2. amps-preamps
  3. 1243286496

6C33C-B tubes

I have 35w p/p Class A monoblocks which use two 6C33C-B tubes per unit. The manufacturer recommends a bias setting of 150mv. Before biasing (once a month), the tubes' measurements rarely deviate more than 10mv over/under the 150mv. Over the last year, I’m guessing that they’ve been in use for about 1000 hours. I have no idea what their expected lifespan might be. So far, biasing is still relatively easy. The manufacturer is no longer around to answer any questions. So, here’s a few for the Audiogon community.

1) For those of you using 6C33C-B tubes, are you able to guesstimate their lifespan in your amp – in Class A operation?
2) Generally speaking, how necessary is it to bias exactly to the manufacturer’s recommendation – in this case 150mv? Is there an acceptable tolerance +/- %?

Thanks! P.S. I’ve been replacing the sockets once a year.
steakster
sksos1
388 posts
 
Can I ask where you are finding NOS 6C33C tubes? I'm getting an Atmasphere Novacron that uses 8 and would like to buy a few extra back-ups. :-)

(Dealer dislcaimer)
jedinite24's avatar
jedinite24
1,503 posts
 
Same here. Where does one find NOS 6C33C tubes from a reliable source? Whenever I've purchased from across the way it was a nightmare. I've had to pay a premium to buy tested tubes from US Vendors.
pbnaudio's avatar
pbnaudio
1,613 posts
 
I have about 8 NOS from the early 80's make me an offer

Thanks

Peter
atmasphere's avatar
atmasphere
11,894 posts
 
If you are ordering 6C33s off of ebay, ask if the tubes are in the original boxes. If not, do not buy.
tortilladc
121 posts
 
I bought a batch of 8 from a seller here named 'audiomisfit'. They came in what appears to be original boxes. Short answer here is the tubes were fine. I paid $285 for 8 but his prices seem to fluctuate.

Read on for the longer answer…

I decided I wanted them tested and got various responses to that plan. Local dealer who sells amps using those tubes said don't bother testing them. Technician who is repairing an amp that uses that tube said don't bother. But I'm stubborn, new to this, curious, and wanted to control for tube quality so I went ahead with it.

Based on suggestions found in older threads here I looked into Upscale Audio, tubeaudiostore (RAM tubeworks) and TC Tubes. From what I can gather, the 6C33B is somewhat difficult to test so the prices I was quoted were higher than for other tubes.

I ended up testing them with TC Tubes ($10 each).
Upscale Audio said they don't test tubes they don't sell. Fair enough.
Tubeaudiostore (RAM) quoted me $200 to test 10 tubes and $5 each tube thereafter.

Turnaround with TC Tubes was 2 business days after receipt. For any of you who are interested in what kind of data you get out of such a test, I’ve posted all of the results below. Some of this is a bit over my head but I’m thankful for the summary and detail on each tube and I feel like this gave me piece of mind about my purchase and may allow me to place them in the amp more intelligently. Tyler was very responsive to my inquiries and I’d definitely use his services again.

https: //drive.google.com/file/d/0B4HpFMtCMjw7S0NEd0t5UEF2MWs/edit?usp=sharing

Hope the link works!
More to discover