WAD Phono2 power supply.

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shane
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#61 Re: WAD Phono2 power supply.

Post by shane »

Ta Dave! Yes that's possible. I'm going to stick a scope on it tomorrow which should show if it's ripple on the HT or heaters.

Voltages are as follows:

HT 259v
60ohm r 1.91v
2n3906 c-e 2.52v
MJE350 c-e 0.71v

Does that sound right?
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#62 Re: WAD Phono2 power supply.

Post by Nick »

Either the current source is broken, or you need more voltage across it. I would aim for at least 20-30v across the current source, so the voltage in needs to be 280 at least if the VR tubes are regulating at 259, the voltage across the 2n seems oj, but I would expect the mje to be doing the heavy lifting.
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#63 Re: WAD Phono2 power supply.

Post by shane »

Ok, that gives me something to work on tomorrow. I suspect the supply voltage is low. Bit more measuring to do...
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#64 Re: WAD Phono2 power supply.

Post by shane »

Took some measurements just now. So I'm getting 230v out of the second transformer which gives me 286.2v out of the diode bridge. I then lose 3.6v across the 100r (282.6v) and 18.9 across the choke (263.8). Finally, I'm losing the last 4.47v across the current supply, giving HT of 259v.

Is the loss across the choke excessive? It's 7uH, with a DCR of 510 ohms.
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#65 Re: WAD Phono2 power supply.

Post by pre65 »

Using Ohms law the current draw is

A) Choke 510r 37ma

B) resistor 100r 36ma

So near enough.

I might have some other chokes, I'll check the DCR on them.
Last edited by pre65 on Tue Jul 04, 2017 12:44 pm, edited 1 time in total.
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#66 Re: WAD Phono2 power supply.

Post by shane »

Yup. Got that. What I'm getting at is do I need a choke with a lower DCR in order to increase the voltage into the current supply, or is it not that simple?
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#67 Re: WAD Phono2 power supply.

Post by Nick »

If you need a tad more voltage then play with the resistor (100r) value.
But given that you are only dropping 3.6v across that, its not going to help much is it.

230v Ac should give you more like 320v. I would either find a choke with lower DCR or mix and match VR tubes to aim at a lower HT. Say a 0A2 and 0C2
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#68 Re: WAD Phono2 power supply.

Post by pre65 »

shane wrote: Tue Jul 04, 2017 12:41 pm Yup. Got that. What I'm getting at is do I need a choke with a lower DCR in order to increase the voltage into the current supply, or is it not that simple?
Just amended my last post.

That was my thought, but you can't gain a lot of volts. If you halved the choke resistance you would gain about 9.5v.

How many extra volts do you need ?
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#69 Re: WAD Phono2 power supply.

Post by shane »

According to Nick the current supply needs about 20v across it. Given that the gas tubes are regulations at 259, then I need about 280v out of the choke. Just looked at the choke again, it looks like it's 15mH, rather than the 7mh I thought it was.
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#70 Re: WAD Phono2 power supply.

Post by shane »

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#71 Re: WAD Phono2 power supply.

Post by Nick »

No. You need a choke for the purpose of DC soothing.

Try without the choke in circuit and see how that goes.
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#72 Re: WAD Phono2 power supply.

Post by shane »

That's what I like. Simple solutions.😀
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#73 Re: WAD Phono2 power supply.

Post by pre65 »

shane wrote: Tue Jul 04, 2017 1:11 pm According to Nick the current supply needs about 20v across it. Given that the gas tubes are regulations at 259, then I need about 280v out of the choke. Just looked at the choke again, it looks like it's 15mH, rather than the 7mh I thought it was.
I thought the choke was 15H, not 15mH ?

Those are common mode chokes you link to Shane, not what you need.

I've measured some other chokes I had but the DCR is no less than the one you have.

Would putting a small capacitor (1uf motor run) before the 100r resistor give you enough of an increase ?
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#74 Re: WAD Phono2 power supply.

Post by shane »

Hmmm. Choke out of circuit. Hums like a mad bugger.

Not going to be able to do any more investigations for a week now due to work schedules, but I'll look for a better choke in the mean time.
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#75 Re: WAD Phono2 power supply.

Post by Nick »

What were the voltages like?
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