[NLRS] Amp Driving Me NUTS...

[KBØNLY]

Anyone got some amp repair experience that can offer some suggestions here???

I have a RF Concepts 4-110 that I just bought, needs repair, had about 40w of output when I got it.  This uses a MRF646, 45w driver, and a pair of MRF648’s, 60w finals, for 100-120w of output.  They seem to vary a bit but that’s not the issue here.

My first thought was the driver was bad, upon opening it up I found this unit didn’t have the optional attenuator propagated on the board, the last two of this exact model amp that I had rebuilt I found the MRF646 driver was blown from being overdriven.  So the first thing I did was grab a new 646 from my spares and replace it, along with new caps for input and output matching as long as I was doing it.  This didn’t increase the output of the amp any, still about 40w.

The next step I took was to replace the MRF648 finals with a fresh new set I also had in my spares, the power output actually dropped to about 25w of output.  What the heck??  I checked and rechecked and rechecked everything.  Replacing all the caps on the input and output matching, checked the bias and set it to .70 volts per device while keyed up without drive applied, everything looks like it should, I’m stumped!!!  

Anyone offer some constructive ideas here??  The forums online have been nothing but stupid responses like send it here or there for repair.  I would have done that in the first place if I wanted to... HI HI


73,

Scott KBØNLY