hello, i make frank 6sn7 preamp (Again 😀)
this one also hum. but! no hum if only one tube in socket! half good 🙂
disconnect heater supply. hum dissapear. music play for 3 seconds during.
so it should think i need better heater supply? right now use lm7806 feed both tubes.
did i troubleshoot correct though? heater disconnect then no hum so heater problem?
this one also hum. but! no hum if only one tube in socket! half good 🙂
disconnect heater supply. hum dissapear. music play for 3 seconds during.
so it should think i need better heater supply? right now use lm7806 feed both tubes.
did i troubleshoot correct though? heater disconnect then no hum so heater problem?
No, you haven't done enough. You may have a faulty tube. Tubes can develop heater cathode shorts and that will cause hum. Swap teh tubes around and see. You may have incorrectly wired the heater circuit. For preamps the heater supply should be centre tapped and the centre tap earthed. You don't say how bad the hum is. You could have an eath-loop problem - the heater current of one tube could be causing a volt drop that is getting into the input.
hello, i make separate heater supply- 2 lm7806 each. hum same. but funny, hum less when output bypass cap on 7806 snipped off.
have many new 6sn7. issue same.
hum only when both tubes plugged in. one tube, any tube, either side plug in no hum. very confusined...
earth center tap even if dc? 1k ohm both sides then earth? thank you.
have many new 6sn7. issue same.
hum only when both tubes plugged in. one tube, any tube, either side plug in no hum. very confusined...
earth center tap even if dc? 1k ohm both sides then earth? thank you.
Sorry, I missed that you said you are feeding heaters from LM7806's.
Could be filter electro in DC supply feeding LM7806(s) is missing, too small, or faulty. Could be motorboating.
Perhaps your "hum" isn't hum at all but is motorboating. Check for motorboating by bridging coupling capacitors with another or the same value - if hum sound changes in nature or frequency, motorboating is your problem. Check one side of heater circuit is effectively earthed - you could be getting positive feedback thru heater-cathode leakage, if your 6SN7's were sold to you as NOS but are in fact used.
I suspect that the redcution in "hum" when the 7806 output cap is removed could come about this way: Without the cap the 7806 goes into oscillation at a supersonic frequency. This frequency couples in to the tubes and causes them to overload. You can't hear the oscillation because its supersonic, but you hear the effect of the overloaded tubes and the following power amp being less able to amplify the "hum".
Could be filter electro in DC supply feeding LM7806(s) is missing, too small, or faulty. Could be motorboating.
Perhaps your "hum" isn't hum at all but is motorboating. Check for motorboating by bridging coupling capacitors with another or the same value - if hum sound changes in nature or frequency, motorboating is your problem. Check one side of heater circuit is effectively earthed - you could be getting positive feedback thru heater-cathode leakage, if your 6SN7's were sold to you as NOS but are in fact used.
I suspect that the redcution in "hum" when the 7806 output cap is removed could come about this way: Without the cap the 7806 goes into oscillation at a supersonic frequency. This frequency couples in to the tubes and causes them to overload. You can't hear the oscillation because its supersonic, but you hear the effect of the overloaded tubes and the following power amp being less able to amplify the "hum".
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hello, thank you i check motorboarding. sorry, my english bad. will use google translate extensively for clearer picture.
it's very frustrating for me because my last build did no hum. i print out several frank's 6sn7 pre pcb because it sound so good. i will have 3 frank preamps for home and work 😀
last build- same pcb, same everything but different tube sockets. no hum. this build, hum.
what confuse me is how it doesn't hum with only one tube inserted. maybe current starvation in heater? but i utilize same everything as my good build.
it's very frustrating for me because my last build did no hum. i print out several frank's 6sn7 pre pcb because it sound so good. i will have 3 frank preamps for home and work 😀
last build- same pcb, same everything but different tube sockets. no hum. this build, hum.
what confuse me is how it doesn't hum with only one tube inserted. maybe current starvation in heater? but i utilize same everything as my good build.
The rated heater current of a 6SN7 is 0.6 A. So you will need one LM7806, well heatsinked, for EACH 6SN7, with a bleed resistor for start up. OR, a booster PNP power transistor around a single LM7806. Otherwise the LM7806 will keep shutting down. You could call that a form of current starvation I suppose. Not the usual term for it though.
No hum with ANY one tube removed is more a symtom of motorboating (not motorboarding). Motorboating is where a circuit with two or more tubes goes into oscillation due to output signal getting into the input by some unintended feedback path, usually via the HT power rail. It usually manifests as a loud humming noise in your speakers. It is not a question of fitting a better power supply though, it is a question of working out what's wrong with what you have - perhaps a faulty, missing, or incorrectly sized capacitor.
No hum with ANY one tube removed is more a symtom of motorboating (not motorboarding). Motorboating is where a circuit with two or more tubes goes into oscillation due to output signal getting into the input by some unintended feedback path, usually via the HT power rail. It usually manifests as a loud humming noise in your speakers. It is not a question of fitting a better power supply though, it is a question of working out what's wrong with what you have - perhaps a faulty, missing, or incorrectly sized capacitor.
