SE Electronics 5600a PSU

[dgmc440]

My son helpfully flicked the voltage selector from 230 to 115 while powered on (we’re in Australia on 240 mains) and has bricked the PSU. What would have been fried? My electronic knowledge is fairly basic although I’ve repaired numerous things over the years by carefully following instructions. Any help would be greatly appreciated!

note: this is not the 5600a II. sE tell me the newer PSUs are not compatible

 

[Khron]

Internal photos, at least?

 

[Tubetec]

Finding a schematic might be a logical first step .

Sometimes theres a primary fuse incorporated into the IEC mains inlet , if not maybe in the enclosure itself , thats worth a check , but also remember every component downstream of the transformer got double the voltage it expected
You could try checking the primary winding in the transformer for continuity , just in case thats gone open

 

[Tubetec]

Is the 5600 the two tube mic ? Would be nice to have a pick over the circuit diagram of that unit and see whats going on inside .
Try and get SE to send you the schematics maybe .

 

[dgmc440]

I'll see if I can get a schematic from SE; I've had no luck online. A diagram for the later model on this forum brought me here. I couldn't see a fuse but I'll have a closer look. A couple of caps are bulging a bit.

 

[dgmc440]

OK, stand down. There is a fuse... All good now.

 

[Gus]

I would first check the power transformer as others posted
One cap is definitely bad from the leak you can see at the vent lines in the aluminum. The others might be damaged as well

Next and this is going to be a bit of work
Not powered up, check every component you can with a DMM, cap tester etc.
I have found that when something it damaged like this it is better to check every thing you can before powering up again
The reason I am writing this is because of the visible leakage at the cap

What are the markings on the 8 pin IC? That will let you look it up and get an idea of what the circuit is around it.

 

[RuudNL]

I guess the IC is a NE555. Timer for the relay.

 

[Tubetec]

I guess you found the fuse behind the IEC panel , I had typed another message but must have forgot to post .

When you say all good now , did you go ahead replace the fuse and apply power ?
Gus got there already but I was going to suggest cold testing for shorts with the multimeter before applying power
Even if the unit has sprung back into life , at least replacing any of the caps that have bulged would be a good plan at this stage .

So anyway , interesting to see the inside of the power unit , looks like a standard regulated Dc heater supply , HT looks passively smoothed but has a timed delay before the relay applies it .
How long does it take before the relay clicks in ?

Have you seen the relay type arrangement in other modern mic supplies Ruud ?
Whats your opinion on a delay to allow the heater to warm up from cold before HT is applied ?
I'd tend to prefer a simple slow ramp up of HT due to the use of large value caps rather than the extra complexity of timers and relays , which ultimately apply the HT with a bump . I have one tube mic PSU with a standby switch , You can hear a suddebn rush of electrons in the mic output the moment the HT is applied , the nice thing about a slow ramp up is the sound fades up from nothing without any extraneous noise whatsover , same thing after power down , no abrupt bumps or clicks ,the HT just gradually drains down, the heater cools and the sound starts to fade away over the course of 15-20 seconds .

Good power up and down behaviour ie lack of clicks bumps or other noises is always a nice attribute in a mic, being at the front of the gain chain means any noises get amplified , Most phantom powered gear comes on with quite a bump , I usually set input gain to minimum and make sure the channel output is muted before engaging it , otherwise your liable to get a very loud bang over the monitors , not good .

 

[RuudNL]

All famous high quality microphones (U47, U67, M251 etc.) used a power supply without a relay.
Never had problems with those relay-less power supplies...
Some microphones (Blue for example) use such a long delay time, that you sometimes think: "is it going to happen today"?

 

[TLRT]

All famous high quality microphones (U47, U67, M251 etc.) used a power supply without a relay.
Never had problems with those relay-less power supplies...
Some microphones (Blue for example) use such a long delay time, that you sometimes think: "is it going to happen today"?

I saw ruined u47's, As the psu has one voltage only with high current(40mA is high compared to standard triode mics when the tube heater burns outs the the psu voltage goes too high and kills the capsule and it can make other troubles. I usually add a passive protection circuit to these psu's which doesnt add any extra noise like zeners.

 

[RuudNL]

The U47 (VF14) was a strange design anyway!
One voltage (105 V.) for filament and +HT.
(Without a load the voltage of the original power supply could be as high as 370 V!)
As far as I know this is principle is never used again...
The filament voltage in the U47 was about 35 V, while the VF14 was rated for a filament voltage of 60 V.
Personally I have never seen a VF14 with a defective filament.
But as always...better be safe than sorry!

 

[dgmc440]

I guess you found the fuse behind the IEC panel , I had typed another message but must have forgot to post .

When you say all good now , did you go ahead replace the fuse and apply power ?
Gus got there already but I was going to suggest cold testing for shorts with the multimeter before applying power
Even if the unit has sprung back into life , at least replacing any of the caps that have bulged would be a good plan at this stage .

So anyway , interesting to see the inside of the power unit , looks like a standard regulated Dc heater supply , HT looks passively smoothed but has a timed delay before the relay applies it .
How long does it take before the relay clicks in ?

Have you seen the relay type arrangement in other modern mic supplies Ruud ?
Whats your opinion on a delay to allow the heater to warm up from cold before HT is applied ?
I'd tend to prefer a simple slow ramp up of HT due to the use of large value caps rather than the extra complexity of timers and relays , which ultimately apply the HT with a bump . I have one tube mic PSU with a standby switch , You can hear a suddebn rush of electrons in the mic output the moment the HT is applied , the nice thing about a slow ramp up is the sound fades up from nothing without any extraneous noise whatsover , same thing after power down , no abrupt bumps or clicks ,the HT just gradually drains down, the heater cools and the sound starts to fade away over the course of 15-20 seconds .

Good power up and down behaviour ie lack of clicks bumps or other noises is always a nice attribute in a mic, being at the front of the gain chain means any noises get amplified , Most phantom powered gear comes on with quite a bump , I usually set input gain to minimum and make sure the channel output is muted before engaging it , otherwise your liable to get a very loud bang over the monitors , not good .

My unit, externally, is a lot more rudimentary; no printed warnings or model numbers. We've had it for fifteen-odd years. But the fuse holder is blindingly obvious! I'd been searching internally. I confess I did power up immediately to check if the fuse remedied the power issue, which it did. But I will now look at some other maintenance work, particularly those bulging caps. Thanks for the advice.