KT-77 Blues - 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 26th February 2007, 01:31 AM   #1
diyAudio Member
 
TubeHead Johnny's Avatar
 
Join Date: Jan 2005
Location: The emerald city, Seattle, WA.
Default KT-77 Blues

Hi Folks!

I recently read rave reviews on this site about the relatively new JJ KT-77 to replace my older (but still working) Electro-Harmonix EL34's, so I ordered a quad from the TubeDepot. What I understand is the KT-77 is electrically identical to the EL34, right? I figured I could just pop them in my amp and just have to tweak the bias setting just a tad and that's it.

I turned the bias pots fully counter-clockwise and connected my DMM across one of the 10 ohm cathode resistors, then I flipped the power switch. The TubeDepot gave these tubes a bias rating of 39 mA, so I figured each push-pull pair should be adjusted around 78 mA.

After power was applied, I noticed I could not make an adjustment...the reading was just all over the place. I'd get it around 75 mA and then it starts to climb uncontrollably. Then it starts to hum and motorboat. The music sounds distorted.

Here's the strange part. When I take the tubes out and flip the channels, the problem stays in the left channel. When I go back to my old EL34's, the problem disappears, there is nothing wrong with the amp.

Has anyone here had any problems with the KT-77's? My amp is a Dynaco ST-70 clone running in Ultra-Linear mode. It has separate 10K bias pots for each channel. Plate voltage is around 480 volts.

Thank you all in advance for your input,

~~~Johnny~~~
  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
The Blues. steenoe Music 179 12th September 2011 02:19 AM
Trends Ta- 10 blues... merlin2069er Class D 2 21st July 2009 02:40 PM
PPI A600 amp blues... kainoasun Solid State 0 1st July 2007 08:20 PM
More Sansui blues bulgin Analogue Source 0 8th May 2007 09:40 PM
DIY Blues Chad Solid State 2 25th October 2001 03:34 AM


New To Site? Need Help?

All times are GMT. The time now is 03:03 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