GZ34 anode load resistor calculation -help
I'm a bit rusty on calcualtions.
Hammond transformer 374BX (240VAC primary)
Secondary winding 375V-0-375V, DC resistance measured about 105 Ohms DCR.
GZ34/5AR4 tube rectifier used here.
Current load measured at output to amp circuit = 130mA
Rectification is RC filtering 32uF > 75ohm > 32uF > output = 130mA @ 440VDC
Can any guru calculate what's the optimum value resistors to install at the GZ34 anodes?.
I'm a bit rusty on calcualtions.
Hammond transformer 374BX (240VAC primary)
Secondary winding 375V-0-375V, DC resistance measured about 105 Ohms DCR.
GZ34/5AR4 tube rectifier used here.
Current load measured at output to amp circuit = 130mA
Rectification is RC filtering 32uF > 75ohm > 32uF > output = 130mA @ 440VDC
Can any guru calculate what's the optimum value resistors to install at the GZ34 anodes?.
Hi coolmaster ,
To calculate the exact value , I need to know :
1 ) The primary DC resistance ( 240 VAC winding )
2 ) If the DC resistance measured ( 105 ohms ) is
for the total secondary winding ( 750 V ) , or is
for each secondary’s half ( 375 + 375 V )
With these informations , I will calculate the EXACT
resistor value , you need to connect at EACH ANODE
of the GZ34 .
I am waiting .......
Carlos
To calculate the exact value , I need to know :
1 ) The primary DC resistance ( 240 VAC winding )
2 ) If the DC resistance measured ( 105 ohms ) is
for the total secondary winding ( 750 V ) , or is
for each secondary’s half ( 375 + 375 V )
With these informations , I will calculate the EXACT
resistor value , you need to connect at EACH ANODE
of the GZ34 .
I am waiting .......
Carlos
I've made the measurements again.
Primary 0-240VAC tap in use = 8ohm DCR (total winding)
Secondary 375-0-375 = 99ohm DCR (total winding DCR)
The second winding on each half from 0-375 is not exactly equal, slightly off by 4-5ohms.
My input voltage is exactly 230VAC in operation, incoming supply being regulated by a huge AVR.
Eversince new, its after half hour the tranny becomes a little too hot for my liking and giving me the jitters its bad for the tranny on the long run. I'm sure the circuit hasn't exceeded the current capacity ratings for other windings. The amp is typically a Mullard 5-20. As mentioned earlier, the current draw is only 130mA. Tranny rated at 175mA at HT winding. The DC is C-R-C filtering, 32uF-100ohm-32uF.
Thank you.
Primary 0-240VAC tap in use = 8ohm DCR (total winding)
Secondary 375-0-375 = 99ohm DCR (total winding DCR)
The second winding on each half from 0-375 is not exactly equal, slightly off by 4-5ohms.
My input voltage is exactly 230VAC in operation, incoming supply being regulated by a huge AVR.
Eversince new, its after half hour the tranny becomes a little too hot for my liking and giving me the jitters its bad for the tranny on the long run. I'm sure the circuit hasn't exceeded the current capacity ratings for other windings. The amp is typically a Mullard 5-20. As mentioned earlier, the current draw is only 130mA. Tranny rated at 175mA at HT winding. The DC is C-R-C filtering, 32uF-100ohm-32uF.
Thank you.
Here's the formula (you might have to wait 10 seconds for the advert to vanish so you can view the page)
It's near the bottom under "Minimum Limiting Resistance"
http://www.freewebs.com/valvewizard/fullwave.html
It's near the bottom under "Minimum Limiting Resistance"
http://www.freewebs.com/valvewizard/fullwave.html
Hammond transformers tend to get hot. The 3XX series are cooler running than the 2XX series because they are rated for 50Hz operation. You are in a 50Hz country, so they will get warm.
I am using Allied 6K7VG and 6K56VG transformers (made by Hammond, but cheaper than the same Hammond TX) near their maximum ratings. They get hot enough that you don't want to put your hand on them for more than a few seconds. I have been using these for over 10 years (dozens of HiFi and guitar amps) with zero failures.
