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is a red led an attenuator circuit?


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The old valvejunior mod web site had a 7watt garden lightbulb attached to the output's; that did attenuate the output. there was concern's about 'what if the light bulb burnt out?" which would open the circuit and the OT would become unloaded which you know is not a good thing on a tube amp

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turns out it is a lightbulb and not an led..

so I guess that guy should find out about that!


that just looked deceptive to me. I would never have put that in just for the silliness of the big dome, let alone count on a

cheap *** light bulb.

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I'll see if this post works; I have a word doc that's close to 210pages, and I have some of the stuff from the old VJ site in it. Here goes... This is from Dennis the moderator of the valvejunior web site.


"Light bulb power attenuator

It sounds ridiculous, but these little 5w amps were still a little loud for bedroom practice if I wanted Real Tube Tone. So I also added an ultra-simple little light bulb power attenuator to the output

Now I've honestly never read about anyone doing this before, so maybe I invented it (oops, looks like not, folks have brought prior art to my attention), but I did some experimenting using low voltage outdoor light bulbs as power attenuators and found some really fun sounds. It's a bit dicey and you have the match the bulbs exactly to the power output of the amp, but you can get some really neat attenuation/compression effects.

A light bulb’s resistance varies as a function of the voltage applied. At lower voltages, the light bulb doesn't light and it has a very low resistance. As more voltage is applied, the light bulb begins to glow and its resistance increases. When the light bulb is full on, it is dissipating quite a bit of energy as light and its resistance has gone way up.

So think about this: a light bulb carefully selected to match the power output of an amp acts as a very interesting organic compressor, with the attack time dictated by the turn on time of the incandescent filament.

I ended up putting a seven watt 12v light bulb in each of these amps and providing a second pair of output jacks wired with this light bulb in series with them. This reduces the amp's volume level to a perceived "about half" and also adds this fun gentle compression effect.

Now don't try wiring a single seven watt 12v light bulb in series with the output of your Marshall. It'll probably just instantly burn out. I did experiment with different numbers and wattages of bulbs with my Fender Bassman head, and got some nice results, but you'll need to tailor a network of these bulbs carefully to the output of each amp. I even found a way to wire groups in parallel/series arrangement so certain groups turned on first and 2nd and 3rd groups turned out at only the loudest levels. I used coloured 4w bulbs wired in parallel groups of 2, 3, and 4, so green ones came on first, then yellow, then red. But that's only on more powerful amps, and I digress.. "

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Turns out I couldn't upload the pictures and I didn't feel like putting them on a photo bucket somewhere.


Note: This mod has been done with the "old" VJ modd'ing crew..

I would not attempt this because of the downside of the open OT circuit and have just stuck with the resistive attenuation and the VVR circuit attenuation.

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