How to build the F5

Jump to Latest
#782
6L6 said:
It is CRC. The resistors are on tabs in the back of the photo.

EDIT - And as I hit the 'post' button, I see your comment above... We must have been typing at the same time!
Click to expand...

I hope it works out that I used the same resistor value as in the original PSU schematic. I also want to spend the 2.2k 3W resistor right behind the rectifier so it actually is a RCCCRCCC config.

Cheers,
Mallard
 
#787
FLG's right.

You keep referring to the bleeder resistor as another "R" in your power supply filter circuit. It's not. It's there to run from your power rail to the ground, and to discharge (....."bleed" the voltage from.....) your capacitors once mains power is removed. It's there for your safety.

Place this resistor (the BLEEDER resistor) across the last set of capacitors in your power supply (the ones "furthest" from the rectifier--again, one from your + rail to ground, and another from your - rail to ground.
 
#789
Firework

Oh Sh..😱

See what happend to my first rectifier start up. It was a loud bang with lighting...everything a real good firework needs 🙁 I've done it seperately.
The picture shows the 2nd channel, 1st one was ok. I only changed the
ground connection from - of the cap to + of the caps.
Of course all four diodes a dead now. Luckily I have a good source of it 😀

But I guess i made some soldering error... assuming that can be the onle reason for such a bang, right?

Cheers,
Mallard
 
#790
tinitus said:
why on the last caps 😕
Click to expand...

Tinitus, actually, it doesn't matter that much on a relatively low voltage supply. This is particularly true when the "R" in the CRC network is relatively low resistance--in this case, both capacitor banks (the first and second "C) will discharge about the same, at the same time.

I put the bleeder on the last set of capacitors, from force of (construction0 habit. In large tube systems (like transmitters), the "R" value may be pretty high (and there may be several CRCRC stages). In addition, many well-designed tube transmitter power supplies are self-contained, and only the final DC voltages exist outside the power supply "cage". For such a design, it's best to quickly discharge the final set of caps (i.e., typically the final power amp's plate voltage) as it exits the power supply. For this reason, that's where I put my bleeders--on the final set of caps, so that any cap-stored HV external to the power supply is reduced relatively quickly. Again, this is more of an accepted practice on HV systems.

Having said that about HV and transmitters and bleeders, I still work with "one hand in my pocket", and I still use a "shorting wand" when working on HV transmitters. (One of our transmitters puts out 32 MEGAWATTS of RF.....and you only need to screw up one time, to get your obituary published!)
 
#791
Mallard, you state "The picture shows the 2nd channel, 1st one was ok".

I'm confused. Do you actually mean "rails" when you say "channel"? You have two rails in your power supply--one ~+24 VDC and the second at ~-24 VDC.

....or do you actaully mean "channel", as in the left and/or right channel of your amp? (And are you actually doing your initial tests, with your amp boards connected? Please say no....)

And yep--to crack a power semiconductor's case with accompanying smoke/fire, I'd say you have a direct short in your power supply. Time to drag out the DMM and start taking some resistance readings.
 
#793
CanAm Man said:
Mallard, you state "The picture shows the 2nd channel, 1st one was ok".

I'm confused. Do you actually mean "rails" when you say "channel"? You have two rails in your power supply--one ~+24 VDC and the second at ~-24 VDC.

....or do you actaully mean "channel", as in the left and/or right channel of your amp? (And are you actually doing your initial tests, with your amp boards connected? Please say no....)

And yep--to crack a power semiconductor's case with accompanying smoke/fire, I'd say you have a direct short in your power supply. Time to drag out the DMM and start taking some resistance readings.
Click to expand...

Sorry for confusing, I mean by channel the left and the right side! And I say NO - my amps are not connected, I'm not crazy.
Yeah try and error can cost a lot of money and nerves.
 
#794
Did you use a fuse at all when you plugged in the PS? That could have saved your diodes.

Anyways, two suggestions : check that ALL your caps are connected correctly : ie + to + and -Ve to -ve.
Also Check that you REVERSED the polarity on your bridge. As well as the caps. on the -ve side.

I screwed it up in the beginning as well, but I had a fuse and it just kept blowing the fuse.
 
#797
tinitus said:
would a bigger bleeder resistor drain the caps slower ?
Click to expand...

Yep.... a bleeder resistor with a higher resistance would drain the caps at a slower rate.

Other factors not considered, the drain rate over time would look very much like an RC "decay curve", with the voltage on the cap impacted by (1) initial voltage applied (2) size (mfd) of the filter capacitor, and (3) size (ohms) of the bleeder resistor.

Ken
 
#798
dazed2 said:
Did you use a fuse at all when you plugged in the PS? That could have saved your diodes.

Anyways, two suggestions : check that ALL your caps are connected correctly : ie + to + and -Ve to -ve.
Also Check that you REVERSED the polarity on your bridge. As well as the caps. on the -ve side.

I screwed it up in the beginning as well, but I had a fuse and it just kept blowing the fuse.
Click to expand...

Hmm... I had a fuse but with 4Amps... I changed to 1.25A.
Regarding your 2nd suggestion: till now I thought the + pol on a bridge is always the same. So I connected the + from the bridge to + of the cap and the - pol of the bridge the - of the cap. For the positive side of the PSU the - of the caps goes to gnd. For the negative side the + goes to gnd. Thats the only difference i see.

Sorry, it's my 1st PSU 😱

Cheers,
Mallard
 
You must log in or register to reply here.
Top Bottom