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My Singlepower Supra Experience - Why mine almost blew up like a Hand Grenade (and yours might too) - Page 21

post #301 of 314
As I'm current away from home, I'm unable to take any images of the transformer, or the uncovered transformer for that matter since it will require me to unscrew the PCB.

I've spent the last few minutes comparing mine with mrarroyo's MPX3 and mine sports a similar transformer other than the fact that mine does not sport a spec label and wired for EU(220V).

I understand the issues of the need for the bleeder resistors across the caps and the underspeced voltage switch(which would be more tricky to mod), but
since I'm not touching the large caps all the time, and neither am I fiddling with the voltage switch, I'm not that worried about them(unless they are exploding risks).

Shouldn't the main issue at hand be the danger of the "exploding amp" which after sifting through the thread is caused by the overheating of the filament/HV diodes by the wrongly spec'ed transformer/capacitors? If so and since mine does not sport any discoloration at all should I be concerned? As far as I remember, I'm running a 6SN7WGTA as input and 2X E182CC as output...

I guess the one consolation I got is that I'm currently off on a trip and have no chance of blowing my head off!

Edit: I just realised that of the 3 portable amps and 1 desktop amp that I own, all(three) of the makers have have ceased to exist...
post #302 of 314
Quote:
Originally Posted by fongalv View Post
I understand the issues of the need for the bleeder resistors across the caps and the underspeced voltage switch(which would be more tricky to mod), but
since I'm not touching the large caps all the time, and neither am I fiddling with the voltage switch, I'm not that worried about them(unless they are exploding risks).

Shouldn't the main issue at hand be the danger of the "exploding amp" which after sifting through the thread is caused by the overheating of the filament/HV diodes by the wrongly spec'ed transformer/capacitors? If so and since mine does not sport any discoloration at all should I be concerned? As far as I remember, I'm running a 6SN7WGTA as input and 2X E182CC as output...
The resistors across the large capacitors do serve as bleeder resistors, but they also serve as balancing resistors. They balance the voltage fed to each cap so equal voltage is fed to both. Without them, one cap may fail or, on turn on, more voltage may flow into one than the other. If this happens, the voltage the capacitor is rated for may be exceeded. Bad things could happen in that event. This is very easily remedied.

My interpretation of the photos show solder migrating away from the solder holes around the filament diodes.



The diodes in the lower left corner show very little solder in the hole-throughs. I would venture a guess that if you were to flip the board, you would see signs of scorching on the board. The definitive test is to measure the voltage at the tube sockets (pins 7 & 8) with tubes in and turned on with a set of cans plugged in. If the voltage is less than 6.1 you may want to consider replacing the transformer with one that will allow higher current for the filament circuit. Also consider replacing the filament diodes with higher current rated ones that would raise the body of the diode off the board so it can radiate heat away from itself safely, rather than having it trapped by the board. Add the resistors as a safety measure.

Good luck and happy holidays.
post #303 of 314
Very interesting observation. How high current for the diodes if the Transformer is not replaced?
post #304 of 314
Use as high current a diode as you can fit. The biggest problem will be to get rid of the heat generated by the current passing through the diodes. Something like a large bridge rectifier bolted to the back of the chassis may work best to radiate away the heat.

This will not help if the voltage is too low, but it will allow the AC to DC function to be done a bit more safely.

Using a different transformer is the absolute best way to go with these amps. You can reduce the high voltage to something safer that the parts already in place can handle and increase filament current to provide the correct voltage that the tubes need to operate correctly.
post #305 of 314
My diodes were relocated to the back panel.

post #306 of 314
Quote:
Originally Posted by mrarroyo View Post
My diodes were relocated to the back panel.
Miguel, a few pages back you showed how you had replaced one set of diodes with new, larger ones with heat shields.

These aren't the same diodes moved to the back of the case, are they? I can't see where the white wires lead from.

Was it hard to get the transformer cover off? I haven't tried.

Which diodes are these and were they overheating, or did you just replace them for safety sake.

Also to Bolder...Miguel put a dual voltage PT in my amp and hooked it up for 240/230. I haven't taken the cover off, but I feel no heat through the case or cover. None. It's cold at low power. I wonder if he could have put in a bigger one? I peeked on the backside of my board and I can't see any discoloration or solder movement signs around any of the diodes. But I haven't been willing to disconnect the whole board to get at the PT.

I am very grateful for the input on this thread.
post #307 of 314
Hi Frihed89, my work w/ the diodes was bad at best and a much wiser person corrected my work. Although tedious I had no problem taking the transformer cover, just work in a well lit area and have various tools available including socket/tip extensions (thin ones) and a flashlight.
post #308 of 314
The 120 volt versions usually used Hammond transformers. There is a 120/240 series of Hammond transformers, that is probably what was used.

What matters is what the filament current spec is. A fairly easy way to determine if your transformer is undersized is to measure the filament voltage. It should be as close to 6.3 volts DC as possible. If it is low, then it may be that the transformer is undersized for the current required.

