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Post by frankie on Mar 24, 2022 9:08:22 GMT -7
**** THE BIAS RESISTOR/CAP CHANGE IS ONLY APPLICABLE TO OLDER JETTAS!!!!! SN: ff49215 and OLDER! IF IT AIN'T BROKE, DON'T FIX IT! *****
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Post by adam on Mar 24, 2022 19:04:28 GMT -7
Awesome! Thanks for taking the time to share and show that.
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Post by markT on Mar 25, 2022 3:13:21 GMT -7
Great instructional video Doc! .....but I don't need it. My JETTA does not rattle. But if it did, now I know a quick fix! Thank you~
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Post by doctorice on Mar 26, 2022 15:07:51 GMT -7
I was unaware of Doc's change to the values of a couple of circuit components. But I think I'll leave my early production Jetta as is. I did have tube rattle and Z's McGyver fix solved the issue.
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Post by frankie on Mar 29, 2022 12:27:23 GMT -7
I was unaware of Doc's change to the values of a couple of circuit components. But I think I'll leave my early production Jetta as is. I did have tube rattle and Z's McGyber fix solved the issue. Often times you'll find the physical dampers will be enough. The cathode bias adjustment was included for extra security in the sense that we didn't want to have continuing tube warranty issues with rattling tubes. There is a touch of difference i the bias adjustment, I could see folks preferring it the old way, though some will appreciate the added headroom. Since implementing these changes we have got maybe 1 single tube warranty issue.
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Post by slyfox on Jun 8, 2022 17:12:39 GMT -7
Great video. Where might one obtain the parts list and what online supplier might you recommend?
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Post by nick0 on Jun 8, 2022 17:27:17 GMT -7
Great video. Where might one obtain the parts list and what online supplier might you recommend? Links are in the description below the video.
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Post by slyfox on Jun 9, 2022 5:54:43 GMT -7
Great video. Where might one obtain the parts list and what online supplier might you recommend? Links are in the description below the video. Thanks, I was watching the video embedded in the post not directly on youtube. Thanks for clarifying.
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Post by Don A on Jun 9, 2022 14:31:32 GMT -7
I watched this video even though I don't own a Jetta (at this time)! I just like amps- playing them, building them, working on them, seeing them being worked on...
This video is a big part of what I like about Dr. Z- very communicative, and as transparent as is practical while running this type of a business.
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Post by nick0 on Jun 9, 2022 19:26:56 GMT -7
Links are in the description below the video. Thanks, I was watching the video embedded in the post not directly on youtube. Thanks for clarifying. You're welcome!
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Post by slyfox on Jun 14, 2022 8:45:38 GMT -7
The link for the sprague atom at the tube depot is out of stock at the moment. I am planning to undertake this upgrade in my Jetta as it has an older serial number and have experienced some rattle as I've inched up the MV. Can anyone verify if this part that is available at the tubestore.com is the same one as linked to from the youtube video parts list? Here is the link: www.thetubestore.com/atom-electrolytic-capacitor-10uf-150v
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bigez
New Member
Posts: 46
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Post by bigez on Jun 14, 2022 19:09:09 GMT -7
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Post by rootspicker on Sept 12, 2022 16:26:49 GMT -7
Hello, I’m a first time Dr. Z owner and new member of the DZ forum. I love my Jetta and am anxiously awaiting for one last part to arrive so that I may undertake this mod.
Strangely, when I took some time to examine the tubes and chassis area more closely, I noticed that the previous owner had installed silicon tube dampers but had not reinstalled the ‘shark bite’ tube retainers. I’m thinking that maybe when the dampers were installed underneath the 7591 sockets, whoever did the work found that the 4-40 machine screws were too short and left the retainers off to get sufficient bite on the threads. (The 5AR4 rectifier tube does have the retainer installed.)
So, this leads me to ask two quick questions: 1. Can someone please confirm that all Jettas came with retainers installed for the power tubes? 2. Can anyone who has successfully done the tube rattle mod comment on whether they noticed any difference in tone? I have experienced some PT rattling and want to clear that up, but don’t want to lose the “magic vibe” that makes the Jetta so special!
Any comments or experience from forum members would be appreciated. Thanks!
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Post by rootspicker on Sept 12, 2022 16:27:43 GMT -7
Hello, I’m a first time Dr. Z owner and new member of the DZ forum. I love my Jetta and am anxiously awaiting for one last part to arrive so that I may undertake this mod.
