Bad news to read. Would you kindly enlighten me about "low voltage drop rectifier (5AR4) and a choke with probably low DCR"
Just note that, as Francois said, 300 ohms may be a bit much. Something between 250 and 300 should do, but unfortunately it
is difficult to give an exact value.
Also the dissipation is expected to be around 5W, therefore anything of 15W and up is fine, there are plenty of cheap high power resistors in metal cases.
6A3sUMMER is right in pointing out that again you have to achieve a steady quescent state before you measure your volteages (and calculating your currents, dissipation, etc). On the other hand, if something is amiss you don’t want to burn up your precious EL84s.
Rather than burning up B+ volts to heat with a resistor I also favor 6A3sUMMER’s approach of dialing-in the correct B+ with a psuedo-choke input filter but didn’t want to get into those details (yet) - probably better to do this with the aid of PSUDII to get the input cap value correct with fewer trails.
Francois, thanks for your reply.
Ive been uploading schematic, but of course i've never specified the exact components fitted, but yes they are 300 ohms.
I've been thinking (strange for me!) that R1 (150 Ohm 5 Watt) was suggested to be changed in order to 'remove' any remaining PSU noise.
Perhaps wiring in circuit a 150 Ohm 5 Watt, to begin with, check the B+ and if needed increase the value closer to what jcalvarez has suggested?
If in the original design R1 is only a 5 watt, increasing the wattage to a 25 Watt seems a bit high?
To use the PSUDII simulator is way beyond me......
How does the circuit of R2-150K, R4-150K and R3-30K effect the B+?
Could these values be altered to lower the B+ ?
Again thanks for your assistance
The rectifier and the choke both have internal resistance, therefore some voltage is lost (dropped) across them:
Different rectifier tubes have different internal resistance, therefore the voltage lost in the rectifier varies. It happens that the 5AR4 has a very small internal resistance, therefore the voltage lost is very small.
It is a similar situation with the choke. DCR is Direct Current Resistance, basically resistance due to the fact that a choke is a long wire. That resistance means there will be a voltage drop across the chole when you apply DC current. Chokes with relatively small inductance like yours tend to have a low DCR, less voltage drop. But I do not have details for the choke you got.
Back to the 5AR4, there are tables around the net, not sure how accurate they are:
Indeed he is right. Changing the input cap to 10uF should do the trick, at least according to PSU designer.
Thanks 6A3sUMMER for your reply.
B+ secondary winding = 610-612VAC
Choke: 1.5H 200mA
Would you mind explaining what happens when: -
Disconnect the 47uF cap that is before the choke and then connect it to the point right after the choke (in parallel with the 150uF cap).
Now, the B+ is probably a little to low, so . . .
And then connect a 1uF cap right before the choke, where the 47 uF cap was before.
A 0.5uF, 2uF or 3uf cap might be needed to put the B+ at the voltage you want it.
Again many thanks
B+ secondary winding = 610-612VAC
Choke: 1.5H 200mA
Would you mind explaining what happens when: -
Disconnect the 47uF cap that is before the choke and then connect it to the point right after the choke (in parallel with the 150uF cap).
Now, the B+ is probably a little to low, so . . .
And then connect a 1uF cap right before the choke, where the 47 uF cap was before.
A 0.5uF, 2uF or 3uf cap might be needed to put the B+ at the voltage you want it.
Again many thanks
Its just amazing the support given here, my warmest thanks to you all.
Changing the input cap to a 1uF etc. i dont really understand the electronics behind this move, but obviously 6A3sUMMER and you guys know your stuff.
I wonder if the Tubelab designer G.Anderson might shred some light? I actually emailed him yesterday, hopefully he'll reply soon.
I now need to read fully all the posts that have appeared here today.
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I tried the suggestion of 6A3sUMMER in PSU Designer II with different values.
I got the biggest voltage drop at C1 with a capacity of 1.5µF.
A change from C2 to 150µF did not produce any significant values.
I got the biggest voltage drop at C1 with a capacity of 1.5µF.
A change from C2 to 150µF did not produce any significant values.
