aard,
This is great, I get it and the circuit you worked up is perfect. I can just duplicate the circuit for the other triode and have stereo.
What is the resistor between Rbadj and the cathode for? If I put 12.6V across pin 4 and 5 is pin 9 at 0v, 6.3v or 12.6v. I am going to guess 6.3v but...
At least know I understand referencing the heater to the cathode so that they are both at the same potential, but how is the cathode's high voltage not going to fry the heater circuit or is more of a matter of current?
So if the capacitor values stay the same, as well as Rg how do the values for Rb, Rbadj and Ri change?
Do I take the current value of Rb, 470 ohms, and divide it in half? Is that where the new resistor just off the Cathode came from?
So we would two 220 ohm resistors is series now with a pot parallel to the second one. What would be a good size pot be for this?
Also the resistor going to ground from the output, what is the need for it?
Thanks
Riki
This is great, I get it and the circuit you worked up is perfect. I can just duplicate the circuit for the other triode and have stereo.
What is the resistor between Rbadj and the cathode for? If I put 12.6V across pin 4 and 5 is pin 9 at 0v, 6.3v or 12.6v. I am going to guess 6.3v but...
At least know I understand referencing the heater to the cathode so that they are both at the same potential, but how is the cathode's high voltage not going to fry the heater circuit or is more of a matter of current?
So if the capacitor values stay the same, as well as Rg how do the values for Rb, Rbadj and Ri change?
Do I take the current value of Rb, 470 ohms, and divide it in half? Is that where the new resistor just off the Cathode came from?
So we would two 220 ohm resistors is series now with a pot parallel to the second one. What would be a good size pot be for this?
Also the resistor going to ground from the output, what is the need for it?
Thanks
Riki
hi dude! Sorry for the delay but I've been snowboarding. Yeah, its summer here, but we have an indoor skifield locally, so whats a guy to do...
Yep - easy to duplicate the other side isn't it!
THe resisitor to the cathode is the one that ensures you always have bias, regardless of how you trim the adjuster. Otherwise, you could crank the adjuster to 0V bias which is a bit of a disaster as it leads to grid current flowing and potentially damage to the tube. Make it around a 220 ohm to give you a minimum bias of about -1.2 to -1.3 V. Ish. I never to the real math unless I have to!
If you have 12 v across 4 and 5, you will have 6 v at 9 AS LONG AS YOU ARE REFERENCING JUST THE HEATER CURRENT CIRCUIT. If you were to measure from ground to 9, you should have around 140v - we elevated that point well!
The 140V doesn't fry the circuit because there is no current flowing in the 140V section of the heater circuit - there is no earth connection, remember? So we have it held high at a static 140V, while the 12V does the work of supplying heater current. Cool trick. The resistor Rel is there to ensure that, even if we have a little accident, any current is going to be minimal. Thats why its not a critical value but MUST be there.
Rg is just a guess in this circuit. 470k is fine. So is 330k. No one cares, as long as its in that ballpark and no more than 1M. Sure, you could get ultra-critical and work out an optimum value, but I don't think thats the purpose of your work here is it?
Excellent deduction on the work to do on Rb - thats entirely correct. The pot isn't too critical in value either - say 2x to 5x the bias resistor value should do it.
The resistor to ground at the output is your load - its gotta be there, yes. Make it 100k. Everyone else does.
Got your power supply sorted yet?
Yep - easy to duplicate the other side isn't it!
THe resisitor to the cathode is the one that ensures you always have bias, regardless of how you trim the adjuster. Otherwise, you could crank the adjuster to 0V bias which is a bit of a disaster as it leads to grid current flowing and potentially damage to the tube. Make it around a 220 ohm to give you a minimum bias of about -1.2 to -1.3 V. Ish. I never to the real math unless I have to!
If you have 12 v across 4 and 5, you will have 6 v at 9 AS LONG AS YOU ARE REFERENCING JUST THE HEATER CURRENT CIRCUIT. If you were to measure from ground to 9, you should have around 140v - we elevated that point well!
The 140V doesn't fry the circuit because there is no current flowing in the 140V section of the heater circuit - there is no earth connection, remember? So we have it held high at a static 140V, while the 12V does the work of supplying heater current. Cool trick. The resistor Rel is there to ensure that, even if we have a little accident, any current is going to be minimal. Thats why its not a critical value but MUST be there.
Rg is just a guess in this circuit. 470k is fine. So is 330k. No one cares, as long as its in that ballpark and no more than 1M. Sure, you could get ultra-critical and work out an optimum value, but I don't think thats the purpose of your work here is it?
