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Post by glumlord on Oct 21, 2019 22:32:33 GMT -7
i have a couple specific semi-technical question regarding the Jetta and the 7591 power tubes.
Can anyone confirm what brand the stock tubes are?
I’ve Heard that some current production 7591’s are closer to 6L6/5881 spec, are the stock tubes a true 7591?
Lastly, is the Jetta capable of running older or NOS 7591’s if I wanted to change them out at some point?
I am still completely sold on the Jetta, but just wanted to know if these issues have come up.
Thanks in advance for any information that can be provided!
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Post by dcarver on Oct 21, 2019 23:04:59 GMT -7
Hi Glumlord, welcome to the forum. Regarding the Jetta output tubes, there's a link on the Dr. Z web site home page on the "Support" drop down menu to the "Tube and Bias Info" page. Here's a link: drzamps.com/support/tube-info/Looks like the stock output tubes are Tung-Sols. I don't know if there is a difference between old 7591's and current ones, so I can't help you with your other question. |
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Post by DRZ on Oct 22, 2019 2:20:31 GMT -7
i have a couple specific semi-technical question regarding the Jetta and the 7591 power tubes. Can anyone confirm what brand the stock tubes are? Tung-Sol reissue 7591 . I’ve Heard that some current production 7591’s are closer to 6L6/5881 spec, are the stock tubes a true 7591? Yes they are true 7591's , they are accompanied with the original Tung-Sol 7591 data sheet for design purposses.. They are as close as posable to the NOS Tung-sol 7591. No they are NOT 6L6 / 5881 spec you can not exchange them/ swap them. Lastly, is the Jetta capable of running older or NOS 7591’s if I wanted to change them out at some point? Yes NOS 7591's will drop in replace the re-issue Tung-Sol 7591. I am still completely sold on the Jetta, but just wanted to know if these issues have come up. Thanks in advance for any information that can be provided! |
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Post by glumlord on Oct 22, 2019 8:06:21 GMT -7
i have a couple specific semi-technical question regarding the Jetta and the 7591 power tubes. Can anyone confirm what brand the stock tubes are? Tung-Sol reissue 7591 . I’ve Heard that some current production 7591’s are closer to 6L6/5881 spec, are the stock tubes a true 7591? Yes they are true 7591's , they are accompanied with the original Tung-Sol 7591 data sheet for design purposses.. They are as close as posable to the NOS Tung-sol 7591. No they are NOT 6L6 / 5881 spec you can not exchange them/ swap them. Lastly, is the Jetta capable of running older or NOS 7591’s if I wanted to change them out at some point? Yes NOS 7591's will drop in replace the re-issue Tung-Sol 7591. I am still completely sold on the Jetta, but just wanted to know if these issues have come up. Thanks in advance for any information that can be provided! Thanks for taking the time to answer my questions Doc! after I originally posted this yesterday evening, I did some research on new production 7591's VS. original era and found that the Tung-sol's rate very good in comparison(which you obviously already know) as do the EH 7591. I've got a pair of original Ampeg branded Sylvania from my '64 Jet J-12a that I'll be excited to compare as well once I've had a chance to get to know the Jetta. Thanks for all you do, I'm so ridiculously excited for this model. It's exactly what I've been looking for and I feel like it was made specifically for me! |
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Post by frankie on Oct 22, 2019 10:56:47 GMT -7
Thanks for taking the time to answer my questions Doc! after I originally posted this yesterday evening, I did some research on new production 7591's VS. original era and found that the Tung-sol's rate very good in comparison(which you obviously already know) as do the EH 7591. I've got a pair of original Ampeg branded Sylvania from my '64 Jet J-12a that I'll be excited to compare as well once I've had a chance to get to know the Jetta. Thanks for all you do, I'm so ridiculously excited for this model. It's exactly what I've been looking for and I feel like it was made specifically for me! Sent to me from a customer: audiokarma.org/forums/index.php?threads/tung-sol-7591a-tests.625099/Tung Sols are the best production 7591 you can currently buy. |
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Post by glumlord on Oct 22, 2019 11:33:24 GMT -7
Thanks for this frankie, I look forward to reading through that review. For anyone that might be looking for more info, I found this article to be pretty informative as well. tronola.com/html/7591a_tubes.html |
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Post by perryr on Oct 22, 2019 23:17:48 GMT -7
Dr Z is the master of finding that sweet spot where the current production tube is happy and delivering all the goodness it’s got to give in the socket/circuit he designed for it. Many builders use textbook circuits (that are 60+ years old) and load current production tubes that may not be so happy and able to do its best in the position. Dr Z finds the voltage, bias, negative feedback, gain, etc where the tube performs and reliably delivers the tone it’s capable of, and then of course deploys it in a total design to deliver something killer... he’s done it time and time again!
