retube VTL amp

Piezo: Just as I opined above (and it is only my opinion, folks) concerning retailers who charge a premium for additional burn-in and testing/matching beyond what is done at the tube factory itself (obviously speaking only of new production tubes now), I have not found that paying extra for Groove Tubes-labeled tubes is any guarantee that small-signal tubes will show problems at any lower a rate than just buying them from the low-cost tube sellers who offer matching (sometimes at a nominal fee, sometimes not). The same goes for RAM in my experience; just like buying your tubes from an amplifier manufacturer, I haven't found that the extra cost signified in the relabeling is reflected in any greater reliability.

Andy at Vintage Tube Services indicated to me that this is because (paraphrasing now) the burn-in and testing regimens of most of these outfits is procedurally insufficient to predict meaningful outcomes, and that the cost involved to do it right would be prohibitive applied to new production tubes, which he feels are in themselves typically too inherently problematic or low-performing to justify it anyway.

To what degree that viewpoint is correct or not I don't know, but my best strategy so far has just been to buy new tubes at the lowest cost, watch for any problems to develop, and deal with replacing them under warranty if any do. Whenever I've paid more for supposedly superior burn-in and testing/matching (and relabeling if applicable), I've experienced problems after installation at rates seemingly no lower than when I buy from a discount source or when I walk into a guitar store.

To your question about a "Groove Tubes Mullard knock-off 12AX7", Groove Tubes is not a tube manufacturer but a tester/relabeler/reseller; Mullard is just a legacy trademark name these days, not an actual tube manufacturing company; and VTLs don't use 12AX7's, so whatever the tube you refer to actually is, I'm sorry but I haven't heard it. About your last sentence, I believe that most of the tube amp manufacturers who sell their own relabeled tubes do say they perform some burn-in and testing on them, but again I haven't personally found this claim to correlate with any decrease in defect or failure rates that might justify the often-substantial extra cost.

hmmm, sounds like i may have bought the spheel and just got lucky with the groove tube thing. cheap is always good and your experience level with retubing is a lot higher than mine. thanks for the input.

as to the 12ax7 mullard knock offs are the only ones i've seen marketing them that's why i applied the name. I'm pretty sure they are russian made. The ax7 is a very common preamp tube with a bit more gain than an AU7 and those two are interchangeable. I assumed that there is interchangeability with the at7s as well wich may be a bad assumption. thanks

Zaikesman - thanks for all the tips with tube install & debugging. it will come in handy.

can u elaborate on "less tubey" about using KT88 instead of 6550. i hadn't considered anything but 6550. i recall reading somewhere Luke Manley recommends only 6550s for his VTL amps.

i will experiment with the input tubes. very good idea.

thanks again.

VTL has fitted SED KT-88's to new amps on special request (it is a drop-in substitute for this application and will bias normally without modification, unlike the KT-90 according to VTL). From to what they related to me, they like this tube as much or better than the 6550C in the upper range, but still prefer the latter from the lower mids through the bass. I feel the Electro-Harmonix KT-88EH is more extended, tighter, and has more specific tonality in the bass than the SED 6550C's, but is not voiced as richly from the mids on down, and is at the same time more extended and cleaner from the mids on up, so the overall balance is on the leaner side compared to the 6550C's. (I haven't heard the SED KT-88's.) I personally would find a tonal balance somewhere between these two tubes to be nearly ideal, but given the choice, I favor the clearer, quicker, and more harmonically open presentation of the KT-88EH with most material, even if its basic character might want somewhat for richness of the fundamentals in direct comparison. But I'm something of a clarity, palpability, and openess freak, and others will gravitate toward the plusher balance of the 6550C and not care as much about giving up a little in the way of fine textural detail, 'floaty-free' imaging, or soundstage 'air'. (I prefer to adjust tonal balance at the input tubes when push comes to shove, and I also find I particularly like triode mode on my MB-185's better with the KT-88EH's than I do with the 6550C's, which seem not to thrive as much in this mode.) The phrase "less tubey" refers mainly to less added harmonic warmth and less treble roll-off along with more control in the bass - or put another way, more 'solid-state'-ish attributes, if you will.

Piezo: Although a 12AX7 might function if substituted for the 12AT7 in this position, I don't have plans to find out, because performance would probably suffer since the two tubes don't have the same electrical parameters (12AX7 is higher-gain) and the circuit was designed around the 12AT7.

Zaikesman - thank you. the mb250 runs in triode only, so it is worth considering & also to get a different perspective. "tubes rule"

btw ... it will cost about 33% more to get the tube set from vtl for the mb250s.