Question on Hybrid Bridge using 5AR4

[cjctan]

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.....

[revintage]

In the ballpark of 350V AC(not more) would be OK.

[Rod Coleman]

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).

[cjctan]

Thank you both for your inputs.

Originally posted by Rod Coleman

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).

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....

[zigzagflux]

Rod almost exactly specified my power supply at 380V dc. I use the Hammond 193J. Runs very quiet, so you shouldn't have any issues.

[Rod Coleman]

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?

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.

[cjctan]

Originally posted by zigzagflux
Rod almost exactly specified my power supply at 380V dc. I use the Hammond 193J. Runs very quiet, so you shouldn't have any issues.

zigzagflux,
Thanks for you input.
I will use the 193J for the Choke-input filter.

[cjctan]

Originally posted by Rod Coleman


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.

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

[Rod Coleman]

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.

[cjctan]

Hi Rod,
Thanks again.
I will try out the PSUD2.

May I know where can I purchase the LCR AG series online?