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New 4d32 SE project looking for critiques / advice
New 4d32 SE project looking for critiques / advice
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Old 18th November 2018, 04:12 AM   #1
evanc is offline evanc  United States
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New 4d32 SE project looking for critiques / advice
Default New 4d32 SE project looking for critiques / advice

I wanted to show this to the community and see what people think. I got the schematic from jack at ElectraPrint. It is wired up and working on my bench as I type. I like the circuit because it is fairly simple.

What might you do differently.

TIA
Evan
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Old 18th November 2018, 05:57 AM   #2
H713 is offline H713  United States
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Jack is an extremely knowledgeable person when it comes to this subject (and if you can afford them I would not hesitate to order his transformers), so I'd be hesitant to change the schematic too much if he designed it. Looking at it, I don't see anything I don't like.

I am inclined to add a little negative feedback, however. I know this is viewed negatively by many, however it should improve the damping factor (worth it since you're running it as a pentode). Many people will disagree with me.
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Old 18th November 2018, 06:06 AM   #3
carlthess40 is online now carlthess40  United States
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Well I have five different types of speakers that I can do some sound testing for you
I few Klipsch. And peerless full range and others Would love to try out someoneís tube build and run the REW for would the sou d looks on paper and my ears. Lol
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Old 18th November 2018, 06:10 AM   #4
jdarg is offline jdarg  United States
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Quote:
Originally Posted by H713 View Post
Jack is an extremely knowledgeable person when it comes to this subject (and if you can afford them I would not hesitate to order his transformers), so I'd be hesitant to change the schematic too much if he designed it. Looking at it, I don't see anything I don't like.

I am inclined to add a little negative feedback, however. I know this is viewed negatively by many, however it should improve the damping factor (worth it since you're running it as a pentode). Many people will disagree with me.
This circuit seems to have a few really bad design choices. No disrespect to op or Jack but this seems to break at least a couple common sense rules imjo and you are going to have some floppy bass with most speakers assuming you can keep 5u4s alive. Drop that 50r and reduce your first cap to 22uf for starters IMHO. But fixing the poor damping will require essentially a redesign of the front end to support the nfb you'll need to tame the df. Now if you are biamping and using this on the top end the df might not be as much of an issue.

Last edited by jdarg; 18th November 2018 at 06:27 AM.
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Old 18th November 2018, 06:30 AM   #5
6A3sUMMER is offline 6A3sUMMER  United States
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420VAC is 594V peak.
44V rectifier drop + 8V 50 Ohm drop is 542VDC

542VDC is far too much for those 450V electrolytic capacitors.
Check your HV secondary voltage rating, and cap ratings.

Last edited by 6A3sUMMER; 18th November 2018 at 06:38 AM.
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Old 18th November 2018, 06:56 AM   #6
H713 is offline H713  United States
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One thing I'm a little confused on is where that 20 watts is coming from. Looking at the 4D32 datasheet (no specs given for SE), it suggests a 3000 ohm P-P load for class AB1. I'm inclined to say that 5K is a little high... and I doubt you're making 20 Watts with those plate voltages.

Not that I'm necessarily the best person to ask, as I obviously missed a few glaring mistakes in my first post (capacitor voltage ratings...). Clearly I'm tired if I didn't notice that. Along those lines, to get the voltages in the schematic, that poor choke is dissipating 18 watts and dropping about 116 volts...

Also, is it just me or does a 4k plate resistor on that 6AN4 seem a tad low? It isn't a tube I'm real familiar with, but the datasheet I found doesn't list an anode load, and suggests a mu factor of 70.

Last edited by H713; 18th November 2018 at 06:59 AM.
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Old 18th November 2018, 01:11 PM   #7
evanc is offline evanc  United States
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New 4d32 SE project looking for critiques / advice
No disrespect is implied and no offense taken. I asked.

I have stacked the first electrolytic caps and they are rated 500 volts so safely within their rating and half the capacitance. The rectifier is a 5u4gb.

Iím using a choke with less DCR so dropping less volts.

I appreciate the time and advice

Thanks
Evan
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Old 18th November 2018, 05:41 PM   #8
H713 is offline H713  United States
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Keep in mind that everyone has opinions on how they would do it, but everyone has a different application and different preferences.

If I were building it, I'd yard out that tube rectifier and go SS, double the filter cap sizes, redesign the front end using a different tube and load it full of negative feedback.

But I'm anything but a purist in this regard, and then you wouldn't even have the original circuit. Not everyone likes SS rectifiers and negative feedback.


One other thing- It's hard to tell from the pictures, but if those big power resistors (chassis mount type) are the cheap stuff from eBay, I'd spring for some nice quality Dale resistors. Maybe I've just had a bad run, but my experience has been that they don't take surge current very well. I've had at least three go open almost instantly on startup with any decent size cap after them. PITA to track down because it's not like you expect them to go open.
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Old 18th November 2018, 08:24 PM   #9
ArcticBrew is offline ArcticBrew  United States
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I modeled the power supply in PSUD II. I used 10 henry and 120 ohms for the choke. I assumed 2528 does not mean ohms or is a mistake. And I assumed 420 volts was an unloaded value for the transformer.

The data sheets suggest 250 volts in AB2 and 300 volts in AB1 on the screen of the 4D32 and 200 volts on the plate of the 6AN4.

With the stated assumptions the 4D32 plate supply is ~420v, Screen supply is ~260v and 6AN4 plate supply is ~200v.

These values match the operating point for the 6AN4 shown in the datasheet.

Steve
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Old 19th November 2018, 02:27 AM   #10
PRR is offline PRR  United States
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Originally Posted by H713 View Post
One thing I'm a little confused on is where that 20 watts is coming from...
It is easy to plot-out.

It does look like 14 Watts for 5K load. The 400V 120mA suggests 3.2k trial load which plots as 21+ Watts at clipping. THD will be high at this extreme swing; also clearly the data-sheet show-off Vg2 of 300V is too high for good linearity at this condition; these can be adjusted.
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