[Amps] RM Italy BLA350

[Steve Thompson]

There's been almost 300V p-p around the input circuits so I'd 
check D1-D3 as well, maybe other diodes too.

Attenuator - it's difficult to predict what to expect depending on 
its internal configuration. Can I suggest you measure resistances 
in-gnd, out-gnd and in-out and post the results, hopefully we can 
help figure it out from those. Also, patch in 50ohms (or something 
close, say 47ohm resistor) from output to ground and measure the 
input resistance.

With the feedback resistors burned out I fear for the FETs, you 
say resistance measurements look 'sensible' - what are you seeing?

Steve G8GSQ

> Hi,
> 
> I have been asked to look at the subject amplifier which the owner accidentally applied 200 watts to the input of. Specification states 12-14 watts maximum drive.
> 
> 
> All 4 of the 18 ohm resistors in the drain to gate feedback are burned up as are 2 resistors on the secondary of the input power sense coupler.
> 
> 
> Have unsoldered the drain and gate tabs and lifted them. Resistance measurements look sensible
> 
> So it looks like a handful of resistors so far
> 
> There is a 3dB input attenuator, monolithic device just marked 3dB, not sure what sort of resistance measurement I should see across it or to ground.
> 
> 
> What else might need to be looked at?
> 
> I have the schematics but there is no circuit description. Does anyone here have experience with these RM amplifiers? It looks fairly well built if a little lightweight but not bad for a 300 watt amplifier.
> 
> 
> Martin, HS0ZED