More voltage on screen than plate?
Just finished a new build based on this design. I used some unused 3.5k ohm transformers I had from a previous kit build which indicated a 46% UL tap. When testing voltages I'm seeing 331 B+, 320 at the plates but 326 at the screen. I'm assuming that I probably need a larger value resistor than the 100 ohm I've got in there based on the triode set-up of the design. Any recommendation on voltage I should be seeing at the screen and/or a resistor size I should be shooting for? I'd rather start off with some intelligently sourced ideas than keep swapping resistors in a cramped chassis. Thanks all!
Just finished a new build based on this design. I used some unused 3.5k ohm transformers I had from a previous kit build which indicated a 46% UL tap. When testing voltages I'm seeing 331 B+, 320 at the plates but 326 at the screen. I'm assuming that I probably need a larger value resistor than the 100 ohm I've got in there based on the triode set-up of the design. Any recommendation on voltage I should be seeing at the screen and/or a resistor size I should be shooting for? I'd rather start off with some intelligently sourced ideas than keep swapping resistors in a cramped chassis. Thanks all!
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Do you mean "more voltage on screen than plate"?
I notice that sch has duplicated parts number. It appears quite normal as screen tap has lower copper resistance (DCR) than the plate winding hence plate drops more voltage. Refer to the data curve for max screen voltage allowed, if the margin is small you can put a bigger resistor in the screen. You should still observe if screen is going red at full output, depending on whether max. screen dissipation (again refer data sheet) is exceeded or not.
I notice that sch has duplicated parts number. It appears quite normal as screen tap has lower copper resistance (DCR) than the plate winding hence plate drops more voltage. Refer to the data curve for max screen voltage allowed, if the margin is small you can put a bigger resistor in the screen. You should still observe if screen is going red at full output, depending on whether max. screen dissipation (again refer data sheet) is exceeded or not.
haha, yes, thank you, my bad, plate not grid....corrected
Looking at the schematic of the kit these transformers came from seems to indicate that this is normal, 5-10v higher voltage measured on the screen. Seemed backwards to be but I see your point here in terms of design.
Looking at the schematic of the kit these transformers came from seems to indicate that this is normal, 5-10v higher voltage measured on the screen. Seemed backwards to be but I see your point here in terms of design.
Really good actually, I dropped the dc heater part because I built it into a very small chassis. Of course i have a little bit of 60hz hum now, tried elevating the heater ct but no luck. Not bad enough for me to worry a lot about. First build from a schematic for me.
i think the remaining hum is likely from your power supply, not the heaters. that power supply attempts to smooth the ripple using brute force which seems to rarely work. simulate that power supply in psud and you'll get a feel for what's happening.
try adding a 100 ohm or 68 ohm resistor between the 2nd and 3rd capacitor before the B+ and reduce the capacitors after the 10k and 5k resistors to 47u. the power supply ripple will be greatly reduced according to psud2.
try adding a 100 ohm or 68 ohm resistor between the 2nd and 3rd capacitor before the B+ and reduce the capacitors after the 10k and 5k resistors to 47u. the power supply ripple will be greatly reduced according to psud2.
Interesting, I'll play around with it and see where that puts my voltages. I'd forgot I'd downloaded that ps emulator. Would guess at 5 or 10 watt resistor should do the trick?
Probably. When you sim it, psud will give the voltage drop across the resistor and power equals I squared R equals E squared over R
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Note also that
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
P = I²R
I in amps
R in Ω
P in watts.
Pretty straight forward… I in amps
R in Ω
P in watts.
P = (100 mA → 0.10 A)² × 100 Ω
P = 1 W
P = 1 W
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
just to clarify, i wasn't trying to be difficult with my earlier answer. i happened to be at a place where i couldn't look up the exact current to answer definitively and didn't want to answer incorrectly.
regardless, you should play with psud and swap in and out capacitors and resistors of varying values to get a feel for what works better and worse with respect to smoothing power supply ripple. you can gain a bunch of insight by doing that and looking at the results and it will make you better at designing these things.
regardless, you should play with psud and swap in and out capacitors and resistors of varying values to get a feel for what works better and worse with respect to smoothing power supply ripple. you can gain a bunch of insight by doing that and looking at the results and it will make you better at designing these things.
bubbazanetti,
Mode:
Are you going to use Triode wired mode?
Are you going to use Ultra Linear mode?
Are you going to use Beam Power mode (Beam Tetrode mode, as some call it)?
Tube type:
Are you going to use a 6L6GC?
Are you going to use any 6L6 tube type that is Not a 6L6GC?
Are you going to use a 5881?
Generally, many Ultra Linear circuits use the 100 Ohm screen resistor, or just a wire.
Because of the voltage drop of the DCR of 60% additional windings to the plate, the screen voltage is almost always larger than the plate voltage.
But with Ultra Linear, the screen voltage reduces at a rate of 40% of the plate voltage reduction, that occurs with signal.
Generally, Beam Power mode has a regulated screen voltage (for best Beam Power linearity). But sometimes a large resistance to the screen from the B+ is used, not as much linearity.
With Beam Power mode, a regulated screen voltage is most often hardest on the screen, versus the Ultra Linear mode, and the Triode Wired mode.
The reliability and tube life often depends on the Screen and Plate voltages, and the answers to the above questions.
