| garbage |
hi all
i am using rca83 fullwave mercury rectifier in my 300b amps.
the 300b is a drd design, with siemens c3g as driver.
am facing a hum problem. seems like psu hum. it does not increase with volume.
psu filtering is done by 8uF/10H/55uF/5H/55uF. ultrapath cap is 45uF.
psu ground and signal ground are separated, but meets at the same point. chassis is grounded to safety earth. does not seem to be a grounding issue as when in breadboard, on a piece of wood, the hum is also there. before this, i used one single ground for psu and signal.(separate grounds did not make much difference)
i have also added 100nF cap across rca83's anode and cathode, tuned the 5H choke with a 0.22uF capacitor, but that still does not seem to reduce the hum much.
any suggestions?
thanks.
garbage |
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| Sch3mat1c |
Er, a mercury type is supposed to use small hash chokes in series with the anodes. Less capacitance the better.
Indeed, you'd have much better luck with silicon diodes, which only have reverse recovery switching issues (easily controlled). Yes, this from a person who, unfortunately, hasn't seen a type 83 in use...
Tim |
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| kmtang |
I don't think the hum is caused by the PS circuit. The C-L-C-L-C 8uF/10H/55uF/5H/55uF filter circuit should provide you with excellent filtering.
The hum possibly from the filament circuitry of the 300B. Did you adjust the hum pot? If you want to further cut down the hum from the filament, it's better to use DC supply for it.
I had hum problem when using Russian made 6SN7. I need to raise the DC potential of the filament voltage to approx 80Vdc to kill the hum generated from the 6SN7 driver stage.
The 300B amp I built was based on the design from JE Lab. |
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| analog_sa |
The hum is definitely not caused by the 83 - it may (i've never noticed) generate some HF hash but it certainly can't make hum.
It might be heater or grounding related or due to magnetic coupling between a power transformer and the c3g |
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| martinab2 |
One of the posts in this thread might be helpful.
"My understanding is that mercury vapour rectifiers have a negative resistance at part of their IV characteristic and that this can combine with the leakage inductance and stray capacitance of the mains transformer to produce a circuit that can oscillate if excited. Since the system is excited at a 50Hz (or 60Hz) rate, this can lead to squegging at a 50Hz rate. Ferrite beads are usually touted as the cure. The RSGB and ARRL manuals are good places to look for information on using these rectifiers."
(don't know how to quote properly on here but the above was posted by EC8010) |
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| analog_sa |
| quote: | | squegging at a 50Hz rate |
Never happened to me but if EC8010 says so it may well be possible. Easy to eliminate the 83 by substituting some sand in its place |
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| garbage |
hi all
thanks for the responses.
i've just changed my speakers from totem model 1 (87db) to an az2 (93db) in order to better match my amps. the hum is killing me now. i can still hear it from my listening position. previously with the totems, i am not able to hear it unless i go within a foot or so. will have to find some way to get rid of that hum...
| quote: | Originally posted by kmtang
The hum possibly from the filament circuitry of the 300B. Did you adjust the hum pot? If you want to further cut down the hum from the filament, it's better to use DC supply for it.
I had hum problem when using Russian made 6SN7. I need to raise the DC potential of the filament voltage to approx 80Vdc to kill the hum generated from the 6SN7 driver stage.
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the 300b heaters are dc. no hum pot, just connected the cathode resistors to the - heater supply. i tried hum pot, but no difference.
i've read that there is a max voltage when raising filament voltages. what is a safe level in my case? an when raising the filament voltages, do i connect to the + or - of the filament supply?
my driver stage is a triode strapped pentode, on ac filaments though. all filaments are floating, ie, not connected to circuit ground.
| quote: | Originally posted by analog_sa
The hum is definitely not caused by the 83 - it may (i've never noticed) generate some HF hash but it certainly can't make hum.
It might be heater or grounding related or due to magnetic coupling between a power transformer and the c3g
...
Never happened to me but if EC8010 says so it may well be possible. Easy to eliminate the 83 by substituting some sand in its place |
seems like most people think that it is the heater of the driver. ok. will look into that. probably go dc for it. i've tried different grounding arrangements, but still there is no audible difference in hum reduction. i'll put in sand as a last resort to isolate the problem, but would very much still like to use the 83.
| quote: | Originally posted by martinab2
One of the posts in this thread might be helpful.
"...Ferrite beads are usually touted as the cure. The RSGB and ARRL manuals are good places to look for information on using these rectifiers."
