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In Reply to: need advise on building a EL 86 power amp posted by wlee on January 23, 2005 at 10:13:39:
Hm, as in the style of transformer used to match long-run 70V Public Address lines to a nominal loudspeaker?
I'd check the bandwidth of those parts before you get much further along with this line of thought. Most oldschool P.A. stuff has roughly the bandwidth of an analog telephone, somewhere in the 300Hz-3KHz range.
Follow Ups:
hi Bill,I have a pair of Bozak CM lab amp with an autoformer with 8ohms and 70.7 volts, The amp sounded real good esp this is an old Ss design with 2N3773 NPN/NPN PP Output. I might try to use the coils if it does not effect the sound... ( well I like this amp a lot and after slight mods and coupling change it sound nicer then most modern SS amp, got a Classe 700 sitting around doing nothing yet)
Some Lundahl or SE amp output with 2K can also be use as autoformer if I connect the secondary in serial with primary... Use 16 ohm as 4 ohms
I'm using a toroid pwr xfmr
to up the Q of an already
hi-Q driver (~1.5) to about 3.5
(trying to get oomph on a 2' open baffle)
This may sound 'off the wall'
Pun Happily Accepted <|:^))
BUT ..... If wound in a certain way
(and lots of them are)
Regular power transformers can do wonders.
I'm going to investigate the '70 volt' trip !
If you can go by the specs
Admittedly, this is a bigger chunk of iron with better specs than I recall from some PA work I've done in the past.
But still.. 40Hz is a _full octave_ above what is even considered a lame minimum.. and cutoff at 18Khz isn't going to be all that stellar, either. I'm also curious how flat the transformer's response is across this stated range, and at what power levels.
Consider that if the idea is to build an OTL amplifier, or at least an amplifier with OTL-like character, the typical bandwidth of an Atma-Sphere power amp is 2Hz (two, not twenty) to around 100Khz
Maybe it's still an OTL if no windings are between the devices ? :)
hi Hitsware,the HAMMOND does seem like a good choice indeed!
Well, It may be a good idea to try the connection in all kind of permutation, perhaps connecting the secondary to the primary in serial etc to make it like and autoformer... whichever that will sound good.
I think I will convert a pair of my EL84 PP mono intergrated amp to EL86 output.... Not sure what will be the upper limit on the EL86 B+, 250V or 280V.... assuming if I use some thing like 30-35ma bias.Best rgds
Hey wlee :)Yea. I ordered a couple for experiments.
Do you know if you can get more extended
low end if running well below rated power ?
For lots of options ........
Wow, this one has many taps.... but wonder if that will compromise the quality?
Perhaps the lower power is well below the core saturaion point?Bets rgds
> Wow, this one has many taps....Yea, and it's an autoformer (for what that's worth
(supposed to be some advantage))?
MCM # 555-7127> but wonder if that will compromise the quality?
I wouldn't think so. You can always cut off the
unused leads after you optimize :)> Perhaps the lower power is well below the core saturaion point?
> 40Hz is a _full octave_ above what is even considered a lame minimum.. and cutoff at 18Khz isn't going to be all that stellar, either.Yea......OK
> I'm also curious how flat the transformer's response is across this stated range, and at what power levels.Those are rated at full power. I think maybe you can go lower @ lower power but I don't remember my xfmr stuff good enough to be sure. Anyways what's the specs of the '0 ohm' (sp?) device recommended by so many here? ....... (the xfmr reccomended to up 4 ohm loads to OTL friendly impedance)
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