[doug s.]

Anyone - When I get my new tube ... To watch the bias for the first few hours can I leave all of my system off with just the one monoblock powered up? Just to make sure it does nothing crazy? And how many hours would you suggest I do this for (if any):

A) Tested tube (like from Partsconnexion); and
B) Untested tube (like direct from Russia).

i don't think you need to go to that extreme.  yust make sure you can be close by during initial listening, maybe even checking the bias every 15 minutes or so the first hour, then every hour the first few hours.  if you don't wanna listen to music during initial turn-on, do make sure you have the speaker connected to the outputs, or at least short the outputs if there's no speaker - tube amps don't like seeing no load when on.  and, after initial turn-on, set the bias a bit low, to let the amp stabilize; then check every five minutes for the first 15 minutes; then reset at proper bias after 30 minutes or so.

i would do the same thing, regardless of whether or not i got tested or untested tubes.  and, i do this even with my mesa baron, which uses 6l6gc tubes...

for my low-power el84, 6v6 & el90 amps, which do not have adjustable bias, i yust closely watch the new tubes, when first installed, to make sure nothing is amiss.  my almarro a205a mkll seems to go thru el84's quite regularly, likely cuz it's left on ~120hrs/week.  (tho the rugged 7189 equivalents seem to last much longer - i have ~8 months on my present pair, which equates to a bit over 4k hours.)  anyways, i have found first signs of failure to be a strange sound thru the speakers, sometimes crackling distortion; this can then be werified by examining the tube, to find one glowing too much...

doug s.

[bunky]

I love tubes and i dont mind biasing power amplifiers but the beauty of having the autobias circuit on the VK60 was that i would just plug the power tubes in and the amp would self maintain the bias and i did not worry about it.you could really heat a room with that amp 

[doug s.]

I love tubes and i dont mind biasing power amplifiers but the beauty of having the autobias circuit on the VK60 was that i would just plug the power tubes in and the amp would self maintain the bias and i did not worry about it.you could really heat a room with that amp 

i have never minded biasing either, as long as the pots & test points are on the outside of the amp.  from what i have read, auto-bias extracts a small sonic penalty, but i don't know how true that is - the overall design needs consideration, methinks.

you are certainly correct - four 6c33c's can definitely sub as space heaters.   it would be nice to be using them today... 

doug s.

[rockadanny]

dougs - thanks again! great info for a tewb-newb like me. 

[Ericus Rex]

You can do this if you want but you probably should at the very least have your speaker connected.  The biasing might not be accurate without a load on the tube.

Anyone - When I get my new tube ... To watch the bias for the first few hours can I leave all of my system off with just the one monoblock powered up? Just to make sure it does nothing crazy? And how many hours would you suggest I do this for (if any):

[Ericus Rex]

Search the Music Reference circle with "self-biasing".  I started a thread about exactly what this means a while back and got some great responses.  Turns out 'self-biasing' isn't an accurate depiction of what's going on.  It's more like 'lowest common denominator' biasing.  Convenient?  Absolutely!  Good for sound?  Not so much.

I love tubes and i dont mind biasing power amplifiers but the beauty of having the autobias circuit on the VK60 was that i would just plug the power tubes in and the amp would self maintain the bias and i did not worry about it.you could really heat a room with that amp 

[rockadanny]

So I got a new tube from Partsconnexion. I set the amp's biases (both dials as there is one dial per output tube) to lowest settings, installed it, and fired it up. I watched it's voltage climb steadily while it warmed up. But it kept climbing, beyond the recommended maximum bias setting of 20v. I checked the other (good) tube and it had levelled out somewhere below the minimum recommended bias setting of 16v, as expected.

I put a known good tube in that slot and retried - the tube acted normally, levelling out at below 16v (remember, this is with the bias setting to lowest). I put the new tube in a different slot and it's voltage again climbed to over 20v. So its not the amp but the tube which is acting badly.

This seems to me that this is a bad tube. Do you agree? Or should I let if climb further before judging? And if so, how high? I realize these tubes are very unstable when new, but is this normal?

[doug s.]