(don't know how to quote properly on here but the above was posted by EC8010) |
i noticed that thread after i posted this. (sorry moderators... :eek: )
where should the ferrite beads be placed? along the heater supply of the 83?
ps. i think there is no method of cross-post quoting. you are not alone there. ;) |
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| martinab2 |
| Ferrite beads or rf chokes would do the job - Insert them in the leads between the transformer and the plates of the 83. Scrap switchmode power supplies are always useful for sourcing the sort of chokes you will need |
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| garbage |
ok, i guess the ferrite beads should be placed nearest to the anode of the 83? would one on each anode do fine? or should i just put more?
thanks. |
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| audiousername |
| quote: | Originally posted by garbage
i've read that there is a max voltage when raising filament voltages. what is a safe level in my case? an when raising the filament voltages, do i connect to the + or - of the filament supply? |
The heater must be within 120V of the cathode - or so I think... the datasheets are in German, and I don't read German :(
You connect the centre tap of the 6.3V winding to a potential divider to raise it 40V or so above the voltage at the cathode. If you have no centre tap, connect two 100 ohm resistors in series across the winding, and connect the centre of the two resistors to the potential divider.
| quote: | Originally posted by garbage
my driver stage is a triode strapped pentode, on ac filaments though. all filaments are floating, ie, not connected to circuit ground.? |
Floating heater potentials are generally bad. You would prefer to determine it rather than let the other what-nots in the circuit and the valve determine it for you. It may also be the source of the hum.
| quote: | Originally posted by garbage
where should the ferrite beads be placed? along the heater supply of the 83? |
As Martin (and Tim) has already said, in series with each of the anodes.
A question please, the title of this thread is "rca83 hash" - does this mean that you are getting a low frequency - 50Hz or 100Hz or so with few higher harmonics, or buzz/hash with low frequency stuff but also more audible (and more annoying :( ) higher frequency components? |
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| martinab2 |
I didn't spot the bit about floating heaters earlier, but I'm definitely in agreement with Jason there - floating heater supplies are a bad idea.
I would attend to that before trying anything else as its very likely to be the cause of your hum problem. |
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| garbage |
| quote: | Originally posted by audiousername
The heater must be within 120V of the cathode - or so I think... the datasheets are in German, and I don't read German :(
You connect the centre tap of the 6.3V winding to a potential divider to raise it 40V or so above the voltage at the cathode. If you have no centre tap, connect two 100 ohm resistors in series across the winding, and connect the centre of the two resistors to the potential divider.
Floating heater potentials are generally bad. You would prefer to determine it rather than let the other what-nots in the circuit and the valve determine it for you. It may also be the source of the hum.
...
A question please, the title of this thread is "rca83 hash" - does this mean that you are getting a low frequency - 50Hz or 100Hz or so with few higher harmonics, or buzz/hash with low frequency stuff but also more audible (and more annoying :( ) higher frequency components? |
hi audiousername
i've already made a dc rectifier for the c3g heaters.
rectifiers followed by 4700uF/4700uF/4.7uF/0.1uF, followed by lm317 with 100R and 1000R trimmer.
will put this in some other night...
i will ground my c3g heaters to circuit ground to see if the hum goes away first. the 300b filaments are floating, that's ok right? cos i did try to ground it, but i think it causes some shorts... 300b is DHT. ;)
forgot to get the ferrite beads when i was at the store...
oh, the hash is low frequency. only audible in the woofers, and does not increase with volume. doesn't help when i've got 8" woofers. |
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| audiousername |
| quote: | Originally posted by garbage
i will ground my c3g heaters to circuit ground to see if the hum goes away first. the 300b filaments are floating, that's ok right? cos i did try to ground it, but i think it causes some shorts... 300b is DHT. ;) |
Quite right. Don't ground the 300B's filament, that would be bad. By doing so you remove bias :hot: |
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| garbage |
my power trans for c3g winding is 3.15-0-3.15.
the CT is grounded.
currently i am using ac with 1R2 on each filament pins to drop the voltage to slightly below 6.15vac.
i am not sure if i am able to ground one of the pins, so i did not try grounding my supply, but instead i put in the rectifier and regulator.
with the regulator putting out 6.10vdc, i fired up the amps, but the hum/hash on the woofer is still there. next, i tried grounding the ground filament to circuit ground with a wire in hand, but the hum/hash did not reduce. this wire however, became hot, so i removed it.
the anode and cathode of the 83 have a ferrite clamp on it, but it does not seem to make any difference to the hum/hash levels.
