DIY Attenuator HELP PLEASE

[jplaudio]

Lightbulbs can make very effective over-current protection in some cases, but as a speaker emulator?  :!: NO... forget that one quickly.

The impedance will start off too small (100W lamps have a very low resistance when cold) and then quickly get too large, never fully recovering to the too small area... but everything is 100% RMS output dependant. They work great for regulation in Wein bridge oscillators because they sit in the feedback loop (taking advantage of their negative resistance), or for a sort of over-current breaker in testing amps and appliances, but as a speaker load.... no chance. BTW: Neons will not work in the slightest for this application. Those are a totally different animal.

I would hate to see somebody blow their amp trying this.  

Incandesent lamps have been used for many years as both current limiting devices in series with the load (compression) or for noise reduction in parallel with the load. THD uses this in their amps and attenuators for noise reduction(expansion). Examples for use wth tube amps can be found in the RDH.
Neon lamps require a "trigger" voltage to start conducting. they are typically used for overvoltage protection for speakers in a crowbar type circuit.
An incandesent lamp used as  a current limiting device will not give the same results as the MASS motor and/or a resistive attenuator. Proper selection of the lamp used will determine the amount and onset of the compression effects.

[V!N]

I believe a 100WATT MASS motor and possibly adjustment of the resistors. The resistors as shown are pretty darn soft as far as output volume goes.

You will need a higher power rating on the resistors.

Would anybody know what values would be the best for these ? I am most interested in building an attenuator, using the MASS motor and the Mini-MASS design.

I have e-mailed Ted (Weber) with this question as well, but so far .. no respons.

Also, I heard a 50 Watt Attenuator for a 50 Watt amp might not fit, better is to leave a margin so nothing will break or melt down when the amp is cranked. What about it ?

Thank you,

Vincent

[V!N]

.. no one ? :cry:

[zonta]

Well I have used light bulbs as dummy loads before with two tube pa amps and none of them blew out even after several hundreds of hours usage.

However they were some cheap stuff which you could buy for 25$ from ebay so I would be risking just 50 bucks and I was couraged to try it (it worked though).

Now I have a Peavey Delta Blues and I am afraid to use a light bulb as a dummy load because it costs 400 bucks.    :roll:

Check this out from Aikenamps:

http://www.aikenamps.com/DummyLoad.pdf

Extremly simple dummy load schematic which works at 2-4-8 and 16 ohms selectively.

I have not build it yet and would love to hear about it if someone does. It would not take  more than 20 minutes to build that one.

And there is also this one (again from aikenamps and again very, very simple):

http://www.aikenamps.com/spkrload.html

However Veber's MASS Motor seems like the best deal since it is a real speaker (without the cone which means being totally silent) that reacts like the real thing does.

I had emailed Ted Veber about it and asked if it was modified some how and here is his reply:

It is the voice coil, spider, small magnet,  and voice coil wires. It is
exactly like a speaker, unmodified

[zonta]

Ok I could not resist and tried a lightbulb on my peavey as a dummyload.  :lol:

I run the amp that way for about an hour (volume level at 4) and nothing blew out so far.  

I think I am going to continue using it that way.  

Err should I?  :roll: