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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 08 Dec 2012, 18:26 
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Suncalc wrote:
mwhouston wrote:
... 60W. It is a PP not SE.
I really didn't think much of it for $13K a pair.
I know that I'll probably step on a bunch of toes, but I don't see the point in running big triodes in PP AB1. You get a lot of power but it destroys the thing you use a triode for in the first place; nearly pure 2nd order harmonic distortion. The minute you go PP the 2nd order harmonics get mushy and when you bias for AB1 you get extended harmonics. In PP operation, I much prefer the pentodes and BPTs run in UL. For the big triodes, I'll aways trade power for sound and run them SE class A only.

I'll get off my soapbox now. :soapbox:

@Magnus: Do you have an image of your power tubes?
@Matt: I sat close to one of the 6' speakers last night (8 people in the room) and swear I could hear an edginess in the sound that, to me, sounded like higher harmonics distortion. With the SE 845s my friend had before that edginess was not there. With the 845s they had stacks of power (28W) into 92db efficient speakers in a small room and a real good delivery of music. I felt they lacked passion though. I was never moved but did enjoy their sound.

A very respected builder down my way (who winds all his own OPTs) says there is NO good argument for paralleling triodes. He claims it really destroys the true triode sound with very little power advantage. I would be the last to knock PP amps knowing how good a performance Bruce gets from his oddwatts and the development he has put into them. But Bruce knows what he is doing and picks good performing pentodes and respected power tubes designed to do the job well.

300Bs in PP. Not good.

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PostPosted: 08 Dec 2012, 19:51 
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mwhouston wrote:
300Bs in PP. Not good.


Ooooohhh, please explain. I have a customer interested in one and I don't want to make him a lemon :hot:

Cheers!

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PostPosted: 08 Dec 2012, 23:10 
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Geek wrote:
mwhouston wrote:
300Bs in PP. Not good.


Ooooohhh, please explain. I have a customer interested in one and I don't want to make him a lemon :hot:

Others may be able to explain better. I think, for me, it is more of a gut feel, than a well informed statement. I just feel tubes like, 300Bs, 45s, 2A3s even 211s and 845s are meant to fly solo. These tube posses the qualities which make SET amps what they are. Sorry to be a little vague.

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PostPosted: 18 Dec 2012, 08:56 
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I didn't want the fuse holders visible and don't expect to ever have to change a fuse. The fuse holders and soldered directly to the 300B socket.

I surely hope so but good design warrants the unexpected and mechanical pressure/torque from opening/closing the fuse holder will likely cause problems with the solder connection. Not trying to cause confrontation here. If I really wanted the fuse on the socket like that, I would just get a fuse with leads hanging off and solder it on floating, much like you did but without the "case". Cheaper, easier to service, like the one on the left...and you can shrink it afterwards too.

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PostPosted: 18 Dec 2012, 11:30 
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The pigtail type of fuse was suggested by Suncalc as the better alternative. Really I don't ever expect to have to change the fuse. It's a little like life insurance, you hope you never need it. Also I try to use what is on hand rather than buying more "stuff". I have a room I can barely get into and gear overflowing everywhere. Anytime I can make do I am at the moment.

I feel better though that the tubes are protected 100% from over current. As you may have read I had one bipolar Ck short but the amp wasn't in my care at the time and there had been some fiddling under the bonnet by another. The fuse has only been in place for only a few weeks but the amp has been in play a lot. So far so good.

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PostPosted: 19 Dec 2012, 08:15 
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Yea I scrolled through more pages of this thread and see suncalc posted something similar sorry for being repetitive and not reading the full thread! I don't always have lots of time for forums with work, kids, life happens etc.

However, I never knew they were called pigtail fuses so I learned something, and you guys have some good posts to read too. Suncalc especially. Thanks.


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PostPosted: 24 Dec 2012, 01:48 
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mwhouston wrote:
The pigtail type of fuse was suggested by Suncalc as the better alternative. Really I don't ever expect to have to change the fuse. It's a little like life insurance, you hope you never need it. Also I try to use what is on hand rather than buying more "stuff". I have a room I can barely get into and gear overflowing everywhere. Anytime I can make do I am at the moment.

I feel better though that the tubes are protected 100% from over current. As you may have read I had one bipolar Ck short but the amp wasn't in my care at the time and there had been some fiddling under the bonnet by another. The fuse has only been in place for only a few weeks but the amp has been in play a lot. So far so good.

Yes I have quoted myself. Why? Because a fuse has blown. I'm yet to check that it is actually a fuse and\or the bypass cap has shorted but quickly touching the tops of the 300Bs proved the left one was extremely hot and the right one just hot. The left channel was working and the right channel not. So my guess is the HT to the right tube is off and thus a blown fuse. I am going to increase the fuse value to something like 120mA. Hope this falls within the current handling capabilities of the 300B. If I find the bipolar bypass cap has shorted I may remove both and look for some better caps.

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PostPosted: 26 Dec 2012, 00:01 
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I appears it is just a fuse only.The next value up In M205 size fuse is 160ma. Can someone confirm 160ma does not exceed what a 300B can handle.

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PostPosted: 26 Dec 2012, 00:12 
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I use 250mA fast blow types... they pop loooong before the 300B will. ;)

Cheers!

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PostPosted: 26 Dec 2012, 01:36 
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Geek wrote:
I use 250mA fast blow types... they pop loooong before the 300B will. ;)

Cheers!

What is max current for 300B

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