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GZ34: getting too much voltage drop

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Posted on February 11, 2017 at 06:13:55
banpuku
Audiophile

Posts: 1008
Joined: January 19, 2006
 The GZ34 rectifier is supposed to have a voltage drop of 17V. Per the attached schematic, it appears as though there is too much voltage drop, as the voltage measured at the GZ34 pin is 290V. Is this voltage drop reasonable or is something wrong here? I thought I would be getting about 300-310V coming out of the GZ34. Thoughts?


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UPDATE: Resolved by vetmedrobert@gmail.com.

You have 670 volts into a choke. the formula is VAC*0.45, or 670*0.45= 302.5 volts. This for a full wave rectifier as you have in your schematic. Then you must allow for the rectifier voltage drop which depends upon your circuit's current draw.

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Voltage Drop = Current Goes Up Somewhere Else..., posted on February 11, 2017 at 07:17:26
Interstage Tranny
Audiophile

Posts: 3063
Location: Eastern
Joined: October 4, 2006
 First, choke input filter drops High Voltage B+, but allows more current draw than a cap input filter power supply.

Is your GZ34 testing strong ? Then, either the power tranny has limited current available, or your amp circuit is drawing more current than you anticipated. Have you checked the amp tubes ? If voltage goes down, current goes up somewhere. Ohm's Law always applies...

It might be beneficial for you to do some more research concerning Ohm's Law, Voltage Drops and inherent power supply losses. Google searches can help and link to some fantastic online calculators and specialty audio engineering sites. pspatial.com and sengpielaudio.com are only two great sites which have significant audio-related info. The math gets easier as you reread and apply the formulae. Electrical and electronic theory can be overwhelming, but only if you let it confuse you. Sometimes, simply remembering wording or a formula is all that is needed to understand the next "step" involved. Rereading often, and voila, the inner brain's lightbulb glows; then planning and devising can eventually become an instinct....

 

RE: GZ34: getting too much voltage drop, posted on February 11, 2017 at 07:33:11
vetmedrobert@gmail.com
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Posts: 453
Location: Ontario
Joined: September 20, 2007
 You have 670 volts into a choke. the formula is VAC*0.45, or 670*0.45= 302.5 volts. This for a full wave rectifier as you have in your schematic. Then you must allow for the rectifier voltage drop which depends upon your circuit's current draw. To me 290 volts seems if anything a little high but perhaps your wall voltage is a bit higher than what the power transformer is rated for. Hope this is useful.

 

RE: GZ34: getting too much voltage drop, posted on February 11, 2017 at 07:38:41
banpuku
Audiophile

Posts: 1008
Joined: January 19, 2006
 Very helpful, Thank you!

 

RE: GZ34: getting too much voltage drop, posted on February 11, 2017 at 07:47:17
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Pat
If you are using a JJ GZ34,switch over to a vintage or reissue Mullard.Is this the same 2A3 SET amp you are driving Quad ESL63s with?
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Voltage Drop = Current Goes Up Somewhere Else..., posted on February 11, 2017 at 07:52:32
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 IT
He was driving Quad ESL63s with a single 2A3.If I were him,I would go with the JJ 2A3-40 and boost the B+ as it would give him more power and better dynamics.An innerstage would help him a lot with class A.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

If you are looking to boost your B+, posted on February 11, 2017 at 08:19:46
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 you can add a small cap before L1. Depending on how many volts. My experience on playing with a small cap is that a value under .5uf will add around 5 volts. At 1uf it will be around 10v. By 5uf the voltage gain will be nearly the same as a capacitor input filter. On one amp i installed a 5uf vitaminQ on a switch so i can have it in or out of circuit and the difference is large. with no C1 340vdc with 5uf added 450vdc depending on the load.

 

RE: GZ34: getting too much voltage drop, posted on February 11, 2017 at 08:39:59
banpuku
Audiophile

Posts: 1008
Joined: January 19, 2006
 Mikey,

Yes, this is for my 2a3 amp that I am using on the Quads. Why do you prefer the Mullards?

