Using EZ80 rectifier which uses a 6.3V filament transformer. But transformer puts out 7.8 volts. I want to reduce this to 6.3 volts. My understanding is EZ80 is rated at 0.6 amps. So...
7.8-6.3 volts = 1.5 volt drop / 0.6 amps = 2.5 ohm resistor value.
I had a few 1.8 ohm resistors and soldered 1 each to each of two transformer secondary leads....and still measure 7.8 volts. Where is my error?
7.8-6.3 volts = 1.5 volt drop / 0.6 amps = 2.5 ohm resistor value.
I had a few 1.8 ohm resistors and soldered 1 each to each of two transformer secondary leads....and still measure 7.8 volts. Where is my error?
did you check that your tube's filament is drawing current?
the way it looks is your tube isnt drawing current.
the way it looks is your tube isnt drawing current.
In one acronym: RMS
This site explains it well:
http://www.alpharubicon.com/altenergy/understandingAC.htm
This site explains it well:
http://www.alpharubicon.com/altenergy/understandingAC.htm
Hi,
you could add two power diodes in series to drop about 1.3 to 1.4Vdc and same in reverse for the other halfwave.
Not quite the same but maybe good enough. Comments to this non-tube guy!
Yes, Hacknet is right, the resistors only drop voltage when they are carrying current. Open circuit voltage does not change (no matter how big the resistors are).
you could add two power diodes in series to drop about 1.3 to 1.4Vdc and same in reverse for the other halfwave.
Not quite the same but maybe good enough. Comments to this non-tube guy!
Yes, Hacknet is right, the resistors only drop voltage when they are carrying current. Open circuit voltage does not change (no matter how big the resistors are).
Mike,
When you said you measured 7.8v after you added the resistors
was the tube connected? If the tube wasn`t connected there
would be no current draw thus no voltage drop.
If this was the case it brings up another question. When you
measured the transformer voltage was this with the tube connected? Transformers measure a little higher when they
are not connected. With small transformers this open circuite
voltage can easily be 20% or higher than when undrer load.
When you said you measured 7.8v after you added the resistors
was the tube connected? If the tube wasn`t connected there
would be no current draw thus no voltage drop.
If this was the case it brings up another question. When you
measured the transformer voltage was this with the tube connected? Transformers measure a little higher when they
are not connected. With small transformers this open circuite
voltage can easily be 20% or higher than when undrer load.
riotubes said:
Did you measure at the transformer? You should indeed have 7.8V there. The 6.3 is at the tube pins....
Jan Didden
Ahhh...got it. As many of you suspected, I was testing without the board hooked up to the transformers. I was cautioned to measure the secondaries b4 hooking them up to the circuit to see if voltage was too high. I'm learning. I studied a schematic of the EZ80 and also followed the 6.3v trace and 0v trace to the tube pins. I measured the voltage at the pins: 7.4 without the resistors (down from 7.8v at the secondaries) and 5.4 with the 1.8 ohm resistors in the secondary path prior to the board's wire terminals.
This surprised me as I anticipated needing 2.5 ohm based upon my original calc of 7.8-6.3=1.5 / 0.6 amp = 2.5 ohm requirement. I had only 1.8 ohm resistors on hand. Now I'm down to 5.4 volts. This is more than 10% below the 6.3v requirement. So I conclude that the circuit is drawing a current different from the EZ80s rated current of 0.6 amp. I'm not yet entirely comfortable measuring current. I need to study how to do this.
This surprised me as I anticipated needing 2.5 ohm based upon my original calc of 7.8-6.3=1.5 / 0.6 amp = 2.5 ohm requirement. I had only 1.8 ohm resistors on hand. Now I'm down to 5.4 volts. This is more than 10% below the 6.3v requirement. So I conclude that the circuit is drawing a current different from the EZ80s rated current of 0.6 amp. I'm not yet entirely comfortable measuring current. I need to study how to do this.
Hi,
measure the voltage drop across your dropping resistor.
Your measurment accuracy is the worse of the DMM or the resistor accuracy.
I=V/R
measure the voltage drop across your dropping resistor.
Your measurment accuracy is the worse of the DMM or the resistor accuracy.
I=V/R
With the help from y'all, I feel like I've made some progress in learning how to measure voltage in a circuit. I replaced the 1.8 ohm dropper resistors with 1.2 ohm and I've increased voltage from 5.4 to 6.0v. The EZ80 rectifier tubes specs 6.3V for filament...so I think I'm within tolerance and OK.
