KT88 Usable range - 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 28th November 2006, 07:54 AM   #1
diyAudio Member
 
croccodillo's Avatar
 
Join Date: Mar 2005
Location: Bergamo
Default KT88 Usable range

Hi all,

I have a doubt:

I'm building and trying a SE parafeed amplifier, the output tube is a triode-connected JJ KT88, driven by an hybrid CCS set at 100mA (another KT88 -in pentode mode- with a cascode mosfet).

I would like to try now a dynamic current source.
This thing is something like the ACS developed by Nelson Pass.
The CCS working mode has to be divided into CC and AC.
With DC (idle) the CCS is a true CCS, sourcing 100mA.
With AC the CCS become a variable current source: higher the load current, higher the current in the CCS, up to 150mA.
Lower the load current, lower the CCS current, down to 50mA.
Give a look to Nelson Pass site, and to his US patent 5710522, or read the Aleph30 manual at his site.

The B+ is of 300+300V (central tap), well regulated.
There's also a -120V for the bias.

The driver is made with a 6N6P, connected to the +300V (half B+), loaded with a CCS (for now set at 20mA).

The final schematic will be something like this (the driver stage will be modified, and LTP will be tested).

The other side of the output transformer will be connected to the power supply enter tap (+300V).

The output transformer has an impedance of 2500 Ohm.

I would like to set the output tube idle working point at 330-340V, that @100mA means 34-35W of heat dissipation.

Which such data, I would like to swing the output tube from a minimum of 130V@150mA to a maximum of 530V@50mA, while the upper tube (CCS) will swing from 60V to 400V.
Considering the output impedance this will weans an output power of about 8W.

My question is:
Is it possible to run the KT88 tube with an anode voltage over 500V?
As told, I would like to run the output tube up to 560V, while the curves reports data only to 500V.
Is the KT88 stable and linear up to, let's say, 550-600V?
Consider also that at at highest voltage the current is limited.

Ciao,
Giovanni
__________________
In Nomine Libertatis Vincula Edificamus,
In Nomine Veritatis Mendacia Efferimus.
  Reply With Quote
Old 28th November 2006, 02:13 PM   #2
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Quote:
Is it possible to run the KT88 tube with an anode voltage over 500V?
Yes, it is possible. Dig up a data sheet for the TT21. The "guts" of a TT 21 and a KT88 are the same. The anode in the TT21 is top cap connected, which permits a HIGH B+ rail voltage. You must hold the screen grid voltage down and under no circumstances exceed the dissipation ratings for both the plate and g2.
__________________
Eli D.
  Reply With Quote
Old 28th November 2006, 07:24 PM   #3
Giaime is offline Giaime  Italy
diyAudio Member
 
Giaime's Avatar
 
Join Date: Oct 2004
Send a message via MSN to Giaime
Quote:
Originally posted by Eli Duttman


Yes, it is possible. Dig up a data sheet for the TT21. The "guts" of a TT 21 and a KT88 are the same. The anode in the TT21 is top cap connected, which permits a HIGH B+ rail voltage. You must hold the screen grid voltage down and under no circumstances exceed the dissipation ratings for both the plate and g2.
I'm with Eli. I have an amp here that runs Sovtek 6550 at 575V, with 310V on the screens. Very nice blue glow from the residual gas
  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
Full Range Speaker for SE KT88 build breakthastatic Full Range 19 8th June 2009 02:10 PM
Attenuator step sizes in the usable listening range rick57 Chip Amps 3 1st August 2006 08:27 AM


New To Site? Need Help?

All times are GMT. The time now is 02:55 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