Pat

 

RE: GZ34: getting too much voltage drop, posted on February 11, 2017 at 12:20:38
sideliner
Audiophile

Posts: 208
Location: NYC
Joined: August 22, 2013
Contributor
  Since: December 15, 2023
 *******************************************
UPDATE: Resolved by vetmedrobert@gmail.com.

You have 670 volts into a choke. the formula is VAC*0.45, or 670*0.45= 302.5 volts. This for a full wave rectifier as you have in your schematic. Then you must allow for the rectifier voltage drop which depends upon your circuit's current draw.

*******************************************************


I disagree.

At the output of the filter: VDC=0.9*Vrms(trans. sec.) for choke input

At the output of the filter: VDC=1.41*Vrms(trans. sec.) for capacitor input

At the INPUT of the filter: Vrms(rectified) = Vrms(trans. sec.) - Vdrop of the rectifier.

In this case the potential at the rectifier's cathode should be 335V-15V or about 320V (GZ34 Vdrop = 16V at a draw of 200mA) and not 290V. Perhaps it's just a bad tube as in a low emission/transconductance specimen or the transformer has an issue. Did you verify that the no-load-voltage across both half's of the trans secondary is as specified?

 

RE: GZ34: getting too much voltage drop, posted on February 11, 2017 at 13:42:27
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002
 0.9*Vrms(trans. sec.) for choke input works out to .45*Vrms when the transformer secondary has a grounded CT.

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

 

here you go, posted on February 11, 2017 at 13:57:33
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002



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

 

RE: GZ34: getting too much voltage drop, posted on February 11, 2017 at 14:05:48
sideliner
Audiophile

Posts: 208
Location: NYC
Joined: August 22, 2013
Contributor
  Since: December 15, 2023
 This is correct and it's not my point of contention. It's of course either 0.9x taking it from one end of the transformer to the CT or 0.45x taking it from end-to-end. My point is that at the input of the filter - be it choke input or cap input, the VAC RMS is equal to the RMS at the secondary minus whatever drop occurs at the rectifier.

In this case the math simply doesn't work out to justify the 290V at the rectifier's cathode as shown on the attached schematic. That's why I suggested that the OP confirms that the no-load voltage at the secondaries is as it should be.

 

RE: GZ34: getting too much voltage drop, posted on February 11, 2017 at 16:07:00
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002
 "My point is that at the input of the filter - be it choke input or cap input, the VAC RMS is equal to the RMS at the secondary minus whatever drop occurs at the rectifier."

No. A cap input filter will cause the voltage and charging currents to be higher at the cathode of the rectifier tube.

A critical inductance choke input will cause the voltage and charging currents to be lower at the cathode of the rectifier tube.

Cap vs. choke input filter changes the way the rectifier tube works.

The equation "VDC=0.9*Vrms(trans. sec.) for choke input" or "VCD=1.41*Vrms for cap input" is the input to the filter.

I just ran a sim 335-0-335 into a 5ar4 with a critical inductance input choke and depending on the DCR of the power transformer secondary and the total current draw, 290vdc at the cathode of the 5ar4 is about right.

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

 

RE: here you go, posted on February 11, 2017 at 17:45:26
BenM
 That looks like the diagram in the Hammond Transformers catalog.

 

RE: GZ34: getting too much voltage drop, posted on February 11, 2017 at 18:35:35
sideliner
Audiophile

Posts: 208
Location: NYC
Joined: August 22, 2013
Contributor
  Since: December 15, 2023
 You are right, I thought more about this after I posted my last response and it occurred to me that the losses incurred in the filter from input to output can only be the resistive losses in the inductor (DCR) and/or resistors. From this realization alone it's obvious that the difference between 1.41x Vrms and 0.9x Vrms in the two types of filters is due to the topology.

The capacitor input simply charges to the peak value of the voltage waveform, hence the x1.41 factor. So to correct my earlier statement, the voltage at the output of the filter is that of the input minus the resistive losses of the chokes and resistors which of course depends on the current draw of the amp.

So, the voltage of 290V present at the rectifier's cathode is actually in line with the expected result.

 

RE: GZ34: getting too much voltage drop, posted on February 11, 2017 at 23:27:19
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Reliability mostly.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

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