Brand New PSVane KT88s blew 3 fuses and 3 5AR4 Rectifiers in ST70

So I have been using Gold Lion KT88s in my VTA board ST70 with a new PS60 that has a higher power rating.  I have done the yellow sheet diode fix on the rectifier socket and the Triode / Ultralinear switches.  I just leave it in Ultralinear most of the time.  Anyway, with the Russian tubes not being shipped with the war going on I decided to order some PSVane KT88s from China.  Keep in mind that I have been using the Gold Lions for almost a year without problems.  So I put in the PSVane KT88s after I had dialed down the bias on all 4 pots.  While I was setting the bias, I got "lightning in a bottle" on my 5AR4 then blew the fuse.  It didn't even run long enough for me to dial up the voltage to .5.  So I thought that maybe the settings for the bias were still too high so I dialed them way back, replaced the 5AR4 and tried again.  I got the same thing.  So after blowing my last 5AR4 (a Gold Lion no less) and another fuse, I put in my solid state rectifier and tried again.  While it ran for about a minute, it then blew a fuse.  So, I replaced the fuse and put the Gold Lion KT88s back in and it works just fine (except for the hum I now have that I didn't have before).  I checked all of the new PSVane KT88s on my Jackson 648 and they all check good and no leaks.  

Anyone have any suggestions?  I am out $250 for the tubes right now and had to order another $100 of 5AR4s to replenish my stock.  Any experts on here with Jackson 648 experience and have any suggestions for testing?  I feel like I got a bad tube as 3 of the 4 tubes shipped with bubble wrap on them inside the tube box but one didn't have the bubble wrap.  I would really like some direction on how to properly check these tubes for everything on my tube tester.  I don't know if I am checking the leak and life time correctly.  

Also since I don't have another tube as of yet, would a solid state rectifier cause hum in the speakers?  It happens on all inputs from the preamp (Phono, Receiver, CD etc).  The hum coming through the speakers increases in volume with the volume control.  The multi-Capacitor is around a year old and I bought it new (not NOS).  There was no hum before the "lightning in a bottle" happened.

Please don't tell me I need a better tube tester.  I got what I could afford at the time.  I would just like some direction.

Thank you,

Mark

Ouch - don't know what to tell you - I did receive some excellent help and fast replies for my issues on AudioKarma.org - you might post there as well.

I assume when you say VTA board ST70 - that this is not a complete VTA ST70 but an older ST70 w/the board?  Bob mentioned in my quick search that the Transformer need updating to handle the larger tubes but the standard VTA 70 is good for KT88 and 6550s.

Try AK for suggestions too.

Best of luck!

Yeah I knew that but thanks for taking time to respond. I have the PA060 (I think I gave the wrong model number in my first post) from Triode Electronics ( http://www.triodeelectronics.com/mq060.html ) which is supposed to handle the extra power required. I have also been using my Gold Lion KT88s for almost a year without any issues. This just happened with the new PSVane KT88s. I was really hoping for a tutorial on how to thoroughly test them on my Jackson 648 tube tester to find out which one is causing the problem. It does take a minute or so to blow everything so I am sure when one of them warms up it get shorted and causes the issues.

Thank you again though for taking the time to respond.

Your tube tester is probably fine. The problem is with most tube testers is they don't test tubes under real world conditions and not at anywhere near real working voltages.
I suggest that you make a lightbulb current limiter to put in series with your amp. It's just a plug and socket with a lightbulb socket spliced into one side of the line so it's in series with the amp you are testing.

Use a 200w bulb so it has a low enough resistance to pass enough current to the amp. Use your solid state rectifier in the amp seeing as it didn't blow when the problem showed up.
plug in one output tube at a time. the bulb should get momentarily brighter and then dim down as the tube's heater warms after the tube has been in for a minute or so (as long as it would take to blow the fuse normally) not if the bulb is lit and how bright. Pull that tube and plug in the next one. If you suddenly get one that causes the bulb to glow much brighter that is the one causing you problems.

Thanks ELBill34! I didn't use a bulb but I did put the tubes in one at a time and when I got to the bad one it blew the fuse. I am still not convinced that they weren't mislabeled and that they were really KT-120s. They wouldn't bias and even with the POTs turned all the way on the VTA board, none of the tubes would come down to .5V. The lowest I could get them was .7V and one was close to .9V.

Thanks for all the replys! The tubes are on their way back to China.

Going to be very interesting to see what China does with the tubes you sent back.....keep us informed.