yet to try is to raise the heater voltage. as of now, i have reverted to ac on the filaments. to raise the heater voltage, do i put in dc or ac into the CT of the filament trans winding?
short of using dc on the 83 filaments or changing rectifiers, i've almost tried everything...
is there an easy drop-in rectifier for 83? a ux-4, that can take 450-0-480 of HV from the power trans?
rgds
garbage |
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| audiousername |
| quote: | Originally posted by garbage
my power trans for c3g winding is 3.15-0-3.15.
the CT is grounded.
currently i am using ac with 1R2 on each filament pins to drop the voltage to slightly below 6.15vac. |
If your filament winding is providing 3.15-0-3.15 under load, there is no reason to use dropping resistors. It is disappointing that grounding the centre tap did not solve your problem... it was the most obvious thing wrong there.
| quote: | Originally posted by garbage
i am not sure if i am able to ground one of the pins, so i did not try grounding my supply, but instead i put in the rectifier and regulator. |
Ground what pin?
| quote: | Originally posted by garbage
with the regulator putting out 6.10vdc, i fired up the amps, but the hum/hash on the woofer is still there. next, i tried grounding the ground filament to circuit ground with a wire in hand, but the hum/hash did not reduce. this wire however, became hot, so i removed it. |
What do you mean by grounding the ground filament?
| quote: | Originally posted by garbage
the anode and cathode of the 83 have a ferrite clamp on it, but it does not seem to make any difference to the hum/hash levels. |
The ferrites should be in series with each of the anodes of the 83. By the way, with directly-heated rectifiers, the input to the power supply filter should come from the centre tap of the filament winding, unlike indirectly heated rectifiers like 5AR4/GZ34 which should take it from pin 8.
| quote: | Originally posted by garbage
yet to try is to raise the heater voltage. as of now, i have reverted to ac on the filaments. to raise the heater voltage, do i put in dc or ac into the CT of the filament trans winding? |
It should be 6.3V AC RMS or 6.3V DC. Significantly raising or lowering the heater voltage (say more than 5%) will reduce the life of the valve.
You should never allow DC into a transformer which was not designed for it.
| quote: | Originally posted by garbage
short of using dc on the 83 filaments or changing rectifiers, i've almost tried everything... |
Using DC on a rectifier filament is a waste of time because you have lots of ripple voltage there as well, which is far more significant than the little variations caused by AC heating.
| quote: | Originally posted by garbage
is there an easy drop-in rectifier for 83? a ux-4, that can take 450-0-480 of HV from the power trans? |
When it comes to hard vacuum rectifiers, a 5Z3 (essentially UX-4 based 5U4) or an 83-V might be suitable for replacement, but neither will have as good regulation and as low a voltage drop as the 83 because of its mercury-vapour construction.
Note that there are many causes of hum, quite possibly it has nothing to do with the valves themselves. It may be an earth loop, magnetic coupling between the power transformer and output transformer, or a whole variety of other things. I recall your posting of a picture of the internals of this amp a little while ago, and it appeared quite crowded inside. |
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| audiousername |
A link to the thread where garbage posted lots of pictures of his amp.
Those transformers look quite close to the underside of the C3g, where some low-level circuitry lives... |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by garbage
the 300b heaters are dc. no hum pot, just connected the cathode resistors to the - heater supply. i tried hum pot, but no difference. |
And THERE is likely your problem. Why?
Your DC supply is not regulated. It will likely have a few 100mV Hum on it. Consider adding some filter chokes and additional capacitors to it and make a virtual centertap from two 10R Resistors.
Also, connect the centertap of the C3g heater to around +20V, this reliably reverse-biases the parasitic cathode/heater diodes.
You might want to have a look at a few of my recent (300B) amp's and pick up on a few of the tricks I use.
Sayonara |
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| garbage |
| quote: | Originally posted by audiousername
What do you mean by grounding the ground filament?
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ok, think i get it. grounding of the filaments is only thru the CT.
if i want to float the filament supply, how do i do this?
| quote: | Originally posted by audiousername
The ferrites should be in series with each of the anodes of the 83. By the way, with directly-heated rectifiers, the input to the power supply filter should come from the centre tap of the filament winding, unlike indirectly heated rectifiers like 5AR4/GZ34 which should take it from pin 8.
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my rectifier filaments winding is just 0-5vac. no CT. the input to psu supply filter is taken from pin 4.
| quote: | Originally posted by Kuei Yang Wang
And THERE is likely your problem. Why?
