Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joesatch on March 30, 2022, 09:51:16 am
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i been installing the humdinger on all my builds. I'm thinking that i could tune in the humdinger then just replace each side with a resistor at a given value and remove the pot? After all i really only adjust the pot once.
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That didn't seems a good idea
The use of the pot Is as to achieve a fine regoulation
using resistor I don't think It will be easy to have the exact values you need also if you go with paralleled and in series resistors
Franco
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In addition, if you change tubes and the resistance is slightly different, the heater circuit will be out of "balance."
And, it's more work! Pot, solder, done.
Hmm, that sounds like a good way to get the job done!
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The humdinger mainly aims to minimise the net hum voltage that is capacitively coupled in to the input tube input grid circuitry, but can also minimise other similar coupled hum in to other parts of the wiring/circuitry. As such, its 'tune' typically relates to wiring and part layout, and not to the tubes - but there could be some difference in internal capacitances within tubes. So yes you could tune with a pot and then replace with resistors, although perhaps best to check with a few tubes first to see if they all have the same minimum tube setting.
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You're taking a simple and well tested solution, and making it more complex. Personally, I think you'll be lucky to match the resistance of each of the two legs of the humdinger pot accurately enough to make it work well. When I've used a humdinger, and it's not often, the range where the balance is achieved is usually small (I'm not measuring, just going by the rotation of the pot).
To be fair, I build mostly low gain amps, and I know joesatch builds mostly high gain rockets where heater induced hum is more of an issue than what I have to deal with.
Everyone has their way of doing things, and their reasons, and if it works -- well, great! That's what makes amp building so challenging and fun.
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Just a little trivia sidebar... Fender either used a real HT center tap or grounded one side of the filament string until the AB763 amp models were discontinued. Then they switched over to using two 100Ω resistors as an artificial center tap.
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Just a little trivia sidebar... Fender either used a real HT center tap or grounded one side of the filament string until the AB763 amp models were discontinued. Then they switched over to using two 100Ω resistors as an artificial center tap.
I recall that the 5U4 rectifier version of the Princeton Reverb is shown with balancing resistors for the heater circuit https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_reverb_bf_aa1164.pdf
Though the GZ34 version is shown as being balanced via a winding CT https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_rev_gz34_aa1164.pdf
The exception that proves the rule :icon_biggrin:
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I recall that the 5U4 rectifier version of the Princeton Reverb is shown with balancing resistors for the heater circuit https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_reverb_bf_aa1164.pdf
That schematic shows a real CT and the 100Ω resistors.
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That schematic shows a real CT and the 100Ω resistors.
Wow! Belt And Braces! And I have been told you can't do that!
Is it real? Or was Leo not sure which was cheaper until the quotes came back and he looked through the surplus pile.
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Recommendation. Don't try this at home.
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Don't try this at home.
I won't -- it doesn't make sense and using one or the other has always worked for me.
But, what would happen? There is very little if any current flowing through the CT wire, and a small amount of current (to ground) limited by artificial CT resistors on the active leads. Seems like it could set up for a possible ground loop, but shouldn't be a disaster otherwise. No?
By the way, when I was looking at Merlin's website just now, I see he is coming out with a new book soon on Power Supplies. Yippee!
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Nothing gonna blow up.
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(https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fi.kym-cdn.com%2Fentries%2Ficons%2Foriginal%2F000%2F000%2F521%2F13809242.b4f8cba9.1200x1200o.60dc4f38b621.jpg&f=1&nofb=1)
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Leo prolly was concerned about the cost of two 100 ohm resistors when a CT was present. What were his engineers trying to prove?
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I recall that the 5U4 rectifier version of the Princeton Reverb is shown with balancing resistors for the heater circuit https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_reverb_bf_aa1164.pdf (https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_reverb_bf_aa1164.pdf)
That schematic shows a real CT and the 100Ω resistors.
Those 2 x 100 ohm R's look like they were drawn in by hand later and not from Fender.
Look at the ground symbol for the 100 ohm resistors.
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yes looks like an alteration.
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Hi,
old thread, short question:
In an amp with two independent heater voltages (6,3V power tubes, 12,6V preamp tubes) I need two humdingers, right?
Happy new year and thanks
Christian
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Usually in old gear the Humdinger was only on the preamp heater PS
But you can do as you prefer, this also if the Power Section is less prone to Humm
Franco
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So for some reason we're now calling a hum-balance control a "humdinger"?
Now how & when did that all get started? The idea has been around since at least the mid-60s IIRC.
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Now how & when did that all get started? The idea has been around since at least the mid-60s IIRC.
Long pre-dates tubes. https://en.wiktionary.org/wiki/humdinger
In the sense of heater hum, is covered in the 1940 edition of Radiotron Designers Handbook. Chapter 24 "Hum" pp 199-202, see pg 201 point #2.
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I was referring specifically as applies to the case of the hum pot.
I recall my great-grandmother, born in the late 1890s, using the term "humdinger".. as did my grandmother, her daughter.