Isolation Transformer Question - 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 November 2009, 09:38 PM   #1
diyAudio Member
 
Join Date: Oct 2009
Default Isolation Transformer Question

Hi all! I bought a silvertone record player that had two 50eh5 tubes paired with a 35w4 rectifier. Hot chassis design. So I read up on installing an isolation transformer and bought a hammond 169RS. Thought I hooked it up correctly and .... ... nothing (no power comming from the secondary windings????). I read some more about the combination of a 35w4 rectifier and an isolation transformer and read that "half wave rectification" is bad for the transformer. Might this be my problem? Do I have the leads from the secondary side of the transformer reversed (is that possible, as both were yellow and unlabled)? Sorry for the noob questions, but this is my first time messing with a hot chassis tube design.

Any help would be greatly appreciated. I'll send pics soon.

Cheers,
Tony
  Reply With Quote
Old 5th November 2009, 10:20 PM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
First, let me congratulate you on your immediate recognition that an isolation transformer is VITAL.

Second, I would guess that the no-voltage is because of miswiring. Disconnect the secondary leads, hook them to an AC voltmeter, then power up the primary and see what you have. And do this very carefully!
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 6th November 2009, 10:18 AM   #3
diyAudio Member
 
tubesteve's Avatar
 
Join Date: May 2009
Location: since 1998 in China as an electronic consulting design and testing engineer
Send a message via Skype™ to tubesteve
half way rectification loads a transformer with a DC component which may drive it into saturation, no transformer likes that........
  Reply With Quote
Old 6th November 2009, 01:33 PM   #4
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
A schematic (of hte amp) would be really helpful if you have one.
  Reply With Quote
Old 6th November 2009, 09:03 PM   #5
diyAudio Member
 
Join Date: Oct 2009
Thanks for the help guys. I did a little more reading and found a helpful page. I bought some epoxy 3 amp diodes and will make a bridge rectifier and install it in line with the 35W4 tube as shown on this link.

Fixing the half-wave rectifier problem

Hopefully this will eliminate all problems. I'll send pic and the results soon!

Cheers,
Tony
  Reply With Quote
Old 10th November 2009, 09:43 PM   #6
diyAudio Member
 
Join Date: Oct 2009
Well that helped. I now have the heaters glowing, but no sound coming out? Hmmph... I've done a little repackaging as you'll see in the photos below. I am trying to make a nice little desk amp for work. I did not change any of the wiring of the original amp, since I have no schematic. I replaced the capacitors, checked the resistors, and crammed it all into a nice little box. I'm not sure what I should be checking next. Any suggestions on the voltages I should read on the 50eh5 tubes? The original power was soldered onto pin #2 of the 35W4 rectifier, then went in series with the power for the turntable, then came back and tied onto pins 4 and 5. I read online that pin 2 on the 35w4 rectifier goes to nothing so I hooked the power from the rectified isolation transformer to pins 4 & 5. Sorry if I'm rambling, but I'm drawing a blank as to why I've got no sound....

Click the image to open in full size.
Click the image to open in full size.

Any thoughts would be greatly appreciated!

Cheers,
Tony
  Reply With Quote
Old 10th November 2009, 11:52 PM   #7
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
Did the amp work before you modified it?

I suggest making sure that you have the correct heater voltages and B+. You can do this (relatively) safely by pulling the tubes and measuring from the top of the tube sockets.

~Tom
  Reply With Quote
Old 30th November 2009, 06:23 PM   #8
diyAudio Member
 
Join Date: Oct 2009
Well I worked before I re-boxed the amp, and now after a few nights of scratching my head and checking every solder point, it's making music. Due to the cramped box and a not so pretty layout it's got a bit of a HUMMMmmmm. I tracked the problem down to a grounded input compounded with a cold joint on an output transformer.

That aside, I'm pretty pleased with the outcome. Now onto taking the original 5" drivers and making some funky cabinets for them. I'm thinking of making some half sphere's on a lathe and play'n with hole sizes on the back until I get the sound just right.

More to come.

Cheers,
Tony
  Reply With Quote
Old 30th November 2009, 07:28 PM   #9
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Maybe my eyes are deceiving me, but it looks as if the negative terminal of the bridge rectifier is connected to the bottom of the volume control.
IF this is the star earthing point then it's ok. If not then your earthing scheme is probably causing the hum.
  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
Isolation Transformer Question Captn Dave Tubes / Valves 6 28th April 2009 03:30 PM
Question about how to wire an Isolation Transformer gpapag Everything Else 91 27th April 2009 04:48 PM
Isolation Transformer question Jack Torrance Power Supplies 7 2nd January 2007 08:37 AM


New To Site? Need Help?

All times are GMT. The time now is 09:21 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