"Patrick Turner"
I said...
Amp has wear and tear and looks 20 years old, but it sure ain't from 1965.
You said...** Those 3 PCBs are a dead give away.
Well yes, but it is know as a Fender "Deluxe Reverb" reissue.
The full name on schema is "Deluxe Reverb Amplifier". No need to nit pick
Phil.
** Fender models go by their face plate names.
There IS a "Deluxe Reverb" and also there IS a " Deluxe Reverb-Amp".
Hundreds of models exist with only small name variations between them - eg
there are distinct models called " Twin Reverb", "Twin Reverb-Amp" and "The
Twin" which even owners mix up all the time.
No nit picking happening on my part.
This tiny amount of NFB does hardly anything to flatten the
signal at the speaker. The signal response at has a 6dB peak
at 100Hz and +6dB at 2kHz, relative to 1kHz level. So the
Vo merely outlines the speaker Z which is to be expected..
** Err - no
Regular guitar ( and most other) speakers don't double impedance with a one
octave change in F above 1kHz. It takes 2 octaves, at least.
The rise in Z above the minimum Z at about 300Hz is due to
increasing XL in series with RL of speaker, and the eventual
increases in ZL IS 6dB per octave.
** Not so.
You need to do an impedance test and stop assuming.
The *soft* iron pole pieces of a speaker magnet have LARGE eddy current
losses and so the impedance rises much less rapidly with F than if
transformer lams were used.
Look at almost ANY published speaker impedance curve :
http://www.electrosmash.com/marshall-mg10
Bottom of page:
7.5ohms at 250 Hz ( = minimum) then
9ohms at 1 kHz
18ohms at 5.5 kHz
36ohms at 16 kHz
.... Phil