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In Reply to: RE: 5ar4 arcing fuse blowing on Scott 299b posted by Steve Franklin on March 14, 2015 at 13:08:52
Did you place a load tube in the unit: say at least a 12AX7.
If not the B+ will continue to rise as it has no where to go
Follow Ups:
No load was added. I was unaware i needed to . Thanks.
Im double checking my caps and will do that..
sf
Did you replace the selenium rectifier for the negative bias supply/dc filament?
Yes. 4a 400v bridge has been installed and the dropping resistor changed to 25 ohm / 5 watt .Filament voltages are correct. Source voltages rise to about 15 vdc NEGATIVE befure arcing starts and fuse pops. Im using 1.5 fast fuse.
My wiring has been triple checked. C1,c2 and c3 have been opened and are all negative common to the can.c1and c2 caps have been checked and are ok for value , esr and polarity.
sf
Fuse should be 2.5A sloblo. Did you replace the caps in the bias supply? Have you tried it with all the tubes installed. Caps in bias supply are hooked up with + grounded except for one if I remember correctly. The original can for bias supply says common positive on it.
Edits: 03/15/15
Tube amps should use a slo blo fuse. 1.5 sounds a bit small to me
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