Big Brown Amp

[alkuz1961]

I decided to take a chance and show another of my amp projects. Amplifier for my friend. Nothing special, regular #183, but with 6L6G in power section. Output transformer InMODout.
After a while, a friend complained that he played mostly at home, and it was very loud. The Master had to be set to the very minimal position, but this is bad for the sound. It was decided to try to install power scaling. To do this, was purchased a kit from London Power. The kit included a BIAS unit and the power supply voltage regulator.
Given that the circuit works with high voltages, I tried to isolate it from the chassis as much as possible. Although the instructions have recommendations to use the chassis as a heat sink. I preferred to use an external radiator, on an insulating base, with fans.
Also, for the correct operation of the amplifier at low voltage, it was necessary to install an additional PPiMV. As a result, two controls had to be installed on the back of the amplifier - the power scale and PPiMV.
In practice, this turned out to be inconvenient to use. And subsequently, these two controls were replaced with a one rotary triple switch with fixed volume and power levels. We selected up the values of the dividing resistors "by ear".

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[alkuz1961]

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[alkuz1961]

On this video the Power Scaling is off

[norburybrook]

lovely build again



it's gone form a green light to a red light.....




M

[alkuz1961]

...it's gone form a green light to a red light.....

If I understand correctly - is this a comment about the indicator? Unfortunately, it is now difficult to find non-super-bright LEDs. And they're reali annoyingly bright! I could only find a red indicator with a weak glow, and replaced it.

[norburybrook]

...it's gone form a green light to a red light.....

If I understand correctly - is this a comment about the indicator? Unfortunately, it is now difficult to find non-super-bright LEDs. And they're reali annoyingly bright! I could only find a red indicator with a weak glow, and replaced it.

yes I have some on foot switches and they can been seen from space


M

[martin manning]

You can always increase the current limiting resistor to dial the brightness down. You could also rough-up the lens to make the light more diffuse. I've not tried it yet, but an easy way to do that might be to put the LED in a drill and spin it against a Scotch-Brite pad with light pressure.

[ChopSauce]

Yet another beauty you built ...

Have you tried limiting the current in the (bright) LED to a few 5 mA as Martin recommended on another post?

[Guy77]

Another great build congratulations! Lovely cab too!
Great location to place your Power Scaling kit. how did you get the power for the fans?

Cheers
Guy

[dorrisant]

You can always increase the current limiting resistor to dial the brightness down. You could also rough-up the lens to make the light more diffuse. I've not tried it yet, but an easy way to do that might be to put the LED in a drill and spin it against a Scotch-Brite pad with light pressure.

Just a few scuffs with approx 220 grit sandpaper works wonders.

Yet another lovely build. Very nice work!!

[alkuz1961]

You can always increase the current limiting resistor to dial the brightness down. You could also rough-up the lens to make the light more diffuse. I've not tried it yet, but an easy way to do that might be to put the LED in a drill and spin it against a Scotch-Brite pad with light pressure.

I installed an led in the housing, with a built-in limiting resistor, for 12V,
Like this:

DOC002941536.jpg

In this case, the replacing the indicator completely was less troublesome than replacing inside resistor.

....how did you get the power for the fans?

Unfortunately I can't remember exactly how I connected the fans in this amp. Most likely it was a relays power line. But I can say for sure that it was a serial connection of two 12V fans to a 12V source. Half the voltage for each of them reduces the speed of rotation and the noise they create.

[dorrisant]

You can still post a dropping resistor on either of the leads going to the led. It will just add to the series resistance that's pre-installed. I find that around 7k is plenty bright. Most of those have 1-2k preinstalled.