n_maher said:
Sorry to hear the bad news. 🙁 For what it's worth, I've got the same 1.5 amp fuse I stuck in mine when I first powered it up this summer. Hope you figure out what is wrong. Which power tubes are you running?
With my very limited experience, I would guess that you have a short cct. I would start by checking the power supply. My experience has been that the solid state diodes can fry in this design, but with me it happened in association with the implementation of the standby switch. Did you fit solid state diodes? As you do not have a switch on the front panel, I am guessing probably not, but if you have - check they have not shorted out. If they have, I would suggest removing them and just sticking with valve rectification. Next I would check the power supply capacitors. As you said the music slowly faded, maybe a capacitor failed and you heard it dying. If it is not the caps, perhaps remove all of the valves and then power on to see if you still have the short and report back.
Good luck with the trouble shooting,
Chris
Good luck with the trouble shooting,
Chris
I was running a pair of EH EL34s that supposedly ran a little on the hot side. But I removed them and tried powering the amp with just the rectifier in place and still no joy. I'm sure we'll get it sorted, there's only so much that can go wrong.Ty_Bower said:
Yes, I did but they should not really part of the equation right since the requisite switch is not installed? I've only run the amp with valve rectification and really only had the diodes in there as a future option.chrish said:
I'll check the caps with my meter shortly as well as power it up with no tubes and report back the results.
Ok, in circuit the power supply caps test weird, almost as if C1 and C2 are in parallel. If I disconnect them from the pcb they both test as expected, 40uF for C1 and 200uF for C2.
I'm hesitant to try powering it up even minus the tubes given that strange condition. The caps measured fine even in-circuit yesterday prior to initial powerup. Any suggestions?
I'm hesitant to try powering it up even minus the tubes given that strange condition. The caps measured fine even in-circuit yesterday prior to initial powerup. Any suggestions?
Ty_Bower said:
Not a dead short, no, it measures 55ohms out of circuit. I don't know if that's normal or not.
55 ohms sounds reasonable for a filter choke.
Just for fun, have you tried metering the FREDs for continuity in either direction? They should measure high resistance in one direction and low resistance the other.
Just for fun, have you tried metering the FREDs for continuity in either direction? They should measure high resistance in one direction and low resistance the other.
Ty_Bower said:
I haven't checked the FREDs but I removed the pcb for inspection (all appears well) and was just going to pull them to eliminate them as a potential failure point.
I have burned through 2 sets of FREDs. I have since just yanked them out and I do not plan to replace. This was causing my short circuit and blowing fuses.
Just running tube rectification and all is well...
Just running tube rectification and all is well...
Ok, just measured the FREDs in circuit, D1 measures pretty much as Ty described, very high resistance in one direction (5M) and lower in the other (70k). D2 is different measuring 20k in one direction and 17k in the other. Does that point to a potential problem/solution?
I'm going to check the rest of the board components with my DMM and see if anything is measuring weird and if not I'll pull the FREDs and reinstall the pcb and see if I still get the same odd behavior from C1 and C2. Here's to hoping it's as simple as getting the SS rectification parts off the board.
I'm going to check the rest of the board components with my DMM and see if anything is measuring weird and if not I'll pull the FREDs and reinstall the pcb and see if I still get the same odd behavior from C1 and C2. Here's to hoping it's as simple as getting the SS rectification parts off the board.
cjkpkg said:
Thanks for posting that, it gives me hope. I'm off to yank the FREDs and will report back shortly.
One end of each of the FREDs goes straight to the high voltage secondary winding of the power transformer. The other ends of the FREDs are connected together via a trace on the circuit board. If one (or both) FREDs goes bad, you'll end up shorting the HV winding of the PT. That'll draw a lot of current and blow pretty much any fuse you stick in there, regardless of whether or not you installed the switch at SW1.
I never bothered to install the FREDs in my Simple SE. They're still sitting in the bag.
I never bothered to install the FREDs in my Simple SE. They're still sitting in the bag.
Ok, with the FREDs gone both C1 and C2 still measure the same in circuit. 🙁
But I powered it up without tubes and nothing went boom, the power trafo appears to check as expected. Unloaded voltages to the pcb are about what I'd expect, a bit north of 400VAC for each 'leg'. I'm going to check the rectifier tube that I was using last night and see how it tests. Let's hope that it was just its time to die or something like that.
Figured I'd stop padding my post count and actually just wait until I'd actually done more and combine it all into one post. 🙂
Step 1. Rectifier tests just fine in my tube tester.
Step 2. Test B+ with only the 5AR4 in place (last night this would cause a fuse to blow). Test is successful, B+ builds nice and slow to an unloaded 550V @ C1 which seems about right based on my fuzzy math.
I'll wait to see if anyone thinks I should check anything else before trying to fire it back up with the rest of the tube compliment. In the mean time I'll check the tubes that I was using and see if there's anything off there too.
But I powered it up without tubes and nothing went boom, the power trafo appears to check as expected. Unloaded voltages to the pcb are about what I'd expect, a bit north of 400VAC for each 'leg'. I'm going to check the rectifier tube that I was using last night and see how it tests. Let's hope that it was just its time to die or something like that.