Your DC supply is not regulated. It will likely have a few 100mV Hum on it. Consider adding some filter chokes and additional capacitors to it and make a virtual centertap from two 10R Resistors.
Also, connect the centertap of the C3g heater to around +20V, this reliably reverse-biases the parasitic cathode/heater diodes.
You might want to have a look at a few of my recent (300B) amp's and pick up on a few of the tricks I use.
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hi KYW
hmm... initially i had a regulated 300b filament supply via a lm338. it was mounted to a large heatsink. unfortunately i think it blew. both channels within seconds of each other, sending my 83 to glow super blue. i switched it off immediately. ever since then i just have rectifiers, caps and dropping resistor to get correct voltage for the 300b.
during my prototype stage, the filaments were regulated, but i still experience the same hum. at that time, i thought it was the proximity of the drd choke to the psu chokes(drd choke was in between both the psu chokes).
i'll check out your circuits to see how you wire your 300b filaments and the floating method. |
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| audiousername |
| quote: | Originally posted by garbage
if i want to float the filament supply, how do i do this? |
You shouldn't. Anyway, there is no need to in this circuit. |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by garbage
ok, think i get it. grounding of the filaments is only thru the CT.
if i want to float the filament supply, how do i do this? |
Resistor divider from +B or from the 300B Cathode, capacitor across the lower part. And note, I strongly recommend that you do bias/float up the heater of the driver. I remember a pair of very hummy paraglos of a friend, Bias the heaters of the driver, quiet. The hum was 50Hz BTW, very funny wavform and quite audible.
| quote: | Originally posted by garbage
my rectifier filaments winding is just 0-5vac. no CT. the input to psu supply filter is taken from pin 4. |
That should be fine.
| quote: | Originally posted by garbage
during my prototype stage, the filaments were regulated, but i still experience the same hum. at that time, i thought it was the proximity of the drd choke to the psu chokes(drd choke was in between both the psu chokes). |
Is the hum fundamental 50/60Hz or 100/120Hz?
Sayonara |
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| audiousername |
| quote: | Originally posted by audiousername
You shouldn't. Anyway, there is no need to in this circuit. |
Just to nip any possible confusion in the bud... What I meant is that referencing the heater of the C3g to a higher potential with a voltage divider as Thorsten and I have suggested is a good thing, leaving it unreferenced is a bad thing - and is unnecessary. |
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| garbage |
| quote: | Originally posted by Kuei Yang Wang
Resistor divider from +B or from the 300B Cathode, capacitor across the lower part. And note, I strongly recommend that you do bias/float up the heater of the driver. I remember a pair of very hummy paraglos of a friend, Bias the heaters of the driver, quiet. The hum was 50Hz BTW, very funny wavform and quite audible.
Is the hum fundamental 50/60Hz or 100/120Hz?
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i was thinking of taking it from 300b cathode initially.
i noticed in one of your circuits for bias/floating of heater... in order to float the heater of the driver, i'll have to take the resistor divider from 300b to the CT winding of the heater, and then ground the center point with 2 resistors where the c3g filaments are. would this be about right? |
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| garbage |
| quote: | Originally posted by audiousername
Just to nip any possible confusion in the bud... |
sure. you were right about the confusion part. ;) |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by garbage
i was thinking of taking it from 300b cathode initially.
i noticed in one of your circuits for bias/floating of heater... in order to float the heater of the driver, i'll have to take the resistor divider from 300b to the CT winding of the heater, and then ground the center point with 2 resistors where the c3g filaments are. would this be about right? |
No, just 1 resistor from 300B Cathopde to heater centertap, RC from heater centertap to ground.
Sayonara |
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| garbage |
| quote: | Originally posted by Kuei Yang Wang
No, just 1 resistor from 300B Cathopde to heater centertap, RC from heater centertap to ground.
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ok. help required here.
now i'm confused as to how to bias/float my c3g heaters.
i initially intended to take the voltage across R1 as shown below(numbers in blue were my design values, in red are measured values.):
if i run one resistor from the 300b cathode to heater CT, this would result in a resistor having to drop 244vdc(264v-20v). any suggested values for the R series C from heater CT to ground?
thanks. |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by garbage
ok. help required here.
now i'm confused as to how to bias/float my c3g heaters.
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Why not use 220K from the 300B Cathode to to C3g Heater centertap, this will add around 1mA current draw to the 300B and should be harmless, a Resistor of 1W Rating is suggested. Then use a 18K...22k (0.5W suffices) resistor to ground from the C3g Centertap.
