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Hi
Would anybody have any answers to the following?
I purchased a brand new Jadis DA8 Valve power amp. After a few weeks there was a crackle and bang and a valve went( right channel ). The amp went back to Jadis who could find no fault with the amp other than the blown Valve. They sent another brand new replacement. Same happened again. Off it went back to jadis same result as last time. They decided to send another new unit. In the meantime I borrowed a used AR Vs110 and after a couple of weeks the same thing happened to this amp.
Something has got to be wrong at my house, I have had the voltage checked etc can not find any problems. The amp has its own seperate ring main.
In summary the dealer and everyone is scratching there heads. I have taken delivery of the 3rd amp the tube lasted 3hrs then went pop.
Any ideas or posible solutions would be much appreciated.
Thanks
Follow Ups:
Not sure if that would result in a blown tube but it would explain why it's always the power amp that goes and why it's always the same channel.Use a multimeter to check for continuity between the red and black wires in your speaker wire while moving it around. Of course there shouldn't be any.
Do the same with the interconnects (although I would have thought a shorted interconnect would take out the preamp rather than the power amp).
Or there might be a problem with the speaker crossovers. If you can, try opening up the speaker on that side and see if there are any loose wires or signs of sparking etc. Maybe try swapping the speakers over and see if the tubes blow on the other side, although that might be an expensive way to check. Do you have any other speakers you could try for a while?
When you say you have had the voltage checked, what exactly do you mean? Was monitoring equipment connected to the mains to measure voltage value range over a period of time, say, a day, or a week, a fortnight? Or, was a simple ‘snap shot’ of mains voltage values taken? And, by whom? I think, given own experience of mains supply voltage values, here in the East Midlands, value range of voltage supplied needs to be ascertained.Secondly, is the mains transformer for the power amplifier rated for 240v? I own a Canary CA-601MkII valve/tube pre-amplifier made in the US but supplied to the UK. It has a 220v rated mains transformer. Fine for, say, the French market, but not too great for the UK. I operate the unit with an isolation transformer that also cuts the voltage supplied to the unit. Internal voltages are then of a value appropriate to the valves utilized. Without, given the voltage supplied to home, which conforms to EU harmonization of voltage supplied to domestic consumers, but yet allows UK suppliers to supply at a value above the nominal 230v, the voltages seen by the valves would significantly stress the valves, many of which are difficult-to-come-by and expensive NOS. Depending on the operating conditions of the design, which might operate the valves at the upper limit, a high mains voltage, from own experience, might push the valves to fail. I might add that I use isolation transformers, from British Audio online, for all the audio equipment operated. The main unit utilized has voltage reduction and I run all items, whether rated 230v or 240v — the Border Patrol SE300B PSU is rated nominally 230v while the Audio Note DAC2.1x Balanced is rated nominally 240v — from isolation transformers. I routinely suffer high voltages close to the upper limit permitted by EU harmonization.
Thanks for your response I have monitored day and night for weeks. The min voltage is 245 and it goes to a max usaully at night of 253v. The operation window of he amp is up to 265v. I would assume this is a built in safety margin. The dealer has taken readings from the transformer. there is no probs here either. I know baffling!! Oh well anyone got any other ideas will be much appreciated.For the record I am runing a AR LS25 Pre and AR CD3 with no probs at all. The Valves in the power amp are EH.
Nathan,The answers that everyone is giving you, Sean in particular, are correct. As a practical matter, measure the AC voltage between pins 2 and 7 on one of your output tubes sockets if you are using any of the output pentodes that Sean mentioned. If your voltage is greater than 6.3VAC, that's the problem.
Now, you can reduce that voltage. You can desolder the two wires into the socket from the power transformer and put two 0.1 ohm/5 watt resistors in series with the leads from the power transformer and you'll likely never have a problem again. Unfortunately, the second you lay a hot soldering iron on that amp, you are going to void your warrantee with Jadis and those folks aren't going to deal with you anymore. Do you really want that? Consequently, your only option is to use a power conditioner or even a high current variable autoformer to reduce your line voltage. Remember, though, that the real standard that you need to meet is the voltage between pins 2 and 7 of your output tubes' sockets. So long as that voltage is 6.3VAC to, as Sean mentioned, 5.7VAC your amp should operate fine.
Before setting aside the direction I suggested, might I ask you a few questions?Firstly, when the failure first occurred, in the manner you described, I presume there was no red glow on the plate of the output valve that failed; correct so to presume? I would think I am correct to presume this because you wrote the manufacturer could find no fault. If a bias resistor, for example, had been implicated with current draw running away in an auto-biasing circuit, that resistor would indicate failure, and there would be little doubt about it. Again, your description of failure would not suggest bias circuit failure but heater failure. I must ask, also, is the circuit auto-biasing?
With the new unit supplied after return of the first unit, was the problem with the same channel, and if so, in the same tube location? Or, was the problem in another tube location? I know you mention use of a substitute AR power amplifier and the problem with it, and the inference drawn, but I would, nevertheless, like to know.
I appreciate your reply to my first posting in the thread, but I must ask again is the mains transformer rated on the primary 220vAC, 230vAC or 240vAC?
Do you know the voltage being supplied to the heaters of the output valves? (Nominally, the tap on the secondary side would be expected to be 6.3v.) If you do, is that voltage between 5.7v and 6.9v, that is, within the range, 6.3v +9.52/-9.52%? And, if it is, and the voltage varies with input voltage variation, what is the value of heater voltage for the 245v minimum input voltage you mention?
You mention EH tubes, but which type? EL34, 6550, KT88, or KT90? Have you used but the one type/designation, that is, not substituted another set of output tubes of a different designation/type?
I start eliminating things first. Clearly, you've been treating the symptoms and not the root problem.Have you had any other power-related problems? Any new additions or rewiring done in the residence? Have you had any severe weather that might have affected the delivery of power in some way (fallen tree limbs, lightening, etc)? Have you confirmed that the grounding system in your house is solid? Have all the connections in the load panel been cleaned and tightened? Have your confirmed that the outlets are wired correctly? Have you confirmed that you're not sharing 2 separate lines from the load panel? Have you got the gear hooked up to the cable system via a Home Theater/TV or similar device?
I wouldnt' start throwing AC conditioning equipment at the problem until you're clear what exactly is wrong. I knwo its frustrating but ordered diagnosis is your best option.
Cheers,
Are you confident with the tubes you've been using? Any way to try different brands? Perhaps you should post the brands here and see if they have reliability issues. That seems far fetched to me, but it clearly doesn't have to do with your mains - otherwise, why would it be in only one channel? Still, what about plugging the amp into another outlet? Does the same thing happen?I'm not aware of anything your preamp could be doing to cause the amp to blow tubes, but maybe someone here knows that possibility.
beg, borrow, or buy one... they may not be the best for sonics, but you could at least determine if you are getting big spikes in your AC. I live in an older neighborhood and my AC can vary depending on local usage.
Inductive loads on the mains can cause spikes, e.g. a fridge that doesn't have an effective suppressor. A separate ring mains won't buy you much protection from spikes. At the very least, you could try to protect the amp with its own suppressor but a regulator would be even better.
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