KT88 Minimum Mounting Distance - 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 18th October 2007, 12:52 PM   #1
diyAudio Member
 
Rob11966's Avatar
 
Join Date: Jun 2007
Location: Australia
Default KT88 Minimum Mounting Distance

Hi Folks,

Need some advice. I am just making up a chassis for a KT88 70W power amp (Dynaco MK III) with 2 KT88 output tubes. I am having a spot of bother with the layout. For various reasons that are not worth getting into, I can only get about 3 inches from center pin to center pin. The factory specs recommend a minimum distance of 4 inches. With my layout there is at least 3cm (sorry about the mixed units) between the tubes even between the widest part of the glass envelope.

What do you guys think - is this far enough apart for heat dissipation (the tubes will only ever be running at 75% of there maximum possible output even at full volume) or do I need to do a major redesign? It seems to me that many of the commercial amps space the tubes much closer than the tube manufacturers recommendations.

Has anyone had any personal experience?

Thanks in advance for the advce.

Rob
  Reply With Quote
Old 18th October 2007, 01:11 PM   #2
traf is offline traf  United Kingdom
diyAudio Member
 
Join Date: Jun 2007
My old Beard P101 operated quite happily with about 10mm between each of the 8 KT88s. My current Primaluna makes do with about 8mm or about 2.25in between centres.

I would have thought that provided you have decent ventilation top and bottom to allow a convection current (air not elec!) to be established you should be fine.
  Reply With Quote
Old 18th October 2007, 01:11 PM   #3
diyAudio Member
 
Brett's Avatar
 
Join Date: Jan 2002
Should be fine. It seems I can barely get a sheet of paper in between the O/P tubes on my Fisher receiver and they were original factory when I got it and sounded fine. I use one bottle diameter between tubes as my minimum in my own hifi designs, and add forced air or convection cooling on the same centres for pro/MI gear.
  Reply With Quote
Old 18th October 2007, 01:13 PM   #4
diyAudio Member
 
stoolpigeon's Avatar
 
Join Date: Feb 2007
Location: Laputa
Hi Rob,

I have a friends TVA-1 which uses KT88 spaced at 4 inches.

SP
  Reply With Quote
Old 18th October 2007, 01:39 PM   #5
Account Disabled
 
Join Date: Sep 2004
Location: Earth
Do it! 3cm are fine.
Some guitar amps place the tubes really close too!
It'll be great for the tubes to have the same temperature! haha
.... I just remember this from one guy that was placing the tubes really close for this reason! Matched heat!

I don't mean it!
  Reply With Quote
Old 18th October 2007, 02:59 PM   #6
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
The old Bell & Howell cine projectors used KT88's that were so crammed in with other components to be nearly touching. And they still ran on.
  Reply With Quote
Old 19th October 2007, 03:14 AM   #7
diyAudio Member
 
Rob11966's Avatar
 
Join Date: Jun 2007
Location: Australia
That's all reassuring news. I will proceed with my design. I liked the account of the projector but I presume it had some enormous fan cooling it down?
Rob
  Reply With Quote
Old 19th October 2007, 03:37 AM   #8
diyAudio Member
 
Join Date: Oct 2004
Location: Adelaide South Oz
Rob,
Do you have a copy of Morgan Jones "Building Valve Amplifiers"?

In there it discusses how the heat from tubes like the KT88 and similar is mostly thrown out 2 sides, which are the flat sides of the tube anodes. If you have the KT88s less than 4" apart then at least make sure the anode flats are to the side and not in the line running through the tubes.

In the picture attached I think that means that the holes you see in the outermost structure should be in the line through the tubes. That is the heat will mostly be radiated from what is the left and right sides of the picture.

Others: Please correct this if I've got that wrong!!!

Cheers,
Ian
Attached Images
File Type: jpg kt88.jpg (4.4 KB, 267 views)
  Reply With Quote
Old 19th October 2007, 10:50 AM   #9
diyAudio Member
 
Rob11966's Avatar
 
Join Date: Jun 2007
Location: Australia
Hi Ian,

Yes, I do have a copy. To be honest for some of the issues that I have encountered, I have found the experience of this forum a little more practical - not to say that I haven't found 'Building Valve Amplifiers' useful of course!

Cheers,

Rob
  Reply With Quote
Old 19th October 2007, 01:03 PM   #10
Account Disabled
 
Join Date: Sep 2004
Location: Earth
Ian you're totally right.
It's better if the tubes are at 90degrees each other!
  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
what is the mounting depth and mounting diameter of this? lemans23 Multi-Way 2 26th October 2005 10:52 PM
DSP XO > Minimum Phase? amo Multi-Way 8 19th October 2003 08:33 AM
Any minimum distance from driver to port? Circlotron Multi-Way 4 27th December 2002 11:23 PM


New To Site? Need Help?

All times are GMT. The time now is 12:08 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