Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 82lespaul on March 05, 2019, 07:29:32 pm
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Hello. Just completed a Mojo 5E3 build and I have a few questions. The forum members provided great assistance on my 62 Gibson Falcon restore so I'm back.
The power transformer is Mojo 756 with a rated 384v @ 75 mA secondary. No heater CT so I did the two 100 ohm resistors from pilot light to ground. I am performing first power on with no tubes installed and plugged into a DBT.
Wall voltage is 121VAC. I measured 121.3 VAC at fuse holder to chassis ground.
The rectifier heaters measure 5.77 VAC (is this too high?)
The power tube heaters measure 7.41 VAC (V3 and 4). is this too high?
The pre amp heaters measure 7.35 VAC (V1 and 2). Is this too high?
Lastly, the high voltage secondary at the rectifier (pin to chassis ground) measure 397.9 and 397.6, respectively. Is this to high?
I do not want to continue and power up with rectifier tube till I am sure. I let the amp run for at least 20 minutes while I measured and everything seems fine.
Any advice is greatly appreciated.
Doug
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It's normal for all voltages to be high when no tubes are plugged in. I'm not concerned.
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As always thanks for the quick response. I will proceed with the rectifier tube.