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PostPosted: January 23rd, 2017, 6:50 pm 
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Joined: October 21st, 2013, 6:53 pm
Posts: 270
Hi All

I have a EL34 type tube amp.
A couple years ago I started rolling tubes, and I found some pretty nice Psvane UK reproductions that I liked. They have been in service for this whole time, and I have had zero issues with them.

I found some listings on Ebay however for a new (even more premium) Psvane EL34PH Phillips Holland Reproduction, so I bought a quad. (preamp and predriver tubes are still 6sn7 Psvane UK reproductions I bought around the same time as the UK output tubes).

When I got the box of four tubes, I was excited because everything looked really premium. Pretty quickly however, I located two tubes that had some minor cosmetic flaws. One was a little bit of glue squeezing out between the base and the glass on one tube, that I didn't find any evidence of on the other three. Another was that the painted Psvane label on one tube, when it was located in the mount, didn't face straight ahead. And the last was that the shape of the glass on one tube was slightly differently shaped than then glass on the other three.

I know! I'm knit-Picking almost stupid, irrelevant details, but I didn't find any of those imperfections in the four Psvane UK tubes I bought a couple years ago!

I wouldn't have thought too much about it because the tubes sound brilliant, but today (day 3 of the tubes being in service), I turned on my cold amplifier, and there was a spark in one of the tubes. A slightly loud "pop" coming through my speakers accompanied it, and afterwards I found the offending tube had a little bit of brown residue on the inside of the glass near the top of the tube that I have seen on tubes before after prolonged use, but was not present on the other three.

Apparently there was no damage, because the amplifier still works perfectly fine, but I don't want to take too many chances with this happening again.

I don't suspect there is anything wrong with the amplifier, because I have swapped in several differnet complements of tubes, and it has never done that before.

If it does happen again I'm going to swap the UK tubes back in.

Does anybody have any Ideas what might be happening?

Did I get faulty tubes?

Maybe I bought seconds of something some sort of un-official Psvane seller?

I set the bias current to the figure the literature with the tubes indicated. Would there be anything funny happening here?

I like the Phillips Holland better than the old UK tubes, so if I can resolve the problems, that's the tube I want to use.

If I have to buy new ones I will, but I would like to have some comprehension of why I'm suddenly having this problem with the tube I bought.

Thanks,
Any advice would be welcomed!

Chris


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PostPosted: January 24th, 2017, 11:18 am 
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Joined: July 24th, 2015, 4:17 pm
Posts: 930
Location: Parkville, Maryland
I can imagine your disappointment. I expect that the "sparks" was either a short between one the of the grids and the plate or cathode. Either the PSVane folks are getting sloppy or you may have stumbled on to factory rejects. I would hope the manufacturer throws them out -- or at least relies on an employee to throw them out.

My recommendation would be to buy either the Russian EL-34s or those made by Tesla. They sound good and have a reputation for reliability.

Another possibility would be to roll in KT-88s. They're pin compatible with EL-34s and can stand the plate voltage usually used with EL-34s. Of course fixed bias would be needed to dial them in -- say 38ma cathode current. i am not sure cathode bias designed around EL-34s would be suitable.

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Walt


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PostPosted: January 24th, 2017, 12:04 pm 
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Joined: February 28th, 2013, 1:19 pm
Posts: 325
Allegedly, the problem with Chinese tubes quality control procedures are that they do not actually reject (destroy) tubes that are sub-par, they are just sold for a lower price (often as a lower "grade"). Buying off eBay is a gamble. The problem with Chinese quality control extends well beyond tube manufacture, but includes critical items such as steel, fasteners, building materials (sheetrock) and almost anything else they make. They sell both the parts that meet the required specifications, usually for export in well supervised production facilities, but also the rejects domestically for a lower price, where they re-inter and pollute the market, and there is no easy way to tell the difference.

David


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PostPosted: January 24th, 2017, 12:44 pm 
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Joined: July 24th, 2015, 4:17 pm
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Location: Parkville, Maryland
I agree with David because of the reported corruption in China; however, I have never had a bad Chinese tube -- other than a pair of PS Vane 845s. Some of my faves came from Shuguang -- especially the ca. 1960s KT-66s that are about as close you can get to the vintage Genelex KT-66. Same goes with the 300Bs and 845s.

Now let's talk about PS Vane. I got sucked into the PS Vane marketing and sprang for a matched pair of the top-of-line 845s. They sounded terrible (harsh and edgy) and I sent them back for a refund. The vendor never questioned my reason.

Caveat Emptor

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PostPosted: January 24th, 2017, 1:30 pm 
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Joined: October 21st, 2013, 6:53 pm
Posts: 270
Yes, I suspect I got rejects based on the cosmetic flaws I noticed relatively quickly.

My Psvane UK versions were practically flawless. I bought them on ebay too.


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PostPosted: January 24th, 2017, 5:15 pm 
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Joined: June 4th, 2013, 2:39 pm
Posts: 159
I've stopped buying new tubes from eBay. I've had several EH 300Bs go south on me well before their time. I imagine they were "B" grades or rejects from other dealers. It's not worth the savings.


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PostPosted: January 25th, 2017, 6:25 pm 
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Joined: March 1st, 2013, 11:12 am
Posts: 40
I had this exact problem with some PS Vane EL34's. Rachel at Grant Audio explained that there was a problem with the screen grid in the early batches of the tube and that they had to make a change in the design to fix it. The screen grid takes to much current and will melt down. Don't use them- they may take out your transformer. She gave me a new set, no questions asked. Doubt you can get that to happen with Ebay but good luck.

It's a shame that the tube has problems, I think they have a lovely sound but I never let them run when I'm not around.

Charlie


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PostPosted: January 25th, 2017, 7:59 pm 
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Joined: October 21st, 2013, 6:53 pm
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charliewphelps@gmail.com wrote:
I had this exact problem with some PS Vane EL34's. Rachel at Grant Audio explained that there was a problem with the screen grid in the early batches of the tube and that they had to make a change in the design to fix it. The screen grid takes to much current and will melt down. Don't use them- they may take out your transformer. She gave me a new set, no questions asked. Doubt you can get that to happen with Ebay but good luck.

It's a shame that the tube has problems, I think they have a lovely sound but I never let them run when I'm not around.

Charlie


Hey Charlie,

After a lot of looking I found Grant Audio.

I have removed the offending tubes, but the performance from the short live audition I had, was that this particular model of tube was a fantastic upgrade to my system.

Do you think I just got a bad lot :(

I would like to purchase a quad from Grant and take another try. They claim there tubes are after-manufacturer tested, and to some degree warranteed.

Or, should I just look somewhere else for my next upgrade?

Thanks,

Chris


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PostPosted: January 25th, 2017, 8:09 pm 
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Joined: March 1st, 2013, 11:12 am
Posts: 40
I've had good luck with my replacement set. I've also had good luck with Grant Audio. I met Rachel at RMAF several years ago and she is a great person. Unfortunately her partner, Ian Grant, died of cancer a while ago. I don't know how things have gone since then but I've always had good luck with Grant Audio in the past. As I pointed out she replaced my tubes, no problem. I really love the sound of the Phillips based PS Vane tubes - I think they are the best sounding new EL34. If you can get some Type II originals you will be better off with reliability with the same sound. Won't be cheap though.

Charlie


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PostPosted: January 25th, 2017, 8:42 pm 
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Joined: January 15th, 2015, 7:19 am
Posts: 898
Location: Baltimore MD
Doughs tubes has been good for me, purchased numerous sets from him over the years. He does pre testing like many legitimate company's do. Very fair pricing and fast shipping


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