Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tubenit on August 21, 2017, 12:56:36 pm
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Given Charlotte, NC is in the 98% solar eclipse path within the next hour ...................... I decided to name it after the event.
I have had this Carolina Overdrive Special 5879 plus amp that original had a PAB (preamp boost). I hardly ever used it and it made a BIG jump in volume and wasn't as smooth as I wanted. It had a little high end hash/grind that I wasn't fond of. So, it was there unused for the most part.
I wondered what would happen if I used a cathode bypass cap, or cathode bypass cap with resistor paralled or simply a paralleled resistor with the 8.2k cathode resistor on the 3rd gain stage on the clean channel? I spent two hours trying all kinds of combinations of caps, caps & resistors and resistors paralleling the 8.2k. I tried a 220uf there, 1.5k there, 2.2uf with 3.9k etc. etc. etc. ...............
I ended up liking a 10uf/100v cathode cap paralleled with the 8.2k resistor. Never have used a cathode cap with such a large value resistor. Typically you have a 100k/1.5k plate/cathode ............... I've got a 120k/8.2k.
However, I found I also liked a 10uf and 5.6k in series then paralleling the 8.2k. So it's now called the Carolina Eclipse Boost mod. :thumbsup:
Ironically, I found the larger cathode resistor 8.2k with 10uf much smoother in tone and sweeter in harmonics then 1.8k with a 2.2uf to 10uf range cap. I have no idea why but it just has more sweet harmonics, IMO. I have NO idea if this idea would work well with other amps but I try to pass on "new ideas" with the hope someone might find it useful?
Nothing new about paralleling a switchable cathode bypass cap, but I haven't seen that done with this large of a cathode resistor? Nor have I seen a toggle switch option to send the 10uf directly to ground (large boost) vs. 5.6k tail to ground (more modest boost)
Anyhow, I like it! The toggle switch having the 10uf with 5.6k tail resistor to ground paralleling the 8.2k is very nice. Using the 10uf directly to ground really gives a very pushed driven overdrive tone with some sustained feedback.
With respect, Tubenit
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So 14 months on, I'm curious if you are still liking this Eclipse Boost mod?
I'm currently playing around with DIYLC, learning the how to use it and laying out a CoS clone of my own (actual building will need to wait until after I've move interstate in the new year).
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Yes, I liked it a lot. ……………………..
AND, I needed the toggle switch for something different and so it's not in the amp right currently. But yes, it was a nice boost & used it frequently.
With respect, Tubenit