Thank you for the confirmation... Yes it will have a 10-turn pot and external bias points.xtian wrote:Your bias plan should work fine. You may have to adjust the dropper resistor value, so just tack it in while testing. Are you going to have an adjustment pot?
Jim Kelly Build
Moderators: pompeiisneaks, Colossal
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dorrisant
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Re: Jim Kelly Build
"Education is what you're left with after you have forgotten what you have learned" - Enzo
Re: Jim Kelly Build
Hello all and a happy new year!.
any idea what would be the proper choice for the OT? i mean, it's quite clear the impedance range, but would the original OT be a bassman/concert or any other similar OT type?
tHanks for any hints !
paolo
any idea what would be the proper choice for the OT? i mean, it's quite clear the impedance range, but would the original OT be a bassman/concert or any other similar OT type?
tHanks for any hints !
paolo
Ciao from Italy.
Paolo
Paolo
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dorrisant
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Re: Jim Kelly Build
A few more things ready... Changed bias tap on PS board, rewired OT for longer leads, back and front plates cut and drilled - forgot the 30w/60w switch, wired as much of the controls as feasible for now. One more coat of paint on the chassis too.
I also used the base of a GE 44 bulb to house a color changing LED for the pilot... This is cooler than I thought. I used a white pilot jewel and this thing looks like an opal when you stare straight into it... Mesmerizing!!
While I was changing out the leads on the OT I ran some tests on it. I was assuming it was a 4K3 primary, it is not... It shows about 3K6 @ 4Ω, 3K7 @ 8Ω and 3K9 @ 16Ω. I'm not sure how this aligns with the original OT for these amps... If this one doesn't work I can always change it out.
Does anyone have an idea what the original measurement was?
I also used the base of a GE 44 bulb to house a color changing LED for the pilot... This is cooler than I thought. I used a white pilot jewel and this thing looks like an opal when you stare straight into it... Mesmerizing!!
While I was changing out the leads on the OT I ran some tests on it. I was assuming it was a 4K3 primary, it is not... It shows about 3K6 @ 4Ω, 3K7 @ 8Ω and 3K9 @ 16Ω. I'm not sure how this aligns with the original OT for these amps... If this one doesn't work I can always change it out.
Does anyone have an idea what the original measurement was?
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Last edited by dorrisant on Wed Apr 21, 2021 6:23 pm, edited 1 time in total.
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dorrisant
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Re: Jim Kelly Build
OK... Got it all together and brought it up on the Variac - no smoke. Had to install virtual CT for preamp filaments to get rid of ground noise. Built a small rectifier and filter for the LED pilot. Changed out bias dropping resistor, ended up putting my original value back in.
The first thing I noticed was that the plates looked a bit low... Running at 417v as opposed to the 480v shown on some of the old schematics. Maybe I need a few more mA in the PT. I'm using JJ 6V6S and the 350-350 PT as outlined in the original post.
I initially thought that there might be an oscillation causing some loss there but no, not the case.
As far as tone... it certainly cuts the mustard. I did not play it much last night but our regular rhythm player did. He was loving it... Very clear and super punchy. These opinions were echoed by the same player and he is usually playing an ODS #124 that I built sometime back. This is definitely a different animal. I'm really liking it. Looking forward to getting a bit more time with it in the next few days. Overall, it sparked a song writing session and will be recorded with in the next few months.
I will get it back on the bench in a bit... Gotta get some other stuff out of the way, I played long enough yesterday.
The first thing I noticed was that the plates looked a bit low... Running at 417v as opposed to the 480v shown on some of the old schematics. Maybe I need a few more mA in the PT. I'm using JJ 6V6S and the 350-350 PT as outlined in the original post.
I initially thought that there might be an oscillation causing some loss there but no, not the case. As far as tone... it certainly cuts the mustard. I did not play it much last night but our regular rhythm player did. He was loving it... Very clear and super punchy. These opinions were echoed by the same player and he is usually playing an ODS #124 that I built sometime back. This is definitely a different animal. I'm really liking it. Looking forward to getting a bit more time with it in the next few days. Overall, it sparked a song writing session and will be recorded with in the next few months.
I will get it back on the bench in a bit... Gotta get some other stuff out of the way, I played long enough yesterday.
"Education is what you're left with after you have forgotten what you have learned" - Enzo
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dorrisant
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Re: Jim Kelly Build
Finally! I went to post some pics of this build and it worked!
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"Education is what you're left with after you have forgotten what you have learned" - Enzo
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dorrisant
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Re: Jim Kelly Build
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dorrisant
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dorrisant
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dorrisant
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dorrisant
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dorrisant
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Re: Jim Kelly Build
Jackin' up the post count today...
More to come when I re-wrap the combo enclosure.
More to come when I re-wrap the combo enclosure.
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"Education is what you're left with after you have forgotten what you have learned" - Enzo
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Smokebreak
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Re: Jim Kelly Build
Looks amazing man! Nice work, I totally remember when you started building this
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dorrisant
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Re: Jim Kelly Build
Thanks man! It's been together for a while. I had a customer that bought it recently and I have to finish the details. Figured I'd post some porn here.
"Education is what you're left with after you have forgotten what you have learned" - Enzo
Re: Jim Kelly Build
Very nice, mate!
Those knobs are very cool. I'm sure they make the amp sound better.
Those knobs are very cool. I'm sure they make the amp sound better.
I build and repair tube amps. http://amps.monkeymatic.com
Re: Jim Kelly Build
that's a gorgeous build.
https://tfrelectronics.com/
https://oshpark.com/profiles/TFRelectronics
https://oshpark.com/profiles/TFRelectronics