Thanks!
This was my first amp DIY project I've ever done. Really its about the first DIY project I've ever done. And I'm damn proud of it. It couldn't have turned out any better...
Nick
This was my first amp DIY project I've ever done. Really its about the first DIY project I've ever done. And I'm damn proud of it. It couldn't have turned out any better...
Nick
OK people. I'm freaking out.
I think my amp just died.
I was listeing to music like normal. Volume about half way. And I hear a thump and the music is instantly gone.
I didn't know what to do so I started swapping tubes thinking one might have blown???
No go.
I then pulled the cover off and had a look around. Nothing is visable to my eyes. I haven't pulled the pcb yet to look on the other side yet. I did look through the tube holes with a flashlight real quick to see if I noticed anything that stood out. I didn't see anything.
Could I have a bad transformer?
When I turn the amp on the fuse blows instantly. The amp doean't even try to power up. .
I feel sick.🙁
Can anybody tell me what to look for or what to test?
Nick
I think my amp just died.
I was listeing to music like normal. Volume about half way. And I hear a thump and the music is instantly gone.
I didn't know what to do so I started swapping tubes thinking one might have blown???
No go.
I then pulled the cover off and had a look around. Nothing is visable to my eyes. I haven't pulled the pcb yet to look on the other side yet. I did look through the tube holes with a flashlight real quick to see if I noticed anything that stood out. I didn't see anything.
Could I have a bad transformer?
When I turn the amp on the fuse blows instantly. The amp doean't even try to power up. .
I feel sick.🙁
Can anybody tell me what to look for or what to test?
Nick
(1) Don't Panic.
If it was built by man, it can be fixed by man. Usually. Although not always economically.
IF you have terminals on the board suggest pulling ALL power transformer leads off the board and putting wire nuts on them (or electrical tape if you have no [wire] nuts).
With the power transformer NOT connected to anything, plug it in.
I had a 71A monoblock do the same thing, and it was a shorted, ancient NOS power transformer; the winding insulation had aparently just gotten old and failed. Pissed me off royally.
After you eliminate the PST as a cause, you can work "forward" through the amp to find the cause.
If it was built by man, it can be fixed by man. Usually. Although not always economically.
IF you have terminals on the board suggest pulling ALL power transformer leads off the board and putting wire nuts on them (or electrical tape if you have no [wire] nuts).
With the power transformer NOT connected to anything, plug it in.
I had a 71A monoblock do the same thing, and it was a shorted, ancient NOS power transformer; the winding insulation had aparently just gotten old and failed. Pissed me off royally.
After you eliminate the PST as a cause, you can work "forward" through the amp to find the cause.
Speaker posts isolated from the chassis, I hope ?
I've seen some people use the super cheapies with poor isolation washers that allow the terminal to short to the chassis if it gets wiggled.
Is yours tube or solid state rectified? That appears to be a 5AR4 on the chassis.
I've seen some people use the super cheapies with poor isolation washers that allow the terminal to short to the chassis if it gets wiggled.
Is yours tube or solid state rectified? That appears to be a 5AR4 on the chassis.
Jeb-D. said:
Well... Yes. But they were kind of iffy. ONe of them had the isolation washers melt down a little last time I was doing some soldering on the binding posts.. But nothing looked like it was shoorted. And the amps been playing beautiful music for quite a while now,
The amp is switchable between SS and tube rectifaction.
Whould a shorted binding post blow fuses like it is?
Either way I am going to check them when I get off work today. I was too tired and upset last night to work on it lat night...
Nick
Cut the FREDs (solid state diodes) out. I will bet they have shorted. Many have had this problem.
They usually blow or short during the powerup surge, but anything can happen if they have been stressed. Are you using surge limiters? Which rectifiers were you using when it died? If it blows the fuse instantly when using tube rectification when no tube is installed, then it is most likely either the FREDs or the power transformer or a random short in your wiring somewhere.
Do what ha said:
1) Disconnect the power transformer from the PCB and put wire nuts on the wires. If you can turn it on without blowing the fuse then the power transformer is probably fine.
2) Hook-up the 5V and 6.3V heater windings back to the board. If the tubes light up when power is on, then you know the problem's in the HT side.
Russ
Do what ha said:
1) Disconnect the power transformer from the PCB and put wire nuts on the wires. If you can turn it on without blowing the fuse then the power transformer is probably fine.
2) Hook-up the 5V and 6.3V heater windings back to the board. If the tubes light up when power is on, then you know the problem's in the HT side.
Russ
It would, if the tubes were installed and it's playing audio. But not on initial power on.
I was thinking blown FREDS, like the others have mentioned. But the appearance of the tube rectifier threw me off.
The others have already given some good advice where to start.
Another thing is that when using terminal strips with stranded wire, it's a good idea to tin the exposed wire before screwing them into the terminal. Otherwise you can get a straggler that finds it's way to the neighboring terminal.
The most likely cause for blown fuses is the FRED diodes. The IXYS parts that were in the parts list have become increasingly unreliable. The early versions were bullet proof, but the ones currently shipping fail. This has to do with their lack of an "avalanche rating" coupled with some process change in their parts that occurred about two years ago.