I am using Allied 6K7VG and 6K56VG transformers (made by Hammond, but cheaper than the same Hammond TX) near their maximum ratings. They get hot enough that you don't want to put your hand on them for more than a few seconds. I have been using these for over 10 years (dozens of HiFi and guitar amps) with zero failures.
Merlinb: Thank you for the link. Have calculated out the resistor required. Just installed in 75 ohm (2X150ohm in parallel,what I've got in hand) and so far so good after listening to some music for he past hour.
tubelab.com : Yes, its 50hz here and I just didn't feel too good about it being hot enough not to touch for more than few seconds, but its been like that for 2 years now, just itching to see if I could make it run cooler. Had no idea Hammond mains tranny run hot. I always thought its similar to any other brand or make, when properly sized and implemented. Other than that, everything else is just fine.
tubelab.com : Yes, its 50hz here and I just didn't feel too good about it being hot enough not to touch for more than few seconds, but its been like that for 2 years now, just itching to see if I could make it run cooler. Had no idea Hammond mains tranny run hot. I always thought its similar to any other brand or make, when properly sized and implemented. Other than that, everything else is just fine.
Limiting resistors
Hi all,
Mullard quote in their maintenance manual fro a GZ34 400v on the anodes and a capacitor input smoothing filter a total resitance of 125R per anode. So for your transformer which is 50R per half you need to add 75R to make the 125R which is exactly what you have done. The reason for the resistors is to limit the current as the GZ34 is a fairly low impedance rectifier, so if you hot switch it, it could draw excessive current and either flashover or strip the cathode.
John Caswell
Hi all,
Mullard quote in their maintenance manual fro a GZ34 400v on the anodes and a capacitor input smoothing filter a total resitance of 125R per anode. So for your transformer which is 50R per half you need to add 75R to make the 125R which is exactly what you have done. The reason for the resistors is to limit the current as the GZ34 is a fairly low impedance rectifier, so if you hot switch it, it could draw excessive current and either flashover or strip the cathode.
John Caswell
My experience parallels SY's pretty closely, I don't pad the resistance and never use more than 50uF input capacitance.
I have found that adding a 1N4007 in series with each plate is quite effective in preventing flashover whether the tube is hot or warming up - and use these religiously in any application where the secondary voltage is greater than 750VCT.. I'd do that in lieu of the 75 ohm resistors which needlessly degrade regulation in a class a/b amplifier.
I have found that adding a 1N4007 in series with each plate is quite effective in preventing flashover whether the tube is hot or warming up - and use these religiously in any application where the secondary voltage is greater than 750VCT.. I'd do that in lieu of the 75 ohm resistors which needlessly degrade regulation in a class a/b amplifier.
Hi COLLMASTER ,
Sorry for the delaied reply .
Your transformer itself , has an intrinsic natural impedance of
about 69 ohms , the 5AR4 / GZ34 , needs a 110 ohms impe-
dance per plate , so you ONLY NEED to complete this value .
You need to connect ONLY a 47 ohms x 5 Watts wirewound
resistor at each anode of 5AR4 / GZ34 . It’s enough !!! No more,
and your tube rectifier will be correctly protected .
If you are using a higher value , you are wasting energy and
decreasing the power supply regulation .
I hope it helps you . Regards ,
Carlos
Sorry for the delaied reply .
Your transformer itself , has an intrinsic natural impedance of
about 69 ohms , the 5AR4 / GZ34 , needs a 110 ohms impe-
dance per plate , so you ONLY NEED to complete this value .
You need to connect ONLY a 47 ohms x 5 Watts wirewound
resistor at each anode of 5AR4 / GZ34 . It’s enough !!! No more,
and your tube rectifier will be correctly protected .
If you are using a higher value , you are wasting energy and
decreasing the power supply regulation .
I hope it helps you . Regards ,
Carlos
Hi all,
Thank you for the valuable guidance.
