I just completed a parafeed headphone amplifier. I had originally wired for the "Western Electric" output topology, shown below, without a cathode resistor bypass cap on my output tube (45). I was getting quite a bit of 60Hz noise on one channel, narrowed the source to some coupling to the right channel 45 filament regulator, but was unable to eliminate it.
Instead, I added a capacitor across the cathode resistor, but kept the parafeed transformer return to the top of the cathode resistor, an output design discussed in one of John Broskie's parafeed Tube CAD articles.
Here is my question - is the Western Electric topology and the design shown in Tube CAD one and the same, and the "bypass cap" across the cathode resistor remains out of the signal path? According to John, it does.
Regardless, it has created an AC path to ground for my 60Hz noise and solved my issue, I'm just curious why the Western Electric output does not use this capacitor.
Instead, I added a capacitor across the cathode resistor, but kept the parafeed transformer return to the top of the cathode resistor, an output design discussed in one of John Broskie's parafeed Tube CAD articles.
Here is my question - is the Western Electric topology and the design shown in Tube CAD one and the same, and the "bypass cap" across the cathode resistor remains out of the signal path? According to John, it does.
Regardless, it has created an AC path to ground for my 60Hz noise and solved my issue, I'm just curious why the Western Electric output does not use this capacitor.
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An old cathode may not support noise floor buffering without backend demodulation. Without cathode capacitor, the tube is up-modulating to higher frequencies internally. Lowering the cathode resistance will increase effect but will be less nuanced and will significantly decrease cathode life. The backup is to ditch the cathode and measure filament buffering through a grid or through the psu.
Also the buzz helps to dissapate charge soak in old transformers with a diminished magnetic permiability aka coupling. The front end resistance drops and the coupled output resistance goes through the roof. In my honest opinion a good transformer is worth many tubes since they operate in such close proximity.
In the end, fun tubes will flatline and repolarize to their new environment irregardless.
Also the buzz helps to dissapate charge soak in old transformers with a diminished magnetic permiability aka coupling. The front end resistance drops and the coupled output resistance goes through the roof. In my honest opinion a good transformer is worth many tubes since they operate in such close proximity.
In the end, fun tubes will flatline and repolarize to their new environment irregardless.
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In my experience, the bypass cap is still somewhat audible with parallel feed.
I would not leave off the bypass cap.
I would not leave off the bypass cap.
Thank you both. The bypass cap will stay since it has resolved my noise problem. Not too concerned about audibility, very happy with the sound with the bypass cap in place, perhaps at some point I will compare how it sounds with and without, but the 60Hz noise that results when removed is intolerable. The amplifier is dead silent with it in place.
Some 10 years ago i picked up the hobby of tube electronics again after i let it drop out of my hands when i was about 15 years of age. I have learned a lot more about (tube) electronics by visiting forums like this and reading books about elementary (tube) electronics.
Now i gahthered enough knowledge about (tube) electronics to know this contribution is complete and utter nonsense.
My struggle with this contribution (and many more by the same contributor) is that it probably does not violate forum rule no. 3 (= Not allowed: Intentionally posting incorrect or flagrantly dangerous information).
I do however think that contributor "brightcity" is not obeying forum rule 4 (= Not allowed: More than one account per person.). The nick "coolcity" and the (banned) nick "rellik" are used by the same person.
Now my point. For visitors or members of this forum (or any forum) who are still at the steap point of the learning curve, it can be confusing to read this kind of contributions to a thread, especially if the thread started with a question.
To "brightcity": Why don't you spend some of your time on study instead of posting on all kinds of forums, pretending you own some specific equipment and/or need to know something about it, just to get attention (or whatever)? I really think you are smart enough to get a realistic grip on (tube) electronics.
Maybe i violated forum rule 1 (= Not allowed: Disruptive behavior of any sort, including offensive language, trolling, threadjacking, insults, intimidation, harassment or other disrespectful or antisocial behavior) by posting this contribution. If i get banned for this … well i think i can still live with myself.
Hmm...I thought that response was odd. "Gosh, have never come across these topics in all of my reading!" I thought to myself. Only been at it for six months, but glad I don't have to dig into "backend demodulation" and "charge soak dissipation". This is supposed to be a joke?
Please leave suggestions and commentary to the moderators. Please stay on topic as well.
Not going to comment about how many off topic comments my presence on forums generate, but it is alot
As the moderators have already split this thread due to previous commentary, I would prefer to be left alone
Not going to comment about how many off topic comments my presence on forums generate, but it is alot
As the moderators have already split this thread due to previous commentary, I would prefer to be left alone
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brightcity,
Your contribution was completely false and misguiding. Perhaps you might decide to learn something before trying to contribute as your knowledge seems to be well below a complete newbie. You have things you need to unlearn.
Once you know enough to contribute positively, you will probably find you aren't the center of attention and can live a normal and peaceful life. Until then, expect a response from members when you post absurd things as you had in post #2
-Chris