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Post by Magic Dragon on Feb 3, 2024 9:17:29 GMT -7
My 2014 Racing Stripe has not been modded and doesn't have it.
The photos I've seen of the new PPIMV Ghia's don't have it.
Anyone know when it was removed from the circuit and why?
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wally
New Member
Posts: 27
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Post by wally on Feb 3, 2024 11:54:54 GMT -7
My 2013 racing stripe Carmen Ghia does not have the conjunctive filter. It also has the 2.2m NFB resistor. I might have to change that???
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Post by bubs42 on Feb 4, 2024 8:39:52 GMT -7
So just an interjection. I have 3 Gold Plate Z28’s and have owned 3 early route 66’s. I take gut shots of most of my old amps just as reference to see that when I bring another amp in I can tell if anything has been messed with. Well not one of the 6 amps is exactly the same, but I can’t say that without putting them right next to each other they sound any different. If they do it’s very minor or subtle. If it sounds good, it sounds good.
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Post by Magic Dragon on Feb 4, 2024 12:10:43 GMT -7
So just an interjection. I have 3 Gold Plate Z28’s and have owned 3 early route 66’s. I take gut shots of most of my old amps just as reference to see that when I bring another amp in I can tell if anything has been messed with. Well not one of the 6 amps is exactly the same, but I can’t say that without putting them right next to each other they sound any different. If they do it’s very minor or subtle. If it sounds good, it sounds good. I am an engineer who has built, modded, repaired tube amps as a hobby since the late 1980s. While I appreciate that layouts and minor component adjustments occur, that is not the case here. For example: I own 2 Maz 18s, both factory updated to MKII spec. They each have different plate to cathode (dull/snubber) cap values on V1. I believe the updates and voicing are tailored to some degree to the desires of the owner paying for the update. In the case of the Ghia, and the Hammond AO-35 on which it is based, there is a conjunctive filer across the output transformer's primary winding. The purpose of this corrective network has been explained by Dr. Z himself in interviews and on this forum. I began looking into this because my 2014 Ghia sounds very different than a friend's 2000 Ghia. Mine is much brighter and becomes increasingly so as the amp is overdriven. In reviewing both amps, I discovered that mine is missing the conjunctive filter circled in the picture of the 2011 Ghia in my first post. This is not a minor component adjustment. This is a removal of a complete circuit from the amplifier that Doc has stated in a Tonequest interview: "affects the primary impedance of the transformer and allows frequencies to be very flat, or balanced. From say, 100Hz to 3K,". It appears, from the photos I can find, and Wally's post here, that the conjunctive filter circuit was removed from the amp sometime between 2012-2013. As has been documented, the amp had been revised 4 times previously to this latest revision, which appears to be an intentional revoicing of the amp. I suspect it may have been removed because more and more players wanted that "Vox chime" and this modification gives that in spades. I have also read of issues related to capacitor failure in the circuit associated with power tube failure. Thus, it may have been removed to enable the ETL certification of the amps. It is a straightforward modification to add it back into the circuit. I just thought I'd ask here to see if anyone knew of when (now established by Wally's post) and why the change was made.
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Post by DRZ on Feb 4, 2024 15:37:17 GMT -7
As I recall it was in mid 2011. My amps were going through ETL Certification , and it was removed on request of the examiners . Even though it was safe , the possibility of failure could have been serious , and considered a safety issue.
Z
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Post by Magic Dragon on Feb 4, 2024 19:20:01 GMT -7
As I recall it was in mid 2011. My amps were going through ETL Certification , and it was removed on request of the examiners . Even though it was safe , the possibility of failure could have been serious , and considered a safety issue. Z Thank you. I think I'm going to clip it back in and see how I like the sound. The Ghia is one of my favorite amps clean but I don't much get on with it overdriven.
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