6F8G's any good? - 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 29th November 2006, 02:56 PM   #1
JoshK is offline JoshK  Canada
diyAudio Member
 
Join Date: May 2004
Location: Toronto, ON
Default 6F8G's any good?

I recently was browsing some notes on tubes and I came across the 6F8G. I read in the spec sheet that its sections are very similar to the 6j5 apart from interelectrode capacitances. I have also been reading Morgan Jone's chapter on tube (valve) selection and the analysis he did on the *sn7/*n7 family.

I am wondering how the 6F8G ranks among its peers. It certainly has cool factor written all over it. I thought it was strange that according to what I can tell from its spec sheet that one grid is hooked to the grid cap and another is to pin 5. That seems strange to me. Does this make one triode any different than the other, via interelec cap?

I was wondering if anyone has any experience with it, tested it or compared with the *sn7 family?

Josh
  Reply With Quote
Old 29th November 2006, 04:40 PM   #2
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I looked it over and according to the data sheet it is basically a pair of 6J5 in a single envelope - other than the obvious grid cap issue I suspect it would perform very much like a 6SN7. Good find I'd say.. I'll bet it is not too common though, I haven't run across many in my travels, but not being the current tube-du-jour it is probably pretty inexpensive too.

On the differences in inter-electrode capacitances I would expect that the differences would be swamped by external capacitances anyway, and the one that counts most Cgp (miller capacitance) is the same in both sections.

I'd certainly use it..
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 30th November 2006, 12:15 AM   #3
GRD is offline GRD  United States
diyAudio Member
 
Join Date: Jul 2004
Location: CA
Josh,

I built a VTV linestage using 6F8G's instead of 6SN7's for 2 reasons. First, a lot of people praise the 6SN7's that are quite pricey. The 6F8G's are basically old stock 6SN7's that are lower priced. So, you can get round plates, etc. and see if they are indeed the holy grail. Second, and equally important to me was they looked cool. I haven't compared to any other 6SN7 so I can't comment on how they stack up. The other SN7 oddity is the 2C22 - a rabbit ears 6J5. And then there are the 7N7's - a 6SN7 in the local socket. The tube limits are a little different than some of the 6SN7's, so see the datasheet.

Grant
  Reply With Quote
Old 30th November 2006, 02:04 PM   #4
JoshK is offline JoshK  Canada
diyAudio Member
 
Join Date: May 2004
Location: Toronto, ON
Thanks.

What prompted this obviousy was Morgan Jones's discussion on the *sn7 family and how good they were. I had always liked the sound of octal line stages I had heard over other tube line stages (not controlling for circuit obviously).

I came across some old 6f8g's and wondered if they were good, and of course, they look damn cool.
  Reply With Quote
Old 30th November 2006, 03:28 PM   #5
diyAudio Member
 
Join Date: Sep 2002
Location: VA
I built a PP 807 amp a while back for a friend and I used 6F8G tubes in place of 6SN7s and it sounds great. 6C8G is another variant and sound nice in linestages. 2C22 tubes as already mentioned also work great.

Dave
  Reply With Quote
Old 30th November 2006, 03:49 PM   #6
GRD is offline GRD  United States
diyAudio Member
 
Join Date: Jul 2004
Location: CA
One observation on the 6F8G - They can be somewhat microphonic. I ended up using Herbie's tube dampers which fixed any problems. I think it might be related to the size/shape of the bottle.
  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 makes the good guitar pickup sound so good? darkfenriz Instruments and Amps 15 1st March 2009 11:46 PM
Good general purpose opamp with good DC specs? speakerguy79 Parts 1 17th November 2006 04:10 AM
Good switch for Stepped attentuater, Good cheap RCA jacks pjpoes Parts 20 10th March 2005 08:47 PM
Pioneer TS-W304C- anyone have good design for it? and is it good for home sub? XteveX Multi-Way 7 28th April 2004 04:05 AM


New To Site? Need Help?

All times are GMT. The time now is 02:11 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