Very carefully, measure the voltage on pins 7 & 8 of any of the tube sockets when the tubes are in and the amp is turned on. BE VERY CAREFUL! THERE ARE VERY DANGEROUS VOLTAGES INSIDE THIS AMPLIFIER!!
post #309 of 314
6.3 V it is. Now I just have to figure out if I want to replace all the diodes...I'm just not sure they need it.
post #310 of 314
Quote:
Originally Posted by Bolder View Post
The resistors across the large capacitors do serve as bleeder resistors, but they also serve as balancing resistors. They balance the voltage fed to each cap so equal voltage is fed to both. Without them, one cap may fail or, on turn on, more voltage may flow into one than the other. If this happens, the voltage the capacitor is rated for may be exceeded. Bad things could happen in that event. This is very easily remedied.

My interpretation of the photos show solder migrating away from the solder holes around the filament diodes.

The diodes in the lower left corner show very little solder in the hole-throughs. I would venture a guess that if you were to flip the board, you would see signs of scorching on the board. The definitive test is to measure the voltage at the tube sockets (pins 7 & 8) with tubes in and turned on with a set of cans plugged in. If the voltage is less than 6.1 you may want to consider replacing the transformer with one that will allow higher current for the filament circuit. Also consider replacing the filament diodes with higher current rated ones that would raise the body of the diode off the board so it can radiate heat away from itself safely, rather than having it trapped by the board. Add the resistors as a safety measure.

Good luck and happy holidays.
Thank you for the observations Bolder. Now that I'm back home, I just need to settle down before I start to make a mess when disassembling the amp and checking the diodes in detail.
post #311 of 314
My SDS-XLR just died the other day and I just came across this site. It looks like the thing to do is to contact Bolder about getting it checked out/fixed, right?
post #312 of 314
That would be the best thing to do unless you can DIY. The SDS-XLR which I've seen was a mess so a number of things could be wrong, undersized filament transformers, under rated capacitors, diodes and resistors not large enough to handle the current they had to pass i.e the usual Single Power mess.
post #313 of 314
Quote:
Originally Posted by Tyson View Post
I've had the Supra SE for a while now, and have quite a collection of 6sn7, 7n7, 12sn7, 2c51, vt-231's, 12at7's, 12au7's, 6922's, ecc99's, 6bl7's, etc... to "tube roll" in the amp. I also use Lawton Audio (Denon) LA-2000's, which are a pretty difficult load, being down in the 25ohm area.

I was never super happy with the sound I was getting. Hence the purchase of all the various tubes.

But, no matter what tubes I used, it always sounded a bit weak and there was that intermittant noise (faint, but noticeable during quiet passages).

I figured it was just a poor match with the very difficult Denon's, even when using the 6bl7's and the high voltage setting on the amp.

Finally, I decided I'd just go ahead and sell the amp and get the Zana Deux Transformer amp instead. But I wanted to give the Supra a check-up with a good tech before selling it to anyone.

So, I called someone I trusted, Wayne Waananan at Bolder Cables - Store for The Bolder Cable Company - to have a look at it. He worked with Kevin Gilmore and Mike Galusha (a couple of genuine tube circuit guru's). They asked me to take some pics and send them to him. Pics below:















As can be seen, those are not premium quality parts, far from it. But here's the rub - those 2 big @ss soup can sized capacitors? They are rated for 450v. Not bad, except the voltage from the transformer is 530 Volts! Now, even though they are connected in series, there is not a leveling resistor(s) in place between them. That means there is a high degree of danger that they will blow up, Yes, BLOW UP LIKE HAND GRENADES!!!!.

So, obviously this thing needs extensive repairs to get fixed. The power transformer is putting out WAY TOO MUCH voltage for this circuit. And the (cheap) parts in there are not rated to handle anywhere near this level of voltage. And because of the way voltage, current, and low impedance loads work, that means it's putting out 2.5mW of power to the Denon's (and only 1.2mW in Class A). That's pathetic. And there's 500v in the case just waiting to escape and kill your @ss. Grrrr. When I think about the fact that my 2 year old daughter likes to listen to my headphones it enrages me.

Back on topic - the changes needed are 3 fold - 1) Get a new input Power Transformer that's better quality and is half the voltage of the current one. 2) Replace the cheap, incorrectly spec'd parts in the power supply with better, appropriately spec'd ones (ie, get some HEXFRED diodes, and some Solen Film caps to replace the cheap electrolytics). 3) Optimize the output to be transformer coupled and use much better quality caps in the output circuit (ie, Obbligato film in oil caps and Sowter & Lundhal transformers).

The cost in parts alone adds up very, very quickly.


In the meantime, I suggest ANYONE that owns a Single Power amp to contact Wayne at Bolder Cables to see about getting it checked up. These amps ARE NOT SAFE.


Wayne was able to identify several major problems on mine just from an understanding of the circuit, combined with hi-rez pics I sent of the internals, and telling him the values of various parts on the board.

Tyson,

Your PICS look so much different then mine. I would say that it wasn't even done by the same person.

Can someone evaluate my PICS to tell me if I am in trouble or not?

I have the SinglePower MPX3-12SN7




Thanks.
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post #314 of 314
Pics not uploaded
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