Excellent deduction on the work to do on Rb - thats entirely correct. The pot isn't too critical in value either - say 2x to 5x the bias resistor value should do it.
The resistor to ground at the output is your load - its gotta be there, yes. Make it 100k. Everyone else does.
Got your power supply sorted yet?
aard,
No big deal, I went off to bed after writing the last response and again I can not thank you enough for all your help.
As for the heater circuit, that explains something I have noticed with the Magnavox I am working on, when I take a voltage reading to ground for each leg of the heater at a tube I am reading 18V and I know I should see 6.3V. Should I be taking the readings from leg to leg?
I thought it might have more to do with the resistor stopping the current and not to do with voltage.
Ok so I leave Rg at 470K, I have a resistor kit on order, 20 resistors of the most common values used in tube amps. I can always play with this value also while I have it bread boarded.
Rb becomes a 220 and Rbadj is a 220 paralleled by a 660 pot.
After some looking I found two options for the, the first is a 1K audio taper
01 - More Info for item R-VA-8MM-1A
The other is a 500 ohm linear trim pot
01 - More Info for item R-VT500L
I will keep looking in case these will not work.
How about this one 500 ohms: http://tinyurl.com/ybaj3w2
Should there be a load resistor on the input also?
Thanks aard and I hope you had fun snowboarding, I have always wanted to try that, but as I live in New Orleans, snow does not last very long.
Riki
No big deal, I went off to bed after writing the last response and again I can not thank you enough for all your help.
As for the heater circuit, that explains something I have noticed with the Magnavox I am working on, when I take a voltage reading to ground for each leg of the heater at a tube I am reading 18V and I know I should see 6.3V. Should I be taking the readings from leg to leg?
I thought it might have more to do with the resistor stopping the current and not to do with voltage.
Ok so I leave Rg at 470K, I have a resistor kit on order, 20 resistors of the most common values used in tube amps. I can always play with this value also while I have it bread boarded.
Rb becomes a 220 and Rbadj is a 220 paralleled by a 660 pot.
After some looking I found two options for the, the first is a 1K audio taper
01 - More Info for item R-VA-8MM-1A
The other is a 500 ohm linear trim pot
01 - More Info for item R-VT500L
I will keep looking in case these will not work.
How about this one 500 ohms: http://tinyurl.com/ybaj3w2
Should there be a load resistor on the input also?
Thanks aard and I hope you had fun snowboarding, I have always wanted to try that, but as I live in New Orleans, snow does not last very long.
Riki
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Hi Riki - thought about it overnight. You may want to double the size of the lower bias resistor ie make the upper one 220, the lower 470 and increase the value of the pot to around 2.2k. Use a linear pot, not log or taper. A trim pot is fine. This setup will give you a wider range to adjust over and play with without going stupid. (I forgot to consider the fact that the pot and lower resistor are in parallel when I suggested the first set of values)
Don't forget - this is all at 140V above ground. It'll sting some if you touch live! Probably won't kill you, but your elbow will hurt from whacking whatever it hits when you jump. Make sure you take all precautions when fitting the parts and when working on them. You will probably want to adjust the bias while its live - think about that and what it means for your safety.
On measuring the heater voltage - measure leg to leg for heater supply voltage and either leg to ground for any elevation voltage.
For what its worth, I've always wanted to try New Orleans, but there isn't a lot of it around here! (we had a bit float by a couple of years ago, but I understand most everyone did)
Cheers, Ashton
Don't forget - this is all at 140V above ground. It'll sting some if you touch live! Probably won't kill you, but your elbow will hurt from whacking whatever it hits when you jump. Make sure you take all precautions when fitting the parts and when working on them. You will probably want to adjust the bias while its live - think about that and what it means for your safety.
On measuring the heater voltage - measure leg to leg for heater supply voltage and either leg to ground for any elevation voltage.
For what its worth, I've always wanted to try New Orleans, but there isn't a lot of it around here! (we had a bit float by a couple of years ago, but I understand most everyone did)
Cheers, Ashton
Ashton,
I was thinking about that also, so if I use the 220 for Rb1 and the 470 for Rb2, we have a minimum ohm rating of 220 ohms and a max of 607 ohm.
Trust me, I keep reminding myself about the voltage. The highest DC I normally deal with at work is 24v, but the AC voltage go up 4160V. I just apply what I know about dealing with the AC to dealing with the DC here.
Ok, so if I measure 18v leg to ground then it has been elevated 12v?
Any time you want to come to New Orleans let me know.
