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PostPosted: 08 Sep 2018, 15:38 
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Hi, Strange on the mismatch, All the ones I have tested are rather close A-A. Some meters can be fooled by inductors. I usually use an actual inductance meter to check them. IMO KT77s have and entirely different sound than the KT88s. This is part of what makes tube gear fun. You can "roll" tubes and get all sorts of different sound. EL34s are also different from the other two types.

Good listening
Bruce

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PostPosted: 09 Sep 2018, 02:18 
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Hi Bruce,
I haven't measured inductance, just the Rdc. I had both Edcor and Lundahl side by side and I used same Fluke 87. I won't be surprised if the A-A inductances in the Edcor match, as you said, but the Ip balance will be wrong by design or the two tubes will see few volts difference in the plate voltage. To my understanding these transformers don't have the more complex links between the primary sections that compensate for the longer outer turns, hence the Rdc difference. I wonder if they have sections at all. In addition, the secondaries taps are most likely lossy (because properly paralleled secondary sections need soldering to reconfigure as is in the more expensive designs) and give best frequency range from the 16 ohm tap that probably nobody uses...
Edcor OPTs are decent sounding, my point is that you get what you're paying for.


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PostPosted: 21 Sep 2018, 04:31 
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Hi, I've just moved back to the UK and after repairing the damage the postal system did to my amps, I finally fired them up for the first time last night. The tubes are drawing way too much current. I've had a quick look over, but before I go into a really deep search I just wanted to check one thing.
The transformers are the Edcor XPWR002-120V which are listed on the website as being for 60hz, I was under the impression that mains frequency wouldn't affect the PT, but am I wrong here? could this be why I'm drawing too much current?

cheers
Josh


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PostPosted: 21 Sep 2018, 09:47 
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Hi Their transformers are designed to handle the 50HZ. That transformer as I recall does not have a 220-240 volt primary option. Are you using 220-240 volts AC Mains? That would cause serious damage to several components. If not then I would suspect that the LM317s have failed for some reason. It is pretty much the only way you can get excess current. Let us know what the outcome is.

Good listening
Bruce

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PostPosted: 21 Sep 2018, 10:27 
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Hi Bruce, I'm using a 120v step/down transformer to run my whole hifi, but hadn't thought about the Frequency thing being an issue, also gonna have to replace the motor and PSU in my turntable.
Yeh Edcor just confirmed that the transformers wouldn't work properly at 50hz, so will have to sit and wait a few months until a new pair turn up.
I had thought about the LM317, but it would be some kind of coincidence for them to both go (same problem on both amps) at the same time after 5years of constant use.
Well it looks like it'll be another 3months without tubes, hopefully the proper transformers will put it back to normal.

cheers for the quick response.
Josh


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PostPosted: 23 Sep 2018, 20:55 
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Hi, I suppose I should have asked...how much excess? A little, a lot? Commercially we have been using the same transformers on both 50 and 60 HZ AC and this is the first instance I have been notified of that it was an issue. Most curious. The LM317s really don't care what the voltage across the tubes is or what frequency the AC is. They will hold the current to the set value unless they have failed or the circuit that they are in has failed. I would see if possibly there is a ground issue with the pots, 1 ohm resistors or cathodes that might be at fault. At worst the difference in the power transformer would lower the B+. This would not however cause increased current flow. There is certainly no harm in replacing the transformers, but I don't think that is what is at fault. If there is any chance that the circuit (amps) were put on the higher ac mains voltage for even 30 seconds then the LM317s could have shorted through due to over voltage when they tried to regulate the current. The voltage on them would go to something around 80 VDC and that would cause nearly immediate failure. They typically fail shorted through. That would give really high current measurements. Less likely causes, you might also check to see if the heat sink(s) is shorted to ground or the insulators if used have shifted. A remote possibility is if the step down transformer is of the auto transformer type and there was a spike on the AC line after the amps started to warm up. It could pass that along to the circuit and fry the lM317s. Possibly if when it is connected it might put an inductive caused spike of its own as well. Ground fault conditions might cause excess voltages as well. Check the AC mains for good grounding etc. Remote possibilities, but possible. Let us know the outcome.

