The Red Light District - another PP EL84 amp

[mod_evil]

This amp will be a circus! tsc tsc tsc...

 

[Variac]

Building on EC's efforts, 86 LED's. One LED on each symbol could be used as a standby indicator

You have to scroll to see it with my pdf reader

 

[Variac]

Maybe easier to see:

 

[poobah]

Good detail work Variac,

The cat missed one swish on the feet of the second symbol.

My infinitely limited knowledge of Kanji tells me that could be huge.

The first symbol means "city" or "city of". I'll leave it to everyone's imagination as to what the second symbol means.

 

[SY]

Well, it IS the name of Tokyo's Red Light District.

 

[poobah]

SY,

We're workin' on it... asbestos we can.

 

[kenev]

SY,

Nery nice and interesting project.

What about some impressions on the sound of this amp?

Regards, Evangelos

 

[pinkmouse]

Well, the original version I saw had another parallel row, 7 x 7 x 2, giving us 98 leds to play with...

 

[Merlinb]

LED's are notioriously unreliable when run in series or parallel from the same supply without individual surrent limiters- just a warning.
Won't a 133k anode resistor on the first ECC81 triode be pushing way into non-linear operation?
You might want to add a build-out resistor to the cathode of the cathodyne for balanced output.

 

[SY]

Won't a 133k anode resistor on the first ECC81 triode be pushing way into non-linear operation?

Quite the contrary, that's a particularly linear spot to operate it. At the full 11V peak output needed to drive the output stage, THD of the voltage amp is less than 0.03%.

Regarding LED reliability, you might check out what Bob Pease had to say in his book "Troubleshooting Analog Circuits."

 

[SY]

Evangelos, my comments on the sound will be in the article that Bas is publishing. I'll say briefly that you will not believe that this is a 15W amp. There are several tricks (the LED array is one of them) which optimize the overload recovery characteristics so that clipping is almost un-noticeable.

 

[Variac]

I've never made a tube amp. This one might just be what pushes me to do so.

Poobah, The second symbol has four "feet" Which one are you referring to? We could refer to them as 1 is extreme left and 4 is extreme right.

 

[anatech]

Hi Mark,
Do it!
Even simple ones are rewarding.

-Chris

 

[EsE]

I'm also looking for a good amp to build. Wich transformers do you recommend for this amp? And I've never seen a screen like that before..

 

[SY]

You want something which is 8k plate-to-plate with a 15W or better rating. I used Dynaco iron and also tested UTC LS series. Both worked great. The next few will use James.

By adjusting the RC network on the plate of the first stage, you should be able to get any decent OPT of the right impedance to work.

 

[pinkmouse]

SY, you may have missed my question, but is there a reason you dropped the leds down from 7x7 to 7x6?

 

[SY]

I did miss it, sorry. The answer is a screw-up in the drawing.

As it happens, there's not much difference between 6 and 7 strings, about 5.5 ohm versus 4.5 ohm.

 

[poobah]

Variac,

You got it right bud... EC's layout was missing the small leftward extension on the bottom of the 3rd foot.

I have no dictionary with that symbol. The missing extension might change the meaning from "girl of service" to "cow for hire".

 

[EC8010]

And I thought that little squiggle was a drawing error...

 

[Andrewbee]

"cow for hire" "red-light district" Oh My!