Have to mod K-502 to 4Ohms from 8

[udailey]

So I am going to put together the K-502 amp from AES. It looks like a good and fun amp, especially since I have never done this (it looks easy). I spoke with Perry over at Hemp Acoustics and he says this would be great for his FR4.5c speakers and I asked for plans for a speaker cabinet since all plans on his site are for 8"+ speakers. He says he is emailing me some plans for a cabinet that will use 2 of the 4.5" speakers for each cabinet but that the amp will need to support 5.6Ohms. Well, I will probably have a fire if I hook up this 8Ohm stereo amp to these speakers but I would like to build the speakers and use this amp if it I can modify the amp to handle the speakers. I dont know how to do this and while I worked in an electronics manufacturer for 5 years basic electrical theory was not part of my job. Can someone please tell me what I need to do to correct the amp before trying it out on these speakers and melting something?
Thanks so much,
Uriah

Link to the add on AES : http://www.tubesandmore.com/scripts.../elevclients/cemirror/ELEVATOR.FXP?item=K-502

Maybe I will get lucky and the transformer will have 4Ohm outputs as well as 8Ohm but I have no reason to believe that this is the case yet. If it did have 4Ohm outputs what would I have to do? Would I have to change anything except the windings that were attached to the output?

 

[chrish]

If you know the impedance of the output transformers you can always replace them with something else.

I have just built a small push pull amp using 6BM8 valves (similar to the 11BM8s that your project uses). I am using Edcor transformers. If you want to keep the project cheap, these may do the trick: http://www.edcorusa.com/products/transformers/xpp/xpp15-4-8k.html

I am sure that some other more experienced members may have some input, but I have used this amp with the smaller (10 watt) 8 Ohm output version of the above transformers on my 4 Ohm speakers with no problems. If you build the amp with the supplied transformers on your 4 Ohm speakers I suspect that you will just have less reflected load to the amp, with slightly higher output power and higher distortion.

Cheers,

Chris