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Dirty-South Blues Harp forum: wail on! >
Question for the Amp guys
Question for the Amp guys
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Noodles
138 posts
Jul 22, 2012
9:15 PM
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I’m not sure, but to my ear my ’64 Champ seems to be capable of much more than I’m getting out of it. I play through a custom JT-30 with a hot element and a Shure PE54.
I got the amp in 1973. It was sitting in my buddy’s basement, unused for about 7 of the 9 years it had been in existence, so I bought from him. I used it to jam, perhaps 3 times after that. Then it went to long-term storage until recently. So, for it’s age, it has had very little playing time.
It may be time to get it checked out. But, before I reluctantly take it to a local guy, I wanted to get some advice. I don’t want a solder junkie just swapping caps, resistors and tubes unless necessary.
Here’s what I’m experiencing. I’m not getting the over-driven tone or enough bottom end. Occasionally, you can hear a slight "ringing" when it's cranked up. Is that normal?
My understanding is that caps tend dry out when not used much.
The champ is 100% original. Tubes are: 1-5Y3GT, 1-6Y6GT and 1-12AX7. There are no hums, crackles, crunches or any other foreign noises when the amp is on. It is dead quiet. The speaker is also original.
So, if it were you, and you wanted it gig/jam ready with that “tone” and bottom end that blues harp players look for, what would you advise me to do to get this baby roaring like a vintage blackface Champ should.
You guys know what I’m after.
Thanks
Last Edited by on Jul 22, 2012 9:25 PM
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Rick Davis
551 posts
Jul 22, 2012
11:04 PM
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It's a Champ! It should sound barky and compressed. When you turn it up past 5 it won't really get any louder; just more compressed and distorted.
The ringing sound can be a tube that has gone a bit microphonic. Tap gently on the tubes with a pencil while the amp is on and warmed up... see if that causes the ringing noise. If so, replace the tube.
Or, the ringing could be plain old feedback.
Does it still have the original Oxford speaker?
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-Rick Davis
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Noodles
139 posts
Jul 22, 2012
11:11 PM
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@Rick Davis
Does it still have the original Oxford speaker?
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Yes, Rick
8EVXK581 printed on rear of speaker. I tapped the tubes as you suggested - no ringing. Also, should I be concerned about the Caps?
Last Edited by on Jul 23, 2012 12:16 AM
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5F6H
1275 posts
Jul 23, 2012
1:14 AM
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Yes, you should be concerned about the caps, if they are from 1964, they ceased to do their job effectively some time in the mid 80's.
Replace the caps in the cap can with discrete caps, 500v rating. 40-50uf for B+ node, 20uf everywhere else. Ground main & screen caps to a PT bolt, ground the preamp cap to the input jack ground. You can leave the old can in place for aesthetics, snip off the solder tabs inside the chassis & lay the new caps over the can.
Replace the 25uf/25v cathode bypass cap at 6V6 pin 8 with a 25uf/100v cap as this cap will have at least 25v on it, probably more. Whilst you are there replace the 1W 470ohm cathode resistor with a 5W item.
Also replace the bypass caps at 12AX7 pins 3 & 8 with caps of the original value & rating.
This will restore your amp to it's proper performance. It's not particularly likely that you will have to change any resistors (other than any you murder whilst changing caps) or coupling caps.
"So, if it were you, and you wanted it gig/jam ready with that “tone” and bottom end that blues harp players look for, what would you advise me to do to get this baby roaring like a vintage blackface Champ should."
Regarding "that tone" & "bottom end"...well, it's a BF champ, it'll have BF champ tone & bottom end. It'll only have the sound "harp players" are looking for...if they are looking for BF champ tone. They're fairly flexible, clean at moderate settings, barky when overdriven....if you mic it/line it out go easy on the volume control.
A GE5751 is a good choice for the preamp tube.
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Last Edited by on Jul 23, 2012 2:14 AM
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Rick Davis
552 posts
Jul 23, 2012
7:18 AM
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As always, excellent counsel from 5F6H. I agree about the 5751 preamp tube.
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-Rick Davis
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SuperBee
441 posts
Jul 23, 2012
7:44 AM
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It's a beaut little amp. I was gonna remark on it in the "show and tell" thread, but this'll do. Beautiful example, seems almost a shame to get it dirty now having kept it clean for so long. Then again, the real shame would be in not using it. I'm opposed to collecting for the sake of it, philosophically, and I certainly don't need another small amp, but after I saw this one I found myself thinking about getting maybe a silverface champ to keep company with the Princeton. Folly, I wont do it. Nice amp.
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Noodles
141 posts
Jul 23, 2012
7:46 AM
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@5F6H
@Rick Davis
My sincere thanks to both of you.
Noodles
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