randall rh200 head cuts out at 4ohms

[ray-p]

cool, ill let you know if it works out.
why will this work differently than the volume controls on the guitar or preamp?

[phatt]

Hi raypist,
              It's effectively a master volume that is left alone once set.
Ideally this would be a *Fixed* Voltage divider *inside the Amp* but that's
going to make a lot of work for you.

When an Amp is designed there is a limiting value before the main power Amp which has nothing to do with the master volume on the front.

IF a master volume was the only limiting R across the signal path before the main power stage then the guitar player would not know how much volume was safe.
Much like a popoff valve on a turbo engine,,, without it the driver has no way of knowing when to back off the throttle (master volume) and the engine would certainly self distruct.

In your case my guess is the Amp is not designed well enough to cope with 4 ohm loads.   A fan won't fix it,,, nor a bigger heat sink.
Output transistors with a bigger *Current Capacity* would likely fix it but then you would have to rebuild the whole output section.  :duh
Makers want to make their gear as loud as they possibly can as the competition is fierce,, so in the end they push things to far and this is the result.

I'm just showing you the simplest way round the issue if you are prepaired to loose some of that extra power.
You may find that 8Ohms is all round a better solution.
IMExperience 8 Ohms is giving the power amp a better chance of coping with hot enviroments and gives a better margin of error,,,, keeps it away from the danger zone of * to much current dissapation *
Phil.

[Anthrax Zygote]

I also have an rh200 and it used to cut out when it overheated (consistently at 4ohms) so I removed the front panel and cut the cloth out then I removed the rear panel and cut a large \________/ pattern out of it to allow safe heat dissipation and that has seemed to cure it so far however I'm going to add Marshall style vents to the top as well as an extra measure. Typically overheating is the problem with most randalls in general and if you can modify your head box to allow for better heat dissipation it helps dramatically.

[J M Fahey]

Amen to it.
Try to mount some kind of fan, iy will always help.