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Selmer Corvette cap job and tweeks
Hi all,
For years, I've had this croc-skin Selmer Corvette kicking around, that I bought in a junk shop. It's a small 3 watt Champ-style amp with an 8" speaker, EL84 power tube, and tremolo.
http://www.vintagehofner.co.uk/selme...c/futcorv.html
I like it because it gets incredibly dirty when cranked up, but it hummed badly ever since I bought it. So finding myself with a bit of free time and nothing better to do, I decided to give it a cap job.
I just used regular Taiwanese electrolytics, after all, it was a budget amp when it was new!
They are cheesy brands like "Suntan", "Forever" and "HL". I made my own "multi-section" caps by taping them together with electrical tape. I used the nearest preferred values: 47uF instead of 32uF, 22uF instead of 16uF, 10uF instead of 8uF, and 22uF for the 25uF cathode bypass caps. I didn't bother replacing any of the Wima plastic film caps, as I'd heard these last practically forever.
I'd also heard that all of these Champ-style single-ended amps hum loudly even with perfectly good caps! Because they are single-ended with no feedback, they have very poor rejection of power supply ripple. So I went one step further, and replaced the 250 ohm resistor in the power supply filter with a large choke. I plan to use this amp as a "Herzog" to drive another amp, so I want it hum-free. I added an extension speaker jack too, it wouldn't be much of a Herzog without one!
After putting back together, it worked first time! The hum was completely gone, and I'd swear it had more gain. I tried out the new extension jack by plugging it into a 2x12" cabinet, and I was pleasantly surprised, it sounded much louder and really vicious! The "Elac" brand internal speaker starts to flap and fart a lot after about 11 o'clock on the volume control.
I wonder if those "Forever" brand electrolytics will still be good after another 40 years?
For years, I've had this croc-skin Selmer Corvette kicking around, that I bought in a junk shop. It's a small 3 watt Champ-style amp with an 8" speaker, EL84 power tube, and tremolo.
http://www.vintagehofner.co.uk/selme...c/futcorv.html
I like it because it gets incredibly dirty when cranked up, but it hummed badly ever since I bought it. So finding myself with a bit of free time and nothing better to do, I decided to give it a cap job.
I just used regular Taiwanese electrolytics, after all, it was a budget amp when it was new!
They are cheesy brands like "Suntan", "Forever" and "HL". I made my own "multi-section" caps by taping them together with electrical tape. I used the nearest preferred values: 47uF instead of 32uF, 22uF instead of 16uF, 10uF instead of 8uF, and 22uF for the 25uF cathode bypass caps. I didn't bother replacing any of the Wima plastic film caps, as I'd heard these last practically forever.I'd also heard that all of these Champ-style single-ended amps hum loudly even with perfectly good caps! Because they are single-ended with no feedback, they have very poor rejection of power supply ripple. So I went one step further, and replaced the 250 ohm resistor in the power supply filter with a large choke. I plan to use this amp as a "Herzog" to drive another amp, so I want it hum-free. I added an extension speaker jack too, it wouldn't be much of a Herzog without one!
After putting back together, it worked first time! The hum was completely gone, and I'd swear it had more gain. I tried out the new extension jack by plugging it into a 2x12" cabinet, and I was pleasantly surprised, it sounded much louder and really vicious! The "Elac" brand internal speaker starts to flap and fart a lot after about 11 o'clock on the volume control.
I wonder if those "Forever" brand electrolytics will still be good after another 40 years?
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