jmg
Junior Member
Posts: 53
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Post by jmg on Mar 4, 2019 21:27:48 GMT -7
Why do both my power tubes stay glowing at equal brightness when in half mode?
Just curious. Thanks for you answers in advance.
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Post by Chilly Gibbons (Todd T.) on Mar 5, 2019 3:19:53 GMT -7
The heater filaments on all tubes will be on and glowing regardless of whether or not a tube is operating. It would not be practical to switch heaters on and off in circuits that remove tubes to decrease power. That said, the Z Plus probably uses a different topology such as pentode/triode switching to reduce power which would keep both tubes active in parallel single-ended operation.
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jmg
Junior Member
Posts: 53
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Post by jmg on Mar 5, 2019 10:53:09 GMT -7
Hey Todd. Thanks for the reply, man. In the Z-Plus video below, the Doc describes the full-power, half-power switch this way: "So what that does, it engages either full power in both 6v6s, or half power, just one." That led me to think I'd see one tube (the disengaged) with more of a standby amount of glow, and the other (engaged) with full glow, so to speak. But it's interesting, both power tubes glow evenly in half power mode. What I see in the tubes is more like the pentode/triode switching you describe, right? But what Doc is describing in the video (see 4 min mark) is different, no? Thanks for any help in advance, and anyone else, feel free to chime in. I love knowing how this great amp operates.
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jmg
Junior Member
Posts: 53
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Post by jmg on Mar 15, 2019 17:34:04 GMT -7
So does anybody know? Crickets. haha.
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Post by Chilly Gibbons (Todd T.) on Mar 15, 2019 18:27:18 GMT -7
So if Doc does switch one of the tubes out of operation, he will still has heater voltage applied to both tubes. The glow you are seeing is the heater filament surrounding the cathode. As long as the power switch is on, the heaters will glow in all tubes. When standby is switched off, high voltage is applied to the plate and screens bringing the tube into its operating class (A,AB - most common).
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Post by DRZ on Mar 16, 2019 1:30:15 GMT -7
So does anybody know? Crickets. haha. It is a little more complicated than stated above. I really don't want to give away all my design secrets. But I will say it is NOT Triode/Pentode that's the sissy way to achieve almost half power, used by many amp builders. The Z Plus is a TRUE Class A single ended device. The OT's secondary impedance is calculated for two 6V6's running in Parallel. By removing drive signal to one tube , as well as other trick, only one 6V6 is outputting but it still places the correct load on the OT, so change in tone is not perceivable, only half wattage from one tube. As mentioned in the past, the Single Ended Parallel output was the brain child of Joe Walsh . It is a design that is used in Hi Fi applications to exact higher output wattage at true single ended Class A operation. The half power circuit is my spin. It makes the Z Plus a big sounding Fender Champ with one 6V6 and a 12" speaker. Or a unique 15 watt amp in true Class A with both 6V6's firing , kind of a cool Fender Princeton tone. If you haven't tried a Z Plus you owe it to yourself to find one and plug in, you'll be pleasantly surprised . Z
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Post by Rockerfeller on Mar 16, 2019 4:00:38 GMT -7
So does anybody know? Crickets. haha. But I will say it is NOT Triode/Pentode that's the sissy way to achieve almost half power, used by many amp builders.
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jmg
Junior Member
Posts: 53
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Post by jmg on Mar 19, 2019 10:00:16 GMT -7
So does anybody know? Crickets. haha. It is a little more complicated than stated above. I really don't want to give away all my design secrets. But I will say it is NOT Triode/Pentode that's the sissy way to achieve almost half power, used by many amp builders. The Z Plus is a TRUE Class A single ended device. The OT's secondary impedance is calculated for two 6V6's running in Parallel. By removing drive signal to one tube , as well as other trick, only one 6V6 is outputting but it still places the correct load on the OT, so change in tone is not perceivable, only half wattage from one tube. As mentioned in the past, the Single Ended Parallel output was the brain child of Joe Walsh . It is a design that is used in Hi Fi applications to exact higher output wattage at true single ended Class A operation. The half power circuit is my spin. It makes the Z Plus a big sounding Fender Champ with one 6V6 and a 12" speaker. Or a unique 15 watt amp in true Class A with both 6V6's firing , kind of a cool Fender Princeton tone. If you haven't tried a Z Plus you owe it to yourself to find one and plug in, you'll be pleasantly surprised . Z Ah. A little secret sauce. No problem then, Doc. I'll just enjoy my Z Plus and let it be like the Beatles. : ). One thing though, I tend to run my Z Plus on half power about 80 percent of the time. Sounds great. Will this create more wear on one of the power tubes over time?
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Post by headshrinker (Marc) on Mar 19, 2019 11:14:00 GMT -7
As I understand it, both tubes will wear at the same rate, because of that secret sauce.
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Post by Chilly Gibbons (Todd T.) on Mar 19, 2019 14:29:00 GMT -7
Yep, same with the Lux’s half power circuit
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Post by rollyfoster on Mar 1, 2020 13:30:33 GMT -7
Do the power tubes in the Plus have to be matched?
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Post by purpletele on Mar 1, 2020 14:25:58 GMT -7
Do the power tubes in the Plus have to be matched? Yes
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Post by headshrinker (Marc) on Mar 1, 2020 18:50:57 GMT -7
I'm no expert, but as I understand it, since it is a dual single ended design, they may not have to be since they are operating sort of independent of each other. Again, as I understand it, theoretically in that design, you wouldn't even have to use the same type of output tube. For instance, you could use one 6L6 and one 6V6. That's theoretically with that design. Though that may affect the output transformer match. You are on your own if you try it and others may know more.
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Post by premiumplus (Dave) on Mar 2, 2020 6:58:19 GMT -7
The Z-Plus is specified to use matched output tubes.
The amp is a parallel output configuration. That means that the plates of the output tubes are going to be tied together. With unmatched tubes, one tube is going to be trying to pull the other tube up to its level while the other tube is trying to drag it down; they'll be fighting each other.
And since it's a true Class A circuit, the output tubes are going to age at the same rate whether they're both driving a signal or one is just idling in 1/2 power mode.
From the Z website tube specs for Z-Plus: "Z-PLUS V1: Tung Sol 12AX7, V2: JJ ECC83, V3: JJ ECC81, V4: Tung Sol 12AX7, V5: JJ ECC83, V6-7: JJ 6V6 (matched), V8: Shu Guang 5AR4 Recommended Bias Point: Cathode Biased (no re-biasing necessary) Fuse Value: 1A 250V SLO 1.25″ x .25″
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Post by headshrinker (Marc) on Mar 2, 2020 9:39:42 GMT -7
I stand corrected.
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