I got a Zmaster back in May, loaded with new production tungsol 5881’s. I’ve had a pair of brand new in box, perfectly matched (as in clones), brown base original old stock tungsol 5881’s in my stash for years just waiting for the right tweed styled amp to load them into. So, after spending a good while getting to know the Zmaster I decided to give the NOS Tungsols a run. First thing I did was hook up my compubias to get the bias measurements of the tubes in the amp so I could restore to original if/when needed. Next I installed the NOS and measured on the compubias, to my amazement the NOS and stock tubes biased exactly the same, within 1ma. The NOS pair bias was perfectly matched as well. Next, the tone test.. well, the NOS pair didn't sound as nice. The stock tubes had a nicer sparkle and were a bit warmer, I suspect the NOS maybe wanted a bit hotter bias but rather than mess with it any further is was pretty obvious that adjusting the bias would at best get me a tone that was on par with the stock tubes, though most likely still not have the sparkle of the new prod tubes. I promptly reinstalled the stock tubes and ordered me up a pair of spares to have on hand. What I’d did confirm though is that the new prod 5881’s measure up just like the old ones in this circuit.
So, not saying NOS 7591’s won’t sound better or different, just don’t be surprised if the new prod 7591’s sound better in the Jetta! I look forward to the day I get to plug into one of them bad boys :^)
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Post by glumlord on Oct 23, 2019 11:56:28 GMT -7
Dr Z is the master of finding that sweet spot where the current production tube is happy and delivering all the goodness it’s got to give in the socket/circuit he designed for it. Many builders use textbook circuits (that are 60+ years old) and load current production tubes that may not be so happy and able to do its best in the position. Dr Z finds the voltage, bias, negative feedback, gain, etc where the tube performs and reliably delivers the tone it’s capable of, and then of course deploys it in a total design to deliver something killer... he’s done it time and time again! I got a Zmaster back in May, loaded with new production tungsol 5881’s. I’ve had a pair of brand new in box, perfectly matched (as in clones), brown base original old stock tungsol 5881’s in my stash for years just waiting for the right tweed styled amp to load them into. So, after spending a good while getting to know the Zmaster I decided to give the NOS Tungsols a run. First thing I did was hook up my compubias to get the bias measurements of the tubes in the amp so I could restore to original if/when needed. Next I installed the NOS and measured on the compubias, to my amazement the NOS and stock tubes biased exactly the same, within 1ma. The NOS pair bias was perfectly matched as well. Next, the tone test.. well, the NOS pair didn't sound as nice. The stock tubes had a nicer sparkle and were a bit warmer, I suspect the NOS maybe wanted a bit hotter bias but rather than mess with it any further is was pretty obvious that adjusting the bias would at best get me a tone that was on par with the stock tubes, though most likely still not have the sparkle of the new prod tubes. I promptly reinstalled the stock tubes and ordered me up a pair of spares to have on hand. What I’d did confirm though is that the new prod 5881’s measure up just like the old ones in this circuit. So, not saying NOS 7591’s won’t sound better or different, just don’t be surprised if the new prod 7591’s sound better in the Jetta! I look forward to the day I get to plug into one of them bad boys :^) thanks for the anecdotal reassurance. There is definitely no question that Doc Z goes to great lengths to make sure his designs are both classic and modern all at the same time. His meticulous usage of the best parts that can be found today is what has drawn me to his amps for so many years. My original questions were not meant to put his design into question, but rather the manufacturing and design of current production 7591's. It's an uncommon tube type and I know that in many cases, like KT66's, you have to be careful which brands you are using if you plan to run them with amps that are specifically designed around the specs of that tube. still anxiously, yet patiently waiting for my name to come up for a Jetta from Sweetwater! |
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Post by perryr on Oct 23, 2019 23:11:15 GMT -7
Awesome, look forward to your review, I’m sure it’ll knock your socks off!
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