Figured I'd stop padding my post count and actually just wait until I'd actually done more and combine it all into one post. 🙂
Step 1. Rectifier tests just fine in my tube tester.
Step 2. Test B+ with only the 5AR4 in place (last night this would cause a fuse to blow). Test is successful, B+ builds nice and slow to an unloaded 550V @ C1 which seems about right based on my fuzzy math.
I'll wait to see if anyone thinks I should check anything else before trying to fire it back up with the rest of the tube compliment. In the mean time I'll check the tubes that I was using and see if there's anything off there too.
n_maher said:
Watch the voltage rating on the power supply capacitors whenever you power up an amp with the rectifier in and the output tubes out. Unloaded voltages are going to be higher than loaded, and might exceed the power supply caps ratings. In your case, your caps seem to be high voltage motor runs and other 630V rated parts, so I'd think you will be OK.
If the B+ comes up just fine with the rectifier in and the other tubes out, then you will be safe to run it (assuming the other tubes don't have any shorts). Watch those EL34EH carefully to make sure they aren't doing this:
http://www.diyaudio.com/forums/showthread.php?postid=1624989#post1624989
Ty_Bower said:
Yeah, I thought about the caps and the only ones that I'd really be worried about are the motor run caps but from what I've heard those are pretty conservatively rated at 370VAC (no DC rating on the label).
I also tested the EL34s on my Jackson 648S tester, both test as borderline bad. They are literally on the line between good and bad so I guess that I'll put them aside and try the KT88s that I have and hope the amp doesn't kill them. 🙂 I'll also try and take some B+ readings with the full compliment installed to make sure that it's within spec. I love having a couple sets of grabbers now so I don't have to come anywhere close to live components.
Look for another report shortly.
So I fear something is still not right.
I got one successful test of B+ with all of the tubes installed so I hooked up a pair of speakers. B+ started to rise nicely and then pop, there goes another 2A fuse. So I put in another fuse, disconnected the speakers and tried again. Pop, more landfill material.
So I'm letting things cool down now fearing that the semi-warm tubes may have caused an inrush spike and then I'll test B+ again with no output load to see if even that condition is stable. Perhaps I should amend my Xmas list to include some fuses?
Question: what should I be measuring for resistance across the outputs with no power applied? I'm getting essentially a short condition and that doesn't see quite right to me but it's the same for both transformers and it would seem unlikely that I killed them both, doesn't it? They didn't even get warm to the touch when I had the amp running for the better part of an hour last night and otherwise I don't know what or where else to look for a problem.
I got one successful test of B+ with all of the tubes installed so I hooked up a pair of speakers. B+ started to rise nicely and then pop, there goes another 2A fuse. So I put in another fuse, disconnected the speakers and tried again. Pop, more landfill material.
So I'm letting things cool down now fearing that the semi-warm tubes may have caused an inrush spike and then I'll test B+ again with no output load to see if even that condition is stable. Perhaps I should amend my Xmas list to include some fuses? Question: what should I be measuring for resistance across the outputs with no power applied? I'm getting essentially a short condition and that doesn't see quite right to me but it's the same for both transformers and it would seem unlikely that I killed them both, doesn't it? They didn't even get warm to the touch when I had the amp running for the better part of an hour last night and otherwise I don't know what or where else to look for a problem.
I had one of the Sovtek "5Y3GT" (looks kinda like a 6106, but has a voltage drop more like a 5V4, and when they rate it at 140 ma, they mean it - much more than that kills them) do that same thing this week in my Simple SE
B+ would rise normally, then pop a fuse. On close inspection, some of the oxide had visibly flaked off the rectifier cathode, leaving bare metal to arc to the plate.
You have something breaking down at high voltage. I would suspect your rectifier, or an electrolytic cap on your B+ rail.
I always use smallish fues. No sense in having a transformer blow to protect your fuse.
Win W5JAG
B+ would rise normally, then pop a fuse. On close inspection, some of the oxide had visibly flaked off the rectifier cathode, leaving bare metal to arc to the plate.
You have something breaking down at high voltage. I would suspect your rectifier, or an electrolytic cap on your B+ rail.
I always use smallish fues. No sense in having a transformer blow to protect your fuse.
Win W5JAG
Agree on the use of small (but adequate) fuses, I'd certainly rather blow those than something truly expensive.
The question remains about the output trafos which I hope someone can comment on soon. Otherwise I certainly have other rectifiers that I can try if it comes to that. I've certainly run a higher current B+ (although lower voltage) through this rectifier before in another amp.
The question remains about the output trafos which I hope someone can comment on soon. Otherwise I certainly have other rectifiers that I can try if it comes to that. I've certainly run a higher current B+ (although lower voltage) through this rectifier before in another amp.
I thought your OPT cases were floating above ground? If they are above ground, how can they pop your power supply unless the OPT primary is shorted to the secondary?
I would think the resistance between a primary and secondary lead in a normal OPT shoud be extremely high, maybe infinite, but I have not measured it.
Win W5JAG
I would think the resistance between a primary and secondary lead in a normal OPT shoud be extremely high, maybe infinite, but I have not measured it.
Win W5JAG
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