The one disappointment is that the 6dj8 SRPP circuit of my Dac tube stage requires 200V for B+, and I was measuring 222V after a 6800 ohm resistor on the B+ in the stock circuit (and 283V before this resistor). I want to get closer to 200V. So:
283V-222V / 6800 ohm = 0.00897 A
So 9000 ohm x 0.00897 A = 81V drop or 283-81=202 V
Well, I couldn' find a 9K ohm R, only 7.5K Ohm at the local parts store. I thought this would give me:
7500 x 0.00897 A = 67V drop or 283-67=215V a step in the right direction. I measured 269V !!!! more than the 228V generated with the lower 6800 ohm resistor. Could the resistor's tolerance be that crappy or did I error somewhere?
The one disappointment is that the 6dj8 SRPP circuit of my Dac tube stage requires 200V for B+, and I was measuring 222V after a 6800 ohm resistor on the B+ in the stock circuit (and 283V before this resistor). I want to get closer to 200V. So:
283V-222V / 6800 ohm = 0.00897 A
So 9000 ohm x 0.00897 A = 81V drop or 283-81=202 V
Well, I couldn' find a 9K ohm R, only 7.5K Ohm at the local parts store. I thought this would give me:
7500 x 0.00897 A = 67V drop or 283-67=215V a step in the right direction. I measured 269V !!!! more than the 228V generated with the lower 6800 ohm resistor. Could the resistor's tolerance be that crappy or did I error somewhere?
I think in your curcuit, connecting the tube filament directly to the transformer winding is the best choice.
That 7.8V will drop a lot when you actually put yourself a load on it. At least try if for long enough to measure what voltage you get at the tube pins. Running a 6.3V tube a little bit hot for a moment won't hurt it.
That 7.8V will drop a lot when you actually put yourself a load on it. At least try if for long enough to measure what voltage you get at the tube pins. Running a 6.3V tube a little bit hot for a moment won't hurt it.
Since with a lower B+ your circuit may draw less current, I would have gone with the 10k resistor instead of 9k.
Just the obvious questions (sorry), it sounds like either the resistor is not 7k5, or a part of your circuit has come away (solder joint for example).
Just the obvious questions (sorry), it sounds like either the resistor is not 7k5, or a part of your circuit has come away (solder joint for example).
9K resistor
Riotube:
As described, you can't find 9K resistor from the store, only 7.5K available, why don't you use 7.5K series with a 1.5K to achieve 9K exact value.
WE CONSIDER HOW TO MANIPULATE OUR BRAIN
Riotube:
As described, you can't find 9K resistor from the store, only 7.5K available, why don't you use 7.5K series with a 1.5K to achieve 9K exact value.
WE CONSIDER HOW TO MANIPULATE OUR BRAIN
I might just try that. The 7.5K were bogus. The store didn't even spec the brand. Very little voltage drop at all. They were the only value the parts store carried that was close to 9k.
I had purchased some kiwame 20K R via mail order at the suggestion of another builder of this dac, given he observed a near 200V. After having gone from 6800 to 7500 with worse results, I had nothing else on hand, and decided to try to 20K. It gives me 170V. Is this too low?
If too low, I'll order some quality 10k and 15k ohm resistors.
I'm reading Bruce Rozenblit's Beginner's Guide to Tube Audio Design and there's a chart that shows the nonlinear relationship of a change in plate current with a change in plate voltage. This has certainly helped explain my experience this weekend. Using ohm's law, I would calc the current based on the voltage drop across a resistor of certain value, and then use such current to help calc the ohm rating needed to achieve a certain voltage. I could only inch closer.
I had purchased some kiwame 20K R via mail order at the suggestion of another builder of this dac, given he observed a near 200V. After having gone from 6800 to 7500 with worse results, I had nothing else on hand, and decided to try to 20K. It gives me 170V. Is this too low?
If too low, I'll order some quality 10k and 15k ohm resistors.
I'm reading Bruce Rozenblit's Beginner's Guide to Tube Audio Design and there's a chart that shows the nonlinear relationship of a change in plate current with a change in plate voltage. This has certainly helped explain my experience this weekend. Using ohm's law, I would calc the current based on the voltage drop across a resistor of certain value, and then use such current to help calc the ohm rating needed to achieve a certain voltage. I could only inch closer.