BTW, what is your house line voltage to the amplifier?

I use a VARIAC and keep it right at 120V so the voltage is always the same.

Arremondo, that variac will follow your incoming line voltage. Also, I run mine @ 117vac. Just a thought, Dale

Holy Crap Mark, I just has this exact same experience last night. Ordered a Matched Quad KT88s that all tested good on my tester and exact same experience. I put them in my Mark 3s and blew fuse and also took out one GZ34 like your story exactly. Could only reach 3/4 bias... I am not going to screw around I will send these back.  What was the outcome when you send them back and what did they say? They asked me to mail them back or fill out the Ebay form which method did you go with? This post is like Mirror image of what happened to me last night.

Sorry for the late reply. Had surgery and I don't think i got an email that the thread had been updated. I ended up sending them back but the Chinese company just stopped responding so I went through eBay and they refunded my money. You are the 3rd person to have this happen so I am almost positive that they are selling KT120s as KT88s.

The problem is the GZ34 has to operate at nearly 100% of maximum capacity to supply enough dc. Current to meet fhe amps basic needs. Its a great tube, but inadequate in this s is to reolace the single GZ34 with 2 parallel 274B Emissions labs mesh plate tubes. Roy built me both an St70 and VTA120 to my specsNd was impressed with the results. If the 274b from Emission Labs are too coztly , I have good news. You can use JAN Sylvania 5V4G. In the st70, and sork nearly as well. The results’ are amazing. Drop me a note at tv and I detail it. Not difficult, but has 4 little know crucial steps you must do.
Thanks.,Frank
PS. I tried PSVane 274b and they will NOT work!!! I’ll ddtail it later

the best tube tester in the world is the amp you are using the tubes in, as ElBill34 said, tubes testers don't test tubes using real world voltages and currents.
If you buy a matched set of tubes those tubes should all bias at nearly the exact same point (EZ to see by looking at the position of each bias pot on the board).
Also, the 5U4GB is an excellent rectifier rated at 10% higher current than 5AR4 and costs less.

I have thought about using the 5U4GB but I read that it starts up immediately where the 5AR4 is slower which allows time for the heaters in the tubes to heat up prior to getting voltage.  This is the reason I have been using the 5AR4 and not the 5U4GB.  I also read that by putting in the yellow sheet diode fix, the voltage is effectively cut in half since it is cutting half the AC signal.  I actually have a few of the 5U4GBs but it works fine with the 5AR4 when the Non-garbage PSvane KT88s are installed.

I also have a matched set of Genelex Gold Lion Platinum KT88s that sound fantastic.  This whole thing started because I was going to try and save the Gold Lions and put in cheaper KT88s for daily use after Ukraine started.  There was no hum prior to those garbage, worthless, piece of junk PSvane's.  I learned my lesson but I am still fuming that they caused this issue and messed up my amp.

I do have the Tubes4HIFI classic VTA board with the capacitance upgrade installed on it also.

I can seriously reduce the physical hum by pushing down on the output transformers. This still makes me lean to the issue being the output transformer(s) and not anything else.  I will still check the diodes, resistors etc. as mentioned before (especially since I have something like 100 1N4007s) but I am not convinced that is the problem causing the hum.  Also, the hum doesn't come through the speakers it is just irritating to hear it when I get close to it.

I would be interested in seeing the schematic for the dual 274B Emissions labs mesh plate tubes circuit though.

Mark

arremondo wrote:I have thought about using the 5U4GB but I read that it starts up immediately where the 5AR4 is slower which allows time for the heaters in the tubes to heat up prior to getting voltage.  This is the reason I have been using the 5AR4 and not the 5U4GB.  I also read that by putting in the yellow sheet diode fix, the voltage is effectively cut in half since it is cutting half the AC signal.  I actually have a few of the 5U4GBs but it works fine with the 5AR4 when the Non-garbage PSvane KT88s are installed.


Mark

The yellow sheet mod DOES NOT cut the B+ voltage in half. It does not reduce the B+ at all except for maybe a few volts due to the drop across the diodes. It simply protects the rectifier tube from the reverse voltage on each half cycle of the AC voltage.

seems your hum problem is mechanical, not electronic, so make sure the mounting screws on your OPTs and PWR XFMRS are tight.
Also the PWR XFMR is usually mounted on rubber or plastic bushings to help isolate any vibration.

The diode mod DOES cut the AC voltage in half, so the rectifier only has to work half as much,
does NOT affect the DC (B+) and usually makes a large improvement in reliability of the rectifier tube