Riki
I was thinking about that also, so if I use the 220 for Rb1 and the 470 for Rb2, we have a minimum ohm rating of 220 ohms and a max of 607 ohm.
Trust me, I keep reminding myself about the voltage. The highest DC I normally deal with at work is 24v, but the AC voltage go up 4160V. I just apply what I know about dealing with the AC to dealing with the DC here.
Ok, so if I measure 18v leg to ground then it has been elevated 12v?
Any time you want to come to New Orleans let me know.
Riki
Great and I actually get it!
Do the Cin of 22nf and Cout of 1.1 microF work, should I just make both ot them 22nf?
Seriously Ashton if you ever make your way over here let me know, at the lest I owe you a drink.
Also I am going to order a resistor kit and a cap kit. My options are getting 5% carbon comp 1/2W, 1% metal film 1/2W and metal oxide 1W flame proof. Flame proof sounds like a good idea, but is it needed?
AS for the caps: Axial high voltage film, Orange dip film, Electrolytic, dipped silver mica, polyester and polystyrene.
I am getting the kits fromhttp://www.justradios.com/.
Thanks
Do the Cin of 22nf and Cout of 1.1 microF work, should I just make both ot them 22nf?
Seriously Ashton if you ever make your way over here let me know, at the lest I owe you a drink.
Also I am going to order a resistor kit and a cap kit. My options are getting 5% carbon comp 1/2W, 1% metal film 1/2W and metal oxide 1W flame proof. Flame proof sounds like a good idea, but is it needed?
AS for the caps: Axial high voltage film, Orange dip film, Electrolytic, dipped silver mica, polyester and polystyrene.
I am getting the kits fromhttp://www.justradios.com/.
Thanks
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mate , if you need flame-proof, its already too late!
Capacitors are not so much a technical discussion as religion as I'm sure you know.
If you have worked out your HF and LF roll-off points, then use whatever you calculated for value. They need to be rated at least 2x the working voltage. Orange drops are fine.
Missed your q about the input load resistor. Yes, you will need one from the input to signal ground. 50k to 100k.
Speaking of signal ground, I presume you are familiar with star grounding. Essence is to ensure your signal ground is separated from power supply ground, and that both have just one common point each. If you want to know more, google star grounding or do a search on this forum.
Chances of me getting to the Big Easy are pretty thin, so I'll make do with photos of your WORKING buffer.
Cheers!
Capacitors are not so much a technical discussion as religion as I'm sure you know.
If you have worked out your HF and LF roll-off points, then use whatever you calculated for value. They need to be rated at least 2x the working voltage. Orange drops are fine.
Missed your q about the input load resistor. Yes, you will need one from the input to signal ground. 50k to 100k.
Speaking of signal ground, I presume you are familiar with star grounding. Essence is to ensure your signal ground is separated from power supply ground, and that both have just one common point each. If you want to know more, google star grounding or do a search on this forum.
Chances of me getting to the Big Easy are pretty thin, so I'll make do with photos of your WORKING buffer.
Cheers!
Nope no calculations for roll-off, got the 22nf from Wizard. I got the Cout by taking the formula at Wizard and inputting 30K instead of 1M. Processor Loop states: 150mV/30K input.
So, Cout=1/(2*Pi*5*30000), yes/no? how would I get this for Cin, use the value of Rg or is there a resistances value for the grid?
Hell, if ya make it to the US. I am always game for a road trip. Tell ya what When I get this thing working, I take a pic of it with a glass of Bourbon.
So, Cout=1/(2*Pi*5*30000), yes/no? how would I get this for Cin, use the value of Rg or is there a resistances value for the grid?
Hell, if ya make it to the US. I am always game for a road trip. Tell ya what When I get this thing working, I take a pic of it with a glass of Bourbon.
Ri.
Again, don't sweat it. I use 0.1uf cos I got a bulk quantity of these rated 630v el cheapo. 0.22 will give a different (but not by much) roll off. Meh, so what? Just stay in the order of magnitude.
Bourbon is good. Neat. A little ice.
Again, don't sweat it. I use 0.1uf cos I got a bulk quantity of these rated 630v el cheapo. 0.22 will give a different (but not by much) roll off. Meh, so what? Just stay in the order of magnitude.
Bourbon is good. Neat. A little ice.
Ok will do, like I said I have order a kit of caps and resistors so I can play around with the values.
Bourbon: Hell, right up my ally, two cubes please.
Bourbon: Hell, right up my ally, two cubes please.
Any thoughts on a power supply?
I need a transformer that will take 120VAC to 280VAC to feed into a rectafier.
