The Guitologist | 12 months ago

In this video we'll answer the age-old question...can a Blackface Fender Twin Reverb AB763 play METAL? We'll show several mods you can make to your vintage Fender Twin Reverb to get MASSIVE amounts of overdrive, distortion, and high gain tones.

[RE: Reverb Bypass "Super Ice Cube" Overdrive Mod]
Since publishing this video, some have asked whether the Reverb Bypass Overdrive Mod will smoke the reverb transformer by changing the load. Let's address that. First, the Input tank transducer is about 77 ohms DC resistance. That DC resistance isn't going away when you short the jacks to bypass the tank. You're bypassing the tank with the AC signal, but you are not removing the DC load the transformer secondary is seeing at any point. It's still there, and it's being put into parallel with the grid leak resistor from the recovery tube, but if you do the math, it doesn't change the DC resistance the transformer secondary sees between its leads. Using ohm's law, the parallel resistance of 77 ohms and 220K ohms is still 76.9731 Ohms. The only way the tank would see a drastically different DC load is if someone turned the mod pot into the "Bypass" position and then unplugged the reverb tank from the "Reverb Output" jack on the amp. This would suddenly remove the 77 ohms of DC resistance on the transformer secondary and it would see 220K ohms instead. So one should be cautious not to do this as I don't know what the outcome would be in that case. Probably nothing if you didn't leave it long, but might smoke the transformer if you did.

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1:10 Introduction & Inspection
2:55 Talk with amp owner
5:56 Capacitor Inspection and Change
15:36 Discussion of Mesa-Boogie Simul-Class Circuit Mod
17:11 First Power On with Variac, Tube Failure
23:02 Tube Testing with Hickok 6000A
33:50 7027A Tube sub for 6L6GC Socket Mod
35:31 More on the Mesa-Boogie Simul-Class
37:50 Master Volume Mod
44:08 6G6 Bassman Presence Control Mod
48:28 Normal Channel Reverb and Mixing Mod
53:51 DISASTER! 7027A won't work!
1:01:38 Super Ice Cube Reverb Bypass Mod
1:05:05 First Tone Test with Cigar Box Guitar
1:08:22 Bias Soviet Russian 6P3S (6N3C) Tubes
1:10:34 How to operate the amp with new mods
1:17:22 DEMO w/ FULL BAND Zio Meteorite

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