An Example:
Look at the 807 Beam Power tube (Beam Tetrode tube as some call it).
Beam Power mode, maximum screen voltage, 300V (original specification).
Triode wired mode, maximum screen voltage, 400V
Ultra Linear mode, 40% Ultra Linear Tap, maximum screen voltage, 340V.
The 807 is similar to the 6L6.
The 807 is a Robust tube.
You can exceed the 807 maximum ratings, but at some point, Robust may become Busted.
Your Mileage May Vary.
Mode:
Are you going to use Triode wired mode?
Are you going to use Ultra Linear mode?
Are you going to use Beam Power mode (Beam Tetrode mode, as some call it)?
Tube type:
Are you going to use a 6L6GC?
Are you going to use any 6L6 tube type that is Not a 6L6GC?
Are you going to use a 5881?
Generally, many Ultra Linear circuits use the 100 Ohm screen resistor, or just a wire.
Because of the voltage drop of the DCR of 60% additional windings to the plate, the screen voltage is almost always larger than the plate voltage.
But with Ultra Linear, the screen voltage reduces at a rate of 40% of the plate voltage reduction, that occurs with signal.
Generally, Beam Power mode has a regulated screen voltage (for best Beam Power linearity). But sometimes a large resistance to the screen from the B+ is used, not as much linearity.
With Beam Power mode, a regulated screen voltage is most often hardest on the screen, versus the Ultra Linear mode, and the Triode Wired mode.
The reliability and tube life often depends on the Screen and Plate voltages, and the answers to the above questions.
An Example:
Look at the 807 Beam Power tube (Beam Tetrode tube as some call it).
Beam Power mode, maximum screen voltage, 300V (original specification).
Triode wired mode, maximum screen voltage, 400V
Ultra Linear mode, 40% Ultra Linear Tap, maximum screen voltage, 340V.
The 807 is similar to the 6L6.
The 807 is a Robust tube.
You can exceed the 807 maximum ratings, but at some point, Robust may become Busted.
Your Mileage May Vary.
Kuroguy,
Correct, he posted a schematic.
But, he also said:
"Just finished a new build based on this design. I used some unused 3.5k ohm transformers I had from a previous kit build which indicated a 46% UL tap. When testing voltages I'm seeing 331 B+, 320 at the plates but 326 at the screen."
Please note the word "Based on".
Without any other information, I can now conclude from His limited words above that He intends to build an amplifier with:
Ultra Linear, 46%.
5881
3.5k primary, and using the 46% UL tap.
326 Volts on the screen.
320V on the plate.
A 5881 maximum screen voltage is 270V (original specification).
What do you recommend to the original poster?
Correct, he posted a schematic.
But, he also said:
"Just finished a new build based on this design. I used some unused 3.5k ohm transformers I had from a previous kit build which indicated a 46% UL tap. When testing voltages I'm seeing 331 B+, 320 at the plates but 326 at the screen."
Please note the word "Based on".
Without any other information, I can now conclude from His limited words above that He intends to build an amplifier with:
Ultra Linear, 46%.
5881
3.5k primary, and using the 46% UL tap.
326 Volts on the screen.
320V on the plate.
A 5881 maximum screen voltage is 270V (original specification).
What do you recommend to the original poster?
Fair enough. I recommend he use 6l6gc (stealth edit) or he add a resistor and capacitor and wire it in pentode.
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6L6GC, it seems as though I'd be in spec with a 46 percent tap running in ultra-linear. no red plating or anything evident.
I'm very new to this. I've built two amps from schematics and they both work and sound pretty good but now I need to understand everything a bit better. Learn just enough to put it together.......listen, read, analyze, learn some more!
Is it possible to set up this whole PS in the emulator? The restrictions on a placing cap after cap without a resistor seem to be prohibiting it. Feel free to hit me up with a pm if anyone has any advice.
I'm very new to this. I've built two amps from schematics and they both work and sound pretty good but now I need to understand everything a bit better. Learn just enough to put it together.......listen, read, analyze, learn some more!
Is it possible to set up this whole PS in the emulator? The restrictions on a placing cap after cap without a resistor seem to be prohibiting it. Feel free to hit me up with a pm if anyone has any advice.
He also said "first build from a schematic" so I assumed (possibly incorrectly) that he built the schematic. Either of us may be correct, 6a3summer. I don't know which one of us assumed correctly.
Ah, that makes obvious sense, haha, thanks!
Only deviation from the original schematic is 1N4007 diodes cause i had them, no dc power supply, and somewhat off-spec output transformers.
Only deviation from the original schematic is 1N4007 diodes cause i had them, no dc power supply, and somewhat off-spec output transformers.
bubbazanetti,
Congratulations.
Glad you built it successfully, and are enjoying listening to it.
I built a low power amp for my computer, it uses an LM334 current sink/12AY7 phase splitter, and 6L6GC tubes in Ultra Linear push pull. Low power works fine for the near field listening I do there (about 3 feet speaker to ear).
Congratulations.
Glad you built it successfully, and are enjoying listening to it.
I built a low power amp for my computer, it uses an LM334 current sink/12AY7 phase splitter, and 6L6GC tubes in Ultra Linear push pull. Low power works fine for the near field listening I do there (about 3 feet speaker to ear).