In Reply to: Help needed ... blown fuse on newly assembled Kit1 posted by fuba on February 20, 2005 at 07:20:50:
The best thing to do is contact Brian if you haven't done so yet. He generally responds very quickly to email.
I'm not an expert with the amp as like yourself I've just finished my kit1.The 6SN7 filament voltage would be a bit of a concern, provided your voltmeter is reading accurately. My reading was 6.4V. Your reading of 7.8V could indicate that your mains transformer is running a little too hot (too much voltage). I'd check the following:
1. That you have the primary windings properly configured for your specified mains voltage,
2. Also measure your incoming mains voltage to see if it is high, i.e. above system spec.
3. Measure the voltage from the 2 anodes of the 5U4G rectifier to ground. The manual says around 420VAC - mine was 430V.It's possible if you run the mains transformer at too high a voltage that it may go into saturation, whereby it would start sucking current and easily blow that little fuse. In that case there should be no damage to the transformer.
BTW, the 300B filament DC voltage won't change with variation in mains transformer voltage because it is regulated. It is a 5V regulator - mine measured 4.95VDC for both 300B's.
If the above checks out OK, then it must be something deeper into the circuit, and again, Brian is the man. By this point in his kit career, he's probably seen every possible problem by now.
Of course it will be interesting to hear the outcome of your scenario, so please share it when you figure out what's happening.
- Frank
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Follow Ups
- Re: Help needed ... blown fuse on newly assembled Kit1 - Frank E 02/20/0517:24:10 02/20/05 (1)
- Re: Help needed ... blown fuse on newly assembled Kit1 - fuba 05:07:02 02/22/05 (0)