6dj8 plate volt
Riotubes:
Actually, don't too much pin point on 9k resistor or 200v dc voltage. In tube circuitry, it suits a wide supply voltage, in 6dj8 tube, it's operating voltage is low, even 60v can active this tube, if the supplied voltage is high, it will produce noise, this tube is suitable for front end operation, not that suitable for srpp cct. anyway take a try and get to know more about this tube.
Answer to AndrewT
you asking about capacitance small got fast sound and vice Vera, that's my experience on tube type amplifier. especially on coupling cct. In psu cct, we always parallel a 0.1uf cap. with the filter cap. this could improve the high freq. response of the amplifier.
WE CONSIDER COMPONENT CHARACTERISTIC
Riotubes:
Actually, don't too much pin point on 9k resistor or 200v dc voltage. In tube circuitry, it suits a wide supply voltage, in 6dj8 tube, it's operating voltage is low, even 60v can active this tube, if the supplied voltage is high, it will produce noise, this tube is suitable for front end operation, not that suitable for srpp cct. anyway take a try and get to know more about this tube.
Answer to AndrewT
you asking about capacitance small got fast sound and vice Vera, that's my experience on tube type amplifier. especially on coupling cct. In psu cct, we always parallel a 0.1uf cap. with the filter cap. this could improve the high freq. response of the amplifier.
WE CONSIDER COMPONENT CHARACTERISTIC
Hi,
I want to believe this
Opinion rather than fact?
But the previous statement seems to be going too far towards dogma.
I want to believe this
because it sound intuitively correct.
Opinion rather than fact?
But the previous statement seems to be going too far towards dogma.
Andrew suggested the 2, 20k Ohm resistors in parallel would give 10k Ohm
These two 20k resistors sit parallel/side-by-side each other on the pcb. To wire these in parallel, would I simply solder a short copper wire across both resistor's leads, on EACH side of the resistors?
These two 20k resistors sit parallel/side-by-side each other on the pcb. To wire these in parallel, would I simply solder a short copper wire across both resistor's leads, on EACH side of the resistors?
Capacitor
Hi. Andrew T:
Action speaks louder than words
If you don't believe what I am talking about capacitor, just do an experiment to prove it. All I said is my previous experience, and is not my opinion.
WE ARE TALKING THE TRUTH, NOTHING BUT THE TRUTH
Hi. Andrew T:
Action speaks louder than words
If you don't believe what I am talking about capacitor, just do an experiment to prove it. All I said is my previous experience, and is not my opinion.
WE ARE TALKING THE TRUTH, NOTHING BUT THE TRUTH
Re: 6dj8 plate volt
Yes, or just connect the legs of each resistor together at each end. Leave some air space between them.riotubes said:
Sometimes.mitwrong said:
OK, thanks to your feedback, I've got voltages that measure within the tolerance range.
However, when turning OFF the Dac, I get a small "CHK" noise at the GFCI outlet in the garages. I have a 30 foot extension cord that goes from this outlet to my workbench. The noice is NOT at the Dac, but at the outlet. AND, during the last measurement test, this outlet is tripped and won't reset. I even went all the way to breaker box and reset the breakers, and reset the GFCI switch. I have been consistently measuring 120VAC at the DAC power inlet. Any thoughts?
Oh, the power scheme for the dac is 120V in via Furertech IEC inlet. Hot goes to fuse holder, then onto DPDT switch. IEC neutral goes to same switch, and then both load and netural from switch go to transformer primary. Of course, IEC ground goes to chassis ground. I haven't changed anything here for weeks.
Any thoughts?
However, when turning OFF the Dac, I get a small "CHK" noise at the GFCI outlet in the garages. I have a 30 foot extension cord that goes from this outlet to my workbench. The noice is NOT at the Dac, but at the outlet. AND, during the last measurement test, this outlet is tripped and won't reset. I even went all the way to breaker box and reset the breakers, and reset the GFCI switch. I have been consistently measuring 120VAC at the DAC power inlet. Any thoughts?
Oh, the power scheme for the dac is 120V in via Furertech IEC inlet. Hot goes to fuse holder, then onto DPDT switch. IEC neutral goes to same switch, and then both load and netural from switch go to transformer primary. Of course, IEC ground goes to chassis ground. I haven't changed anything here for weeks.
Any thoughts?
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