So I got a new tube from Partsconnexion. I set the amp's biases (both dials as there is one dial per output tube) to lowest settings, installed it, and fired it up. I watched it's voltage climb steadily while it warmed up. But it kept climbing, beyond the recommended maximum bias setting of 20v. I checked the other (good) tube and it had levelled out somewhere below the minimum recommended bias setting of 16v, as expected.

I put a known good tube in that slot and retried - the tube acted normally, levelling out at below 16v (remember, this is with the bias setting to lowest). I put the new tube in a different slot and it's voltage again climbed to over 20v. So its not the amp but the tube which is acting badly.

This seems to me that this is a bad tube. Do you agree? Or should I let if climb further before judging? And if so, how high? I realize these tubes are very unstable when new, but is this normal?

sounds like the tube has issues -  you can not lower the bias when the tube starts climbing?   i would call partsconnexion and see what they have to say about it...

doug s.

[zybar]

So I got a new tube from Partsconnexion. I set the amp's biases (both dials as there is one dial per output tube) to lowest settings, installed it, and fired it up. I watched it's voltage climb steadily while it warmed up. But it kept climbing, beyond the recommended maximum bias setting of 20v. I checked the other (good) tube and it had levelled out somewhere below the minimum recommended bias setting of 16v, as expected.

I put a known good tube in that slot and retried - the tube acted normally, levelling out at below 16v (remember, this is with the bias setting to lowest). I put the new tube in a different slot and it's voltage again climbed to over 20v. So its not the amp but the tube which is acting badly.

This seems to me that this is a bad tube. Do you agree? Or should I let if climb further before judging? And if so, how high? I realize these tubes are very unstable when new, but is this normal?

Sounds like a bad tube.

One of the things that I heard about 6C33C tubes is that they benefit tremendously from being "conditioned" when new.  When I had my Audio Mirror amps upgraded by an AC member, he added a feature to my amps that allowed me to only partially heat the tubes.  He suggested that I do this whenever new tubes were purchased in order to get the best out of them.  I'll try and find the details...

George

[el-cee]

Hello Rockadanny,
I wonder know if these 6C33C-B from WWW.GSTUBES.COM site are tested, this is a good question to ask Mr.Anton, he is very kindly.
IF you can made us this favor and inform us the response from Mr.Anton I thankyou a lot.
I receive my order here in Brazil(two 6C33C-B) in 2 weeks(fast to the brazilian postal mail standard).
Regards, Gustavo
P.S.>  To test 6C33C-B tubes is need a tube tester with a septar socket and knowledge to read the measurement,
          something is beyond of me, so I ask to a friend repair tech.

According to Mr. Anton Zverev of GSTube.com regarding test status of
6C33C tubes:

"Tubes we sell are factory tested for the moment of production. We do not re-test tubes. Sorry."

Looks like it's a roll of the dice. At less than $10 apiece, it can be tempting.
Anton did say that the minimum order to guarantee a good price was 14 pieces.
Otherwise, "it will be extremely unprofitable due to customs fees here."

[FullRangeMan]

According to Mr. Anton Zverev of GSTube.com regarding test status of
6C33C tubes:

"Tubes we sell are factory tested for the moment of production. We do not re-test tubes. Sorry."

Looks like it's a roll of the dice. At less than $10 apiece, it can be tempting.
Anton did say that the minimum order to guarantee a good price was 14 pieces.
Otherwise, "it will be extremely unprofitable due to customs fees here."

Hi El-Cee,
Thanks for contacting GSTUBE and inform us this news.
This ''test'' factory is the <OTK> symbol on the glass tube, when the tube is ''OK'' they put this OTK mark.
The military test at the factory is the mark <17> on the tube glass.
A 6C33 may be fine for a military use and do not be useful for a Hi-Fi amp, I know very little about tubes,
but seems using this tubes is making your amp a test device.
But this is a great option if you/we have a tube expert friend to testing these 6C33 before use in a amp!!

In my city there is a tube amp maker that do not buy 6C33 tubes in GSTUBES for do not made the test himself, instead he buy in a tube broker in São Paulo for 55 dollars each !?  This is a mystery to me, why this maker prefer pay more??
Thanks, Gustavo