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Consistently faulty preamp tubes?

J

jddonuts

New Member
Hello, I have recently purchased a Dynavox TPR-3 pre-amp that uses 6n3 type tubes. However after purchasing now two sets of tubes and being sent a single replacement tube, three of the five tubes tested have been faulty after minor usage. The two cheap Chinese tubes the pre amp came with work perfectly fine though after several listening sessions over three weeks time. So far I have purchased only a matched pair of RCA 5670 triple micas and another matched pair of GE five star triple micas. So I am unsure if the eBay seller has somehow consistently sent me faulty/dying tubes or if they are somehow being overdriven by my pre amp. Each time one has failed only one of the channels has been affected, two tubes of which went dead quiet and one that is now very microphonic with a very loud hiss. Not sure how to approach anymore as I find it hard to believe I've just gotten unlucky this many times. Could it be that the transformer isn't fit for the preamp or amount of power being supplied? Poor circuit design? I am a bit lost, so any advice is much appreciated, Thank you!
 
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Personally, I never buy tubes on ebay. Like craigslist, people can lie and you never know what you will be getting. I would buy from a reputable dealer like tubes and more dot com or some other dealer with a good reputation.
 
I think it may actually be caused by the tubes being grossly undervolted. The power transformer in the pre amp is rated for 230v, but I live in the US and have no step up converter. could be wrong.
 
Yes, already bought a step up transformer on Amazon that suits the specs of the preamp/transformer.

Hope this solves the problem. Already wasted $70 on tubes.
 
jddonuts said:
Hello, I have recently purchased a Dynavox TPR-3 pre-amp that uses 6n3 type tubes. However after purchasing now two sets of tubes and being sent a single replacement tube, three of the five tubes tested have been faulty after minor usage. The two cheap Chinese tubes the pre amp came with work perfectly fine though after several listening sessions over three weeks time. So far I have purchased only a matched pair of RCA 5670 triple micas and another matched pair of GE five star triple micas. So I am unsure if the eBay seller has somehow consistently sent me faulty/dying tubes or if they are somehow being overdriven by my pre amp. Each time one has failed only one of the channels has been affected, two tubes of which went dead quiet and one that is now very microphonic with a very loud hiss. Not sure how to approach anymore as I find it hard to believe I've just gotten unlucky this many times. Could it be that the transformer isn't fit for the preamp or amount of power being supplied? Poor circuit design? I am a bit lost, so any advice is much appreciated, Thank you!
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I'd be looking at your newly purchased preamp. Was it purchased new or used?

I looked it up and I'm always a bit skeptical about gear that displays the tubes in little windows and lights them up with LEDs. Be that as it may, you say only one channel quit working. Was it the same one each time?

I think it's highly unlikely that you would have repeated failures if there wasn't an issue with the preamp. Preamp tubes are not generally very fragile and if they are being operated correctly they shouldn't fail.
 
He did say he was using it at 120v when it is a 230v unit. I would think the heater and B+ would be way too low. The OP also stated the Chinese 6N3's supplied worked fine. Im guessing he may have bought tubes from a sketchy seller.
 
I guess I mis-read his comment on that. It seems he has ordered a transformer to get the voltage right but it has not yet arrived. In that case, I hope he hasn't thrown out the tubes that had problems. They might work perfectly fine when the voltage issue is corrected.

There does seem to be a schematic online for an earlier version of this preamp and it runs the tubes at very low voltages. The supply voltage for the tubes is shown as 60v. So, if this voltage was cut in half due to lower wall voltage, it's not surprising at all that they had issues.

http://bilder.hifi-forum.de/max/356912/schaltplan-tpr-2_127043.jpg
 
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