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 16 Nov 2019, 17:36

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 1991 posts ]  Go to page Previous  1 ... 157, 158, 159, 160, 161, 162, 163 ... 200  Next
Author Message
PostPosted: 20 Oct 2017, 09:39 
Offline

Joined: 01 Apr 2017, 19:56
Posts: 49
I believe that the LR8 from the Oddblock can power the Forewatt without problems. With 30 V across it and 10mA load (max rating) it will be dissipating only 0,3 W. The Oddblock only loads it with around 2mA. The Forewatt about 5mA. I see no problems there.


Top
 Profile  
 
PostPosted: 20 Oct 2017, 13:54 
Offline

Joined: 24 Oct 2010, 07:05
Posts: 295
I'm more conservative here. There are tolerances of tubes parameters, parts deviations, mains voltages. I do not know your plans on power supply layout, but the power part has 450V and the driver part is slightly over 300V and the difference is much more than 30V. Yes, you can put a serial resistor to drop some voltage, but it's better to count everything thoroughly.


Top
 Profile  
 
PostPosted: 20 Oct 2017, 14:15 
Offline

Joined: 01 Apr 2017, 19:56
Posts: 49
The Groovewatt is much more stressful on the LR8. 10ma exactly.
A 7,5kohm 3W series resistor (for both channels) can drop 450 to 330 V and then feed the LR8.
It's a matter to drop the voltage after the LR8 and Oddblock with another series resistor to get to 215 V or change the cathode resistors on the Forewatt to power it with the same 300V as the Oddblock.


Top
 Profile  
 
PostPosted: 20 Oct 2017, 21:18 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4049
Location: Arizona, USA
Hi, look for the LR8K4 version. It can handle 2 watts and 25 ma. It is a flat pack but can be soldered to a "surf" board.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 21 Oct 2017, 06:13 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
Hey Bruce,

Sorry if I asked this before, but have you tried a PNP wraparound with a regular LR8? I've had some great luck with that. Keeps the regulator's error amp in the loop, unlike an NPN or MOSFET wraparound.

Cheers!

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


Top
 Profile  
 
PostPosted: 21 Oct 2017, 08:28 
Offline

Joined: 24 Oct 2010, 07:05
Posts: 295
gofar99 wrote:
look for the LR8K4 version. It can handle 2 watts and 25 ma.
Just to mention: according to the LR8 datasheet from here http://www.microchip.com/wwwproducts/en/lr8 the max current for all versions of LR8 is 10mA.
victorzwk wrote:
The Groovewatt is much more stressful on the LR8. 10ma exactly.
In my build there was (stage 1)0.9+(stage 2)0.9+(stage 3)4.5+(voltage setting)1=7.3mA (I did not use the 220k-100k divider for the heaters lifting, just tap off the bottom voltage setting resistor of the LR8) + 0.7-0.8mA of the divider = 8.0 - 8.1 mA. In this case the input voltage is much lower: different version has 230-250V in the input. It helps if we count the mains voltage change (typically in the 10% range). For the 215V out - the input voltage must be not less than 12V higher (227V). Taking 10% mains deviations the max voltage would be 252V and the max power dissipation of the LR8: (252-215)*0.0081=0.3W. In the Oddwatt+Forewatt layout the output voltage is 310V and the power dissipation approaches 0.4W. I didn't consider tube tolerances here which worse the situation.
For the most powerful version of LR8 in D-PAK it means the 18°C temperature increase (if mounted on 25x25mm board), taking 40°C inside the case gives 58°C of junction and max current (due to the linear derating of current vs temperature) 7mA - it seems right equal your estimations. No safety margins for anything.
Not trying to spoil anything. Just my thoughts.


Top
 Profile  
 
PostPosted: 21 Oct 2017, 08:40 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4049
Location: Arizona, USA
Hi, I'm traveling right now...but look at the LR8K4 data from "Linear" Mouser had the K series ones. They are rated much more than the standard 3 pin "N" series.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 21 Oct 2017, 09:40 
Offline

Joined: 24 Oct 2010, 07:05
Posts: 295
I'm afraid Mouser made a mistake and put the current limiting value in place of the max rated current.
From the Mouser page:
Output Current: 20 mA
From the Datasheet (available from the Mouser page):
LR8 provides both current and temperature limiting. The output current limit is typically 20mA and the minimum temperature limit is 125°C. An output short-circuit current will therefore be limited to 20mA.

There is no output current limitation in the current datasheet, but the considerations are given in the Applications Notes AN-H40 from the link I wrote earlier.


Top
 Profile  
 
PostPosted: 22 Oct 2017, 11:13 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4049
Location: Arizona, USA
Hi, Something they don't mention is what happens if you exceed the ratings. If the IC thinks it is going to get too hot or thinks it is going to have too much current it goes into a fold back mode. The current drops to nearly zero and the output voltage drops with it. It will not restart until you completely remove the power source. Just clearing the fault is not enough. If it feeds too large of a filter cap and has a fast ramp up on the input it will do this. Also if you short it out it will probably fail. You can tell as it usually shorts through and will not adjust any longer. As you might guess I learned these quirks the hard way. :|

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 24 Oct 2017, 07:10 
Offline

Joined: 24 Oct 2010, 07:05
Posts: 295
victorzwk wrote:
If I were to implement a Forewatt in the same enclosure as my (stereo) Oddblock using the same LR8 regulated power supply (300 V output), would it be better to use a series resistor to drop the voltage to 215 V (18k ohms @ 4,54 mA). Or to substitute the cathode resistors on the Forewatt (from 470R to 1200R)? Thanks.
Sorry to push answers to side topic, I'll try to answer the main question. In my practice - the more B+ the better. If you follow all Bruce's cautions about cathode-heaters potential I'd prefer not to use the RC dropping circuit and connect the "forewatt" part directly to the same power supply (lower THD, better headroom and so on). I may have missed something in the thread, but where did you find the 470 vs 1200 numbers? With 470R@215V the current is estimated as 5-6mA, while with 1200R@300V the current may be 4-5mA, i.e. 1mA lower. I do not know how it will sound.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 1991 posts ]  Go to page Previous  1 ... 157, 158, 159, 160, 161, 162, 163 ... 200  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 17 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:  
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