Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rundgrenrules on September 22, 2020, 01:58:24 pm
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Hi Everyone, first post. I am building the ValveStorm/Metro JTM45 kit (https://valvestorm.com/JTM45%20Kit).
I have gone with the ClassicTone transformers as I didn't really have the funds to spring for the more expensive transformers. The 40-18054 Power Transformer (http://www.classictone.net/40-18054.html) has some additional wires available for solid state rectification if wanted and a bias tap. The issue I am having is that the spec sheet ClassicTone provides on their website isn't fully helpful to a relative novice like myself. I am confused about several things in terms of wiring this:
1. The RED/YELLOW wire, does this go to the internal fuse holder and then to ground?
2. The ORANGE wires, GRAY, and WHITE wires...I am assuming these are not used for a valve-rectified JTM45 and can therefore be taped off?
3. The RED/BLUE wire, no idea what that is. Bias tap?
I think I have everything else wired up correctly. I have attached a marked-up screenshot of the power section of the schematic color coded with the wiring I currently have, some text for clarification, and a reiteration of my questions.
I also have attached the spec sheet, as my inability to read this has left me wondering.
Any help would be greatly appreciated, I don't want to fire this thing up and blow something right off the bat.
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1. The RED/YELLOW wire, does this go to the internal fuse holder and then to ground? YES
2. The ORANGE wires, GRAY, and WHITE wires...I am assuming these are not used for a valve-rectified JTM45 and can therefore be taped off? YES
3. The RED/BLUE wire, no idea what that is. Bias tap? YES but not needed. Tape it off.
You are correct on the primary wires also.
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You the MAN Sluckey!!!
I am not sure what is being referred to when this PT is referenced in forums as having some lower B+ wires available. Apparently ClassicTone PTs can run high on the B+ and there are some wires that can be used to knock that down. Certainly wouldn't be the ORANGE wires.
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I am not sure what is being referred to when this PT is referenced in forums as having some lower B+ wires available. Apparently ClassicTone PTs can run high on the B+ and there are some wires that can be used to knock that down. Certainly wouldn't be the ORANGE wires.
If you want lower B+ then tape off the two red wires and use the two orange wires.
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AH! Thanks again! Well I will measure the voltages once its done and if they need to come down I'll switch wires. I like a lower B+, usually a sweeter sound and response to me. But I'll shoot for the recommended voltages to start with.
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The orange wires will be closer to the original voltages.
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I completed the build with no issues. Voltages all came out right and the amp functioned just fine.
However, I didn't care for the mushiness of the JTM45 and I am currently converting the build to a 1987 50 Watt Lead circuit. I changed the required board components, under-board wiring, swapped for a 50W OT and am currently onto the power circuit wiring portion of the re-build.
I have a few questions.
Now that I am using a bridge rectifier instead of a tube, should I swap back to the red PT wires for a higher B+ voltage or does it matter either way?
The 50W build calls for a rear panel mounted fuse instead of the internal fuse holder. I'm fine to continue using the internal fuse holder, but the wiring on this fuse is different. Instead of the two red/yellow wires coming out of the PT being wired to either side of this fuse, the 50w build calls for side of the fuse being wired to the choke/OT common and the other side of the fuse going to the bridged positive terminals of one of the 50uf cap cans and then to the standby switch.
If I wire it up like that, what should I do with the two red/yellow wires coming out of the PT?
Thank you!
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Now that I am using a bridge rectifier instead of a tube, should I swap back to the red PT wires for a higher B+ voltage or does it matter either way?
The 1987 50W lead does not use a bridge rectifier. I'd stay with the orange wires until you have it up and running. Then change to the red wires to see if you like that better.
The 50W build calls for a rear panel mounted fuse instead of the internal fuse holder. I'm fine to continue using the internal fuse holder, but the wiring on this fuse is different. Instead of the two red/yellow wires coming out of the PT being wired to either side of this fuse, the 50w build calls for side of the fuse being wired to the choke/OT common and the other side of the fuse going to the bridged positive terminals of one of the 50uf cap cans and then to the standby switch.
If I wire it up like that, what should I do with the two red/yellow wires coming out of the PT?
There is only one red/yel wire coming from that ClassicTone 40-18054 PT. It will now connect to ground.
Thank you!
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