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|8th January 2015, 12:08 AM||#1|
Join Date: Apr 2006
Location: Northeast Ohio
Happy so far on amp build project
I couldn't resist dropping in to share good news on my stereo guitar amp project.
A previous thread I started, was curiosity on some of the members input and their personal experiences regarding heater wiring orientation.
To this point this evening, I have completed the heater wiring, power supply, 5volt and 12 volt regulated circuits for LEDs and dual exhaust fans.
Plus the entire preamp and output circuit on one channel to start out with...
Late last night I fired it up, biasing looks good and B+ tests seemed ok. 494 volts at the plates (EL34 pair). The basic circuit, along with some of my own modifications - is from a Marshall 4140. Yes, the 2x12 combo from around 1980.
I wanted the post P.I. master volume. I currently use a 4140 (slightly modified from original and removed from the combo - made a cabinet for the chassis) but with an old 4x12 cab with 25 watt greenbacks...
This amp build is nominal 50 watt per channel, not 100 watt like a 4140.
Last night when I went for cranking pre and master volumes - the dreaded squeal started at a higher gain setting.
I held off until this evening to check it.
Disconnecting the 100k resistor (feedback circuit) from the 4 ohm output jack stopped the squeal. So I was prepared and proceeded to reverse the plate leads at the octal sockets.
No squeal - awesome. It was 50/50 chance on plate wiring initially...
Plus, I have virtually no hum or noise. Even with the pre and master cranked and all three tone controls maxxed. No oscillations noted. It is a terminal strip - point to point build with star ground scheme. I am very pleased.
I ran a variable output from a stereo I use on my repair bench and this thing cranks. I thought it was interesting that my first "cranked" audio from the radio feed to the amp was "Eruption" by Van Halen.
So, just sharing a happy moment.
Now to build the channel on the other side of the chassis, pretty much a mirror image of the components.
I will borrow a camera when I get this completed for a few photos.
Best of luck on everyone's projects out there.
More to come down the road.
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