Cap Problem with philco 49-1401 - 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 2nd June 2011, 09:36 PM   #1
gto127 is offline gto127  United States
diyAudio Member
 
Join Date: May 2007
Default Cap Problem with philco 49-1401

I just re tubed & recapped a philco 49-1401 but one of the caps keeps blowing after about 15 minutes. It is cap C101. I did measure reverse voltage across it but it is connected exactly as schematic describes. I did use a normal wet electrolytic instead of a dry electrolitic that was in there originally. Would this make any difference? I will be glad to email schematic to anyone that would like to look at circuit. Thanks in advance.
  Reply With Quote
Old 2nd June 2011, 09:50 PM   #2
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Are you sure you orientated the capacitor the same way as the old one ?

I would need to see a schematic to say which way around it should go.

Could be it was a unpolarized electroyltic in there.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 2nd June 2011, 10:13 PM   #3
gto127 is offline gto127  United States
diyAudio Member
 
Join Date: May 2007
Yes the old one was polarized I put in like the original. [IMG]C:\Documents and Settings\user.USER-44C8A002F3\My Documents\My Pictures[/IMG]
  Reply With Quote
Old 3rd June 2011, 10:27 PM   #4
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Quote:
Originally Posted by gto127 View Post
Yes the old one was polarized I put in like the original. [IMG]C:\Documents and Settings\user.USER-44C8A002F3\My Documents\My Pictures[/IMG]
That didn't work, need to use "advanced edit mode/manage attachments" and then be sure to actually upload the photograph.

Note that if you measured reverse voltage across that cap it is more than possible that the schematic symbol as drawn in your schematic is backwards. Or did you install (new) solid state rectifier diodes and put them in backwards?
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan

Last edited by kevinkr; 3rd June 2011 at 10:31 PM.
  Reply With Quote
Old 3rd June 2011, 11:06 PM   #5
gto127 is offline gto127  United States
diyAudio Member
 
Join Date: May 2007
Thanks for tip on attachments. The rectifier is a tube 50Y6GT . Since my last post I got a dry paper electrolitic & put in circuit & radio has played for an hour so far without cap blowing. I am concearned though because the reverse voltage has risen from -20 to -65 volts. I sure hope these type caps aren't flamable.
  Reply With Quote
Old 3rd June 2011, 11:10 PM   #6
diyAudio Member
 
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
Eek! Sounds like that cap is in backwards to me. As Kevin said,the schematic may have been incorrect with respect to the polarity of that cap.
  Reply With Quote
Old 3rd June 2011, 11:17 PM   #7
gto127 is offline gto127  United States
diyAudio Member
 
Join Date: May 2007
Just uploaded schematic.
Attached Images
File Type: jpg philco 49-1401 power circuit.JPG (161.2 KB, 48 views)
  Reply With Quote
Old 3rd June 2011, 11:20 PM   #8
diyAudio Member
 
Mr. Zenith's Avatar
 
Join Date: Aug 2009
Location: Central NC
Make sure the plates of your rectifier tube aren't glowing. I once put the electrolytics in backwards in an old 1930's era Stewart-Warner radio set. The "tubes all lit up" (as they say on eBay) for about 15 minutes, but the radio still didn't play. It turned out I almost succeeded in melting the 5Y3! I have no idea why the electrolytics didn't blow...
  Reply With Quote
Old 3rd June 2011, 11:20 PM   #9
gto127 is offline gto127  United States
diyAudio Member
 
Join Date: May 2007
I did reverse the cap but I get no voltage on C102A & no sound.
  Reply With Quote
Old 3rd June 2011, 11:28 PM   #10
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
This appears to be a half wave voltage doubler and the cap appears to be oriented correctly in the schematic.

The voltage across that capacitor has a substantial AC component across it and a lot of cheap digital meters don't work properly under such conditions. The current through this cap is also significant in that not only does it have to cope with the ripple current, but also the entire load current of the radio it is powering on a continuous basis - a very demanding situation. A film capacitor (>= 400V rating) with a high continuous current rating might be a safer long term solution here.

Measure the voltage at the capacitor connected to the cathode of the other half of the rectifier that feeds the rest of the PSU. If this voltage is correct then the supply is working correctly.

Something else to note is that this radio/phonograph is line operated and is potentially extremely dangerous to work on. I strongly advised the use of an isolation transformer when troubleshooting this radio..
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan

Last edited by kevinkr; 3rd June 2011 at 11:37 PM.
  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
1946 philco amp, tuner, record player tryonziess Tubes / Valves 2 26th May 2010 01:29 AM
Interesting old Philco electrostatic tweeter peace brainerd Multi-Way 0 8th March 2010 10:56 PM
1946 Philco Tube Receiver tryonziess Tubes / Valves 18 1st February 2010 11:54 AM
Roll Chart for 6DJ8/6922/7308 on Philco 9100 help thuan98 Tubes / Valves 0 25th March 2009 06:39 PM
Philco power tranny diagram/5u4 supply Dr.Frankenstein Tubes / Valves 0 7th September 2004 11:08 PM


New To Site? Need Help?

All times are GMT. The time now is 09:50 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