Heathkit transformer replacement... - 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 12th August 2011, 02:48 AM   #1
diyAudio Member
 
Join Date: Apr 2010
Location: New England
Default Heathkit transformer replacement...

Hello all, I have an old pair of heath amps, usually I'd be on here blathering on about issues with the Power amp, an AA-121 (EL-34 PP stereo)- but now I am going to blather on about an issue with the matched preamp.

The Preamp is an AA-141A unit and what has happened is that I lost plate voltage the other night running the tuner quietly.

After poking around with the meter, I have determined that the B+ tap on the power transformer has gone open. Must've popped the winding. It still powers up and I have filament heat and a pilot light on the front, so I know that at least the 6 volt taps are still working, but that doesn't amount to a **** hole in a snow bank without voltage on the plates.

Now, the heathkit part number on the top of the xfmr is 54-71, and after googling around I have come up with zilch, so I may have to order an aftermarket unit.

The question is, what the hell am I looking for. I've never had to buy a transformer before.

With a designed input voltage of 117VAC I have 2 6.3V taps for the filaments and a 238V tap after a couple of Selenium diodes for the B+ supply. I never had a meter on the winding while it was working, so I dont know what the actual voltage on the winding was. These numbers are "what I should have" according to the schematics.

What does having a transformer re-wound usually cost?
  Reply With Quote
Old 12th August 2011, 02:54 AM   #2
diyAudio Member
 
thaumaturge's Avatar
 
Join Date: Aug 2011
Location: Utah
Best bet is find another piece of old tube equipment, like a really old tek scope. They had oodles of transformer taps to choose from. Physical size would of course be a consideration. Doc
  Reply With Quote
Old 12th August 2011, 03:01 AM   #3
diyAudio Member
 
Join Date: Apr 2010
Location: New England
I am a bit of a nostalgia freak -I would never dismantle a piece of equipment like that for some iron unless it was total and utter junk.

I've got a couple of old Tek 564B's and I love them both.

But yeah, physical size is kind of a big deal and the iron on my old tek is huge.
  Reply With Quote
Old 12th August 2011, 04:23 AM   #4
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Finding a suitable replacement power transformer should not be very difficult. But I can't find a schematic on line. Only pictures of the inside, so I know about what physical size tranny you need. Can you post the diagram here? Even if you can scan just the power supply area and post that. There may well be something from Edcor, Hammond or even eBay that will work.

Also, I have had luck in the past repairing transformers much like yours. You have to remove the shells and perhaps even the outer layer of insulation to find a break. Sometimes the break occurs near the top where the lead wires are attached. If it's really open, you have nothing to loose by trying.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 12th August 2011, 04:52 AM   #5
diyAudio Member
 
Join Date: Dec 2008
Location: Victoria, BC
If you post a picture of your transformer, it would help.
Is it a 'laydown' - type?
  Reply With Quote
Old 12th August 2011, 05:16 AM   #6
diyAudio Member
 
Join Date: Dec 2008
Location: Victoria, BC
Quiet evening here, so I hit Google for a bit.

Looks like the 54-71 was used in several Heathkits, including the AA-20 and SP-2. Looking at those schematics (available online) the PT has a 117/120 v secondary (ie 1:1 winding ratio with the primary), feeding a voltage doubler to give a B+ in the 290volt range.
Finding a 120volt 'isolation' transformer that can handle a few (50?) mA should be pretty easy, but.... My guess is that there's not a lot of extra room on the chassis? So you'll need something with the 6.3 vAC for the filaments as well if there is no room to add a 2nd transformer. You can figure out how many amps of heater current you need from the tube specs.
That should get you started......

PS- Any ideas on what caused the HV secondary to fail?

Last edited by VictoriaGuy; 12th August 2011 at 05:18 AM.
  Reply With Quote
Old 12th August 2011, 01:47 PM   #7
diyAudio Member
 
Tom Bavis's Avatar
 
Join Date: Jun 2002
Location: Macedon NY
If there's room for another transformer, a Triad 120:120V transformer is about $15 new. I have a couple of transformers with 120V and 6.3V windings - and 230V could be used as well, with a full-wave bridge, or 230-0-230 with a center-tap full-wave. The seleniums should go anyway. What are mounting dimensions? MAXIMUM transformer size?
  Reply With Quote
Old 12th August 2011, 04:42 PM   #8
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Rewinding a transformer like this isn't difficult. I saved this article from Radio Electronics -- perhaps a bit difficult to read:

Rewinding Transformers

Good transformers for preamplifiers can be had from old Eico/Heath/Knight test equipment -- get an idea of the output voltage you need. I've repurposed a bunch of Eico audio signal generators for this end.

Lastly, Antek has some low VA torroids for tube stuff on their website.
  Reply With Quote
Old 12th August 2011, 07:06 PM   #9
diyAudio Member
 
Join Date: Aug 2010
Location: Near Eindhoven, the sanctum of the pentode. and among that other things.
Send a message via Skype™ to v4lve lover
Practical Transformer Winding

have a good one
  Reply With Quote
Old 12th August 2011, 07:47 PM   #10
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Edcor could probably make one if you provide the specifications, there might even be a replacement market for this part if as widely used as it seems.

Here: EDCOR Electronics Corporation

You would have to provide them with a very good idea of what you need, (core dimensions, etc.) and note that their idea of customer service may not be yours.. I recently had them make me some custom power transformers which turned out very nicely and were very reasonably priced - yet to finish the project they will be used in.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  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
Transformer from Heathkit A-7 amp bryanz Tubes / Valves 8 28th July 2008 03:50 AM
WTB Heathkit power transformer Original Burnedfingers Swap Meet 6 23rd November 2007 12:58 PM
Wanted: Heathkit power transformer Boris_The_Blade Swap Meet 0 9th June 2007 07:13 AM
Need Help on HEATHKIT W-5M Power Transformer speedemon Tubes / Valves 2 20th March 2007 01:51 AM
WANTED: HEATHKIT W5M power transformer speedemon Parts 1 19th March 2007 04:36 AM


New To Site? Need Help?

All times are GMT. The time now is 01:52 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