.pdf

I will try and redraw with SE driver

aardvarkash
if starting from scratch, there would be better ways, other tubes, etc
thats what you were thinking, right
well, it is a triode driver
shouldnt have had any additional driver, from beginning
dont know why I chose to
maybe because something I read about odd order cancelling

also thought about dedicating it to a horn compression driver

possible 3kohm OPT http://www.lundahl.se/pdfs/datash/1664.pdf

 

[aardvarkash10]

hi tinitus - no - I haven't even looked into whether the schemo is actually feasible with the chosen tubes - that's your baby!

My way, you end up with one less ecc99 being used (the input ecc99 is shared between the two channels, one triode each).

The IT is already intended for phase splitting, so it seems superfluous to do it twice.

THe bias would usually be applied at the centre tap of the IT's secondary as Dave points out. You gain performance as there is no voltage loss across the cathode resistors since they are not there.

 

[Looneytunes]

The IT is already intended for phase splitting, so it seems superfluous to do it twice.

If the IT is doing the phase splitting, is there any advantage to moving the IT to the input, before the first tube? (I've seen this on other designs.) Any disadvantages?

Looney

 

[aardvarkash10]

better psrr and noise rejection IF you have balanced input...

 

[tinitus]

If the IT is doing the phase splitting, is there any advantage to moving the IT to the input, before the first tube? (I've seen this on other designs.) Any disadvantages?

Looney

maybe skip interstage, and drive it with line trafo
probably cheaper as well

ecc99 is a driver, with quite some amplification on its own, but I dont know how much

friends, its yours, if you want

I have learned, and still have no clew
Im tired and will give it a rest

But it was still fun to try 🙂

 

[revintage]

Hey Tinitus,

The configuration is good and the IT is in the absolutely right place if you later on want to go balanced all the way.

Have added the CCS needed to make it work. If you want to, you can also go fixed bias in the ouput stage.

By the way, why not download LTSpice and at first only use it for drawing schematics😉?

 

[planet10]

Like this Lars. If your pre has enuff drive the part in yellow can be left off... i'm not sure if you'd do anything with the centre tap on the primary

dave

edit: revintage beat me to the punch...

 

[tinitus]

thank you 🙂

 

[tinitus]

ok
I had interstage positioned the right way, thanks

But it looked funny because I didnt know how to draw it properly into schematic
Which might have been confusing

Heres what it should have looked like, with some of the additional hints from Revintage
my own version its still a simplification

getting closer 🙂


OPT
specsheet says Ri=2300 ohm
I suppose its plate resistance
but from what I have found, its not always equal to Ra, or required impedance load

Lundahl mentions plate to plate impedance
Due to paralel pushpull, plate to plate ends up the same
And a 3k PP OPT would match, right ?

Lundahl makes a few small size C-core transformers
http://www.lundahl.se/pdfs/datash/1664.pdf

 

[zigzagflux]

Good design. Have you checked with Kevin Carter at K&K regarding the best choice of IT ? I suspect he will suggest the LL1692A given the ECC99 plate resistance.

How about tossing an oil can capacitor between B+ and the common cathode point of the output stage?

 

[tinitus]

Have you checked with Kevin Carter at K&K regarding the best choice of IT ?

good hint

not easy to keep track of all those numbers and variations

how about LL1935 ?
5-60khz
but gives much less options
LL1692A you suggested still seem to have wider frequency range than LL1660

just a small hint to other newbies
when looking at Lundahl site, it may help to go straight to datasheet list, if you know which trafo

 

[Arnulf]

OPT
specsheet says Ri=2300 ohm
I suppose its plate resistance
but from what I have found, its not always equal to Ra, or required impedance load

Of course it isn't. Equal impedance of load as output impedance of tube would mean that half the power is wasted immediately. The higher the ratio in favor of the load, the more power is transferred to the load.

"Normal" (well, whatever one considers normal 😉 ) ratio is at least 2 : 1 or higher. As you will notice in most amplifiers it is somewhere between 3-5 : 1 simply because of diminishing returns with increased load Z because the increase in required B+ for higher load Z is proportional (and the cost of parts associated with higher B+ goes up quite a bit past certain point) yet the effect of increased Z is not.

 

[tinitus]

with Ri(Ra?) of 2300ohm, and considering(or ignoring paralel plates), it sounds like 4-5k OPT would be better choise than 3k ?

Lundahl mentions transformer to be specced plate to plate(pushpull)
But ofcourse they didnt say actual plate to plate impedance/resistance