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In Reply to: RE: Restoration of Leak TL50 plus posted by Tube747 on April 02, 2016 at 23:26:40
What's the DCR of the secondary winding?
To use a 60uf cap in that circuit there would need to be about 125 ohms DCR in each half of the HT winding otherwise the peak current rating of the 5ar4 will be exceeded.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
You can literally run a 5V3 which is about a 4 amp filament and it doesn't break a sweat on the 5 volt winding.The transformer even runs cooler with the 5V4 and if you measure the voltage on the 5v filament winding with the 5V3 installed,it reads exactly the same as with the GZ34 installed..They overbuilt the Leak power transformers and can handle much higher current than the 2 amps the GZ34 draws.
A friend you get for nothing,an enemy has to be bought
It's not the filament winding that needs to have the minimum DCR, it's the HT winding.
And it's not the filament current, it's the peak B+ current through the rectifier tube.
With a cap input filter each diode is only on for a short time each half cycle.
The larger the cap the shorter that time is and the higher the current will be.
The allowable amount of uf is directly related to the amount of limiting resistance in place.
More resistance, more uf allowed. Less resistance, less uf allowed.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre
When charging current goes up,the conduction angle gets smaller and that's why I always pay close attention to the first cap value and not make it too large..
This was on the Leak Stereo 50 that I ran the 5V3/5AU4 with no issues..Being this amp was designed to run several different output tubes which vary in filament current,I would assume they also beefed up the windings on the rectifier filament just by the nature of the size of the transformer.The B+ reading was identical to a metal base GZ34 so I would guess the drop was almost identical with the GZ34.
A friend you get for nothing,an enemy has to be bought
Edits: 04/04/16
How about that? My friend has given me few pieces Continental Capacitor 30uf 650v oil filled cap for the position after the rectifier tube and suggested I put 2 x 50uf 600v after the choke.
The oil cap can mount insider the chassis and those 2 x 600v capacitor to fill the holes on the chassis.
Is that ok??
What value was the input cap (c14) to start with?I wasn't trying to dictate what you can and can't do.
I was trying to point out that physics dictates what you can and can't do.
It all depends on the AC plate voltage, current and the value of the limiting resistance.
When people point out the the data sheet states 60uf as the max value for he input cap, I was just trying to point out that 60uf is only allowable under certain conditions.
Under different conditions the max uf will be different.
The conditions for using 60uf are given in the graph on page 4 of the pdf linked below.
You can use PSUD2 and see if the max plate current rating of the rectifier tube is being exceeded.
Here's an example where 60uf causes a peak current of 810ma exceeding the max rated 750ma because the limiting resistance is too low for the conditions.
Here's an example where 30uf causes a peak current of 934ma exceeding the max rated 750ma because the limiting resistance is too low for the conditions.
Here's an example where 70uf is fine and the rated peak current of 750ma is not exceeded because the limiting resistance is sufficient for the conditions.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 04/04/16
As says, my friend has sold me some Continental capacitor type A 30uf 650v for this position.
Then I might use 2 x 50uf 600v in parallel (total 100uf) after the choke.
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