I am asking about the caps after the 500-ohm resistors... DO they affect the voltage in any way?
The amp requires +150VDC, and I don't know what the rectifier (5Y3GT) requires because I don't know anything about it... or most other tubes for that matter. What is the minimum mA rating I should have? In the circuit, it says 100mA, but I am driving a much lower voltage, so does that matter? In case this matters, the amp tubes are one E88CC and one 6AS7G.
Thanks
t_g,
The value of the smooothing caps will affect the voltage out.
You must get to use the circuit simulator that's been suggested. Then all will become clear to you. The relationship is not easy to explain in words.
The rectifier will need heater power 5volts * xA =5x watts - to add to the transformer VA rating.
For the sake of simplicity VA = watts in this case.
To decide how many mA you need; find the HP-amp tube type, and decide how much current you'll run though it. Multiply by 2 for 2 channels. That's how much DC current. Now multiply by about 1.7, and you will have the AC current.
The 1.7 should be 1.4, but the fudge factor compensates for some other losses that take place.
Cheers,
The value of the smooothing caps will affect the voltage out.
You must get to use the circuit simulator that's been suggested. Then all will become clear to you. The relationship is not easy to explain in words.
The rectifier will need heater power 5volts * xA =5x watts - to add to the transformer VA rating.
For the sake of simplicity VA = watts in this case.
To decide how many mA you need; find the HP-amp tube type, and decide how much current you'll run though it. Multiply by 2 for 2 channels. That's how much DC current. Now multiply by about 1.7, and you will have the AC current.
The 1.7 should be 1.4, but the fudge factor compensates for some other losses that take place.
Cheers,
Frank,
For determining transformer heat rise due to current taken, 1.7 times the DC current is more realistic than 1.4. Of course the exact figure depends on the filter circuit used.
If your transformer maker builds in safety margins for you, you're welcome to use them. I expect nothing.
Cheers,
For determining transformer heat rise due to current taken, 1.7 times the DC current is more realistic than 1.4. Of course the exact figure depends on the filter circuit used.
If your transformer maker builds in safety margins for you, you're welcome to use them. I expect nothing.
Cheers,
INTERESTING.
Hi,
I'm with you...I don't expect any good news form a regular xformer either.
Another point to go into the PSU thread is the importance of the xformer(s).
Well done...now I'll have to split up my post into at least to separate replies for the PSU thread.
Ok.I feel the "Kasteelbier' kicking in already.
Chin,
Hi,
I'm with you...I don't expect any good news form a regular xformer either.
Another point to go into the PSU thread is the importance of the xformer(s).
Well done...now I'll have to split up my post into at least to separate replies for the PSU thread.
Ok.I feel the "Kasteelbier' kicking in already.
Chin,
Ok, I mostly understand what you said, but I am confused in one or two spots...
One the 5volts * xA =5x watts thing, where to I find x... obviously it is some unknown variable but what will it stand for?
Also on the VA thing, if it eqauls watts, which watts might these be? How are they related to other things?
I think I can get the mA thing, though. lol
I am about to try...
One the 5volts * xA =5x watts thing, where to I find x... obviously it is some unknown variable but what will it stand for?
Also on the VA thing, if it eqauls watts, which watts might these be? How are they related to other things?
I think I can get the mA thing, though. lol
I am about to try...
t_g,
Sorry, the x is the heater current of the 5y3. I couldn't remember it.
Power is measured in the unit: watt.
P=I * V (watts)
Where I is the current in amps, and V is the voltage in volts.
Now since ohms law states: V=I*R,
with a little work we can get:
P=V^2/R, and P=I^2*R, which are useful.
Don't forget that mA = A*10-^3.
Cheers,
Sorry, the x is the heater current of the 5y3. I couldn't remember it.
Power is measured in the unit: watt.
P=I * V (watts)
Where I is the current in amps, and V is the voltage in volts.
Now since ohms law states: V=I*R,
with a little work we can get:
P=V^2/R, and P=I^2*R, which are useful.
Don't forget that mA = A*10-^3.
Cheers,
Ok, I almost understand... but kinda not...
I looked up the tubes and got his info:
6AS7G: Heater- 6.3VAC/VDC @ 2.5A max
Plate current- 100mA min. 125mA max
Plate dissapation- 13W
E88CC: Heater- 6.3V @ 365mA
Cathode current- 25mA
Plate current- 15mA
Plate Dissapation- 1.8W
5Y3GT: Heater- 5VAC @ 2A
Plate current- 400mA per plate
max plate current 2.2A
I did try using these formulas for this, and ended up needing about a 250-0-250V transformer with 57VA @200mA. I think I am wrong. Pretty sure, actually...
I looked up the tubes and got his info:
6AS7G: Heater- 6.3VAC/VDC @ 2.5A max
Plate current- 100mA min. 125mA max
Plate dissapation- 13W
E88CC: Heater- 6.3V @ 365mA
Cathode current- 25mA
Plate current- 15mA
Plate Dissapation- 1.8W
5Y3GT: Heater- 5VAC @ 2A
Plate current- 400mA per plate
max plate current 2.2A
I did try using these formulas for this, and ended up needing about a 250-0-250V transformer with 57VA @200mA. I think I am wrong.
Pretty sure, actually...
OK, so far I have
5V*2A=10W or 10VA
After that, I hit confusion... if the amp tubes only get about 2/3 their max value, then the 6AS7G would only be at about 83, but its minimum is 100mA.
Also, if the 6AS7 heaters are 2.5A and the E88CC heaters are 365mA is there not trouble here?
