Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

Those Magnificent Television Tubes
Those Magnificent Television Tubes
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 2017, 01:16 PM   #941
jazbo8 is offline jazbo8
diyAudio Moderator
 
jazbo8's Avatar
 
Join Date: Jan 2011
Location: In Transient
Those Magnificent Television Tubes
Unfortunately, no. Also a page is missing from the 2014 article as well, just our luck... But I think the use of the large shunt capacitor between the control and screen grids may be optional, since it was not connected in the schematic in the 2014 version.
  Reply With Quote
Old 29th November 2017, 08:53 PM   #942
PhilippS is offline PhilippS  Germany
diyAudio Member
 
Join Date: Feb 2013
Quote:
Originally Posted by smoking-amp View Post
One -WILL- have to address the output impedance in some way, since the Twin/Crazy Drive is high output Z by itself. Getting sufficient CFB to do much Z lowering though will incinerate the driver stage when combined with grid 2 drive requirements. Like a total cathode follower output stage running on grid 2!!! Suggest some other (global) approach. Or "Schade" back to the driver cathode.
In this case (conversion to crazy drive) I guess i would need a different output transformer?
  Reply With Quote
Old 29th November 2017, 09:01 PM   #943
smoking-amp is offline smoking-amp  United States
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
There should be no need to change the OT as far as power matching goes. Your schematic in post 931 shows a global N Fdbk loop, which should take care of the output Z, as far as speaker damping is concerned. (no difference between grid 2 drive and Twin/Crazy drive as far as Zout goes)

Last edited by smoking-amp; 29th November 2017 at 09:04 PM.
  Reply With Quote
Old 30th November 2017, 09:05 AM   #944
jazbo8 is offline jazbo8
diyAudio Moderator
 
jazbo8's Avatar
 
Join Date: Jan 2011
Location: In Transient
Those Magnificent Television Tubes
Variation on the same theme, another "4DC" amp from Susumu Soya (MJ 2014 July), this time with 36LW6:

Screenshot - 11_30_2017 , 11_02_05 AM.png

Note the lack of shunt capacitor across the control and screen grids.
  Reply With Quote
Old 1st December 2017, 06:43 AM   #945
ErikdeBest is offline ErikdeBest  Switzerland
mostly thinkerer
diyAudio Member
 
Join Date: Mar 2003
Location: Zürich
Those Magnificent Television Tubes
I did something like this with a 6CB5:
- used a mosfet source follower with about 60VDC on G2
- 100R in the cathode, 70mA, so about 7V over the cathode. This wasn't bypassed however.
- 1 resistor between G2 and G1, and 1 between G1 and Gnd,
- G1 was at about 4VDC, so below cathode potential and didn't pull any current

exact values for both resistor I cant remember.

Objective was to create a low distortion amp with high output impedance (transconductance amp) and a mate used it quite a while to drive his Supravox speaker (15 inch woofer and 8 inch midrange), 1st order Xover - with very good bass

well, reading through it, my thingy was quite different actually - but sounded very nice and will be remeasured one day!
__________________
my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!
  Reply With Quote
Old 1st December 2017, 01:18 PM   #946
smoking-amp is offline smoking-amp  United States
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
Quote:
G1 was at about 4VDC, so below cathode potential and didn't pull any current
This would give "Dual Drive", like George (Tubelab) was experimenting with earlier.
If G1 doesn't draw current, then the grid resistors maintain a fixed voltage divider ratio on the grids. Typically arranged near the internal Mu to get each grid to share 1/2 the work. Only requires 1/2 the drive voltage swing of G2 only drive.

--------------------------------

Jazbo8's posted MJ 36LW6 "Crazy/Twin Drive" schematic above is using a tube I have here, so I'm going to try those 10K/10K resistors with the 36LW6 on the curve tracer here to see what they are doing.

I've also determined that the 12G-B7 tube used in another "Crazy/Twin Drive" schematic (below) is close to a 6GB5 or 21HB5 tube, which I have also. So I'll try those tubes with 14K/10K on the tracer also.
Attached Images
File Type: gif 12GB7SE-screendrive.gif (19.0 KB, 424 views)
  Reply With Quote
Old 1st December 2017, 02:35 PM   #947
smoking-amp is offline smoking-amp  United States
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
UH-Oh!

I just noticed that both of those SE schematics have grid 1 negative, with respect to cathode at idle, according to the posted voltages on the schematics.

SE would be operating in class A mode. So at best, Crazy/Twin mode could only occur for well positive signal voltage swings. Seems unlikely they would be operating with two modes of operation, so these two designs probably never even reach grid 1 current mode for Crazy/Twin drive operation.