Carlos: I think a 5W size is likely insufficient, sensing its radiating a lot of heat, and could risk burning out sometime in future from an experience just not too long ago.
Before I posted the question, I had 110ohm (2 x 220ohm/5W to total 10W rating) and for some unexplanable reason, one of the parallel resistors opened circuit upsetting the B+ to go down by 5%. Lucky I spotted it soon and replaced the defective part and all's well. BTW, the amplifier in question is monoblock configuration and current draw@130mA is for 1 block.
As mentioned earlier, meantime its 75ohm/10W on each side and it's still pretty hot after a while..but I reckon it'll be ok. Meanwhile, I'll let it be there for a while till I obtain better quality resistors from RS or Farnel (Vitreous Enamel type or aluminum clad). Currently its run of the mill quality white coffin type from whatever spares from my stash of usable parts. Due to restricted space underneath, a 10W single resistor won't fit in nicely.
Thank you for the valuable guidance.
Carlos: I think a 5W size is likely insufficient, sensing its radiating a lot of heat, and could risk burning out sometime in future from an experience just not too long ago.
Before I posted the question, I had 110ohm (2 x 220ohm/5W to total 10W rating) and for some unexplanable reason, one of the parallel resistors opened circuit upsetting the B+ to go down by 5%. Lucky I spotted it soon and replaced the defective part and all's well. BTW, the amplifier in question is monoblock configuration and current draw@130mA is for 1 block.
As mentioned earlier, meantime its 75ohm/10W on each side and it's still pretty hot after a while..but I reckon it'll be ok. Meanwhile, I'll let it be there for a while till I obtain better quality resistors from RS or Farnel (Vitreous Enamel type or aluminum clad). Currently its run of the mill quality white coffin type from whatever spares from my stash of usable parts. Due to restricted space underneath, a 10W single resistor won't fit in nicely.
Hi coolmaster ,
If I have understood it right , you have a 5AR4 / GZ34 for each
monoblock , correct ???
In being so , the heat dissipation would be , by the Ohm’s law ,
P = R x I ²
110 ohm x 0.13 x 0.13 = 1.86 Watts ( resistor set will be VERY
HOT ) , but you have a 10 watts total dissipation allowable , then
a safety margin > 5 , that is a GOOD number .
75 ohm x 0.13 x 0.13 = 1.27 Watts ( resistor set will be HOT ) , but calculated the same way as above , the safety margin ~ 8 , and that is an EXCELLENT number .
BUT if you use 47 ohm x 5 W , as I had said , then 47 x 0.13 x
0.13 = 0.80 Watts , then the safety margin would be > 6 , that is
a VERY GOOD number , however the resistor would work A BIT
HOT , but you would not need to worry about that .
As a rule of thumb , in my designs , I do assume that a safety
margin > or = 5 , is OK .
Choose a good quality wirewound resistor , and keep it away from heat sensitive parts , rather in a place where the air can
flow by convection .
Any doubt , feel free to ask . Regards ,
Carlos
If I have understood it right , you have a 5AR4 / GZ34 for each
monoblock , correct ???
In being so , the heat dissipation would be , by the Ohm’s law ,
P = R x I ²
110 ohm x 0.13 x 0.13 = 1.86 Watts ( resistor set will be VERY
HOT ) , but you have a 10 watts total dissipation allowable , then
a safety margin > 5 , that is a GOOD number .
75 ohm x 0.13 x 0.13 = 1.27 Watts ( resistor set will be HOT ) , but calculated the same way as above , the safety margin ~ 8 , and that is an EXCELLENT number .
BUT if you use 47 ohm x 5 W , as I had said , then 47 x 0.13 x
0.13 = 0.80 Watts , then the safety margin would be > 6 , that is
a VERY GOOD number , however the resistor would work A BIT
HOT , but you would not need to worry about that .
As a rule of thumb , in my designs , I do assume that a safety
margin > or = 5 , is OK .
Choose a good quality wirewound resistor , and keep it away from heat sensitive parts , rather in a place where the air can
flow by convection .
