c-j pre amp blowing 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 5th March 2009, 03:39 AM   #1
diyAudio Member
 
Join Date: Aug 2008
Default c-j pre amp blowing tubes?

I have a cj pv2a pre amp that has a problem with the phono tube section. After about an hour of play, I hear a very loud rushing water sound from the speakers. The second tube (5751 ) is much brighter looking, as though the heater is getting too much voltage. The first tube (12AT7A ) then runs cold, no illumination at all, and cold to the touch, as though no voltage at all is going to it. The line stage works just fine. Put in two new tubes, and worked fine for about an hour, now same thing I think i fried the tubes.
What should i check/ do?
Paul
  Reply With Quote
Old 5th March 2009, 03:44 PM   #2
diyAudio Member
 
boywonder's Avatar
 
Join Date: Jan 2008
Location: So.Cal.
Possibly a cold solder joint problem in the heater wiring? If one heater goes open circuit, the other will get a little extra voltage (assuming non-regulated supply).

If you let the pre amp cool off, does it again work normally for a while?

You could check for correct heater voltage at each tube socket with a DVM. The trick will be to check it when the symptoms appear (ie before things cool off). Pull out the tubes and fire the pre up and check the pins in the tube sockets for proper heater voltage. Keep in mind that pins 1 and 6 will have high voltage on them since they are the anodes (probably 200-300v)

Both tubes heaters can be wired as 6V or 12V (series or parallel) heaters so you will need to check pins 4, 5 and 9 for voltage to determine how they are wired if you don't have a schematic. The heater voltage is most likely DC, although it could be AC.

The tube data for the 5751 is here:

http://tdsl.duncanamps.com/show.php?des=5751

and the data for the 12aT7 is here: (same heater wiring)

http://tdsl.duncanamps.com/show.php?des=12AT7
  Reply With Quote
Old 5th March 2009, 05:52 PM   #3
diyAudio Member
 
grhughes's Avatar
 
Join Date: Mar 2005
Location: Cubicle Sweet Cubicle, Springfield, Missouri, USA
Default Sounds like one or half of one of the tube filaments are in series.....

and is acting as a current limiter. First get a schematic and check the voltages. You might re-heat=re-solder pins 4,5,and9 on each socket.
__________________
" "The fool doth think he is wise, but the wise man knows himself to be nothing but a fool." Will Shakespeare
  Reply With Quote
Old 7th March 2009, 01:55 PM   #4
diyAudio Member
 
Join Date: Aug 2008
I don't know how this happened? Definitely not A/c to the pins 4,5 or 9. O volts register.
But in the range of 270 volts on all three phono tubes measured between pins 4 & 5, and 5 and 9 ( o volts between pins 4 & 9 ).After I had "lost"my phono section, a couple of weeks ago I took the unit apart and found the brown wires coming out of the transformer were dried and cracked the last 1/2 inch or so, and the wire (although still soldered well) was green and "frayed", so I cut it off, and resoldered it. thats all I did!
Guess I'll have to take the dang thing apart again.
No real stress on it turning it on with half or all of the tubes out of it is there?
Thanks again for your help
Paul
  Reply With Quote
Old 7th March 2009, 02:08 PM   #5
diyAudio Member
 
Join Date: Aug 2008
I just realized, on the link you gave me to look at the pin wirings, is that a view from the top? I assumed it was, if not , then I measured the voltage on the wrong pins.
Thanks again, Paul
  Reply With Quote
Old 7th March 2009, 02:52 PM   #6
diyAudio Member
 
boywonder's Avatar
 
Join Date: Jan 2008
Location: So.Cal.
On the TDSL data sheets (the links above) The pin callouts are as viewed from the bottom.
  Reply With Quote
Old 11th March 2009, 02:02 PM   #7
diyAudio Member
 
Join Date: Aug 2008
12.7 volts dc between pins 4 & 5
0 volts " " 4 & 9
0 " " " 5 & 9

Also I measure about .1 volts a/c on all tubes between

pins 4 & 9 and 5 & 9

Is this good?
Thanks again

Paul
  Reply With Quote
Old 12th March 2009, 04:31 AM   #8
diyAudio Member
 
boywonder's Avatar
 
Join Date: Jan 2008
Location: So.Cal.
Sounds good to me....maybe one of the experts will chime in here. You've determined that your preamp uses 12.6V DC heaters (not surprising) and you possibly have a little AC ripple on the DC voltage (may be difficult to quantify with a multi-meter).

Were these measurements taken shortly after the problem occurs or when the pre is "cold"?
  Reply With Quote
Old 12th March 2009, 10:46 AM   #9
diyAudio Member
 
grhughes's Avatar
 
Join Date: Mar 2005
Location: Cubicle Sweet Cubicle, Springfield, Missouri, USA
Default Cold solder joints and rotten, crinkled insulation???

I'm not familiar with that design so this is conjecture. In an old unit it is sometimes necessary to cover that rotten crinkled insulated wire with heat shrink tubing or nylon tube braided swording, or replace the rotten wire with new wire. It may be necessary to remove the end bells of the power transformer and investigate where the wires come out of the transformer if the insulation is indeed rotten. 12.6 volts means that the filaments of two sides of a 12ax7 are in series. I prefer parallel at 6.3v but that's just me. This avoids one side of the tube acting as a current limiter and glowing uncontrollably when first turned on. If you would post the schematic then we might be able to help you more. Ray
__________________
" "The fool doth think he is wise, but the wise man knows himself to be nothing but a fool." Will Shakespeare
  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
Tube Noob! need help with tubes lots of tubes therapy_fan Tubes / Valves 15 29th January 2009 10:01 PM
WTT: Various tubes for 6CA4/EZ81 rectifier tubes GordonW Swap Meet 4 27th August 2008 01:37 AM
Silvertone 1482 Blowing Rectifier Tubes Toyman_PA Tubes / Valves 1 4th August 2007 05:06 PM
Velleman K4040 is Always Blowing Output Tubes GeorgeK Tubes / Valves 24 29th August 2006 05:27 PM
blowing up my amp lilnigg99 Multi-Way 1 13th August 2003 11:38 PM


New To Site? Need Help?

All times are GMT. The time now is 03:08 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