The Midlife Crisis - My 833C Amp Build - Page 38 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st September 2013, 03:01 PM   #371
diyAudio Member
 
Join Date: Nov 2003
Location: Bristol
Hi Matthias,

That is very helpful, thank you!

I have found some 8mm clips on Conrad so will order these along with the fuses.

What you have shown is pretty much what I was thinking of

I have been looking for a solution for my GM70 push pull for a while and had given up on fuses for want of finding something suitable.

Thanks again for your help,

James.
  Reply With Quote
Old 21st September 2013, 09:23 PM   #372
Magz is offline Magz  United States
diyAudio Member
 
Join Date: Oct 2009
Location: New Jersey, USA
While waiting for the chassis to be anodized I made up a pair of mounts/heatsinks for the Rod Coleman filament regulators. They are built from a 10mm thick 3.5"x 4" aluminum block, with a salvaged heat sink from an old subwoofer amp screwed on. The filament regulators screw to the side of the block opposite the heat sinks. The blocks are drilled and tapped to mount snugly to the underside of the chassis top plate, so between the block, the heat sink and the top plate I ought to have enough thermal dissipation (hopefully, since I don't know the degC/W of the salvaged heat sinks).
Attached Images
File Type: jpg 833 Amp Filament Heat Sinks.jpg (21.6 KB, 595 views)
  Reply With Quote
Old 22nd September 2013, 07:21 PM   #373
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
The heat sinks look to be about 10x15x5 cm or so. They'll probably have a thermal resistance around 1.5 /W if mounted with the fins vertically. That's my guess based on similar heat sinks.

If you really care, you can always measure the thermal resistance.

Don't forget to use thermal goop between the top plate and the heat sink and aluminum block. Thermal sandwich...

~Tom
__________________
Modulus-86: Composite amp achieving 0.00018 % THD. Damn Good 300B, Novar Spud, 21st Century Maida Reg., Filament Reg., etc.
Neurochrome : : Audio - http://www.neurochrome.com/audio - Engineering : : Done : : Right
  Reply With Quote
Old 22nd September 2013, 11:42 PM   #374
Magz is offline Magz  United States
diyAudio Member
 
Join Date: Oct 2009
Location: New Jersey, USA
Quote:
Originally Posted by tomchr View Post
The heat sinks look to be about 10x15x5 cm or so. They'll probably have a thermal resistance around 1.5 /W if mounted with the fins vertically. That's my guess based on similar heat sinks.

If you really care, you can always measure the thermal resistance.

Don't forget to use thermal goop between the top plate and the heat sink and aluminum block. Thermal sandwich...

~Tom
The sinks are 11x6.5x3cm, so a little smaller. They are also located near the fan intake so hopefully the 33cfm of the fan will boost their heat dissipation somewhat. I used boron nitride heat sink grease between the sinks and the block, and will repeat that at all locations with thermal interfaces. I also plan to use an aluminum clamp to hold down the transistors so that ought to add some dissipation from the other side of the chip as well.
  Reply With Quote
Old 24th September 2013, 10:25 PM   #375
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
The vast majority of the heat will flow through the metal tab of the package as the thermal resistance through that path is much lower than through the plastic package. Unless the clamps make assembly easier, I would probably stick with the normal screw + shoulder mounting method. If you want to get really fancy, you get a torque screwdriver and tighten the screws to the torque recommended by the manufacturer of the thermal washers.

~Tom
__________________
Modulus-86: Composite amp achieving 0.00018 % THD. Damn Good 300B, Novar Spud, 21st Century Maida Reg., Filament Reg., etc.
Neurochrome : : Audio - http://www.neurochrome.com/audio - Engineering : : Done : : Right
  Reply With Quote
Old 25th September 2013, 12:49 AM   #376
Magz is offline Magz  United States
diyAudio Member
 
Join Date: Oct 2009
Location: New Jersey, USA
There is an additional wrinkle here, in that the Coleman regulators will be floated at approximately 250VDC in order to provide the appropriate bias. Rod Coleman himself advised me not to use a metal mounting screw with shoulder washer in order to avoid a potential failure. The way I look at it, I have a couple choices:

1) Ignore Rod's advice. I'm inclined not to.
2) Use a nylon screw. Since nylon doesn't melt until 220C, and the chip would be toast well below that point, it should work...unless it comes loose over repeated heating/cooling cycles. Loctite might help there.
3) Use a clamping bar across the chip package, and maybe a nylon screw through the TO-220 tab as well.

