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Question on Hybrid Bridge using 5AR4

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cjctan

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Joined 2005
#1
Hi All,

I am trying to build a power supply for my SET amp with a B+ of 400V , ~170mA.
If I am going to use a 5AR4/GZ34 with 2 SS diodes, what should be the voltage of my PT Secondary winding? Is the winding voltage 700Vac (NO CT)?

Thanks in advance.....
 
#3
Hybrid bridge works very well. BUT GZ34 is much more reliable and better sounding if (almost) Choke-Input filter is used.

Use 10H 200mA choke (must be specially designed for choke-input duty)
UF4007 diodes
47n 1500Vdc capacitors across trafo secondary to snub recovery pulses
220nF to 680nF 1500Vdc MKP capacitor after rectifier.

If you can find a transformer with 450 to 475V secondary, you can get 400Vdc by adjusting the cap after the rectifier (higher C=higher V).

If you get too many volts, change GZ34 for GZ37 (but need extra heater current).
 
#4
Thank you both for your inputs.



Rod Coleman said:

If you can find a transformer with 450 to 475V secondary, you can get 400Vdc by adjusting the cap after the rectifier (higher C=higher V).
Click to expand...


Rod,
May I know the cap that you are referring above is still for a choke input filter? Meaning it is the cap after the 10mH?
Can the Hammond 193J with DCR=82ohms be used for this choke input filtering?

Am I right to say that if choke input method is used, the secondary winding voltage will be around 450~475V and 350V for Capacitor input?

Thanks....
 
#6
Rod, May I know the cap that you are referring above is still for a choke input filter? Meaning it is the cap after the 10mH? Can the Hammond 193J with DCR=82ohms be used for this choke input filtering? Am I right to say that if choke input method is used, the secondary winding voltage will be around 450~475V and 350V for Capacitor input?
Click to expand...

Use only a small cap after the rectifier (220 to 680nF) to protect the choke from fast voltage changes. This is still choke-input, or more exactly "quasi-choke-input" to give it a fancy name. The value of this cap will adjust the dc volts up or down a little. Use a good quality MKP here, 1500~2000Vdc rating.

after the choke, use a bigger capacitor - 100uF or maybe more.

Yes, 450~475V for choke-input, 350V for capacitor input.

I'd say Choke-input is much better, especially for SE amps.
 
#8
Rod Coleman said:


Use only a small cap after the rectifier (220 to 680nF) to protect the choke from fast voltage changes. This is still choke-input, or more exactly "quasi-choke-input" to give it a fancy name. The value of this cap will adjust the dc volts up or down a little. Use a good quality MKP here, 1500~2000Vdc rating.

after the choke, use a bigger capacitor - 100uF or maybe more.

Yes, 450~475V for choke-input, 350V for capacitor input.

I'd say Choke-input is much better, especially for SE amps.
Click to expand...


Rod,
Appreciate your further explanations.
I have clearer picture now and I will adopt your "quasi" design 🙂

Another question regarding to the cap after the choke. Will a 500V rating cap enough at this junction? As the choke-input and cap-input chart in the GZ34 datasheet will not be accurate in this case. Any idea how to estimate the max voltage after the choke for no load condition for a 475V winding with 680nF snubber cap?

Thanks again
 
#9
With 175mA dc and 400V (or even 430V) from (quasi) choke input, the ripple-current of the 2nd cap will be very low. That means a 450V electrolytic will work - providing the 175mA is sure to be present.

Choke-input supplies need to have a minimum load to work right - and the voltage goes high if the load disconnects.

A quality MKP will be better - Ansar Supersound or LCR AG series - both are 630V. These sound much better, and will not worry if short voltage-spikes happen.

To experiment with cap values and power supplies, you need to get PSUdii !!

http://www.duncanamps.com/psud2/index.html

This runs well using WINE on a Linux system (surely the OS of choice for DIY-mongers), or if you insist, on Windows-98 etc.

To simulate the hybrid-bridge, change the TYPE to "full-wave" vacuum tube" which gives the same outcome.

here's a screenshot with 475V/680n/10H/100uF. shows....400V !!

The big 600V peak at the start should not happen with a slow warm-up rectifier.
 

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#12
PSUD II SIMULATION OF PS

Hybrid Bridge... that is a favorite of mine. Favorite that is, because it is much easier to find a good transformer without centre tap, and because it is easir to balance everything with a bridge.

In the thread, quite long noone mentioned PSUD II. The software is great and provides you with very precise sims of the power supply, especially if you are into entering the right values for everything.

Still, I think that maybe it would be better to assume a bridge of GZ34s in the simulation -- regardless of the fact that only one GZ34 will be used, along with two SS diodes (suggest 1N4007).

About the sound: yes, the choke input ALWAYS sounds better, while the GZ34 is a little muffled by nature and thus not quite so "audiophile" as 5R4 or 5U4 (to mention comparable current rectifiers). Of course, the bridge will "sound" the same as the tube rectifier used, meaning that it is way better than any SS diodes (in bridge or no bridge), at least in my book.

Regards to all,
Alex

PS
Linux rules (but I use dual boot Win/Linux, because not everything works perfectly with Wine). One day, Lin will rule, particularly if Microsoft continues with the "Mistake Editions", i.e. Vista...
 
#14
Re: PSUD II SIMULATION OF PS

Alex Kitic said:
Hybrid Bridge... that is a favorite of mine. Favorite that is, because it is much easier to find a good transformer without centre tap, and because it is easir to balance everything with a bridge.

In the thread, quite long noone mentioned PSUD II. The software is great and provides you with very precise sims of the power supply, especially if you are into entering the right values for everything.

Still, I think that maybe it would be better to assume a bridge of GZ34s in the simulation -- regardless of the fact that only one GZ34 will be used, along with two SS diodes (suggest 1N4007).

About the sound: yes, the choke input ALWAYS sounds better, while the GZ34 is a little muffled by nature and thus not quite so "audiophile" as 5R4 or 5U4 (to mention comparable current rectifiers). Of course, the bridge will "sound" the same as the tube rectifier used, meaning that it is way better than any SS diodes (in bridge or no bridge), at least in my book.

Regards to all,
Alex

PS
Linux rules (but I use dual boot Win/Linux, because not everything works perfectly with Wine). One day, Lin will rule, particularly if Microsoft continues with the "Mistake Editions", i.e. Vista...
Click to expand...


Alex, Thanks for your inputs.....
The reason that I wanted to try out the hybrid bridge is mainly due to the fact that I can simplify the main trans.

After "playing" with the PSUD, it is indeed a superb piece of software.
 
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