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Thread: Converting Bogen chb-35a to more guitar friendly amp (newbie inside)

  1. #71
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    I gutted mine and started over with my own circuit. The transformers are too close together with the same orientation on the stock chassis, so if you turn the gain up then it will hum more than it should. I found that out the hard way but I am stuck with it for this amp. I did a parallel stage on the input into a pentode, then a LTP phase inverter into the power tubes. No negative feedback. Yes I added one preamp tube. I optimized my layout and grounding. I'm getting about 55-60 Watts RMS and it sounds pretty killer. I'm sure you can come up with something to make it sound great! The 7868 tubes are nice too...I would keep them rather than change to something else.

    Greg

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  2. #72
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    I hadn't noticed the transformer orientation. I'm going to take a similar approach and start with a new preamp circuit, but use existing tubes. I'll leave the rest as is from the cathodyne phase inverted forward and see how it sounds.

    MG

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  3. #73
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    Quote Originally Posted by moonsgin View Post
    I hadn't noticed the transformer orientation. I'm going to take a similar approach and start with a new preamp circuit, but use existing tubes. I'll leave the rest as is from the cathodyne phase inverted forward and see how it sounds.

    MG
    Yeah I started with that too, but then gutted it to start over. Ideally I would have moved the transformers away from each other a bit. They are both "Z" mounted, and since they are so close I suspect their magnetic fields interact with each other too much with higher gain. My amp isn't a super hummy beast, and it is unnoticeable in a band context on stage when the music is being played, but the perfectionist in me says that it would hum less if I had made a new chassis with relocated iron.

    I suggest to remove the NFB and see how it sounds. I liked mine a lot more when I did that. I didn't change the power section much at all but I used a LTP phase inverter as it has a distinctive sound that I liked.

    Greg

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