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Some questions on Power supplies [message #9364]

Sun, 27 November 2005 10:43

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Hi guys; Before we embark upon the PP 2a3 I have a project in mind. Since I have all of the neccessary components on had I am thinking of building and semi-designing a PP 6V6 amp from a scematic.
The first thing I need to do is convert the existing tube rectified PS from a Cap input into a choke input and come out with the proper voltages from the PTrans. I have on hand a couple of transformers and am looking at transformer theory in order to decide which one will be most compatible.
Next I would need to persue the proper specs for the output transformers of which I have several on hand. The maths of the applications should be reasonably simple for you guys and doable for me.
So; what I would ask if it is o'kay; is to offer my take on each choice and see if the choices are correctly arrived at.
Would that be of any help in regards to providing an opportunity to do some explanations on a level as simple as mine and see if they work for me?
I can use a 5Y3GT so far looking for 365v out into the filter.
The schematic calls for a filter of 20mk input to a 100ohm to a 60mk to a 5.6kohm to another 20 mk.
I would like to convert that to a choke loaded input.
Thanks in Advance.

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Re: Some questions on Power supplies [message #9365 is a reply to message #9364]

Sun, 27 November 2005 14:01

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

I suppose that B+=365V is for output stage, CRC filter, from 60µF cap, and second RC filter (5k6/20µF) is for phase splitter.
Output DC voltage (365V) from L-input rectifier is 0,9*Utr, minus losses in transformer windings and diodes. In another words, you`d need Utr = 365/0,9 = 405,5V + Ulosses. To find out exact Utr, the esiest solutions is to use PS simulator, Duncan PSU II. You can choose various PS "blocks", and rectifiers. The first step is to measure (with Ohm-meter) primary and secondary resistances of your transformer(s). With full-wave (say 450-0-450V) secondary, measure the resistance of half of the secondary, from 0-450V, rs. Let`s say it`s 50 Ohms. Then measure rp of the primary (0-120V), let`s say it`s 8 Ohms. Then find the turns ratio N=Usec/Upr = 450/120 = 3,75 in this example. Compute the resistance of the transformer,
Rtr = rs + N^2 * rp, in this example
Rtr = 50 + 3,75^2 * 8 = 162,5 Ohms.
The program needs Utr and Rtr. Put a resonable choke, say 10H/100 Ohms and C~100µF after tube rectifier of your choice, loads (constant-current, say 70mA for output stage) and you can see various numbers - currents and voltages, and graphs.
See, for example my 300B "story" , part 3...

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Psud II example [message #9366 is a reply to message #9365]

Sun, 27 November 2005 14:51

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

Here`s the our example - we get little lower voltages, about 344V. For higher B+ you can use the another rectifier or choke with lower resistance.
Note that choke must be dimensioned for ~130mA, and transformer for about 90mA.

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Re: Some questions on Power supplies [message #9367 is a reply to message #9365]

Sun, 27 November 2005 14:56

2wo
Messages: 44
Registered: May 2009

Baron

Hi Guy, if you know what the AC output of transformers that you have, you can go right to Psu2 and cut and try.

Measure the DC resistance per Damir. Or just using the dc resistance of the secondary will be close enough to tell if the transformer could work.

As a rule a choke input filter will give you about .7 of the rated voltage cap input about 1.4

Remember if you have say a 250-0-250 transformer, in Psu2 with a full wave rectifier (normal hook up for a 5y3) you state the transformer as 250V.

If you can’t get a high enough voltage, switch to a full wave bridge (SS or tube) and try again. Only in this configuration, you state the above transformer as 500V

Have fun…John

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Re: Psud II example [message #9369 is a reply to message #9366]

Sun, 27 November 2005 16:31

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Damir; thanks much. What is the value that shows for C1; is that 220nf?
What is the process for replacing a resistor in a pi fiter with a choke?

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Re: Some questions on Power supplies [message #9370 is a reply to message #9367]

Sun, 27 November 2005 21:05

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Guys; I see that the 6v6 will not work with 750vct trans since it needs 350v plate voltage.
6l6 can get by with 300vplate voltage which shoulod work with 750vct. But I wonder what effect a different rec tube would have. Say a 5u4 which should be able to pass greater current to the filter; no?
Thats the kind of speculation I am interested in. Ie; If you find a rectifier circuit that will provide 300 volts on the plate with 150ma current. What changes will occur with the use of different rec tubes?
What is the best way to rectify AC if you need a cap input or a choke input. Doesn't the type of rectifier tube affect the performance of the filter and how much benefit you gain with using a clc or lc filter?
I can run the specs through PSUD II but I am looking more for a theoretical opinion of how to implement the different types of filters/the way to combine rec tube types with CLC or LC ladder filters. In reading different analysis of PS types there are some universal aspects of design that people apply to circuits in specific circumstances.
Example: LC filters should be used in applications where there are wide variations in load current.
Output voltage decreases with increasing current in the LC filter.
These are the types of information that can frame the choices available to the builder. By expressing these simple truths it makes it much easier to begin the design process for a novice.
When you guys start out with the maths and the design programs; those types of facts seem to get lost to the begginner.
Is this helpfull at all?

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Re: Psud II example [message #9371 is a reply to message #9369]

Mon, 28 November 2005 05:56

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

The purpose for C1=0,22µF=220nF (1000 VDC ratings) is to remove voltage spikes and improve HF filtering, see "Valve Amplifiers" by M. Jones - good and detailed explanations about L and C input rectifiers. RDH is a good info, too.
For L-input you must "draw" the minimum, "critical current", about Im~Utr/Lch ~ 45mA, to avoid Udc=1,4*Utr, like in C-input case.
And you can substitute 100 Ohms resistor in CRC filter with a choke with sufficient current ratings, and Rw~100 Ohms, beter filtering.

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Re: Psud II example [message #9372 is a reply to message #9371]

Mon, 28 November 2005 12:41

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Well; I guess I will purchase Morgan's book on amps. It seems to be the bible for home constructors. Thanks Bud.

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Re: Some questions on Power supplies [message #9374 is a reply to message #9370]

Mon, 28 November 2005 14:39

2wo
Messages: 44
Registered: May 2009

Baron

I think you can get the 750VCT transformer to work. If your not dead set on a choke input filter.

Go back to the example that Damir posted.(how do you do that?) Change the transformer voltage to 275, then tinker with the value of the first cap. As you slowly increase the value, the output voltage will rise.
With 10uf I was able to get ~365with 5Y3’s 10uf- 10h- 50uf With a 70ma CS...John

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