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 20th May 2003, 02:00 AM   #1
Morse is offline Morse  United States
diyAudio Member
 
Join Date: Jan 2003
Location: US for now.....
Default Pics of my 6BM8 - The Gnat....

Hi everyone;

Sorry about the delay, but I finally got the pics in of the 6BM8 SET that I've been working on. These are actually pics of the Mk I version prior to it's first extended use trials that showed up the heating problems inherent with the 269JX in this application. The current Mk II not only uses the 270DX trafo (which still runs warmer than I would like, darn it...), but the chassis has some small but important changes, like a 3.2cm x 3.2cm vent on the sidewall nearest the dropper resistor and a vented aluminium bottom plate that is designed to also work as a heat sink for the dropper resistor. Other changes include bypass caps fitted to all electrolytics in the amp.

I'm christening this little one "The Gnat".

All the best,
Morse
Attached Images
File Type: jpg gnat front.jpg (37.8 KB, 1435 views)
  Reply With Quote
Old 20th May 2003, 02:02 AM   #2
Morse is offline Morse  United States
diyAudio Member
 
Join Date: Jan 2003
Location: US for now.....
The Gnat, rear view....
Attached Images
File Type: jpg gnat back.jpg (35.6 KB, 1217 views)
  Reply With Quote
Old 20th May 2003, 02:04 AM   #3
Morse is offline Morse  United States
diyAudio Member
 
Join Date: Jan 2003
Location: US for now.....
The Gnat, interior view
Attached Images
File Type: jpg gnat bottom.jpg (63.9 KB, 1279 views)
  Reply With Quote
Old 20th May 2003, 03:03 AM   #4
diyAudio Member
 
Brett's Avatar
 
Join Date: Jan 2002
That's 'Gnot' a half bad looking amp you have there.
  Reply With Quote
Old 20th May 2003, 03:31 AM   #5
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Nice looking amp Morse... an inspiration to us.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 20th May 2003, 03:41 AM   #6
diyAudio Member
 
Sch3mat1c's Avatar
 
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
Looks nice!

Tim
__________________
Seven Transistor Labs
Projects and Resources
  Reply With Quote
Old 20th May 2003, 05:30 AM   #7
SHiFTY is offline SHiFTY  New Zealand
diyAudio Member
 
SHiFTY's Avatar
 
Join Date: Jul 2002
Location: New Zealand
Congrats! Looks good. A nice neat layout.

I really like the sound of mine, its great. Perfect for low volume listening. BTW NOS ECL82s are pretty easy to come by as well, you should try and pick some up. I also have read good things about the svetlanas.

What circuit did you use for that? And are those output trannies out of an Akai or something?
  Reply With Quote
Old 20th May 2003, 06:31 AM   #8
Morse is offline Morse  United States
diyAudio Member
 
Join Date: Jan 2003
Location: US for now.....
Thanks everyone! As usual I spent far too long worrying over the cosmetics of the chassis, so it's good to know that someone else likes the looks!!

One comment about the box design for anyone else who's thinking of trying it is that (for the first time!!) I had some shrinkage in the cherry that's the top plate. It's 2 pieces of 3-1/2" wide, 3/4" thick cherry that I edge glued with a biscuit between, and there is now a 1mm wide gap between the 2 planks (*grrr!!*) that I've had to fill. If I had it to do over again I'd have laminated a 1/4" thick piece of plywood to the underside of that top deck for stability - and I'd have oven dried it first, myself, to make sure it'd done it's shrinking prior to assembly. Oh well, live and learn....

Hi ShiFtY;

The circuit and all the current data for this version can be found in a couple of posts at: No bang, no flash, just music! Thanks again Dave, for all your help with posting the schematics!!

Actually, all I can say for sure about the OPT's is that they are 5Kr->8r and that they're "...OEM surplus made by Ravenswood Electronics, 1972 date code..." Maybe from a colour TV or a small hifi? It was the tail end of US electronics manufacture, so there was more than a little nostalgia for me in buying 'em.

Hmmm, I've got one pair of RCA NOS 6BM8's (they don't match though - one bottle is a goodly bit taller than the other!) and mostly Svetlanas. This is my last pair of Ei's - one of the first pair self destructed in under 50 hours from a loose internal element, though this pair is closing in on the 100 hour mark (knock on wood!!).

All the best,
Morse
  Reply With Quote
Old 20th May 2003, 06:49 AM   #9
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Quote:
Originally posted by Morse
Thanks again Dave, for all your help with posting the schematics!!
I think i'm going to make you pay for that by letting me put an article on your amp up on my site More than enuff material in these threads to make a good one.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 20th May 2003, 08:17 AM   #10
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Very nice, Morse!

The proportions and symmetry are pleasant to my eyes.
If I was allowed to use wood I hope it'd look like that.

With regard to transformer heating, another thought came to mind:
If you use choke input rectification, the secondary current is no longer taken in short bursts, but over more of the cycle. That means that the transformer heating produced by winding resistance is reduced.
Of course you'd need a new transformer with a higher voltage secondary for this. - And a choke!

Cheers,
  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
6BM8 Equivalent GlidingDutchman Tubes / Valves 11 15th April 2009 06:40 PM
6FD7, 6BM8 or other mashaffer Tubes / Valves 1 9th May 2008 02:14 AM
G2-driven 6BM8 wfmali Tubes / Valves 34 13th February 2008 05:47 PM
6BM8/ Heathkkit S.88 Has only 3 and 15 ohm O/P..? Alastair E Tubes / Valves 6 12th February 2008 12:05 AM
6BM8 Question Peter Menting Tubes / Valves 10 18th September 2004 03:08 PM


New To Site? Need Help?

All times are GMT. The time now is 12:22 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