Code:
PT sec. 333V / L1 = 1.5H 56 Ohm / C2 = 200µF / R1 = 5K Ohm
C1:
100nF - 350V
500nF - 390V
1.0µF - 323V
1.5µF - 293V
2.0µF - 298V
3.0µF - 332V
4.0µF - 367V
PT sec. 366V / L1 = 1.5H 56 Ohm / C2 = 200µF / R1 = 5K Ohm
C1:
100nF - 385V
500nF - 429V
1.0µF - 356V
1.5µF - 322V
2.0µF - 328V
3.0µF - 366V
4.0µF - 403V
PT sec. 333V / L1 = 1.5H 56 Ohm / C2 = 200µF / I1 = 100mA
C1:
100nF - 342V
500nF - 371V
1.0µF - 284V
1.5µF - 284V
2.0µF - 287V
3.0µF - 306V
4.0µF - 341V
PT sec. 366V / L1 = 1.5H 56 Ohm / C2 = 200µF / I1 = 100mA
C1:
100nF - 379V
500nF - 417V
1.0µF - 315V
1.5µF - 314V
2.0µF - 318V
3.0µF - 342V
4.0µF - 384V
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@stonegreen, thank you for doing those PSUDII trials; very kind of you.
Couple of questions: I wonder why you chose to do the transformer secondary at 330-0-330, and 366-0-366. I thought @calpe is measuring ~310-0-310Vac unloaded. The primary resistance of 31 Ohm is probably too low - I wonder if @calpe could measure the actual resistance on his transformer. Also, the amplifier will definitely draw more than 100 ma on average from the HV supply; I think about 170 ma total is realistic.
I suggest you do another trial run with the new parameters to help our friend. However, I am a bit hesitant to to use such a small cap as C1. Minding the ripple current on C1, it must be a film cap, and I would like a value in the range of 2.5-10 uF. Also using a resistor in series prior to C1 will be beneficial, but due to the PCB it would be more convenient to have a resistor in each of the transformer HV leads before they reach the PCB - value about 100 Ohms. I think that could be modeled in PSUDII as one 50 Ohm resistor after the rectifiers and before C1.
Couple of questions: I wonder why you chose to do the transformer secondary at 330-0-330, and 366-0-366. I thought @calpe is measuring ~310-0-310Vac unloaded. The primary resistance of 31 Ohm is probably too low - I wonder if @calpe could measure the actual resistance on his transformer. Also, the amplifier will definitely draw more than 100 ma on average from the HV supply; I think about 170 ma total is realistic.
I suggest you do another trial run with the new parameters to help our friend. However, I am a bit hesitant to to use such a small cap as C1. Minding the ripple current on C1, it must be a film cap, and I would like a value in the range of 2.5-10 uF. Also using a resistor in series prior to C1 will be beneficial, but due to the PCB it would be more convenient to have a resistor in each of the transformer HV leads before they reach the PCB - value about 100 Ohms. I think that could be modeled in PSUDII as one 50 Ohm resistor after the rectifiers and before C1.
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Thanks Stonegreen for assisting.
Just a bit confused by the capacitor values you show.
nF or uF?
6AsUMMER mentioned to fit in place of C1 with values between 0.5uF - 3uF.
C2 would be the original value of 150uF plus placing in parallel the original C1 of 47uF.
calpe,
Your power mains are 50Hz, Right? That means full wave rectification will give 100Hz to your B+ filter.
Cap input filter:
1.5H is about 940 Ohms of inductive reactance, it is preceded by 47uF (leave it in place), and followed by 150uF.
If you replace the choke with a 300 Ohm resistor, yes the B+ voltage will be reduced.
However, the 100Hz ripple on the B+ will go up.
If you choose the simplest solution that does not increase the 100 Hz ripple, then connect the 300 Ohm resistor in Series with the 1.5H choke.
(note: this solution is made easier since we now have more information about your choke, etc.)
Choke input filter:
If you want to use a pseudo choke input filter to drop the B+ voltage, a 1.5H 200mA choke is not nearly enough inductance.
I recommend using at least 5H with at least 200mA rated choke, Hammond 193H for example.
I can see why they used 47uF before the choke, 1.5H does not do a lot of filtering.
Now why would anybody want to use a choke input filter, instead of using a 300 Ohm resistor that gets hot, in order to drop B+ voltage?
Cooler running power transformer.
More stable B+ voltage when a push pull amplifier draws more than quiescent current when the music is played louder.
Less resistors to put heat into the bottom of the amplifier (like the 300 Ohm resistor).
Drops B+ voltage to where you want it.
In answer to your question . . .
Since you had the 47uF cap already, that is why I had you put it in parallel with the 150uF cap, that helps to reduce the ripple a little bit.
But you could save the space used up by the 47uF, but you will need at least a 5H choke to do a pseudo or real choke input filter.
