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    Building, troubleshooting and testing of these amplifiers should only be
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Edcor XPWR059 power problem

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Hi All,
Tried in the Tubelab forum first, sorry for double posting.
My Simple SE has been running without a problem for about a year now, then a couple of days ago the fuse blew while listening to music after a few hours.
It has never done this before, now the fuse constantly blows (1A slow blow)
I tested the amp as follows
No FRED diodes. I use the 5AR4
XPWR059 wired for 240v

Blowing fuses suggests that something is shorted to ground,
checked for continuity;
The hot & neutral tabs of the IEC receptacle
Both tabs on the fuse holder
power switch

None of these indicate continuity, regardless of whether the power switch is open or closed.

Measured the XPWR059
The 6.3V winding 0.4ohm
The 5.0V winding 0.4ohm
The filter inductor (choke) & run cap not connected.

HT secondary coming from the power transformer.
The two red wires 25ohm

CXS8E 25-8-5K
Primary = 4.6Ohm
The secondary windings of the output transformer 0.7 ohm
primary 83 ohm.

So I disconnected all the XPWR059 secondary & Centre tap from the PCB, so the only connection is the power switch + Primary + red HV to my DMM.
I was expecting to test the HV then 6.3v & 5v.
Fuse blows!
The tubes are out at this stage, and the PCB is not connected.
Also the Xfrmr is removed from the chassis, free standing.
just using the switch,fuse & power connector.
I was checking for shorts on the leads.

Does this mean the power xformer is faulty?

Any further tests of the Xfrmr i can do to to determine if its faulty?
Many thanks
Ian
 
Disabled Account
Joined 2010
webby,

You need to eliminate everything. So take the Tx out of the chassis do not use the power connector and connect a 3 core mains lead with a 1A-3A fuse in the plug. Connect all the output secondary windings to a connector block so they are isolated from each other then power up and see what happens. It may be the Tx it could be the mains filter etc. so test the Tx on its own. Remember to Gnd the chassis of the Tx! If it blows with a 3A fuse its stuffed. You could remove the end bells to check you have no trapped cables.

If the mains filter has flashed over it may not show without a megger test! A multi meter output voltage is not enough to recreate the flash over!

Regards
M. Gregg
 
Administrator
Joined 2004
Paid Member
Check the power switch as well, I've had more than one instance where the insulation between the contacts and switch bat failed. Turn on the amp, fuse blows since I use a safety ground. This is a good argument for making sure the safety ground connection is there and working correctly.

Not unlikely that there is a short in the high voltage windings, the clue is whether or not there is a gross difference in winding resistance between the two outer legs of the winding and the center tap. Incidentally 25 ohms sounds a bit low to me, OTOH I have no direct experience with this particular power transformer.
 
Thank you both for the suggestions, very helpful.
Last night i tried the TX wired direct to the power cord, it blew the 3A fuse instantly.
I earthed the TX and used a connector block as advised, and used the mains switch to turn on power for safety.
If I measure from the centre tap and each of the red HV leads, they read 18ohms & 43ohms. one is more than double.
Can I conclude this TX is faulty?
Many Thanks
Ian
 
Transformer primary windings are generally more sensitive then secondaries, but the resistance difference between the secondaries is rather telltale.

my guess: you have a short in your amps HT circuit which melted the secondary windings, and then they shorted together. check the rectifier for shorts before you try another TX. lightbulb trick might be worth while if you do not have a tester

does the fuse blow with nothing wired to the secondaries at all? its a totally trashed transformer in this case, otherwise you have a potentially partialy functioning transformer. for instance if just one HV winding is shot you could use it for running a SS rectifier on the remaining winding, or use the 50v, 5v, or 6.3v windings for future projects.

Edcor is a excellent company, its definitely worth writing or calling them up. they might be interested in seeing what failed about it and give you a new one
 
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Hi All,
Thanks for the input.
The TX blows the fuse with nothing connected to any of the secondary wires.
I will contact Edcor, but unfortunately the postage costs to return it for replacement are way too much. We pay so much more in the UK, about double for the same weight?
I have a friend in the US who ordered the TX's for me, and posted them out.
Ill just get another ordered, I'm missing my Tubelab Simple SE too much!
Cheers
Ian
 
Disabled Account
Joined 2010
webby,

A few things I would do!

With the TX out!

Please check that you have no shorts on the heater supply and HT supply on the amp. To check the heaters pull all the tubes and check across the heater connections should be high resistance. The B+ you can check after the rectifier, caps should charge with resistance setting giving a high reading except for any discharge resistors you have in circuit. Check any bypass caps on the op tubes cathode. Also check all input connections from the Power Tx to chassis Gnd.

Then-

When you fit the new Tx check current on the B+ rail on power up to see how much head room you have left! I would fit a HT fuse on each leg just a temporary measure! Quick blow less than current rating B+ max. Keep your finger on the OFF switch just incase the current tops out!

Remember to connect your speakers..LOL

It's just being carefull.

Regards
M. Gregg
 
fuse before your tube rectifier, as an internal short in there would feed directly into your transformer. if you got a way to power it up with just heater voltage and then test for shorts its probably for the best

also realized my previous post had a serious typo in it... lol i should stop writing posts when im tired

while its all apart, good chance to go ahead and setup for dc heater supply if you don't already?


Heres how i powered up my custom amp for the first time being uncertain of the condition of everything, maybe the procedure will be helpful. keep in mind my fuse choices were with 117v line:

started with 1 amp fast blow fuse on my transformer and wired up the heaters. powered it up and made sure it all was good (in my case, i have a lot of tubes, ~8 amp start 5 amp steady on 12v supply)

with that all set, i upgraded it to a 3 amp fast blow (my TX is rated for 400VA) i put one meter monitoring current coming out of my rectifier and a second one monitoring the voltage on the other side of my filter caps, with all my tubes unplugged. i turned off power before cap voltage exceeded ratings.

then i systematically, one tube at a time installed each one. this way if there is ever a fault i knew precisely the sub-circuit that did it. Soon as i did not need to turn it off between each tube due to filter cap voltage i left it on.

my first start up was rather complex because i have 5 channels in my amplifier, and i wanted to power it up one channel at a time

after i was all done i installed a 3 amp slow blow instead for my final fuse choice.
 
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Antek Inc. should have a suitable transformer for your SSE. They ship via USPS so shipping shouldn't be completely outrageous. They use the flat rate boxes so you can check the cost on USPS's website ahead of ordering.

I'm not related to them in any way, I just use their products.

I'm surprised to hear that you have issues with the Edcor transformers, though. The Edcor OPT's I've worked with have been pretty good. I don't see a reason why their power transformers wouldn't be as well. Have you checked the load on the transformer to make sure you aren't overloading the transformer?

Definitely contact Edcor. They may not want the burnt out transformer back... It's worth an email anyway.

~Tom
 
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i like my Antek transformers as well. the Antek power transformers tend to be stronger then the Edcor. but the neat thing about the Edcor transformer he has is its got 50v for your bias, 5v for your rectifier heater and 6.3v for your tube heaters, all in one transformer.

From my previous talks with Edcor they apparently make transformers of all kinds as an OEM for quite a few manufacturers but for our purposes they seem to be only incredibly interesting as an source for OPT's and chokes
 
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