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Post by patrick555 on May 6, 2023 13:26:50 GMT -7
Alas, I blew a fuse today. Turned the amp on, and it blew within a couple seconds of taking it off standby. I thought I was in good shape, as I always keeps spares of everything. Turns out I don’t have any 1.5A fuses, only 1, 2, and 3 amp. I’ll have to wait until I can order some 1.5 amp fuses to troubleshoot.
I’m sure it will end up being a power tube or rectifier. Hopefully it’s the rectifier. The spare power tube set was quite pricey.
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Post by patrick555 on May 6, 2023 18:44:29 GMT -7
Fuses have been ordered. Power tube prices have dropped $20 per pair so I got another set of those in case. Thankfully I played my Z-Plus all day, which was sounding particularly great with a subtle Mojo Vibe in front.
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Post by jimmydeez on May 7, 2023 9:35:07 GMT -7
where are you picking up power tubes?
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Post by patrick555 on May 7, 2023 10:52:45 GMT -7
Antique Electronic Supply. 6L6WGC-STR Red base. They were $96 per pair last time. Down to. $76 now.
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Post by jimmydeez on May 7, 2023 10:57:21 GMT -7
Interesting... are you noticing a difference between those and the 5881s?
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Post by patrick555 on May 7, 2023 11:08:24 GMT -7
Those are the ones that are factory installed by Doc. You can’t buy the exact ones yet as they are not sold to the public under that brand. But they are the same tube. I have not changed tubes yet as I only have a dozen hours of use on the brand new amp, until the fuse blew. I’m buying the same tubes that Doc uses to make sure there are no sonic changes.
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Post by patrick555 on May 7, 2023 11:10:55 GMT -7
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Post by iluvpunz on May 7, 2023 11:14:55 GMT -7
I'm not positive but the Z28 MkII takes 5881 power tubes and the 6L6 tubes are not a direct replacement. If the amp had 6L6 tubes in it, that may be why you are having problems. My understanding is the amp must be re-biased and possibly components changed if 6L6's are installed rather than 5881's. You might want to check with the Doc or Don.
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Post by patrick555 on May 7, 2023 11:19:29 GMT -7
I haven’t changed any tubes since I bought it brand new. I will be replacing them (if needed) once the fuses arrive. If you follow the link above, the proposed tubes are the exact tubes Doc uses. They are just rebranded. I won’t argue with him. But thanks.
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Post by premiumplus (Dave) on May 7, 2023 12:21:19 GMT -7
I'm curious if the fuse vaporized or if it just looks like a broken open wire.
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Post by patrick555 on May 7, 2023 12:46:41 GMT -7
It turned all black inside the glass. I suppose it’s possible it was a weak fuse. When I go through troubleshooting, following Doc’s advice of removing all tubes and installing one step at a time, I’ll find out the status.
Any tube can go at any time. Only a dozen hours of light low volume use. But tubes are tubes.
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Post by smolder on May 7, 2023 13:02:20 GMT -7
I'm not positive but the Z28 MkII takes 5881 power tubes and the 6L6 tubes are not a direct replacement. If the amp had 6L6 tubes in it, that may be why you are having problems. My understanding is the amp must be re-biased and possibly components changed if 6L6's are installed rather than 5881's. You might want to check with the Doc or Don. “This 5881 / 6L6WGB was first developed by TungSol for the US Military. They are in short stubby glass envelopes. There is no difference between the 6L6WGB or the 5881, they are the same tube. The 5881 has a maximum plate rating of 360 volts at 23 watts and a maximum screen rating of 270 volts at 3 watts.” not sure how the WGC differs from the WGB.
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Post by patrick555 on May 7, 2023 13:41:44 GMT -7
Dr Z’s quote pasted from above:
Yes. They are the proprietary models made for Avi @ Boutique Amp Distributers that Avi is so kind to share with me. I really like them better then the Tung Sol 5881 , which is a great tube, but does have a bit more Tweed tone, a touch more hair on the notes. I liked the Psvane 5881 as it has a richer clean tone and reminded me of a big 6V6 , which covers the old Z 28 much better.
Now Avi is going to sell these tubes , he has a complete line of tube models his company uses, but he is not currently setup to sell to the public yet. In the mean time TAD has a small bottle clear top 6L6 made by Psvane which is the identical tube with a red base. Amplified Parts online carries these TAD 6L6's .
OK I had to go to the shop to get the full name of the TAD 6L6 , as you can see it a long name.
TAD 6L6WGC-STR.
Z
If anyone knows, it’s the man himself.
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Post by iluvpunz on May 7, 2023 16:03:11 GMT -7
Thanks you all! I'm glad to know this. I may have been thinking about the 6V6's in my Cure. That amp now is the 5881's. I stand both corrected and freshly informed about what I tubes I need to be searching out for spares.
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Post by premiumplus (Dave) on May 7, 2023 18:14:04 GMT -7
It turned all black inside the glass. I suppose it’s possible it was a weak fuse. When I go through troubleshooting, following Doc’s advice of removing all tubes and installing one step at a time, I’ll find out the status. Any tube can go at any time. Only a dozen hours of light low volume use. But tubes are tubes. It sounds like an immediate short happened; probably the rectifier or a power tube. You can find out which tube is bad by using a one amp fuse for test purposes. You'll blow the fuse when you find that bad tube anyway, so may as well sacrifice a one amp. Pull all the tubes and then start with the rectifier tube in. If that doesn't blow the fuse, put in the power tubes one by one. You'll find it.
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Post by DRZ on May 7, 2023 19:35:52 GMT -7
Let me just say 95% of the time when the fuse blows instantly after Stand-By is engaged it is the Rectifier tube arcing internally.
Also let me say that I have installed , QA'd and , 24 hour burn in of over 150 matched pairs of Psvane 5881's and only found two bad tubes from from different matched sets. That is an incredible success rate and speaks highly of the Psvane 5881.
To add, an output tube generally needs a few minutes powered up with High Voltage applied to Red Plate, then pull excessive currant and blow the power fuse, just sayin'
Z
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Post by tumeniamps (Tom) on May 8, 2023 10:01:50 GMT -7
Most likely the rectifier tube if its right after taking it off stand by. I'm a big fan of not even using the stand by switch for this exact reason. I haven't blown a rectifier tube (and consequently a fuse) on any amp since I've started this practice. That's just my experience and others may disagree. Maybe the Doctor has a thought on that to offer.
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Post by patrick555 on May 13, 2023 7:27:59 GMT -7
First, Doc, thank you for the response and for the great troubleshooting video you made. You were, of course, correct that it turned out to be the rectifier.
Troubleshooting was a very cool experience. I started with the rectifier, and it didn’t blow a fuse. I put in the power tubes, again it didn’t blow the fuse. BUT I was watching carefully, and I saw the rectifier arc. It looked exactly as it does in your video. A tiny fleck, that looked like an ember shooting from a fire, shot through the rectifier tube. I replaced the rectifier, powered back up, watched everything for a bit. All back to Z 28 glory.
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