I'm leaning toward #3.
  Reply With Quote
Old 25th September 2013, 01:13 AM   #377
diyAudio Member
 
sakellogg's Avatar
 
Join Date: Nov 2008
Location: dixon ill
Quote:
Originally Posted by Magz View Post
There is an additional wrinkle here, in that the Coleman regulators will be floated at approximately 250VDC in order to provide the appropriate bias. Rod Coleman himself advised me not to use a metal mounting screw with shoulder washer in order to avoid a potential failure. The way I look at it, I have a couple choices:

1) Ignore Rod's advice. I'm inclined not to.
2) Use a nylon screw. Since nylon doesn't melt until 220C, and the chip would be toast well below that point, it should work...unless it comes loose over repeated heating/cooling cycles. Loctite might help there.
3) Use a clamping bar across the chip package, and maybe a nylon screw through the TO-220 tab as well.

I'm leaning toward #3.


im no expert at all but, 3 gets my vote.

cant go wrong with overkill.
__________________
I'm not crazy, my mother had me tested
  Reply With Quote
Old 25th September 2013, 07:40 AM   #378
Matt BH is offline Matt BH  United Kingdom
diyAudio Member
 
Join Date: Jul 2009
Location: Cheltenham
Hi Magz, you could also use ceramic insulators under the TO220 packages:

Insulators - heat sink interface material

You can also get longer and slightly thicker insulating bushes for the screws. These need the top of the threaded hole in the heatsink counter boring slightly to allow the bush to sit down on the tab.

I have used these before on floating HT regulators and they work fine, certainly better than mica or silicone insulators. i am not at home at the moment but I can post a photo later if you like.

Cheers
Matt.
  Reply With Quote
Old 25th September 2013, 07:44 AM   #379
работник
diyAudio Member
 
Rod Coleman's Avatar
 
Join Date: Jul 2004
Location: Warwickshire UK
Quote:
Originally Posted by Magz View Post
There is an additional wrinkle here, in that the Coleman regulators will be floated at approximately 250VDC in order to provide the appropriate bias. Rod Coleman himself advised me not to use a metal mounting screw with shoulder washer in order to avoid a potential failure. The way I look at it, I have a couple choices:

1) Ignore Rod's advice. I'm inclined not to.
2) Use a nylon screw. Since nylon doesn't melt until 220C, and the chip would be toast well below that point, it should work...unless it comes loose over repeated heating/cooling cycles. Loctite might help there.
3) Use a clamping bar across the chip package, and maybe a nylon screw through the TO-220 tab as well.

I'm leaning toward #3.
It is possible to use the screw-fixing method across 250V, but a high degree of care is needed in cleaning up the hole (dia 3.5mm please, be sure to allow the shoulder-washer to enter the hole). The finish and flatness of the surface must be carefully inspected.

other considerations:

- the 833 cold filament is probably near zero ohms at turn-ON. The Coleman Regulator soft-starts the filament with a gentle ramp-up of voltage, but the startup interval still applies heightened thermal stress on Q5. The thermal interface must be in good shape!

- The materials of the heatsink, transistor, screw and shoulder washer are all different, so differential expansion may be at work, and a flash-test on a cold assembly does not guarantee that warmed-up, the insulation integrity will be maintained.

- screw method is not preferred in any event. It applies the clamping force to one end of the TO-220, unlike clips and clamps acting on the insulated portion of the transistor body.

- spring clips are purpose-designed to apply the correct mounting force to the body of the TO-220, and are superior to screws in this respect. In addition, there is no insulation weakness at the screw hole.

- for this purpose, I like the Aavid heatsink clips, or the Laird Technologies version that can be screw-mounted next to the TO-220:

TSC607-ZP - LAIRD TECHNOLOGIES - CLIP, 2 X, TO-220 | Farnell United Kingdom

there are many other similar types.

If these are used, there is no need to use any TO-220 screws, and a plain Silicone pad should be used in place of the Mica insulators I supplied. Thermal grease is not usually necessary with sil-pads, provided the interface surface is smooth and carefully cleaned.

3223-07FR-43 - BERGQUIST - THERMAL PAD, TO-220 | Newark

- if the heatsink spreader-bar is hard-anodised, there will be extra insulation safety (anodised heatsinks often present an insulating surface - it's the oxide!).


The only other precaution is to monitor the transistor body temperature during first-time use, using an IR gun-type instrument.
  Reply With Quote
Old 25th September 2013, 01:04 PM   #380
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Quote:
Use a nylon screw.
The common white nylon screws will lose their heads after a year or two of thermal cycling....just say no.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
mono block amps with 2 x 833C overkill ? even possible to DIY? Thesoundmen Tubes / Valves 25 9th June 2014 02:27 AM
Good Source for Nice Analog Panel Ammeters for 833C Build? Magz Tubes / Valves 12 7th March 2013 07:49 PM
Small and portable headphone amp Crisis firefart_1st Headphone Systems 15 26th May 2010 08:24 PM
Midrange + midlife crisis ronzeman Multi-Way 7 1st September 2008 02:39 PM
No More Sound Crisis john2890 Everything Else 1 23rd December 2005 06:50 AM


New To Site? Need Help?

All times are GMT. The time now is 08:41 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2