The minimum capaictance in the heater bias divider would then be a few uF, but why not procure 100uF/50V and just use that?
There is no major issue with some tolerance in that.
BTW, are you absolutely SURE that your noise does not come from the HT line? The DRD circuit originating with jack Elliano has very poor/non at all power supply noise rejection.
You could connect (temporary) a large value electrolytic capacitor bank of suitable voltage rating across the midde capacitor in your supply (55uF) to see if that kills the hum. If so you know it is insufficient +B filtering.
Sayonara |
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| garbage |
Thanks for the reply.
| quote: | Originally posted by Kuei Yang Wang
Why not use 220K from the 300B Cathode to to C3g Heater centertap, this will add around 1mA current draw to the 300B and should be harmless, a Resistor of 1W Rating is suggested. Then use a 18K...22k (0.5W suffices) resistor to ground from the C3g Centertap.
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so the voltage divider is actually this 220k resistor and a 18-22k resistor to ground, with the c3g heater CT between the 220k and the 18-22k resistor. now it's much clearer. with the voltage divider starting at the top of R1, i should get about 20 - 26vdc,
| quote: | Originally posted by Kuei Yang Wang
BTW, are you absolutely SURE that your noise does not come from the HT line? The DRD circuit originating with jack Elliano has very poor/non at all power supply noise rejection.
You could connect (temporary) a large value electrolytic capacitor bank of suitable voltage rating across the midde capacitor in your supply (55uF) to see if that kills the hum. If so you know it is insufficient +B filtering.
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actually i am not 100% sure that it is not due to sufficient psu filtering. i did try removing the ultrapath cap altogether(without cathode cap at 300b, much much less gain though), but that did not produce much difference in hum/hash levels.
i have another spare 55uF cap. although not a large value, but i will try putting that at my middle cap to see if it helps. |
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| garbage |
put in an additional 55uF at 2nd cap but the hum remains.
used a voltage divider of 220k and 8k from B+ to CT of c3g(raised by 22vdc). (easier to solder in the parts from B+) hum still there.
running out of ideas now. i am wondering if the psu chokes and power trans orientation is not correct. below are some pics of the chokes and power trans. can some one comment if their orientation looks ok?
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| analog_sa |
| An even easier way to check if the hum is B+ related is to disconnect the transformer supplying it while listening to changes in hum. |
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| garbage |
| quote: | Originally posted by analog_sa
An even easier way to check if the hum is B+ related is to disconnect the transformer supplying it while listening to changes in hum. |
i am using a double pole triple throw switch(got the switchs here) to turn on my circuit.
first, filaments only are turned on (83, c3g, 300b), then i wait till the mercury is heated, before turning on B+.
when filaments are on, there is always complete silence. the hum/hash is only there when the B+ is turned on.
not sure if this means that it is B+ related. if so, is it due to insufficient filtering or emf/rfi interactions between the windings and cores of the power trans and the psu chokes? |
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| garbage |
just rotated the 2 psu chokes 90degrees.
no difference.
think i shall try to put a choke in the 300b filament supplies and beef up the caps there. this shall be the last attempt to rid hum.
guess i'll have to live with it if this fails to help... :( |
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| analog_sa |
| quote: | | not sure if this means that it is B+ related |
There is no way to know if you don't conduct some experiments. What i proposed is very simple. Get the amp nice and warm, make sure that the hum is clearly audible and remove the B+ transformer connection. The amp will continue working for some time thanks to the PS caps but: there will be no B+ ripple at all and there will be no magnetic coupling between transformers/chokes and sensitive nodes in your amp. If this experiment cures the hum (which i can almost bet it will) you'll then have to find the exact way the hum gets in. |
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| garbage |
| quote: | Originally posted by analog_sa
What i proposed is very simple. |
i see. i'll do just that. ;)
btw, i put in the rectifier, choke(2mH), 4700uF,4700uF,4700uF,4700uF,4.7uF,1R, for the 300b filaments. hum seems lesser.
a measurement via multimeter in ac setting shows 0.011v at the speaker terminals with volume at zero. previously it always showed 0.014v. but the hum is still audible from my normal sitting position.
maybe the hum is from the mur860 rectifiers? will swap in a normal bridge rectifier to see if it helps... |
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| analog_sa |
| quote: | | maybe the hum is from the mur860 rectifiers? will swap in a normal bridge rectifier to see if it helps... |
Maybe it's time for you to realise that rectifiers, whether SS or tube cannot generate hum. 11mV is in fact not too bad; what remains is very possibly only electro-magnetic coupling. |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by garbage
btw, i put in the rectifier, choke(2mH), 4700uF,4700uF,4700uF,4700uF,4.7uF,1R, for the 300b filaments. hum seems lesser.
a measurement via multimeter in ac setting shows 0.011v at the speaker terminals with volume at zero. previously it always showed 0.014v. but the hum is still audible from my normal sitting position. |
How much hum do you measure across the heater?
