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Topics - Jack1962

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Amplifier Discussion / Marshall AVT-150H Output Module
« on: June 23, 2014, 12:58:07 PM »
does anyone here know Marshall's part # for the output modules in the AVT-150H , not the AVT50-62-00 # but the number they insist you have to order replacment modules.

Amplifier Discussion / Scheematic for a Mesa Basis M-2000
« on: January 20, 2014, 06:05:20 PM »
anyone have the schematic for this puppy?

Amplifier Discussion / Peavey MX 112 (VTX series)
« on: October 08, 2010, 10:31:06 AM »
does anyone here have a schematic for this amp?

Schematics and Layouts / Baldwin Professional "Custom" Schematic
« on: June 23, 2010, 12:46:54 PM »
Does anyone here have or know where I can find a diagram for this old Keyboard/Guitar amp?

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Amplifier Discussion / A bit of Amp HIstory
« on: October 27, 2008, 04:58:22 AM »
I found this while cruising the web this morning.

History of the Guitar Amp:

As with the Electric Guitar the origins of the guitar amp aren’t really known. The first guitar amp was probably a hi-fi or pa amplifier. The transistor hadn’t yet been invented. Rickenbacker and Gibson started making guitar amps in the late 30’s. Gibson had a model that was meant to be sold with the ES-150 which was their first hollowbody electric. This was in 1937 where it appeared in the Gibson catalogue. Rickenbacker is known to have manufactured their first electric guitar in 1932 but there is no mention of an amplifier to go with it. When they and Gibson started manufacturing amps they were based on the current amps used in radio and hi-fi amps.

Fender got in to the act in the mid 40’s (1945) with the company was still called K&F Manufacturing. They were also very simple amps and didn’t have any controls (volume or tone). You used the guitar’s volume and tone controls. It wasn’t until after the aliens landed at Roswell J (1947) that Fender introduced their first amp. It still didn’t have any volume, and tone controls. It was the Model 26 which used a 6V6 and Jensen speakers. The transformer was actually mounted onto the speaker rather than inside the amp housing. The first guitar amp with a volume control was the Fender Champion 600. These amps where beginner’s amps (similar to the Champ Amp of today) and used a single 6V6 output tube. Also in 1947 Fender introduced the Dual Pro which had two channels and two volume controls (one for each channel) and a single tone control. These amps where used for the pedal and lap steel guitars as well as hollow and solid body electrics.

In the early 50’s Gibson introduced the Les Paul Amp which used the 6L6 output tubes. It was also of a similar designed to that of the Fender which was based upon the RCA tube application manual. The demand for louder amps came around this time as well. Fender responded with the Tweed Series of amps and most notably the Fender Bassman. These amps had more tone controls (treble, middle, and bass) as well as a Presence control and found the use of the now very popular 12AX7 and 12AY7 preamp tubes. These tubes allowed the amps to have more tone variation than any amp. With the Tweed amps you found one of the first uses of ‘Vibrato’ (modulating pitch changes) and ‘Tremolo’ (modulating volume changes). Each of these functions further advanced the sound of guitar amps.

Vox introduced the AC15 in 1956 which was the first amp to use a class ‘A’ design. The Fender and Gibson amps all where class ‘B’. The Vox amps even though only had 15 watts or so where loud and sounded great when turned up (distortion). They became the amp of choice for England guitarist mainly because Fender amps cost too much. The Beatles for instance used Vox Amps quite extensively. Some of the more important Vox amps are the AC30, AC50, as well as the AC100. The number was the amount of watts the amps put out. There was one great Vox amp called the Vox AC30TB. The TB meant Top Boost which it had because of the addition of an extra tube.

The 1960’s found the guitar amp in even more demand with the start of Rock-n-Roll. Fender introduced there famous BlackFaced amps. These amps were known for their great tone and reliability. These amps are the first Fenders where the controls of the amp are on the front panel instead of the top panel. The Fender Tweeds, Gibsons, and Vox amps all had their controls mounted on the top of the amps so the guitarist could clearly see the amp settings. This change to move the control knobs to the front of panel probably came from the amps being louder. With the amp being louder caused the guitarist to be located further away from the amp. This meant that they couldn’t see the controls if they were on top of the amp. So they got moved to the front. From what I can find out is the Fender VibroVerb was the first amp to have a spring reverb. Gibson had around the same time as this something called a Maestro EchoPlex. The EchoPlex was the first tape delay system that used a ¼ inch tape to record the guitar and then delay it and then play it back. This could be used to create a not so convincing reverb effect.

Amplifier Discussion / Step 1 in the Amp Repair for Dummies Book
« on: July 17, 2008, 09:15:48 PM »
I recently had a Peavey Stereo Chorus 400(The Beast) come in for repair, this amp did nothing. Step #1 visual inspection. The thing had this large steel wheels mounted on it it , If a amp has wheels it's being moved CHECK FOR LOOSE SOLDER JOINTS. I check this thing from input to speaker output before it dawned on to me to check the @#$%  solder joints. I have been doing this for more years than I care to talk about , so in short always check the basics. The loose solder joints where on those 4700uF caps that give you the -43(not 53) and +43 volts the power the power transistors.

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Amplifier Discussion / 6357B NPN Power Transistors
« on: July 13, 2008, 04:15:37 PM »
What's Up

        I'm repairing a Peavey Stereo Chorus 400, 1 of the of power amps transistors (marked 6357B) is bad (smoked, fried, and toasted) took out the emitter resistor with it. anyway I have seached online for this transistor , looked in my Allied cat. , it isn't listed. anybody hear have any idea what this thing cross ref's. to.

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