I'm building a 5AR4 rectified power supply for a preamp I have with one ECC40 valve in it. It's been designed to output 440V HT. As I don't have a variac, would a high wattage dummy load resistor be appropriate?
R = 440 / 30 is about a 15 ohm load. What would an appropriate wattage be? Thanks!
R = 440 / 30 is about a 15 ohm load. What would an appropriate wattage be? Thanks!
30 amps current ??? I don't think you mean that!
30mA makes it 15K, much more reasonable.
W = VxI = 440x0.03 = 15watts approx. So a BIG resistor or a metal clad one on a large heatsink
30mA makes it 15K, much more reasonable.
W = VxI = 440x0.03 = 15watts approx. So a BIG resistor or a metal clad one on a large heatsink
Yes, but - 15watts of heat is a LOT!
So you need to check on the heatsinking, or use (for example) 10 1R5 5W wired in series.
So you need to check on the heatsinking, or use (for example) 10 1R5 5W wired in series.
30mA for a single ECC40??
It has a limit of 10mA per triode section and in preamp duty it is typically run between 1-4 mA.
A GZ34/5AR4 is serious overkill (250mA capacity) here too (not that that stopped me from putting it in a preamp 🙄)
It has a limit of 10mA per triode section and in preamp duty it is typically run between 1-4 mA.
A GZ34/5AR4 is serious overkill (250mA capacity) here too (not that that stopped me from putting it in a preamp 🙄)
You are correct. I got a wonderful deal on a massive PT pulled from a 1960s HF transmitter. The secondaries are:
(2) 5V @ 3A, 6.3V @ 5A, 12.6V CT @ 6A (for balance and noise suppression, thin gauge), and 350-320-0-320-350V @ 1A
I have two Leak preamps that I wish to provide HT and filament for, but not concurrently. However, I would like to expand it's load in the future to include an older Brenell three valve tape recorder whose power supply is fried. I am an amateur and this is my first PS design, though I do realise the GZ34 is a bit overkill for the inital singular valve. 🙂
(2) 5V @ 3A, 6.3V @ 5A, 12.6V CT @ 6A (for balance and noise suppression, thin gauge), and 350-320-0-320-350V @ 1A
I have two Leak preamps that I wish to provide HT and filament for, but not concurrently. However, I would like to expand it's load in the future to include an older Brenell three valve tape recorder whose power supply is fried. I am an amateur and this is my first PS design, though I do realise the GZ34 is a bit overkill for the inital singular valve. 🙂
P = E² / R
I = E / R
And per the original 'mishap' in calculation, don't forget milliamps vs. amps. I calculate about 13 watts on that 15 kΩ resistor. And yes, 10 ea of the 1.5 kΩ resistors in series would be fine. ALSO gives you a "variable resistor" at each tap (but watch the power!)
Indeed … you could put a series of them together
To make a universal resistance chain. This shows that if you were to standardize on 5 watt resistors, the chain has a minimum of 5 watts (of course, single resistor) of dissipation, and a maximum of over 50 watts, based on the “weakest link” being the final resistors. Note also that there are LOT of useful resistance values in the chain!
GoatGuy
I = E / R
And per the original 'mishap' in calculation, don't forget milliamps vs. amps. I calculate about 13 watts on that 15 kΩ resistor. And yes, 10 ea of the 1.5 kΩ resistors in series would be fine. ALSO gives you a "variable resistor" at each tap (but watch the power!)
Indeed … you could put a series of them together
Code:
¹/₂₄ >sum of last R 5
>R value chain of chain max of chain
1.0 1.0 100% 5
1.10 2.1 52% 9.5
1.21 3.3 37% 13.7
1.33 4.6 29% 17.4
1.47 6.1 24% 20.8
1.62 7.7 21% 23.9
1.78 9.5 19% 26.7
1.96 11.5 17% 29.3
2.15 13.6 16% 31.6
2.37 16.0 15% 33.7
2.61 18.6 14% 35.6
2.87 21.5 13% 37.4
3.16 24.6 13% 39.0
3.48 28.1 12% 40.4
3.83 31.9 12% 41.7
4.22 36.2 12% 42.9
4.64 40.8 11% 44.0
5.11 45.9 11% 44.9
5.62 51.5 11% 45.8
6.19 57.7 11% 46.6
6.81 64.5 11% 47.4
7.50 72.0 10% 48.0
8.25 80.3 10% 48.6
9.09 89.4 10% 49.2
10.00 99.4 10% 49.7
11.01 110.4 10% 50.1
12.12 122.5 10% 50.6
13.34 135.8 10% 50.9
14.68 150.5 10% 51.3
16.16 166.7 10% 51.6
17.78 184.5 10% 51.9
19.57 204.0 10% 52.1
21.54 225.6 10% 52.4
23.71 249.3 10% 52.6
26.10 275.4 9% 52.8
28.73 304.1 9% 52.9
31.62 335.7 9% 53.1
34.81 370.5 9% 53.2
38.31 408.9 9% 53.4
42.17 451.0 9% 53.5
46.42 497.4 9% 53.6
51.09 548.5 9% 53.7
56.23 604.8 9% 53.8
61.90 666.7 9% 53.9
68.13 734.8 9% 53.9
74.99 809.8 9% 54.0
82.54 892.3 9% 54.1
90.85 983.2 9% 54.1To make a universal resistance chain. This shows that if you were to standardize on 5 watt resistors, the chain has a minimum of 5 watts (of course, single resistor) of dissipation, and a maximum of over 50 watts, based on the “weakest link” being the final resistors. Note also that there are LOT of useful resistance values in the chain!
GoatGuy
12,6V@6A thin gauge? 6A wire it's so thick you don't wind it on, you fold it.
If 6A I see a nice PP GU-50 power amp in your future 😉
If 6A I see a nice PP GU-50 power amp in your future 😉
That's how it is documented, yes. In reality though, the wire is only 20ga!
Goatguy- That is fantastic! I so happen to have a number of these onhand as well!
Goatguy- That is fantastic! I so happen to have a number of these onhand as well!
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20AWG is that something like 1,5A? Preamp only I guess.
Did you measure the (unloaded) voltages? With no or a light load they could be higher than specified. When you load the 6,3V with considerably less than the rated 5A (i.e. a preamp) you could be overloading your heaters a bit. If it is just a single ECC40 you may as well rectify the 12,6V and run it through a regulator for 6,3V dc.
Did you measure the (unloaded) voltages? With no or a light load they could be higher than specified. When you load the 6,3V with considerably less than the rated 5A (i.e. a preamp) you could be overloading your heaters a bit. If it is just a single ECC40 you may as well rectify the 12,6V and run it through a regulator for 6,3V dc.
I haven't powered the supply yet. I am wrapping up construction as it is very much a homebrew. The design was done in PSUD2 by an aquaintance as my skill with computers is marginal. As I don't have a variac, I wanted to ensure I could test it prior to attaching the preamp.
The plan was to use the 320 secondary to mitigate the low load placed on the transformer with a single valve though your idea regarding the 12.6V tap is good. If I utilise the 6.3V for the heaters, I will need to either run it through a pot or a virtual CT, as it's lacking one.
I won't get back to this until this evening or more likely, tomorrow, due to work.
The plan was to use the 320 secondary to mitigate the low load placed on the transformer with a single valve though your idea regarding the 12.6V tap is good. If I utilise the 6.3V for the heaters, I will need to either run it through a pot or a virtual CT, as it's lacking one.
I won't get back to this until this evening or more likely, tomorrow, due to work.
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