From there the HT/B+ will go to pins 1 and 6. The 12V, AC or DC?, will go to pins 4 and 5.
I need a transformer that will take 120VAC to 280VAC to feed into a rectafier.
From there the HT/B+ will go to pins 1 and 6. The 12V, AC or DC?, will go to pins 4 and 5.
cathode follower has pretty good inherent PSRR so you don't need to go ott on the smoothing. If you can get a choke cheap, well and good, but otherwise a CRCRC should be fine. B+ current is pretty low too, so your C values don't have to be statospheric. PSUD II tells the story. Presume you are going for IN4007 or similar? May want to put some snubbers across them.
Leave your heater supply AC. Keeps it simple.
Cut glass tumbler, heavy weight. Keeps the flavour and temperature better
Cheers!
Leave your heater supply AC. Keeps it simple.
Cut glass tumbler, heavy weight. Keeps the flavour and temperature better
Cheers!
My First Tube Power Supply
Could I use the IN4007 with the circut? Would just need to figure out the values. Guess it is time to learn to use PSUD.
So the heater supply would come straight from the transformer.
Could I use the IN4007 with the circut? Would just need to figure out the values. Guess it is time to learn to use PSUD.
So the heater supply would come straight from the transformer.
yep IN4007 is fine. Model it and see. Plenty of easy available power supply transformers for you in the US of A. Or find an old valve radio and gut it for the transformer - it'll produce all you ever need for this application.
Cool,
I have an old trans that came out of a tube rectified power supply. Might need to see what it is putting out. I have been working with PSUD, but I can't figure out how to put cap bypassed resistor before the diodes.
Oh well back to the work week.
Riki
I have an old trans that came out of a tube rectified power supply. Might need to see what it is putting out. I have been working with PSUD, but I can't figure out how to put cap bypassed resistor before the diodes.
Oh well back to the work week.
Riki
your needs are wildly different. Tim points out two things in his write up - the pre he has built has a LOT of gain (not what you want or even need), and at 150V B+ he had problems getting tubes to bias correctly. I'm not surprised!
If you ever need to build a pre-amp for a guitar, a microphone of some other low output device, this is worth considering, but not today.
PSUD won't let you put a resistor before the rectifier. It assumes all secondary winding resistance is in the winding. Why do you want a res/cap pair there anyway?
If you ever need to build a pre-amp for a guitar, a microphone of some other low output device, this is worth considering, but not today.
PSUD won't let you put a resistor before the rectifier. It assumes all secondary winding resistance is in the winding. Why do you want a res/cap pair there anyway?
In post #34 there is a link to Gabe's website, he helped me with troubleshooting a magnavox tube amp. It had/has some bad resistors.
Gabe puts a resistor before the diode with a cap bypassing the diode to help absorb the spikes from the diode switching off.
I was only interested in the PS section of his drawing. Could I just use one power transformer with 280VAC on the secondary to meet my needs?
Are the values shown a pretty standard starting point?
What would be better a full wave or bridge. Full wave seems simpler, but can't I just buy the bridge?
Riki
Gabe puts a resistor before the diode with a cap bypassing the diode to help absorb the spikes from the diode switching off.
I was only interested in the PS section of his drawing. Could I just use one power transformer with 280VAC on the secondary to meet my needs?
Are the values shown a pretty standard starting point?
What would be better a full wave or bridge. Full wave seems simpler, but can't I just buy the bridge?
Riki
ok, gotcha now.
The resistors are not strictly necessary. They are a precaution, probably because the supply wasn't modelled before it was built. Do your modelling in PSUD and you will likely find its not needed.
The snubbers on the diodes ARE necessary, no question.
Bridge or FW will just depend on the transformer configuration you have. Run what ya brung as they say in redneck motorracing. They are just different means to the same end. FW will tend to have higher transformer secondary impedance and so slower, gentler rise time at start up. Bridge will tend to supply more current for a given package size.
For your purposes and at the voltage/current you are looking for, it doesn't matter too much.
The resistors are not strictly necessary. They are a precaution, probably because the supply wasn't modelled before it was built. Do your modelling in PSUD and you will likely find its not needed.
The snubbers on the diodes ARE necessary, no question.
Bridge or FW will just depend on the transformer configuration you have. Run what ya brung as they say in redneck motorracing. They are just different means to the same end. FW will tend to have higher transformer secondary impedance and so slower, gentler rise time at start up. Bridge will tend to supply more current for a given package size.
For your purposes and at the voltage/current you are looking for, it doesn't matter too much.
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