Since I do not know the current your amplifier will draw, I can not predict the value (uF) of the new cap (1uF, 4uF, 0.5uF, etc.) that is after the rectifier, and at the input of the choke.
Just my opinions.
Have fun building and listening!
Your power mains are 50Hz, Right? That means full wave rectification will give 100Hz to your B+ filter.
Cap input filter:
1.5H is about 940 Ohms of inductive reactance, it is preceded by 47uF (leave it in place), and followed by 150uF.
If you replace the choke with a 300 Ohm resistor, yes the B+ voltage will be reduced.
However, the 100Hz ripple on the B+ will go up.
If you choose the simplest solution that does not increase the 100 Hz ripple, then connect the 300 Ohm resistor in Series with the 1.5H choke.
(note: this solution is made easier since we now have more information about your choke, etc.)
Choke input filter:
If you want to use a pseudo choke input filter to drop the B+ voltage, a 1.5H 200mA choke is not nearly enough inductance.
I recommend using at least 5H with at least 200mA rated choke, Hammond 193H for example.
I can see why they used 47uF before the choke, 1.5H does not do a lot of filtering.
Now why would anybody want to use a choke input filter, instead of using a 300 Ohm resistor that gets hot, in order to drop B+ voltage?
Cooler running power transformer.
More stable B+ voltage when a push pull amplifier draws more than quiescent current when the music is played louder.
Less resistors to put heat into the bottom of the amplifier (like the 300 Ohm resistor).
Drops B+ voltage to where you want it.
In answer to your question . . .
Since you had the 47uF cap already, that is why I had you put it in parallel with the 150uF cap, that helps to reduce the ripple a little bit.
But you could save the space used up by the 47uF, but you will need at least a 5H choke to do a pseudo or real choke input filter.
Since I do not know the current your amplifier will draw, I can not predict the value (uF) of the new cap (1uF, 4uF, 0.5uF, etc.) that is after the rectifier, and at the input of the choke.
Just my opinions.
Have fun building and listening!
Thank you jcalvarez. From your tests C1 would need to be changed to 6.8uF (450V) and C2 to change to a 150uF (450v) to obtain a B+ of 327v ?
Thank you 6A3sUMMER.
Yes our AC should be 240V at 50Hz. Unfortunately, as i've already stated i measured the other day and it was close to 248, thus i used the 250V input on the mains Tx.
Pseudo choke input filter... i need to do some reading about this.
Clearly the changing of the resistor value is a quicker solution, but heat i think needs to be avoided and of course your explanation in your post 437, needs to be taken on board.
I think using a Pseudo choke input filter will be better.
So the choke (ex-R1) will need to be a 5H 200mA, you've recommended the Hammond 193H.
The replacement of R1 to a 1.5H choke was suggested some time ago, to remove 'remaining PSU noise'.
Locally there are no electronic spares suppliers, so everything is ordered from U.K., U.S.A. or suppliers in Europe, adding shipping & import duty costs.
This build will be finished, so i'll be looking into the choke later today.
Install a Pseudo choke input filter
C1 is still mounted before the choke. So this i will need to fit after the choke in parallel with C2 150uF 450V?
Or will i need to change the value of C2 to a 200uF 450V (C1 + C2=200uF) ?
ex-R1 needs to be a 5H 200mA choke? A Hammond 193H.
C1 will need to be tested using values between 0.5uF and 4uF?
With many thanks
Yes our AC should be 240V at 50Hz. Unfortunately, as i've already stated i measured the other day and it was close to 248, thus i used the 250V input on the mains Tx.
Pseudo choke input filter... i need to do some reading about this.
Clearly the changing of the resistor value is a quicker solution, but heat i think needs to be avoided and of course your explanation in your post 437, needs to be taken on board.
I think using a Pseudo choke input filter will be better.
So the choke (ex-R1) will need to be a 5H 200mA, you've recommended the Hammond 193H.
The replacement of R1 to a 1.5H choke was suggested some time ago, to remove 'remaining PSU noise'.
Locally there are no electronic spares suppliers, so everything is ordered from U.K., U.S.A. or suppliers in Europe, adding shipping & import duty costs.
This build will be finished, so i'll be looking into the choke later today.
Install a Pseudo choke input filter
C1 is still mounted before the choke. So this i will need to fit after the choke in parallel with C2 150uF 450V?
Or will i need to change the value of C2 to a 200uF 450V (C1 + C2=200uF) ?
ex-R1 needs to be a 5H 200mA choke? A Hammond 193H.
C1 will need to be tested using values between 0.5uF and 4uF?
With many thanks