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PostPosted: July 3rd, 2019, 11:02 am 
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Joined: June 4th, 2013, 2:39 pm
Posts: 146
I've been working on my Musician' Amplifiers with Heyboer's Peerless S-265-Q copies, and the end results are extremely good. I finally bought a portable CRT scope on eBay, it was $70 from some lab in Minnesota, in perfect condition. Also got a little Koolertron function generator, as well as a Picoscope 2004A for more sophisticated measurements. I've got square waves down, that was easy. ;-). Hoping to do some XY readings to look at phase shifts and so forth, but for now the amps are in good shape. Pretty much what you'd hope for from an "original" triode Williamson: Coherent, good bandwidth, nice full presentation of instruments and voices, wonderful to listen to--no listener fatigue whatsoever. Frequency plot shows it dead flat out to about 70kHz then a gradual rolloff with nothing sticking out after that. Stability is *pretty* good--HF's are stable with .1uF across an 8 ohm load, and LF looks solid, but I'm hoping to do better by tuning the shelf network on the first stage. I also need to get them off the breadboard, because that isn't helping any, with long leads and hookup wire everywhere.

To give you an idea, first pic is 10kHz with no tuning at all. Yikes! Second pic is 10kHz after adding standard Williamson shelf network across the first plate resistor, and adding phase lead cap across the feedback resistor. Third pic is 100Hz response. I want to improve stability without ruining the sound of the amp, so I'm going to tinker some more with the shelf network. I've tried some extreme methods but while stability is very good, the amp sounds unnatural--the frequency balance is off and the amp calls attention to itself, not what you want.

I'll post a modified Musican's Amplifier schematic shortly, and look forward to any suggestions. But I'm very pleased with the results.


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