Strangely, when I took some time to examine the tubes and chassis area more closely, I noticed that the previous owner had installed silicon tube dampers but had not reinstalled the ‘shark bite’ tube retainers. I’m thinking that maybe when the dampers were installed underneath the 7591 sockets, whoever did the work found that the 4-40 machine screws were too short and left the retainers off to get sufficient bite on the threads. (The 5AR4 rectifier tube does have the retainer installed.)
So, this leads me to ask two quick questions: 1. Can someone please confirm that all Jettas came with retainers installed for the power tubes? 2. Can anyone who has successfully done the tube rattle mod comment on whether they noticed any difference in tone? I have experienced some PT rattling and want to clear that up, but don’t want to lose the “magic vibe” that makes the Jetta so special!
Any comments or experience from forum members would be appreciated. Thanks!
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Post by frankie on Sept 13, 2022 5:41:42 GMT -7
Hello, to answer your questions:
1. the Jetta (and all Z amps) only recently started to include the dampers. Roughly around the making of this video. They would have come with shark jaw retainers on all the big bottle tubes before then. They are currently coming with the ring dampers and spring retainers as shown in the video. The bias modification was done much earlier than that, very few Jetta's have the original cathode bias network in them.
2. there will be no difference in tone with the tube spring retainers. The rattle is a mechanical vibration and generally does not transmit through the speakers (if the tubes are rattling at all). However the difference in the bias modification will result in slightly less low end and slightly less overdrive (more headroom).
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Post by rootspicker on Sept 13, 2022 8:55:05 GMT -7
Hello, to answer your questions: 1. the Jetta (and all Z amps) only recently started to include the dampers. Roughly around the making of this video. They would have come with shark jaw retainers on all the big bottle tubes before then. They are currently coming with the ring dampers and spring retainers as shown in the video. The bias modification was done much earlier than that, very few Jetta's have the original cathode bias network in them. 2. there will be no difference in tone with the tube spring retainers. The rattle is a mechanical vibration and generally does not transmit through the speakers (if the tubes are rattling at all). However the difference in the bias modification will result in slightly less low end and slightly less overdrive (more headroom). Thanks for the quick response frankie ! The Jetta has plenty of low end so I’m not concerned about a bit less output from the lower strings of my electrics. Also, since I use OD pedals for dirty tones, more headroom is actually a good thing, IMO. Looking forward to diving in and doing this mod. Once done, I will create a follow up post with my impressions.
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Post by rootspicker on Sept 15, 2022 12:50:34 GMT -7
Hi again frankie So today I removed the chassis from my Jetta and lo & behold, it’s clear that the previous owner already performed this mod! However, upon closer inspection I noticed that while the tech had replaced the capacitor with the specified 10uF 150VDC value, the resistor value is 10W 180 ohms, not the 10W 150 ohm value as prescribed in Mike’s YouTube video. Now, I have the correct resistor on hand and am prepared to swap out the incorrect value that’s currently installed, but I’m curious as to what effect a 180 ohm impedance would have vs the 150 ohm component? (Honestly, the amp sounds pretty good as is!…) I plan on going ahead with the correct resistor anyway, but wanted to get your input. Thanks
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Post by frankie on Sept 19, 2022 12:58:45 GMT -7
Hi again frankie So today I removed the chassis from my Jetta and lo & behold, it’s clear that the previous owner already performed this mod! However, upon closer inspection I noticed that while the tech had replaced the capacitor with the specified 10uF 150VDC value, the resistor value is 10W 180 ohms, not the 10W 150 ohm value as prescribed in Mike’s YouTube video. Now, I have the correct resistor on hand and am prepared to swap out the incorrect value that’s currently installed, but I’m curious as to what effect a 180 ohm impedance would have vs the 150 ohm component? (Honestly, the amp sounds pretty good as is!…) I plan on going ahead with the correct resistor anyway, but wanted to get your input. Thanks On a few of the initial amps that were rattling we suggested either 180 ohm or 150 ohm, to your preference of clean headroom and compression. 180ohm will have the amp run a little cooler, less compression, less output, more clean headroom. 150 will juice the output up a little. The amp is now stock with a 150 ohm. It's still lets you get a good grind from the output tubes and still have decent clean headroom. If you want a clean machine, 180 ohm is fine.
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Post by rootspicker on Sept 27, 2022 6:17:19 GMT -7
OK, so the mod was completed almost two weeks ago and I’ve been playing a number of my guitars through my “new & improved” Jetta. (With the 150 ohm resistor, FWIW)
I’m happy to say that the amp sounds as good or better than before! Whether single coil or HB pups, the amp just sings, the breakup characteristics are smooth, gradual and natural, and there’s not a hint of tube rattle even when cranked. Best amp I’ve ever owned!
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