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

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 23 Feb 2018, 23:28

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 33 posts ]  Go to page Previous  1, 2, 3, 4  Next
Author Message
PostPosted: 07 May 2017, 06:46 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2161
Location: Chilliwack, BC
M. Gregg wrote:
Car parts>> EL34/KT88 or a KT150?


Are three very different tubes. Electrically and sonically.

KT88 is closer to the 6550.

EL34 is in a league all its own.

The KT150 needs to be run much hotter to get the most from it, or you'll be cheaper and as sonically as good as sticking with the KT88.

Cheers!

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


Top
 Profile  
 
PostPosted: 07 May 2017, 09:42 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 599
Geek wrote:
M. Gregg wrote:
Car parts>> EL34/KT88 or a KT150?


Are three very different tubes. Electrically and sonically.

KT88 is closer to the 6550.

EL34 is in a league all its own.

The KT150 needs to be run much hotter to get the most from it, or you'll be cheaper and as sonically as good as sticking with the KT88.

Cheers!


Only my thoughts YMMV..

Ok all things being equal,

plug and play:
5881/EL34/6550/KT88/6L6<<yes all very different>>all very similar. OK the HT may be different but you can get a sort of balance that will allow each to work. (and the 807 plus a few others) just for a laugh.
I even ran all the above types 8 tubes at a time in a vellman K4000 not a single problem in 6 years.
OK the bias needed a doubler to give the range that was about it. HT the same level.
OK the power capability of the tubes is different but they will all work at a mid point setting.
I guess it depends how desperate people are for power.

I heard a tube manufacturer say the electronics and circuits are all different.
So I plugged each one in the same circuit with Fixed bias and adjusted the idle current.
The circuit is very different maybe between a 300B and an EL34.
You can even unplug half a PP if the output Tx is big enough to stop the saturation and even then you could leave both PP to equalise the current and drive one half and it will still work as SE.. :D

Yes the loading is different can you tell by ear? really..does it sound terrible or just different.
Oh look the driver is different er no..oh look the pre-stage is different er no...oh look the bias circuit is different er no just the setting.
Oh look the feedback is different (really) yes OK don't use any..

I think looking at what guitarists do just for a laugh, there is a difference between a guitar circuit and a HIFI circuit well there isn't that much difference on the clean channel. The principle is very similar.

I even run 6C33C OTL with heaters switchable one /two or both to reduce running cost with one half of the tube running or both halves running the difference is a bit tighter in the bass and a little more power..

I have no comment on this but its an interesting read.
The RH amps get a pasting quite often but have a look:
http://rh-amps.blogspot.co.uk/2014/04/

Regards
M. Gregg

_________________
What is the sound of one hand clapping?


Top
 Profile  
 
PostPosted: 07 May 2017, 09:58 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 599
OK just to clarify,

A pentode is easier to drive than a triode or a triode strapped pentode.
But lets be honest here, when people say I want to run a different power tube in my amp.
Tubes will and can be made to run, the tone and power is different.
Its not impossible to run KT88 etc on reduced power..just don't expect to use something like a 6L6 to deliver the same power as KT88.

The point is an amp can be designed to plug and play in HIFI the same as anything else.
Its just the power out has to be controlled.

So the whole point of all this is there is always a work around.
NB this doesn't mean you can fit 6L6 tubes in an amp running KT150 it means you can modify an amp to run different tubes

Regards
M. Gregg

_________________
What is the sound of one hand clapping?


Top
 Profile  
 
PostPosted: 08 May 2017, 09:03 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 599
Hi Bruce,

Just out of curiosity, what happens if you run the tubes with heater only no HT for a few hours before first switch on?
Just wondering if it had any effect?
This is standard practice for 6C33C, some people bake them in an oven. (but this tube has no phenolic base).
Might be moot..just an idea.

The idea would be run tubes with heater only for a couple of hours switch off leave to cool down completely.
Then power up HT and bias..

Regards
M. Gregg

_________________
What is the sound of one hand clapping?


Top
 Profile  
 
PostPosted: 08 May 2017, 09:20 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3552
Location: Arizona, USA
Hi, I don't know on that one. I'll pass along the info. The problem generally seems to be with the screen physical supports. The red is usually in a line with them.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 08 May 2017, 09:25 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 599
gofar99 wrote:
Hi, I don't know on that one. I'll pass along the info. The problem generally seems to be with the screen physical supports. The red is usually in a line with them.

Good listening
Bruce


With the 6c33c it is supposed to align the tube with expansion and de-gas.
I know people had big failures just putting HT and heaters on at first start.

I even ran my 6c33c's for 6 hours heaters only before first start.
It might be moot on the KT,s but I tend to do this for even half an hour with new tubes.
Its a PITA but its worth a try.

You have to watch the PSU caps over voltage

Regards
M. Gregg

_________________
What is the sound of one hand clapping?


Top
 Profile  
 
PostPosted: 08 May 2017, 09:33 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 599
gofar99 wrote:
Hi, I don't know on that one. I'll pass along the info. The problem generally seems to be with the screen physical supports. The red is usually in a line with them.

Good listening
Bruce


Is this screen current failure? (over current)

The voltage isn't higher on the screen than its supposed to be..
Just for interest do they still red plate if you put a zener in the screen?

Regards
M. Gregg

_________________
What is the sound of one hand clapping?


Top
 Profile  
 
PostPosted: 08 May 2017, 09:53 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3552
Location: Arizona, USA
Hi, Not likely as series resistors were tried (it is a U/L design) and even much lower screen voltages did not make it go away. The sound suffered before the red went bye bye. In the amp typically the anode and screen are at virtually the same potential. We have used this for about 8 years now without any issues. It works fine in everything from EL84s to at least here KT120s. All my knowledge points to tube issues.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 08 May 2017, 10:09 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 599
Hi,

So is the anode dissipation correct and they still red plate?

Just trying to break it down in my own mind,
current and voltage on anode are correct?
Screen voltage and current correct?
No heater cathode leakage?
No cathode over current?

Regards
M. Gregg

_________________
What is the sound of one hand clapping?


Top
 Profile  
 
PostPosted: 08 May 2017, 10:40 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3552
Location: Arizona, USA
Hi, Yeah a toughie. Everything in spec. Dissipation below ratings by about 20%. CCS in cathodes. Heaters elevated (because of other parts of the circuit) and voltage there correct so can't have any flow to ground bypassing the CCS. Same output trannies as in many other amps. U/L tap has a few 100 ohms internal and has always be fine. I use a set like it every day as do many folks on the diy and commercial side.

EDIT: The only KT120s I have here are bought a while back and none show this behavior. My main amps are actually running a bit hotter at about 88% as a long term test for durability. After 4 years they are just fine and the tubes test within spec. No red plating ever. During early tests at 95% I did not get any either. At 100% some did show. Since there needs to be a range for aging and subsequent imbalance I set the actual design to be below the 85% level.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 33 posts ]  Go to page Previous  1, 2, 3, 4  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Google [Bot] and 9 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
cron
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy