Rectifier and blown fuse

When a rectifier goes south, does the fuse usually blow too?


Here's why I ask:

Upon powering on my ST-120, I heard a slight crackle and the rectifier arced. The fuse was blown as well. I replaced the tube and fuse and again saw the rectifier arcing then the fuse blew. (It was not a known good rectifier used to replace the first one.)

I re-flowed the solder on the cap*, replaced the fuse and inserted a new Sino 5AR4. The amp works fine now. Typical voltage at my house is 117 - 120V.


* I had replaced this several months ago and it being the most recent change, thought it might be the problem.

jimmeq wrote:When a rectifier goes south, does the fuse usually blow too?


Here's why I ask:

Upon powering on my ST-120, I heard a slight crackle and the rectifier arced. The fuse was blown as well. I replaced the tube and fuse and again saw the rectifier arcing then the fuse blew. (It was not a known good rectifier used to replace the first one.)

I re-flowed the solder on the cap*, replaced the fuse and inserted a new Sino 5AR4. The amp works fine now. Typical voltage at my house is 117 - 120V.


* I had replaced this several months ago and it being the most recent change, thought it might be the problem.

The 5AR4 in VTA-120 and to a less extent VTA-70 is working hard.

A rectifier that has arched is consumed and should be junked.

The yellow sheet mod seems to make rectifiers last longer as flash-over will not
lead to destruction. Recommended !

Thanks Peterh. I guess it's somewhat of a rhetorical question because it happened twice but I'm a tube amp beginner. I'm just curious about the fuse blowing when a rectifier goes south. I'll increase my fuse stock. I plan to upgrade to a Tung-Sol  5AR4 and keep the Sino as a spare.

I do have a SS but just love the look of a tube rectifier. (I did do a search in the Basket but did not find any info on fuses blowing when a rectifier arc's.)


*I'd have responded sooner but I had to get skiing before all the ski areas shut down because of covid-19.

jimmeq wrote:Thanks Peterh. I guess it's somewhat of a rhetorical question because it happened twice but I'm a tube amp beginner. I'm just curious about the fuse blowing when a rectifier goes south. I'll increase my fuse stock. I plan to upgrade to a Tung-Sol  5AR4 and keep the Sino as a spare.

I do have a SS but just love the look of a tube rectifier. (I did do a search in the Basket but did not find any info on fuses blowing when a rectifier arc's.)


*I'd have responded sooner but I had to get skiing before all the ski areas shut down because of covid-19.

Do install the "yellow sheet mod" where a pair of 1n4007 or un4007 is connected in series
with the 5ar4 anodes. This prevents huge currents if the tube flashes thereby saving
fuse and tube.

What’s the yellow sheet mod? I have the 120 and haven’t been on the forum in a while? I had rectifier issues early on but that has since slowed and I haven’t changed my rectifier out in a long time.

Thanks!
Mark