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thank you for clear explain. very good learned.
i am using this circuit,
http://www.diyaudio.com/forums/tubes-valves/141263-frank-s-6sn7-preamp-linestage.html
but my output caps are 2.2uf, and my psu filtering caps are 47uf 400v each. i am doing passive filter- crc-rc (last rc split for each channel) r's are 1k, then 4.7k. also, pull down resistor 100k instead of 1m ohm.
very anxious to find out the problem. tomorrow i jump on it 😀
i am using this circuit,
http://www.diyaudio.com/forums/tubes-valves/141263-frank-s-6sn7-preamp-linestage.html
but my output caps are 2.2uf, and my psu filtering caps are 47uf 400v each. i am doing passive filter- crc-rc (last rc split for each channel) r's are 1k, then 4.7k. also, pull down resistor 100k instead of 1m ohm.
very anxious to find out the problem. tomorrow i jump on it 😀
Hello questions 1. What size is the cap on the output of the heater ? 2. LM7806 has a limit of 2.2 amp at turn on. I have not had a problem at turn on with one o6 per 6sn7 . 3. Is the heater at ground for the 6sn7 ? . Regards
hi, 🙂
1. 1000uf output cap.
2. i even use just one lm7806 my last build for 2 6sn7. no issue. steady 6v
3. yes, the heater is 0 ground. i float it later 1/4th of ht votltage.
1. 1000uf output cap.
2. i even use just one lm7806 my last build for 2 6sn7. no issue. steady 6v
3. yes, the heater is 0 ground. i float it later 1/4th of ht votltage.
That circuit cannot motorboat on its own, assuming it is correctly wired up. Is part or all of the power amp sharing the same HT power supply?
One 7806 for both 6SN7 is not sufficient. Two 6SN7's draw 1.2 amps. The continuous rating of an LM7806 is designed to supply only 1.0 amp continuously. An individual 7806 MAY give you as much as 2 amps or so if heatsinking is really good and the input voltage is the bare minimum to avoid drop out, but that is no guarantee that another 7806 will do the same.
But the solution is simple - just connect a power resistor from 7806 input to 7806 output, sized so that the 6SN7's get about 80% of their current with the peak voltage output of the rectifier. The 7806 will then make up the difference at all times, run a lot cooler, and still regulate just as well.
One 7806 for both 6SN7 is not sufficient. Two 6SN7's draw 1.2 amps. The continuous rating of an LM7806 is designed to supply only 1.0 amp continuously. An individual 7806 MAY give you as much as 2 amps or so if heatsinking is really good and the input voltage is the bare minimum to avoid drop out, but that is no guarantee that another 7806 will do the same.
But the solution is simple - just connect a power resistor from 7806 input to 7806 output, sized so that the 6SN7's get about 80% of their current with the peak voltage output of the rectifier. The 7806 will then make up the difference at all times, run a lot cooler, and still regulate just as well.
thank you. one issue check off. no motorboat then what make one tube not hum?
according to this list, my problem definitely heater. i have no scope. 🙁 have to try all heater solutions...
also with two tubes, the pcb hum to touch. one tube not so. ground loop?
according to this list, my problem definitely heater. i have no scope. 🙁 have to try all heater solutions...
also with two tubes, the pcb hum to touch. one tube not so. ground loop?
My guess would be:
Two tubes draws more current and is pulling the voltage on the input of the voltage regulator down below its ability to regulate. Try a larger capacitor on the voltage input of the regulator.
Two tubes draws more current and is pulling the voltage on the input of the voltage regulator down below its ability to regulate. Try a larger capacitor on the voltage input of the regulator.
Hi, I already try 2 lm7806 reg.
so far and fail
-single lm7806
-bigger transformer for reg
-double lm7806
left to try
-float ground
-lm317 reg
-give up
hehe
so far and fail
-single lm7806
-bigger transformer for reg
-double lm7806
left to try
-float ground
-lm317 reg
-give up
hehe
do you have a drawing of the pcb ?what if pcb design flaw, has ground loop issue?
could my problem be ground loop?
float votalge off ground by 65 volt when you do . RCA says that will be the quietest . Well at least it woas in the 1950's so it should be good now. 317 will be quieter because of the cap bypass on adj leg . Worth doing. Use bypass cap at heater pins.
Regards.
hi 🙂
here is the picture. i make it very small so i can use in amps, small preamps, even dac output 🙂 i think i make too small because tube almost touch eachother. yet no hum in my first build. 😕
Did you try Keit's suggestion? It's a good one, shunt a single power resistor across the input to output of the 7806.
What is the input voltage to the 7806 regulator? Sufficient to prevent drop out?
If you have at least 3.5 - 4.0V across the regulator you can shunt it with an 8 ohm / 10W resistor and this will shunt around 430 - 500mA around the regulator and allow it to regulate.
What is the input voltage to the 7806 regulator? Sufficient to prevent drop out?
If you have at least 3.5 - 4.0V across the regulator you can shunt it with an 8 ohm / 10W resistor and this will shunt around 430 - 500mA around the regulator and allow it to regulate.
hello, sorry bring up old thread. i try make regulator for frank 6sn7 preamp. but want to know if series reg or shunt reg better. is frank's preamp single ended design?
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