For the total amp current, do I use the cathode or plate current? Both? One of them didn't have a cathode current listed, so I can't use that if I need it. And I leave the rectifier current out...
I am about to look at this again- I just had a thought. I think...
5V*2A=10W or 10VA
After that, I hit confusion... if the amp tubes only get about 2/3 their max value, then the 6AS7G would only be at about 83, but its minimum is 100mA.
Also, if the 6AS7 heaters are 2.5A and the E88CC heaters are 365mA is there not trouble here?
For the total amp current, do I use the cathode or plate current? Both? One of them didn't have a cathode current listed, so I can't use that if I need it. And I leave the rectifier current out...
I am about to look at this again- I just had a thought. I think...
TP guy,
You're making this harder than it needs to be. Forget the va crap.
Step 1: Add up all the "cathode currents" of all the tubes in the circuit. This does not include any diodes or rectifiers. You can find all these numbers in any tube manual.
Step 2: Once you have your number, say 100mA, consider the class of service. If it's class A, then you should go at least 2 times the current rating. So, in this example, 200mA.
Step 3: Consider the voltages needed. Usually, for modern tubes, a 300V supply is adequate. This will, of course, be center-tapped.... so in a catalog it will look like 300-0-300. The "zero" means the secondary is tapped in the middle. This will be grounded in most circuits.
Step 4: We need a rectifier. So, we need a 5V from the transformer. A 5Y3 requires 2 amps. So, we need another "secondary 5V winding" on our tranny. The 5Y3 is rated at 125mA as well, so it should be able to power our example circuit.
Step 5: We need filament power. From your tube manual, add up all the filaments currents of all the tubes in the circuit using 6.3V. Let's say we end up with 2.8 amps. So, we also need a "6.3V secondary winding", rated at 2.8A.... 3A will probably be closest.
We're done! We need to go shop for a transformer with these specs:
300-0-300V @200mA, 5V@2A, 6.3V@3A
If you can't find the exact numbers, go higher, but never lower on any of the ratings. Hope that helps!
You're making this harder than it needs to be. Forget the va crap.
Step 1: Add up all the "cathode currents" of all the tubes in the circuit. This does not include any diodes or rectifiers. You can find all these numbers in any tube manual.
Step 2: Once you have your number, say 100mA, consider the class of service. If it's class A, then you should go at least 2 times the current rating. So, in this example, 200mA.
Step 3: Consider the voltages needed. Usually, for modern tubes, a 300V supply is adequate. This will, of course, be center-tapped.... so in a catalog it will look like 300-0-300. The "zero" means the secondary is tapped in the middle. This will be grounded in most circuits.
Step 4: We need a rectifier. So, we need a 5V from the transformer. A 5Y3 requires 2 amps. So, we need another "secondary 5V winding" on our tranny. The 5Y3 is rated at 125mA as well, so it should be able to power our example circuit.
Step 5: We need filament power. From your tube manual, add up all the filaments currents of all the tubes in the circuit using 6.3V. Let's say we end up with 2.8 amps. So, we also need a "6.3V secondary winding", rated at 2.8A.... 3A will probably be closest.
We're done!
We need to go shop for a transformer with these specs:300-0-300V @200mA, 5V@2A, 6.3V@3A
If you can't find the exact numbers, go higher, but never lower on any of the ratings. Hope that helps!
Since I only need 150V, what is the minimum transformer voltage I could use? Isn't the 300-0-300 a bit much for this application?
I am having difficulty finding a transformer too... I just tried to look. If I finf one with a high enough current in mA (150+) then the rectifier heater goes to 3A, and the other ehater will be 2A-about 4A. What is the compromise here?
I am having difficulty finding a transformer too... I just tried to look. If I finf one with a high enough current in mA (150+) then the rectifier heater goes to 3A, and the other ehater will be 2A-about 4A. What is the compromise here?
tpg,
I see your confusion - the "5V@3A" does not mean the transformer draws 3 amps - it means it can feed a demand for 3 amps and still be within its limits.
So... if I have a bunch of tubes that draw 2.8 amps of filament current, any number higher than that rating is ok on your transformer. So, a 6.3V@20A winding would work great - although it's immense overkill.
RE: voltage
150V sounds very low for a supply voltage. Is this the intended plate voltage?
I see your confusion - the "5V@3A" does not mean the transformer draws 3 amps - it means it can feed a demand for 3 amps and still be within its limits.
So... if I have a bunch of tubes that draw 2.8 amps of filament current, any number higher than that rating is ok on your transformer. So, a 6.3V@20A winding would work great - although it's immense overkill.
RE: voltage
150V sounds very low for a supply voltage. Is this the intended plate voltage?
I, too, thought it was a bit low... Here is the scem:
It is using the E88CC and the 6AS7G, and I am not a fan of the original power supply, so I was trying different ones, and really wanted tube rectified, and yours was nice looking to me. And in the notes about this amp, it says C1, C2, R5 is shared between both channels.
It is nice to know I can use higher amp ratings... I found many transformers that could have been used that I ruled out because the A was wrong...
Doesn't the heater supply need to be regulated? Just a thought...
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It is using the E88CC and the 6AS7G, and I am not a fan of the original power supply, so I was trying different ones, and really wanted tube rectified, and yours was nice looking to me. And in the notes about this amp, it says C1, C2, R5 is shared between both channels.
It is nice to know I can use higher amp ratings... I found many transformers that could have been used that I ruled out because the A was wrong...
Doesn't the heater supply need to be regulated? Just a thought...
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