JTM45 Strange Voltages

Get support and show off your MetroAmp JTM 45 kit builds.

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bobh_39
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JTM45 Strange Voltages

Post by bobh_39 » Sun Feb 21, 2016 8:38 am

Hi
I am building a JTM45 and have gone through the startup checklist and my voltages don't match.
This is my first build and don't want to damage anything.
Here are my findings.

I have a question regarding the voltages I am getting during the startup of my JTM45.
Following the Metro instruction sheet here is what I am reading.
Step B
I am reading 122.2 at the power switch.
Step C
V1,V2-V3 pin 4,5 and 9 3.484 VAC
V4,V5 pin 2 and 7 3.484 VAC
V6 pin 2 and 8 5.85 VAC
Step D
Standby Switch 376.1VDC
V4 pin 5 -57VDC
V5 Pin 5 -57VDC
Step E
V1 Pin 1 235VDC Pin 3 2.084VDC Pin 6 252.3VDC Pin 8 2.084VDC
V2 Pin 1 201.9VDC Pin 3 1.376VDC Pin 6 366.7VDC Pin 8 201.4VDC
V3 Pin 1 280.2VDC Pin3 49.8VDC Pin 6 278.4VDC Pin 8 49.8VDC
I am running the Classictone 40-18033 power transformer.
Could it be that the transformer has a higher 475v B+
Any help would be appreciated.
Thank You
Bob Hall

danman
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Re: JTM45 Strange Voltages

Post by danman » Mon Feb 22, 2016 4:05 pm

Are you measuring with tubes installed or not? Are you plugged into a light bulb limiter? If you are not sure of what that is, you should google it and check it out. It is really helpful for new builds and will prevent anything from burning up. What is it about your measurements that worry you? I don't see anything to far out of line. Using a different PT will affect voltages throughout the amp and measuring without tubes installed will create higher voltages. Once they are installed and drawing current, the voltages will come down.

bobh_39
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Posts: 2
Joined: Thu Apr 23, 2015 3:11 pm
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Re: JTM45 Strange Voltages

Post by bobh_39 » Thu Feb 25, 2016 5:24 pm

Thanks for the reply I got it going after researching some similar posts on the forum.
Sounds good just have to get more playing time on it. now to build the combo cabinet.

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