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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


2 posters

    New PSVANE KT88 and my Dynaco MK3s

    bubbasweet
    bubbasweet


    Posts : 91
    Join date : 2016-03-14

    New PSVANE KT88 and my Dynaco MK3s Empty New PSVANE KT88 and my Dynaco MK3s

    Post by bubbasweet Fri Jul 22, 2022 12:00 am

    Wonder what the deal is. I took a chance on a matched Quad of PsVane KT88s. I got em today new in the mail and I tested them and they tested OK on my Stark 966 Tester but when I put them in I blew a fuse on one MK3. So replace it and then got on the Bias right away and I could only achive about 1.40 finally I realized the pot was cranked all the way to one side. The other amp blew a fuse then I tried to bias that one and I could only achieve 1.30 then I realized the rectifier blew. So down a rectifier and 3 fuses I put my old tubes (Russian Mullards) back in and had to turn the pots back to half way and everything worked and biased fine after I replaced the rectifier that had blown. THE PSvane tubes seem to be drawing excessive current for some reason. There is something wrong with these tubes. I cannot achieve proper bias with them. As well I blow 1 rectifier and 3 fuses. I am NOT REAL HAPPY. My amps are working fine with my old tubes in them and bias 1.56VDC fine with pot in center like all the other Brands of tubes I have used in last 15 years. These I cannot bias and they seem like they draw HUGE CURRENT even though they seem to test fine on tube tester. Has anyone else had this problem or know what is going on? Are the tubes bad or do I need to modify the bias resistor before the Pots? Never had to do this before.. Is it possible I need to modify the resistor inline with my POTS in my Mark 3s? i have never had to do this before but is that something that sometimes need to be done for certain brands of tubes? I see nothing technically wrong on the tube tester with them. Note: On both my MK3s Ihave 1K resistor in thebias chain instead of the 4.7K that was recommended for the removed selenium mod. I never changed them because I could achieve the 1.56V fine with room to spare. Could it be that I need to change it to the 4.7K? If so why for these tubes only? i have used several brands with no issue before these PSVANE tubes.


    Last edited by bubbasweet on Fri Jul 22, 2022 1:08 am; edited 2 times in total (Reason for editing : Add to post)
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    arremondo


    Posts : 14
    Join date : 2021-03-11

    New PSVANE KT88 and my Dynaco MK3s Empty Re: New PSVANE KT88 and my Dynaco MK3s

    Post by arremondo Tue Jul 26, 2022 11:12 am

    I had this exact same problem with PSVane KT88s on my Dynaco ST-70.  Exactly.  The only difference was that I lost 3 rectifier tubes and 3 fuses.  When I put the old tubes back in, the amp worked perfectly.  My tubes also tested fine on my Jackson 648 tester but I couldn't even come close to getting the correct bias.  I even turned them all the way up (most resistance) and was still well over 1V (I have the VTA board so the voltage for the KT88s should have been .5V).  Anyway the tubes were pulling way too much current and I couldn't keep it going without blowing a fuse and or lightning in a bottle with the 5AR4 with no input.  

    I ended up sending them back and note to self, no more PSVane tubes from China.  They were also considerably larger physically so I suspected that they were really KT120 tubes and not the KT88s I ordered.  They were labeled KT88 but I don't think there is any way they were really KT88s.  I could be wrong but I found some more Gold Lion KT88s and ordered them and when I put them in they worked like a champ.  

    I have just decided that I won't order any more PSVane KT88 tubes and with your story, I think I am on the right track.
    bubbasweet
    bubbasweet


    Posts : 91
    Join date : 2016-03-14

    New PSVANE KT88 and my Dynaco MK3s Empty Re: New PSVANE KT88 and my Dynaco MK3s

    Post by bubbasweet Wed Jul 27, 2022 5:02 pm

    The worst part is to get a refund via Paypal for defective tubes Canada Post wants 103 Dollars to ship them back to China. So heads up please do not buy PSVANE TUBES ON EBAY FROM CHINA.. I overlooked the posibility of return cost for these and you have to ship to China.. so live and learn.
    bubbasweet
    bubbasweet


    Posts : 91
    Join date : 2016-03-14

    New PSVANE KT88 and my Dynaco MK3s Empty Re: New PSVANE KT88 and my Dynaco MK3s

    Post by bubbasweet Wed Jul 27, 2022 5:09 pm

    ALso you might be right about the 120's possibly as these drew WAY more current when inserted.

    "Kt88 heater current is 1.6Amps per valve the KT120 is 1.9Amps!"
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    arremondo


    Posts : 14
    Join date : 2021-03-11

    New PSVANE KT88 and my Dynaco MK3s Empty Re: New PSVANE KT88 and my Dynaco MK3s

    Post by arremondo Wed Jul 27, 2022 6:05 pm

    I know about the shipping. I had to go round and round with PayPal because the company never did give me the refund and PayPal had to give me my refund. I also bought them on eBay so it was probably the same manufacturer.

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    New PSVANE KT88 and my Dynaco MK3s Empty Re: New PSVANE KT88 and my Dynaco MK3s

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