HOT ROD VS BLUES DELUXE/DEVILLE
The first stages are classic Fender except the BD uses a 22uf cathode bias cap while the HR uses a larger 47uf, which will create a bit more low end.
Coupling cap next is .01BD Vs .022 in HRD. Still a little more low end in the HR. The bright switch in the BD is next. This is a non-standard Fender design, which bypasses a 100k resistor with a 750pf cap. As the 100k resistor is attached to the 250k-volume control, it is only effective in clean mode. The drive control in the HR is between the first and second stage.
The second stage is unbypassed in both amps. In the HR the bright switch is a .068 cathode bypass cap that is non-functioning in drive mode.
The tone stack follows the second stage. They are identical except the HR uses a 130k mid slope resistor, while the BD is 100k. This will create a little less low end in the HR.
The drive control precedes the 3rd stage in the BD, a standard Fender bypassed gain stage. The 3rd stage is used in both clean and drive in the BD.
In the HR the 3rd and 4th stages are used in drive only. This tube is unbypassed. In More drive a 1uf-bypass cap is switched in on the 3rd stage and a 22uf bypass cap is switched in on the 4th stage. (The 4th stage is not used in the BD, but is just waiting to be modded in.)
Note on bypassing. The gain in a tube stage is set by 3 components, the plate resistor, (typically 100k in Fenders, larger for more gain) the cathode resistor, (typically 1.5k in Fenders, smaller for more gain) and a bypass cap that bypasses the cathode resistor. The cathode cap is not always used but when it is, it will increase gain in different frequency ranges. 22uf will increase gain across the entire guitar spectrum. Smaller will only raise gain in higher frequencies.
The master for the drive channel follows in both amps. From there the amps are nearly identical, except the HR has somewhat fuller reverb due to the design of the reverb return. (The reverb circuit and the effects loop are solid state.) The HR has an extension speaker jack that uses the 4-ohm speaker tap on the output transformer. The BD has this tap but it is not used (but could be added by a tech.)
In general these amps are similar. The BD will not stay as clean at higher volumes due to the 3rd stage always being active. The HR has “improved” distortion (drive) with “more drive” added. The HR has fuller reverb and an extension speaker jack. Both are good designs with plenty of classic Fender tone.
May I add that improvements can be made to the Blues. The earliest Blues Deville's used the 2nd stage of V2 as a cathode follower just before the PI. In all but the earliest, the 2nd half of V2 isn't used. This can be modded into the drive channel for huge improvement. (See the Blues Deluxe mod in the Technical section at Duncan Amp Pages...)
The reverb can be improved by clipping C50. Bias adjust can be easily added.
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