New kt88's or 6550 - Page 4 - 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 4th April 2009, 09:24 PM   #31
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Quote:
These are the beasts I have.
The guts of your tubes look the same as some Sovtek KT88's that I have. The date codes on them are 99 10 but they are in the "Tung Sol" shaped glass envelope. If they are the same guts they aren't bad tubes. They don't have the extra heat dissipating fins that the EH tubes have but sound similar and don't blow up when leaned on.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 5th April 2009, 02:26 AM   #32
diyAudio Member
 
Join Date: Oct 2007
I wonder if the tubes shown are "real" Sevetlanas or some of the new ones made by Reflector? I've heard that the real ones are still available in the =C= brand is that true?

A long time ago I used a set of the Sevetlana 6550's in an Ampeg SVT that I repaired and fixed up for a guy and they were really nice tubes. Biasing was easy and they have been in that amp for a LONG time.
  Reply With Quote
Old 5th April 2009, 02:43 AM   #33
diyAudio Member
 
SpreadSpectrum's Avatar
 
Join Date: Nov 2007
Quote:
It says with moderate grid current which does not apply to the more common amp designs. I noticed that you're into more exotic amps, but the average amp should not have G1 grid current unless there is a problem as I see it.
Gold plated grids should be able to handle some grid current, otherwise the 5881 would not have AB2 suggested operating points. Just don't crank it to 11 with sine wave input. I cranked mine to 11 playing music for quite a while and didn't have problems.

Also, the drivers of yesteryear may not have been able to inflict nearly the punishment that source followers can.
  Reply With Quote
Old 5th April 2009, 02:44 AM   #34
rknize is offline rknize  United States
diyAudio Member
 
rknize's Avatar
 
Join Date: Feb 2009
Location: Chicagoland
Send a message via AIM to rknize Send a message via Yahoo to rknize
Those all look like Reflektor plate construction to me (smooth plates, round holes).
  Reply With Quote
Old 5th April 2009, 03:04 AM   #35
rknize is offline rknize  United States
diyAudio Member
 
rknize's Avatar
 
Join Date: Feb 2009
Location: Chicagoland
Send a message via AIM to rknize Send a message via Yahoo to rknize
Older EH KT90 (Reflektor):

Click the image to open in full size.

Tung-Sol reissues (Reflektor):

Click the image to open in full size.

SED KT88:

Click the image to open in full size.
  Reply With Quote
Old 18th April 2009, 02:02 AM   #36
diyAudio Member
 
Join Date: Jan 2009
Location: Michigan
I've had poor experiences with Ruby Tubes KT88s. Unfortunately I had purchased 28 of them in matched quartets over a couple years prior to actually using any of them. I would learn the hard way that 11 of the 28 had major failures very early in their life. Two provided a sparking light show right out of the box, while many others just quit conducting current after about 10 hours of usage punctuated with a few on/off cycles. Though the filament remained lit, plate voltage was still present at it's pin, and fixed bias voltage was still present in it's pin, the cathode current dropped to zero instantly, accompanied by a loud pop in the speakers. I run a 10 ohm cathode resistor on each of four tubes in PPP and monitoring current flow through each resistor, the voltage drop across the 10 ohm went instantly to zero for the affected tube.

When the amp is turned on from a cold start, everything powers up fine and the amp is working magnificently for awhile. Then suddenly a loud pop and one of the four tubes just stops conducting. This problem follows the specific tube, regardless of which amp I place it in. I have even retouched the solder inside the pin ... the problem persists.

After exhaustive testing, I believe the spot welds (or lack of them)between the anode plate material to the electrode wire are no good. Whatever spotwelding current is (might be) used during manufacturing, it may be adequate for small signal tubes with small plates and fine electrode wires, but is inadequate for the big plates and wires. OK, maybe I could accept an occcasional failure every couple years, but repeated failures inside of 10 operating hours, with multiple tubes having identical failure modes ... no .

Ruby's may have a replacement guarantee, but after experiencing the identical failure modes in an inordinately large percentage of the same tube numbers, NO, I am not interested in a replacement.

I am now purchasing Gold Lions.
  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
KT88 and the 6550 duderduderini Tubes / Valves 56 28th October 2008 04:47 AM
KT88 or 6550 cjng74 Tubes / Valves 4 25th November 2007 12:33 AM
KT88/6550 as Triode Ardee Tubes / Valves 11 9th October 2006 03:33 PM
KT88 or 6550? castlesteve Tubes / Valves 3 7th June 2005 10:27 PM


New To Site? Need Help?

All times are GMT. The time now is 08:08 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