The Red Light District - another PP EL84 amp

[SY]

The Red Light District- another pp EL84 amp

I've got a more complete write-up appearing in Bas Horneman's diy magazine, but wanted to put up some schematics for those who want to get a head start. It's easy to build, sounds great, and is a good answer for the common question, "Does anyone know a good 15W amp I can build...?"

First, the basic signal circuitry. Input stage is ECC81 (preferably JJ). Output stage is EL84 (again, JJ is a good choice).

 

[SY]

The power supply. B+1 is for the output stage and runs 300-350V. The regulator is for the screens (idle current adjustment) and runs from 250-300V. Adjust idle current to 85mA per EL84 pair. B+2 is for the driver stage and is 350-400V.

 

[SY]

The LED array.

 

[SY]

I've run this amp on LS3/5A, modified Acoustat 1+1, and NHT Super Zero. The Acoustat needs more power, but the amp didn't do too badly! On the NHT and Rogers, it was close to optimum.

 

[navin]

beautiful SY. I was thinking of mating a small amp like this to a small 4-5" fullrange (tangband, fostex, etc...).

 

[Giaime]

Hello Stuart!

Great design, as usual.

But I NEED to see where you mounted all those leds, how, and would like to see a photo of the amp in the dark 😀

 

[pinkmouse]

Trust me, you really don't want to see any pics of SY's constructions...😉

 

[poobah]

Giaime,

The photos are restricted by the US NAVY... they are trying SY's amp for night time carrier landing lights.

😎

 

[SY]

But I NEED to see where you mounted all those leds, how, and would like to see a photo of the amp in the dark 😀

http://www.diyaudio.com/forums/showthread.php?postid=840474#post840474

And a darker shot:

 

[Andrewbee]

and for the more "creative & artistic" you could change a couple of the red led's for another colour and spell something out... EL 84 POWER
or whatever floats your boat. Why worry about a few milliamps one way or the other for the biasing, whats the worst that could happen?
It may stop working, distort, a runaway tube...

 

[poobah]

I say add a bank of flashing blue LEDs and call it the "SYren"

 

[SY]

Well, the alternate name for this amp is the Yoshiwara. If I can get someone fluent in Japanese to draw out the characters, I might arrange the lights that way.

 

[poobah]

You want Kanji or Katakana?

 

[poobah]

Katakana:

(‹gŒ´)

 

[Variac]

Poobah,
I think you will need to post a scan or something!!
It would be nice to see it in in both scripts to see which lends itself to the LED's best.

SY's construction skills are only eclipsed by his photographic skills!😀

 

[poobah]

I have the symbols... the REAL McCoy... kanji!

Can't post em....

I have little books from my time there... MS PAINT maybe...




😡

 

[poobah]

HERE!

 

[pinkmouse]

Ta. 🙂

 

[EC8010]

Even with 84 LEDs between the channels, you need five more LEDs to do the job. No great problem; use the extra five in the vertical line on the left character and power them from somewhere else...

Edit: Just realised I'd made an error - it actually needs eight extra LEDs. Perhaps the four either side of the left hand character?

 

[poobah]

Maybe the extra 5 could be flashing?

😀