Good listening
Bruce

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PostPosted: 24 Sep 2018, 07:13 
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Hi Bruce, The first amp was drawing about twice as much current as it is supposed to, measuring about 110mV across each of the test points. The second amp I didn't even get to measure, as soon as the relay switched the tubes started to glow purple and a fairly loud hum through the speaker, so I hit the power switch immediately.

You were right about the LM317's, there's an internal short between the Adjust and Out pins on both amps.

I'm not sure if the Step-Down is an auto-transformer, from what I can see through the vents in the plastic casing, it looks like a regular transformer, but I'm not sure.

You said to check if the heat sinks are shorted to the ground? I didn't realise they weren't supposed to be connected to the ground, they're bolted to the chassis and I'd assumed due to the construction of the regulators, that the metal tab with the hole in was for bolting to the heatsink and creating a ground connection. The heatsinks are anodised, is it possible that the coating in combination with the thermal paste has held up from shorting them for years, then the pounding they took shipping across the world has worn through the anodising and created a connection?

I've tried removing them from the heatsinks and there's still a short between the A & O pins. Could that short have caused them to fail?

The Transformers are the XPWR002-120v as a pose to the OEM ones in the kit version. It seems some Edcor transformers are designed to handle 50/60Hz and some just 60Hz, Edcor did confirm that the transformers I have were only designed for 60Hz, if this isn't the problem, I wander if I should cancel the order for new ones or if it'd be better to just use the correct ones for the country. Would rather not spend $270 unnecessarily.

cheers for al your help, much appreciated


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PostPosted: 24 Sep 2018, 11:00 
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Hi, :eek: :eek: First, the tabs on the LM317s go directly to the output terminal. Grounding that will bypass them. The anodization likely made enough of an insulator that they worked. They should have the thin wafers that go under them and the feed through insulators that go in the holes. Google heat sink insulators to see what I mean. They are cheap and keep the LM317s from making electrical contact to the heat sink. The sinks themselves can either be grounded or not. It makes no difference. One thing that did occur to me was that in transporting the amps unless you took great precautions to keep the output tubes from banging around they can develop internal shorts. If one is between the grid and cathode or grid and anode or screen they will try to conduct everything the power supply will deliver. In doing so the LM317 will try to keep the current at the programed amount and in doing so the voltage across it will go up dramatically. It will kill it in a short time.

So what to do. ......insulate the LM317s from the heat sinks. See if there is still a short between the A and O pins then they need to be replaced. Personally I would cancel the transformer order as they are not the problem. It would be nice to check the tubes, but without a tube tester it will not be easy as some faults will only show up under power. I believe I would use an ohm meter and measure resistance between various pins. There should be an open circuit reading between 8 to 2,3,4,5,6 and 7. 2 to 7 should be pretty low in resistance. 1 might go to 8. (usually only in EL34s and not all of them either) Anything different will indicate an internal short. The blue glow in the tubes was gas, it is normally fine. Pretty but not a problem in 99% of cases. The hum was because the tubes were sucking all the power from the power supply and will not harm them for a short duration. Tubes are really robust and can take excessive current for a goodly time period. The biggest problem with tubes is their sensitivity to shock and banging around.

Good listening
Bruce

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PostPosted: 24 Sep 2018, 11:21 
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Wowza!!! can't believe the anodizing held up that long. found the insulators, will order them with a new pair of regulators, are the LM317AVHT a suitable replacement for the LM317HV? all the basic specs look to match up and can get them quickly.

Will go over the tubes and double check, but I wrapped them up well and were in a box that didn't get so battered, also got an old set of JJ's that have lost their sparkle but still work fine.

cheers


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PostPosted: 24 Sep 2018, 11:30 
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Tubes are measuring fine, with no internal shorts and 1.0ohm between pins 2-7


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