Last edited by smoking-amp; 1st December 2017 at 02:37 PM.
  Reply With Quote
Old 1st December 2017, 02:43 PM   #948
ErikdeBest is offline ErikdeBest  Switzerland
mostly thinkerer
diyAudio Member
 
Join Date: Mar 2003
Location: Zürich
Those Magnificent Television Tubes
Indeed. In these cases the cathode resistor is bypassed, in the amp I made it was unbypassed, that is, G1 never became really negative (when G2 and G1 went up, current went up so cathode also went up)
__________________
my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!
  Reply With Quote
Old 7th December 2017, 09:55 AM   #949
DIYBras is offline DIYBras  Brazil
diyAudio Member
 
DIYBras's Avatar
 
Join Date: May 2015
Location: Parana
I just remembered about power law from these modes I've measured and seen here.
Crazy Drive tends to linear law, and Dual Drive tends to a perfect square law.
Will be a good oportunity for compare the measurements and sound.
I cancelled my "multi-mode amp" project due to various factors (priority to others unfinished projects etc.) but someday...
__________________
Making cabinets for OLD projects (better later than never...)
  Reply With Quote
Old 22nd December 2017, 06:46 AM   #950
smoking-amp is offline smoking-amp  United States
diyAudio Member
 
smoking-amp's Avatar
 
Join Date: Dec 2001
Location: Hickory, NC
42KN6 (old style) = 2X parallel 38HE7 beam pentodes

I just got my 1st 42KN6 Sweep tube in off the Bay, and it's the old style type, with two paralleled beam pentodes inside. I've been wanting to measure one of these, since the newer 42KN6 type, with one big pentode inside, is equivalent to the 6KD6, 6LX6, 26HU5 sweep tubes.

I curve traced it next to a 26LX6 and they are fairly close. I can get identical matched curves with the 42KN6 g2 at 85V and the 26LX6 g2 at 75 V, which matches with the datasheet internal Mu's of 4.5 and 4.0 reasonably well. Same grid 1 stepping for both, so matched equiv. gm 1.

Some while back I had speculated that the individual beam pentodes in the old style 42KN6 might be identical (datasheet wise) to the single beam pentode in the 38HE7 tube. So I connected up two 38HE7 pentodes in parallel to curve match against the 42KN6, and they ARE identical, Exactly! Same 85V on g2 and same grid 1 stepping for identical curves.

About 80% of the 38HE7 tubes I've seen bring out the heater separately for the pentode, on pins 10 and 12. Runs on 21V at 0.46 A. The 42KN6 runs at 42V at 0.46 A, so we have a match there. The 42KN6 is rated at 400 mA max DC, the 38HE7 pentode at 230 ma max DC each, so two would be 460 mA.

The 42KN6 is rated at 30 Watts plate diss. and the 38HE7 is rated at 10 Watts, but that is with the 6BJ3 equiv. damper diode operating along side in the bulb. The 6BJ3 damper uses 7.5 Watts of heater power and is rated for 4 Watts of diss. for a total of 11.56 additional Watts in the bulb. Without the damper powered up (using the 21V pentode only heater on pins 10 and 12), the beam pentode should be good for 15 Watts each I figure. So 2X in parallel would give the 30 Watts of the 42KN6. (the 21HB5 beam pentode is very similar in specs to the 38HE7 except bigger fin extensionss on the plate supports, and is rated 18 Watts alone in a bulb)

38HE7 are still on the $1 list. So you can make a 42KN6 (or a near clone of 6KD6, 6LX6... ) for $2 and two sockets.

------------------------------------------

I also got in a 20LF6 Sweep tube to try out (clearly marked, a GE tube with the extra grid 1 cooler fin up top). (came in a 26LX6 box I ordered, so by mistake I think) It curve tests VERY close to the 26LX6, just rated for more Watts. 40 Watts plate, 500 mA max DC, versus 33 Watts and 400 mA for the 26LX6, 6KD6 etc.

I also curve tested a 6MH6 tube I got in, and it is VERY close to the 26LX6 and the 20LF6 too. Rated 38.5 Watts and 500 mA max DC.

I then tried two 18 Watt 21HB5 tubes (which used to be on the $1 list) in parallel to see how they might compare with the 20LF6. Took 85 V on g2 to get the same knee current as the 20LF6 at 75 V. And the combined gm1 of the paralleled 21HB5 tubes was about 15% more than the 20LF6 etc for the same grid stepping.

(21HB5 has like 15% higher gm than the 38HE7 pentode, so was expected) Can get very similar curve tracings to 26LX6 and 20LF6 however, WITH the corrective compensations to g2 and g1. So not -exactly- an equivalent, but close enough, with those compensations. (and 36 Watts versus 40 Watts P diss.)

The 21HB5 plate is about 75% as big as the 20LF6 or 26LX6 plates. It usually doesn't have the grid 1 cooler fin up top like the 20LF6, but some manufacturer models do. (6HJ5 plates are the same size as 21HB5, and have the grid 1 cooler up top, for a 24 Watts rating, instead of 18)

Looks like I won't need to buy any $50 20LF6 tubes now at least. And no more 26LX6's either. Just sockets. (back during those old sale days, I bought a boxed deal of 138 38HE7 tubes for around $35 as I recall, and a big bunch of 21HB5's too. )

Last edited by smoking-amp; 22nd December 2017 at 07:09 AM.
  Reply With Quote

Reply


Those Magnificent Television TubesHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
MOAK: The Mother of All Karlsonators (aka The Magnificent Monster) DeonC Subwoofers 126 23rd January 2015 03:35 PM
Television question... toptip Everything Else 6 23rd October 2012 06:50 PM
Surround sound amp, Sub woofer and television warrennyc Subwoofers 4 3rd January 2005 10:33 AM
distance from television ALFIrE Multi-Way 2 30th March 2004 06:46 AM
Television broken Bull Everything Else 3 21st January 2003 12:08 AM


New To Site? Need Help?

All times are GMT. The time now is 05:36 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki