• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

choke and choke

have'

Member
2005-04-13 10:26 am
pmr
I have build a ps with:
300V ct--1,1uF--10H(138ohm)--14uF--10H(62ohm)--14uF .
As you can see the choke have different resistance 138 and 62ohm.
My question is :does it make a difference if i change the place of the choke ?Otherway: what is the optimal place for a choke?and why?
 
The question is too much generic.
Every application need a different ps, so it's important to know the purpose of ps.
Many other aspect are importants. What kind of diodes(tube or solid state)?
And also there are 2 differents principal types:
1)choke imput: after rectifiers there is a choke, and then a cap(LC)
2)cap input: after rectifiers there is a cap. after this cap you can have a choke or a resistor or nothing. (C or CRC or CLC or CRCRC or CLCLC and so on)

For the question of resistance:
it's probably a different max-current value for the 2 chokes.
I imagine that the 10H/138ohm has about 130-150mA of max-current, the 10H/62ohm about 200-220mA.

Btw you have to keep in mind that it's important to choose a choke properly, because you risk a saturation of the core.
If a choke have a core saturation, it become like a resistor or worse...
For example a choke-input ps need bigger choke than cap-input(ever they are of same value), since it "see" big AC.

Cheers.
 

have'

Member
2005-04-13 10:26 am
pmr
Thanks for the reply.
I'm using tube rectifier (GZ34),and the choke have same inductance 10H~200mA , they only differ in resistance: one is 62ohm the other 138ohm.
Trying on PSUD it give difference.
For a choke input is it better if i use the choke with small resistance after the rectifier?
thanks
 
Using a tube rectifier is a little different from solid state.
First of all it is important to know the current of the load(in mA).
I imagine you will use the ps for a tube amp, but I don't know the current(100mA? 200mA?)!
You are using a cap-input system, CLCLC. So the first cap is too little. GZ34 datasheet indicates a first input cap of 60uF.

Thinking to make a CLC, with a first cap 60uF, your choke, and a bigger cap about 100uF or more, with your 300V-0V-300V you can obtain a DC Voltage between 300V(load about 250mA) and 420V(load about 20mA). If you will use a CLCLC the Voltage will be a little lower. This Values can be little different because It depends also by internal resistances of transformer windings and choke.

If you want to use a choke-input filter(LC), for example using the choke(10H or more) and a cap about 60-100uF, with your tranformer you will have a Voltage between 240V(250mA of load) and 300V(25mA of load).

In the end, you must know your load(current, in mA).
 
You are using a cap-input CLCLC. So the first cap is too little. GZ34 datasheet indicates a first input cap of 60uF.

The 60uF number is the maximum allowed capacitance. Because of the tolerances of electrolytics, a cap marked 60uF is likely to be larger and likely to reduce the life/efficiency of the GZ34. Depending on the load requirements, 5-40uF is a more common range.
 
SY said:


The 60uF number is the maximum allowed capacitance. Because of the tolerances of electrolytics, a cap marked 60uF is likely to be larger and likely to reduce the life/efficiency of the GZ34. Depending on the load requirements, 5-40uF is a more common range.

It's true. Philips datasheet indicates a value between 4uF and 60uF.
But it is also true that it depends on load, and also on tube type. With beautiful nos tubes, like Mullard or philips, 60uF may be a fine choise, and also we can see bigger ones(up to 220uF, but it is a little dangerous for the tube..., the rectifier often "flash" :D ) in commercial amps.

With low quality GZ34s or 5AR4s also a value of 40-50uF can be a problem...

BTW I use also 2 resistances on the 2 rectifier plates. It's a good protection for overloads and help for a "soft" start. Having a good first cap help us with the ripple problem.

Cheers-
 

have'

Member
2005-04-13 10:26 am
pmr
I need 300V ~170mA.
The trans. is 350-0-350V at 190mA.
I'm using the little C (1.15uF)before the first choke to simulate a choke input, does it matter that the choke only 10H ~200mA ?

-How big are the resistance on the rectifier plate?Does it affect the output voltage ?
Thanks.
 
You will get the lowest ripple with the lowest resistance choke closest to the rectifier. You will get the longest tube life with the highest resistance choke closest to the rectifier, although it won't make much difference with your smallish capacitor values. If I were designing a power supply with your parts, I would use the lowest resistance choke first. But I use cheap tubes, and I tend to use large caps.