They usually fail as the amp is switched off due to the inductive spike produced in the power transformer. The issue is magnified with the lower cost hammond power transformers. The amp will then blow the fuse the next time it is turned on. A failure during use is rare but it can happen due to a transient on the power lines.
First try removing the 5AR4. If the amp still blows the fuse, I would remove the diodes. If that fixes the problem the amp can be operated without the diodes, or the diodes can be replaced if the solid state rectifier option is desired. DO NOT use the IXYS diodes. Use the Fairchild Semiconductor ISL9R8120P2 diode. Digikey does not have them.
Mouser # 512-ISL9R8120P2
Newark # 29H0500
The IXYS part number was removed from the Simple SE parts list due to reliability issues. I will add the Fairchild number if I can't find a suitable replacement that is stocked by Mouser and Digikey. I have put the Fairchild parts into all of my amps and tried my best to blow them, they all survived.
I have recently updated several pages on the web site including the Simple SE "tubes and transformers" page to help answer some of the questions about this design. The diode issue is mentioned as is the inrush current limiter.
OH MY GOSH!
I just remembered. There was some sort of power surge when this happened. The power went of for literaly a split second.
I bet this blew the freds. At least sounds like the mos plausable from what you just wrote George.
I'm going to wire the amp back completly and remove the FREDS. Than try again.
I never liked the way SS souned anyway and never used it..
THANKS!
Nick
I just remembered. There was some sort of power surge when this happened. The power went of for literaly a split second.
I bet this blew the freds. At least sounds like the mos plausable from what you just wrote George.
I'm going to wire the amp back completly and remove the FREDS. Than try again.
I never liked the way SS souned anyway and never used it..
THANKS!
Nick
I've been using Fairchild's version of the FRED for a while without any issues. They are cheaper than Vishay's HexFREDs and seem to work just as well.
Speaking of which, I keep meaning to tell you: there is a typo on the Tubelab SE "Tubes and Transformers" page in the "The 45 tube" section. The Allied P/N should be 6K56VG not 5K56VG. I've pasted that into Allied website at least once and was left scratching my head for a moment....
tubelab.com said:
Speaking of which, I keep meaning to tell you: there is a typo on the Tubelab SE "Tubes and Transformers" page in the "The 45 tube" section. The Allied P/N should be 6K56VG not 5K56VG. I've pasted that into Allied website at least once and was left scratching my head for a moment....
Is there anything I need to know about removing the FREDS?
I do I need a jumper wire anywhere?
Nick
I do I need a jumper wire anywhere?
Nick
Get the side cutters. Clip them off the board. Don't put a jumper anywhere near the solder pads where the FREDs went. If you don't have side cutters, you can use toenail clippers.
Most people do not use it especially with the ever escalating line voltages and Hammond over spec transformers. It does give a small power boost for those situations where you need to annoy the neighbors. The SS diodes also run the amp close to the 500 volt maximum rating on the capacitors with todays transformers and line voltages.
OOPS. I still type with two fingers, and one must have gotten on the wrong key. I will fix it ASAP.
The Fairchild diodes are "avalanche rated" for 20 mJ. This means that they can eat 20 milli Joules of energy in the reverse direction without failing. The IXYS FREDS do not have a spec for this. The old ones were fine, the new ones....ZAP! They probably changed the process over to a newer IC fab that does smaller geometry lines and lost some avalanche capability.
The power transformer is a magnetic device that operates with well controlled magnetic fields that smoothly reverse direction 60 (or 50) times a second. This is what makes them work. When the power is abruptly removed the magnetic field instantly collapses inducing a large voltage spike in the secondary. This is the principle that the ignition coil in your car uses to fire the spark plugs. Every transformer responds differently and the newer Hammonds seem worse than others. I have observed a spike of over 2000 volts on a 6K7VG which IS made by Hammond. If this voltage is higher than the reverse breakdown voltage of the diode (1200 volts) the diode will conduct. If the total energy in the "spark" is less than the "avalanche rating" of the diode, nothing bad happens, the diode eats the energy and turns it into heat. The Fairchild diodes are specified to handle 20 mJ of avalanche energy, the IXYS diodes have no specification, so it is unknown how much they can eat.
The migration from older wafer fabs to newer ones is usually a cost issue. The newer fabs process bigger wafers and usually run at higher yields. Both of these bring down the cost of making parts. A lot of semiconductor vendors have been transferring older products to outside fab houses in the far east like TSMC. The new parts may meet all of the published specs, but the avalanche rating was never specified for the IXYS FRED's so the new parts meet their published specs.
FRED's (Fast Recovery Epitaxial Diode) were designed for use in switch mode power supplies where the avalanche energy was small due to the tiny magnetic circuits used at the high switching frequencies. The FREDs had a "fast recovery" from turn off which is needed for high frequency operation (slow diodes will literally melt). This just happens to make them quieter for tube applications. Avalanche energy specifications became important as advances in SMPS technology started relying on it.
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