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I'm working on a friends 2165 RP [GP-1] and found the bias was way low at 6mv at the emitter of the 6CA7 cathode transistors. Set to the recommended 25mv and now I'm getting 60W output, with 2.8Vrms drive signal inserted at the high level return jack.
Balance through the transistors is very close [within 3-4mv] so it looks like the power amp is fine.
However, with a 1Khz sqr wave I see some pronounced overshoot and quite a bit of ringing and I'm wondering if this is typical of this design.
I could not drive the amp to full undistorted output through the preamp and found IC 3a feedback resistor R24 was100K instead of 330K and looked to be from factory that way.
R62 & R63 were 1K instead of 680R [also look to be from factory] and were causing fluctuation on the 16V rails from phaser LFO
Anyone familiar with this?
Mark
First off, why are you
First off, why are you running a square wave through a guitar amp. I am NOT familiar with the rp's at all so I'll shut up now! Variances in components happen in early versions, which you have. Run a normal sine wave and see what it does. Fluctuations could be caused by anything from bad ic's to lead dress to ??? Voltage fluctuation on the IC power? HMMMMMM? Mike
Odd question
Square wave analysis is a fundamental test for all types of amplifiers.
Sine wave tells very little about performance and response...
SORRY. Didn't mean to insult
SORRY. Didn't mean to insult but after 30 yrs of this crap, you never KNOW who you're talking to. That being said, I NEVER use a square wave. Been looking at sine wave all these years and never change. Mike.
Square Wave Analysis
Direct coupled amplifiers respond well to Square wave analysis as there are no reactive components in the signal stream. Music Man Amps are capacitor coupled between stages and transformer coupled from the output to the speaker(s). Capacitors and transformers are murder on square waves so it's not surprising that square wave analysis on MM amps looks "un-square". -Mike Griffin