W30GT tube rolling

Old_School

Well-Known Member
My w30 was layed up for a while, as my main system evolved to the point where it didn't have the inputs I needed, believe it or not (mainly a tape loop). I've pulled it out now and plan to use it as the center piece of a second system, and I was wondering about tube rolling.

When I had it in use I had some bad luck with a couple of quads of KT88s I tried, but it worked fine with a quad of old GE 6550s. Given the value of the 6550s, I'm considering cashing them out, so I was wondering a few things about rolling tubes that are not as close in characteristics as the KT88/6550 types.

First question, do I have to set the bias point differently? If so, where's a good start for EL34s (I have a new Quad on hand, so they'd be the first to try)?

Is the amp capable of using KT90 or KT120? I would think the former would probably be a "yes" as they are fairly close in characteristics to KT88, but I'm not sure the amp has enough grunt for KT120s.
 
The W30 is factory set for optimal performance for KT88 tubes. If using other type of tubes, you only have narrow range of bias adjustment for those tubes and that is not ideal.

I think KT90 is fine but I wouldn't push for KT120.

Hope this helps. We do have a dedicated KT120 amp that can even run KT150 to give you loads of power. I personally do not recommend to roll tubes other than KT88 type into W30 - unless you have technical skills. Unfortunately I cannot give you more technical advice as it is beyond my knowledge at this point.

Best,
Rachel @ Grant Fidelity
 
Hmmm . . . the big sales pitch for the W30 was the ability to roll tubes. :scratch2:

In my W30 I run Shuguang Treasure KT88z's biased at 0.47. I have also run EL34's but don't remember the exact settings. However, Ian recommended 0.35 to 0.40 for standard Shuguang EL34's which he didn't consider to be strong tubes. He also noted that the W30 will easily handle bias up past 0.60.

I do remember that I had to dial the bias down a lot when switching from the KT88's to the EL34's, so I would suggest lowering the bias before inserting the EL34's to avoid overloading them.

Hope that helps.
 
Ian is no longer with us so technical support on tube rolling will be very limited on this discontinued model... I am just on the cautious side for average amp owners who may not have lots of experience in tube rolling.....

Use lots of common sense and happy tube rolling, if you choose to!

Rachel @ Grant Fidelity
 
Thank you Rachel, and my belated condolences - I'm afraid I haven't been keeping up with the news, so I've only just learned of Ian's passing. I was last in contact with you about 3 years ago. I understand your caution, and appreciate it.

Thank you njcanuck, my usual procedure when changing tubes is to dial the bias back all the way, then bring it up, but I usually bring it up to the rated bias point, as I'm not entirely sure what I need to see or listen for to know when I've hit the sweet spot. I started off with Black Treasures, but one decided to commit suicide and take a few resistors with it, and given the price of a new quad, I didn't want to risk it again. I lost the second quad of Shuguang KT88s (standard clear glass ones) in a similar manner when one went wobbly while biasing (fortunately no damage to the amp this time), so I went to the then-NOS GE6550s which are built to last a nuclear war. Since the amp is back on the shelf I thought I'd do some experimenting with different tube types, and I recall Ian saying it could handle any octal based tube, EL34 family, 6L6 family and KT family, though I'm not sure KT90s or KT120s were considered.
 
I still have all the literature but there is no mention of KT90s or KT120s. Based on Ian's previous comments, I think you would be safe with KT90s.

Are you interested in parting with any of your old Treasures? I wouldn't mind having a couple of spares.

Just noticed you are from my old hometown. :thmbsp:
 
Thanks. I probably have two of the treasures left, but I'd have to poke around various bags of tubes and then test to make sure I have two live ones. I may end up using them anyway, as I'd like to try to inform myself about certain sound signatures, so I'm thinking since the bias is by individual tube, there's no reason why I can't have different pairs for each channel, run a mono programme and listen for differences with my headphones.

If you mean The Big Smoke, I'm not from here, which is probably the case of about 50% of the current population. My wife's job brought us here a few years ago, and it's been a blast. I just wish we could afford more nights out - the live music scene here is amazing, whatever genres you like.
 
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