Vibrolux Reverb and Pro Reverb Dropping Resistors and NICE CLIPPING (ETA)

[fiftynine]

Why such a large difference? 4.7k and 1k vs 10k and 10k for the droppers, Pro and VL respectively.

[sluckey]

Because they are different amplifiers. Each of those amps have several different chassis numbers. Neither has an AB763 chassis. Actually, the Vibrolux Reverb uses 10K/10K, and 4.7K/10K, and 2.2K/10K in the slightly different chassis numbers.

[fiftynine]

Both BFProR schematics I can find are 4.7k/1k and the VLR are AA964 10k/10k and AB568 10k/4.7k. Seems Leo was aiming for a bigger voltage drop on the VLR. There's a whopping 390v at the first stage of the BFProR versus 290v (correction, 260v) for the VLR.


I know that the higher the volts, the later the tube breaks up so I'm guessing an overdriven VLR has more pre-amp clipping than a BFProR.

[sluckey]

Tube break up and preamp clipping were not design goals when those amps were new.

[fiftynine]

True, Sluckey.


So if you have two identical amps, ones dropping resistors are 10k/10k (giving ~260/310v) and the other 4.7k/1k (giving ~390/430v), the first amps pre stages will distort earlier so the power section will be amplifying pre-amp clipping and with a smaller signal, clipping the power amp less. So the second amp will be cleaner up to the power section and the power section will see a larger signal giving more power amp clipping when you turn it up?