Choky and others,
Please, have a look at the extremely simplified schematic below. If I set it up like this, will I still need 2 VR stacks? I would not think so, because I limit the current through the stack by means of the current source.
Please, have a look at the extremely simplified schematic below. If I set it up like this, will I still need 2 VR stacks? I would not think so, because I limit the current through the stack by means of the current source.
An externally hosted image should be here but it was not working when we last tested it.
I don't think it is going to work correctly with just one stack. By limiting the imcomming current you may not have enough currrent available for the stack to ignite the gas... if you limit the current available they might not turn on. You have a total of more Current draw from both line stages than the stack is capable of. I think one stack is good for only 40 ma. All line stage circuitry current draw has to be equal to the draw of the actual stack itself for it to work properly. This same is also true of solid state shunt regulators.
Mark
Mark
I am trying to learn something here, and I really appreciate your feedback.
I do not see how I am limiting the current to stack since I am feeding it with 20mA constantly.
I was not aware of the fact that the stack has to draw the same as the all line stage circuitry current draw to work correctly. Please, have a look at Lynn Olsens "Raven" below. A current source feeds 20mA to the VR tube, and 40mA to the ECC99. I do not see how this differs from my simplified schematic.
I do not see how I am limiting the current to stack since I am feeding it with 20mA constantly.
I was not aware of the fact that the stack has to draw the same as the all line stage circuitry current draw to work correctly. Please, have a look at Lynn Olsens "Raven" below. A current source feeds 20mA to the VR tube, and 40mA to the ECC99. I do not see how this differs from my simplified schematic.
But you are stacking two VR-150's so thats twice as much current to operate the pair or 40 ma just for two VR-150's then you have 50ma draw from the pair of line stages.... that is more than one stack of VR-150's will sink. In fact my total current draw off my regulated bench supply is 130ma. Two stacks of VR-150at 80 ma and both line stages at 50ma =130ma. If your line stages draw more current than the VR-150's will sink they might not stay ignited since the B+ may sink below the ignition point of the VR's.
Mark
Mark
A VR150 is specced for 5 to 40 mA. Two (or 10 or any number) in SERIES will still want 5 to 40 mA. Mr Kirchoff figured this out a long time ago. A VR150 works best at 10 to 30mA. I think that the circuit in post #362 has a chance of working is the filaments are all warm before the B+ is applied. Here is my thinking:
Case 1 (all filaments are hot before B+ is applied)
The VR tubes are non conducting at the instant the B+ is applied. The first CCS will attempt to force 75 mA but the combined load is 50 mA (set by the other two CCS's) this will cause the 75mA CCS to saturate ( minimum voltage drop). The voltage across the two VR tubes will climb toward the supply voltage (less the loss in the CCS). If the supply voltage is higher than the strike voltage of the two VR tubes ( 2X 160 to 185 volts) they will fire. They will then consume the extra 25 mA and bring the voltage down to 300 volts. As long as the CCS's are stable the VR current = load current is not a major issue. That rule of thumb was written long before people figured out how to feed a VR tube with a CCS. The CCS must have a low saturation voltage for this to work, which usually means a solid state CCS.
Case 2 (cold filaments when B+ is applied) Nothing is conducting when B+ is applied. The first CCS attempts to force 75mA. The audio tubes associated with each 25mA CCS are cold. The current has only one place to go. All 75mA will go through the VR tubes until the other tubes warm up. This will make them unhappy. How do you fix this? Either delay the B+, OR use two CCS's in place of the 75 mA CCS each feeding a VR stack and a 25mA circuit. Set each one to about 40 mA. That way the VR tubes can eat the entire current until the audio tubes warm up.
Case 1 (all filaments are hot before B+ is applied)
The VR tubes are non conducting at the instant the B+ is applied. The first CCS will attempt to force 75 mA but the combined load is 50 mA (set by the other two CCS's) this will cause the 75mA CCS to saturate ( minimum voltage drop). The voltage across the two VR tubes will climb toward the supply voltage (less the loss in the CCS). If the supply voltage is higher than the strike voltage of the two VR tubes ( 2X 160 to 185 volts) they will fire. They will then consume the extra 25 mA and bring the voltage down to 300 volts. As long as the CCS's are stable the VR current = load current is not a major issue. That rule of thumb was written long before people figured out how to feed a VR tube with a CCS. The CCS must have a low saturation voltage for this to work, which usually means a solid state CCS.
Case 2 (cold filaments when B+ is applied) Nothing is conducting when B+ is applied. The first CCS attempts to force 75mA. The audio tubes associated with each 25mA CCS are cold. The current has only one place to go. All 75mA will go through the VR tubes until the other tubes warm up. This will make them unhappy. How do you fix this? Either delay the B+, OR use two CCS's in place of the 75 mA CCS each feeding a VR stack and a 25mA circuit. Set each one to about 40 mA. That way the VR tubes can eat the entire current until the audio tubes warm up.
You're right! Two in series is the same ...two in parallel double things. Donno what I was thinking.... My hookup with two sets fed from a common source and then each set feeding one 12B4 works great. So this means mine are burnning up about 10ma of extra current when the 12B4 is active. I still think he is borderline in getting it to work and his may be further complicated by having to use relays to delay B+......
The twin sets of VR-150's definately sounds alot better than the solid state pass type regulator board that I was using. Am going to build Allen Wrights Supereg which combines the best of both worlds so we'll see what that one sounds like.....
Mark
The twin sets of VR-150's definately sounds alot better than the solid state pass type regulator board that I was using. Am going to build Allen Wrights Supereg which combines the best of both worlds so we'll see what that one sounds like.....
Mark
And I haven't even blown any of these up yet. While experimenting with VR tubes for a screen grid reg which draws a current which can vary over a wide range, I was using a CCS fed VR stack for the reference which was tied to the base of a large HV NPN transistor (emitter follower) to source the current. The transistor also acts as a capacitance multiplier for a real quiet supply.
Now that I am (temporarilly) between projects at work, I have some time to catch up. I have been adding 1 or 2 pages per week with more to come.
Do the 12B4s benefit from a regulated DC heater supply over just a DC one? I'm thinking of powering up the heaters with the 5V winding, bridge-rectified with a CRC. 5V seems to be too little to be regulated with a 7806. Or can I take 2 5V windings (my transformers has 2 5V windings) to make it 10V, then regulate 12V from the theoritical 14V with a 7812 after the bridge rectifier? Do I hook up the 5V windings by connecting one of the "0" to the other '5" then tap the 10Vac from the unconnected "0" and "5"? The current capability would not differ as if I was using only one winding right?
pengboon said:
first-pretty irrelevant-nice and slow warm up of heater (no flash on especially Philips toobz)
second- somewhat better sounding,mebbe even less noise in critical H-K "installations" .......in any case CCS is evidently (if that is proper word) better for DH toobz, and for IDH toobz that difference is less hearable,but still it is......
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