Have you tried to give the heater a centertap via a pair of resistors? You need to have < 1mV across the heater if you use the negative side of the heater as return for the audio signal (as I believe you do).
Sayonara |
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| garbage |
| quote: | Originally posted by Kuei Yang Wang
How much hum do you measure across the heater?
Have you tried to give the heater a centertap via a pair of resistors? You need to have < 1mV across the heater if you use the negative side of the heater as return for the audio signal (as I believe you do).
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hi KYW
i am measuring 0.125vac on my 300b heaters.
i tried using a pot at the heaters with the cathode resistor wired to the CT of the pot, but the result was the same as before. i've read that many people tried using pot with great success... not for my case though.
now i have 0.01vac on the speaker outputs. this is with rectifier, choke(2mH), 4700uF,4700uF,4700uF,4700uF,3300uF, choke(2mH), 1R6. interesting to note that before the resistor, it is 0.184vac, after the resistor it is 0.125vac. the dropping resistor was 1R2 (2R2//2R7, 10W each) all along(1R stated in the above thread was my mistake).
i have to agree with analog_sa that changing to bridge rectifiers did not make any difference. ;) you never know till you try huh?
guess i will stick to this configuration for now. with my 93db speakers, i barely notice the hum when the cd is not playing, while seated in my listening position.
thanks all for the help. :) |
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| kmtang |
Check the hum at B+ line. Probably, the B+ for the 300B is not clean enough which will introduce hum to the output. By the way, you may try to remove the driver tube to check out first.
Johnny |
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| garbage |
| quote: | Originally posted by kmtang
Check the hum at B+ line. |
i tried to put my multimeter on ac setting with probes on the B+, but could not get a stable reading.
also, when putting back my 300b heater dc circuit, i added a 10000uF cap to the filtering.
so now, it is 4Xmur860, 2.2mH, 4700uF, 4700uF, 4700uF, 4700uF, 10000uF, 2.2mH, 1R2.
the hum when measured across the speaker output terminals with my multimeter in ac setting, gives 0.007V. i guess most of the hum is introduced by the 300b heater circuit. with insufficient filtering (4Xmur860, 4700uF,4700uF,4700uF,1R2) initially, i get 0.014V.
i can safely say that the hum is not because of the 83. ;)
current 300b heater circuit:
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| MelB |
Yo garbage:
I notice earlier you tryed a LM338 to regulate the 5v...those required a 3 volt drop to regulate proberly (ie. 8 volts in..5volts out) Did you have the required drop? I built a couple of parrallel 300B SE's and did the following:..use the 6.3v tap-> bridge rect. -> 68,000uF cap(yo!) -> 6.3v filaments and LT1084 (low drop 5A reg) -> 300B filaments. I think I ended up with like 7.5v after the bridge.....the LT1084 only needs 1V drop to regulate. I think the speakers make more noise without the amp connected than with .. ;) |
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| garbage |
| quote: | Originally posted by MelB
I notice earlier you tryed a LM338 to regulate the 5v...those required a 3 volt drop to regulate proberly (ie. 8 volts in..5volts out) Did you have the required drop?
...68,000uF cap(yo!)
...I think the speakers make more noise without the amp connected than with .. ;) |
hi MelB
i had a 0-7vac winding for my 300b heaters. there's enough voltage headroom for regulation.
that's a big cap for filaments! looks like i need to look into using bigger caps for the 300b filament supply. ;)
thanks for sharing your experience. |
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| MelB |
| Garbage...the only reason I use the large cap is because I also pull the 6.3v I need for the 2 other tubes in the circuit off of it. If you can get a linear regulator to work for your 5v I think you will be very happy with the lack of humm. I remember blowing up the first regulator too...check your grounding. just ground the whole filament circuit once. Think I mixed things up over by the tube socket by running twisted wires over to the tube sockets and putting on another ground wire over there...ooops! Mel |
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