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help with reading a rectifier rating chart ......

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Posted on April 20, 2015 at 06:44:12
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 Trying to make sure I am not over the top with the voltage on my 5ar4 in the 91A clone I just got operational.
I am getting about 860 vac on the plates at full line voltage (430vac per plate). Looking in the RCA tube manual under the 5AR4, under maximum ratings for AC per plate it says "see rating chart". It also says that average output current with cap input filtering is 225mA, or about 113 mA per plate I assume.
Looking at the chart and using 110 mA on the left and 430 vac on the bottom scale puts me below the maximum rating I think, but that is not "without load". Does that mean with all tubes removed? I might still be ok then, but I want to make sure.

 

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RE: help with reading a rectifier rating chart ......, posted on April 20, 2015 at 08:25:54
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 "It also says that average output current with cap input filtering is 225mA, or about 113 mA per plate I assume."

The diodes are never both on at the same time.

If the circuit is drawing 225ma. of current then each diode must be able to deliver 225ma. of current.

Looking at page one of the Amperex data sheet it says with a cap input filter and 150 ohms per plate of series resistance and 450vac per plate the tube will handle 250ma. of current draw.

Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: help with reading a rectifier rating chart ......, posted on April 20, 2015 at 08:42:37
Triode_Kingdom
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Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 "If the circuit is drawing 225ma. of current then each diode must be able to deliver 225ma. of current."

Are you sure that's correct? Isn't the 225 mA noted at the output of the rectifier a DC (RMS) rating? I would think that any diode conducting for a half cycle is only required to deliver half the RMS current.



 

RE: help with reading a rectifier rating chart ......, posted on April 20, 2015 at 09:11:05
Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001
 "Average" current is averaged over time. The individual plate is not conducting half the time, so the output current is twice the per-plate average rating.

Actually in a cap-input filter the plate is conducting for a very short time, making the peak current important. You can see this in a PSUD simulation.

The important tube parameters are the plate dissipation and peak current. Peak current is limited by the cathode capability, and is usually specified. Dissipation is an integral over time of voltage drop times current, which depends on the specific PSU design. Average current is specified as a convenience to designers, and is only accurate in the context of the assumptions used regarding the series resistance and the first stage capacitor value.

 

so the bottom line is?, posted on April 20, 2015 at 09:21:52
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 Sounds like I got at least two different opinions. I have been running it for about a half hour this way and no red plates or any other trouble so far. I am guessing from that fact and from what I got from everyone that it is ok as is?

 

RE: help with reading a rectifier rating chart ......, posted on April 20, 2015 at 09:57:47
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 "Average current is specified as a convenience to designers, and is only accurate in the context of the assumptions used regarding the series resistance and the first stage capacitor value."

Well said.

Thanks.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: so the bottom line is?, posted on April 20, 2015 at 10:14:10
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 The bottom line is that each diode carries half the current. Paul added that simply complying with the DC output rating doesn't mean the rectifier is necessarily within the more important peak current limitation. Peak current varies as a function of input capacitance and the resistance of both the source and load. If you know those values, PSU will give you a good idea as to peak current.

 

RE: help with reading a rectifier rating chart ......, posted on April 20, 2015 at 10:15:13
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 So how do I determine if I am ok or not?

 

RE: so the bottom line is?, posted on April 20, 2015 at 10:20:32
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 I designed this power supply on psud using the parameters actually in the amp now. I just ran it again with no error warnings, so I guess that means it must be ok?

 

RE: help with reading a rectifier rating chart ......, posted on April 20, 2015 at 10:29:19
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 Take a look at the max peak current rating on the data sheet and compare it to the peak diode current (I(D1)) according to your PSU simulation.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: help with reading a rectifier rating chart ......, posted on April 20, 2015 at 10:42:01
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 Ok, thanks.

 

RE: help with reading a rectifier rating chart ......, posted on April 20, 2015 at 10:49:06
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 If I am reading the data sheet right the max peak current rating is 750mA, and my psud sim doesn't get anywhere near that, only 150 mA. Is that because it is such a short duration that it can take that much current?

 

RE: so the bottom line is?, posted on April 20, 2015 at 11:57:35
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 I wouldn't rely on a PSUD warning for this. You should compare the peak current it predicts to the manufacturer's rating, then decide whether you have sufficient safety margin. I can't tell you what that margin should be, in part because all the different 5AR4s behave so differently. Someone else here can probably guide you in that.




 

RE: so the bottom line is?, posted on April 20, 2015 at 13:39:12
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 ok, thanks.

 

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