So what are some good 7-pin, hi mu, low noise/microphonic tubes?? - 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 12th October 2005, 05:01 AM   #1
diyAudio Member
 
aletheian's Avatar
 
Join Date: Apr 2004
Location: Philly
Default So what are some good 7-pin, hi mu, low noise/microphonic tubes??

I want to mess with some 7 pin tubes, but I don't have any experience with them. So what are some good 7-pin, hi mu, low noise/microphonic tubes? I looked up hundreds of data sheets, figuring I'd start by looking at the A.F. or special quality ones first, but I found very little info on usage... other than the VHF specific ones.
  Reply With Quote
Old 12th October 2005, 05:23 AM   #2
Yvesm is offline Yvesm  France
diyAudio Member
 
Yvesm's Avatar
 
Join Date: Jul 2004
Location: Ardeche
Default Re: So what are some good 7-pin, hi mu, low noise/microphonic tubes??

Quote:
Originally posted by aletheian
. . . . other than the VHF specific ones.
No, except the 4HA5 / 6HA5, a remote cut off VHF one !

However, interesting tube with CCS load

http://www.dissident-audio.com/RIAA_PC900/Page.html

Yves.
  Reply With Quote
Old 12th October 2005, 05:32 AM   #3
diyAudio Member
 
aletheian's Avatar
 
Join Date: Apr 2004
Location: Philly
Default Re: Re: So what are some good 7-pin, hi mu, low noise/microphonic tubes??

Quote:
Originally posted by Yvesm


No, except the 4HA5 / 6HA5, a remote cut off VHF one !

However, interesting tube with CCS load

http://www.dissident-audio.com/RIAA_PC900/Page.html

Yves.

Very cool. wish he had some performance data up there.

6ha5, I had considered that one mu over 70, Gm over 14... petty good numbers.

I also looked at the 6AN4, specifically designed for grounded grid, cathode drive, so I thought it would make a nice top element in a srpp/cascode setup.
  Reply With Quote
Old 12th October 2005, 07:09 AM   #4
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
I've never measured a PC900 that met specification for gm...
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 12th October 2005, 08:52 AM   #5
diyAudio Moderator Emeritus
 
ray_moth's Avatar
 
Join Date: Jan 2004
Location: Jakarta
Why would you want to mess around with a remote cutoff pentode? It's non-linear. The 6AU6/EF94 is a miniature 7-pin sharp cutoff pentode that was popular as a microphone amplifier at one time. There are many versions of this tube and some are more microphonic than others. I have a couple of RCA ones that are good but my GE ones are not so good.
  Reply With Quote
Old 12th October 2005, 11:38 AM   #6
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
I've never used a 6HA5 that wasn't microphonic.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 12th October 2005, 02:02 PM   #7
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: South Florida
The 6HA5 is a triode. I never heard of a remote cutoff triode, but I suppose it is possible, but I see no mention of the words "remote cutoff" on the GE data sheet. I tried this tube for driver use with a CCS IC for a load, and a mosfet follower for a buffer (PowerDrive) and found that it worked quite well. The 6HQ5 is similar. I did not try them for low level use, therefore I didn't pay much attention to microphonics.

The 6AU6 is a pentode, and in pentode configuration I have found a very wide distribution in performance. Some are noisy and microphonic, while some are dead quiet. The characteristics of the noise changes from tube to tube. The distortion and gain varies quite a bit from tube to tube, and with the operating conditions. In triode mode the distribution of performance is better, but the tubes that were noisy in pentode mode are still noisy in triode mode. The ocean roar is now a mild hiss. If you have a lot of these you could grade out the good ones. I have at least 1000!

The related 6BA6 IS a remote cutoff pentode, and is generally useless for audio, except for some unusual fuzz type distortion in guitar amps.

For an output tube the 6AQ5 absolutely rocks! Triode or pentode, this one sounds good, and takes quite a bit of abuse, although I did manage to melt the glass on one at 400 volts! It was still cranking out sound when it sucked air! Consider it a baby 6V6, at least that is what the tube manual says. Found in early Gibson guitar amps. There are some similar 7 pin output tubes 6CU5, 6FX5 and others.

For the common stuff 6AV6 is half of a 12AX7, 6AT6 is the same with lower gain. These work as well as their 12A*7 counter parts.

The military type 9002 is an excellent sounding little tube, although the Mu is only 25.

The 6J6 is a 7 pin dual triode. Both sections share a common cathode. You can parallel both sections. I haven't tried this. You can use the tube as a differential amplifier with a CCS in the common cathode pin. This works well, although again some of these are niosy.

The 6AB4 is also a good sounding hi Mu triode, but I only had 3 to try, so I didn't spend much time with it.

The 6AK5 pentode is a good little amplifier, in triode or pentode mode. The tube to tube variation is much better than the 6AU6. I have about a million of these.

The 6AS6 is a pentode with interesting characteristics. G1 and G3 can be used as independent control grids. I have tried this as a vacuum tube VCA, with promising results, but more experimenting is needed.

There are several other VHF type tubes that I have collected, but haven't had the time to try out.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 12th October 2005, 02:48 PM   #8
Yvesm is offline Yvesm  France
diyAudio Member
 
Yvesm's Avatar
 
Join Date: Jul 2004
Location: Ardeche
I admit "remote cut off" is somewhat incorrect, say "variable Gm"

Probably the stated Gm value is only attainable at highest plate current.

Fortunatly, from 10 units (PC900, labelled Philips) I've found 5 that was not seriously microphonic, they just produce a short and damped "ding" when gently knocked with a pencil.
Otherwise, thermal noise is, as expected, vy low.

AFAIR, the RIAA preamp showed around 1% THD for an output level of 7v pp into 20K, not so good, not so bad.

This tube is obviusly not the better choice for the second stage

Yves.
  Reply With Quote
Old 12th October 2005, 05:20 PM   #9
nafunga is offline nafunga  United Kingdom
diyAudio Member
 
Join Date: Jul 2005
Location: Whitstable , Kent. UK
Don't forget the 8532 (Darling Amp) and the EC91 - both very useable.
  Reply With Quote
Old 12th October 2005, 05:46 PM   #10
diyAudio Member
 
aletheian's Avatar
 
Join Date: Apr 2004
Location: Philly
Great stuff guys! I think I'll buy them all and try a bunch out since they are wicked cheap at a buck or two a piece. Thanks for steering me away from the 6AB6. I was going to pick up a few of those.

Hey tubelab, if you want to unload some of those 6AU6 and 6AK5 's. Let me know how much you want for a handfull of good ones... hit me up at alex<at>aletheian.com.

So overall, are partially sheilded triodes decent sounding? Which works better, to ground the sheild or connect it to cathode?
  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
Microphonic s2kov Tubes / Valves 24 7th June 2010 04:20 PM
microphonic sub-miniature tubes? space-cake Tubes / Valves 11 10th October 2008 02:02 PM
are these tubes any good ????? istari knight Tubes / Valves 5 6th September 2005 04:46 AM
Good tubes for Luxman pre-amp Andypairo Tubes / Valves 9 16th December 2003 06:12 AM
Good Low-noise op amp? Michael Rothacher Solid State 3 11th August 2003 06:24 PM


New To Site? Need Help?

All times are GMT. The time now is 09:55 PM.


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