Any doubt , feel free to ask . Regards ,
Carlos
Don't forget that the current in these resistors are actually half wave, so the actual power dissipated is typically half the normal case. Also the current waveform is not sinusoidal so the usual equations can be a bit misleading. I typically use 2W - 3W resistors for values under 50 ohms for these applications, and they don't run very warm for the reasons cited above. (I have measured with a thermocouple.)
Also experience indicates that they are not needed at all in this particular application. The difference in peak winding current is not going to significantly affect the transformer heat load, and they do slightly raise the source impedance of the supply and degrade the regulation as well. I'm totally with SY on this one.
Also experience indicates that they are not needed at all in this particular application. The difference in peak winding current is not going to significantly affect the transformer heat load, and they do slightly raise the source impedance of the supply and degrade the regulation as well. I'm totally with SY on this one.
Hi ,
You are correct Kevin .
Actually the current flowing through each resistor , obviously ,
is not the total current , BUT as I said on my previous post ,
it is ONLY a “ rule of thumb “ , and assuming that the total
current flow through each resistor , the tube will be safe from
harmonics , “spikes” , distorted sinusoide , surges , etc. , etc. ...
and other "things" , that you can not calculate .
About the second topic , excuse-me , but I disagree from you ,
and from SY , the anode resistor of a tube rectifier , is VERY ,
VERY IMPORTANT ( obviously , only when the transformer
impedance is under the required value for any given tube’s
operating point ) .
The anode resistor , prevents cathode stripper , protects the
rectifier against “spikes” and surges , and assures the maximum
useful life of the tube .
They lower the regulation ??? -- Yes , they do , but only a bit ,
because tube rectified power supply , has poor regulation by
itself , and a 47 ohms resistor is insignificant over all .
I think that the advantages are much greater than the drawbacks , so I always recommend to use them ( the resistors ) .
From another point of view : Why every tube rectifier data-sheet
has ( very clearly ) the minimum impedance per plate , that each
anode “ must to see “ in the power transformer ???
Regards ,
Carlos
You are correct Kevin .
Actually the current flowing through each resistor , obviously ,
is not the total current , BUT as I said on my previous post ,
it is ONLY a “ rule of thumb “ , and assuming that the total
current flow through each resistor , the tube will be safe from
harmonics , “spikes” , distorted sinusoide , surges , etc. , etc. ...
and other "things" , that you can not calculate .
About the second topic , excuse-me , but I disagree from you ,
and from SY , the anode resistor of a tube rectifier , is VERY ,
VERY IMPORTANT ( obviously , only when the transformer
impedance is under the required value for any given tube’s
operating point ) .
The anode resistor , prevents cathode stripper , protects the
rectifier against “spikes” and surges , and assures the maximum
useful life of the tube .
They lower the regulation ??? -- Yes , they do , but only a bit ,
because tube rectified power supply , has poor regulation by
itself , and a 47 ohms resistor is insignificant over all .
I think that the advantages are much greater than the drawbacks , so I always recommend to use them ( the resistors ) .
From another point of view : Why every tube rectifier data-sheet
has ( very clearly ) the minimum impedance per plate , that each
anode “ must to see “ in the power transformer ???
Regards ,
Carlos
Let's see.
Sitting there now is 32uf + 32uF/500V filter cap (F & T German)there. I've got another (2 EA) spare 50uF + 50uF/500V cap..how much better or stress anything by replacing the former?.
An affordable Sovtek 5AR4 or JJ GZ34 is resident most of the time, as I believe current production tube rectifiers are equally good as expensive NOS types, which revealed NO audible difference to my ears, unless I'm fiddling and altering component values at the rectifier circuit.
Sitting there now is 32uf + 32uF/500V filter cap (F & T German)there. I've got another (2 EA) spare 50uF + 50uF/500V cap..how much better or stress anything by replacing the former?.
An affordable Sovtek 5AR4 or JJ GZ34 is resident most of the time, as I believe current production tube rectifiers are equally good as expensive NOS types, which revealed NO audible difference to my ears, unless I'm fiddling and altering component values at the rectifier circuit.
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