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Post by oldewoodupes on Oct 10, 2022 20:53:09 GMT -7
Hey Guys, I recently bought a 66, it came with a 5u4 installed and sounds incredible, but I wanted to try the stock 5ar4. When I put a known working 5ar4 in, the 3amp slo blow goes when I switch the standby off. Tried another 5ar4 same thing, pulled both power tubes, still blows. I looked inside and nothing is burned up or loose, nothing obvious. Put the 5u4 back in, works perfect. Any suggestions on what is happening here? Thanks in advance, Josh
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Post by gfreak on Oct 11, 2022 6:51:44 GMT -7
Amp was designed for a 5u4. The 5u4 draws more current than 5ar4.
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Post by oldewoodupes on Oct 11, 2022 11:56:01 GMT -7
Amp was designed for a 5u4. The 5u4 draws more current than 5ar4. On the tube layout sticker in the amp head box it says 5ar4 is the stock recto and 5ar4 is blowing the fuse not the 5u4. Wouldn’t that mean the 5ar4 is drawing more current? Sorry I’m confused
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Post by KeithA on Oct 11, 2022 12:11:37 GMT -7
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Post by premiumplus (Dave) on Oct 11, 2022 13:02:12 GMT -7
That is really strange, because the 5U4 does pull more current than the 5AR4. 3 amps for the 5U4 vs. 1.9 amps with the 5AR4. Here's a link to a cool table on rectifier specifications.
I'd be suspecting your 5AR4. You said that you pulled the other tubes and just changing rectifiers blows the fuse...It's got to be drawing more current.
I'll see if I can post a picture of it too...
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Post by oldewoodupes on Oct 11, 2022 18:02:49 GMT -7
Thanks for the replies guys. It’s possible the head shell isn’t original. Although, tube layout chart in headshell has a date of 2008 and chassis is dated 2009. So I suspect they are an original pair.
Thanks for the recto info. Doesn’t really make sense in my situation, very strange. Like I said I’ve tried two known working 5ar4’s from working amps. They were both JJ’s, so maybe I’ll try another brand, but that shouldn’t make a difference. I can see a small arch flash inside the top of the recto before the fuse blows when I switch the standby off. It doesn’t seem to hurt the recto as it still works fine in my other amps.
The search continues…
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Post by purpletele on Oct 12, 2022 18:43:03 GMT -7
Thanks for the replies guys. It’s possible the head shell isn’t original. Although, tube layout chart in headshell has a date of 2008 and chassis is dated 2009. So I suspect they are an original pair. Thanks for the recto info. Doesn’t really make sense in my situation, very strange. Like I said I’ve tried two known working 5ar4’s from working amps. They were both JJ’s, so maybe I’ll try another brand, but that shouldn’t make a difference. I can see a small arch flash inside the top of the recto before the fuse blows when I switch the standby off. It doesn’t seem to hurt the recto as it still works fine in my other amps. The search continues… It has been my experience with Z amps that you should use the exact rectifier recommended or use an NOS due to the high voltage jolt at start up.
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Post by oldewoodupes on Oct 13, 2022 12:49:28 GMT -7
Figured it out. It was the JJ 5AR4’s, I tried 3 of them, 1 known working tube and 2 new tubes, they all blew the fuse on my 66 and my super reverb. Weird. They are drawing too much current when the standby is flipped. I put in an old Mullard 5ar4 and it works perfect, no fuse blows.
Thanks for all the replies and help. Much appreciated, take care guys
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