Dynaco Stereo 70 Output Transformer - 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
Thread Tools Search this Thread
Old 16th April 2007, 04:26 PM   #1
rudy129 is offline rudy129  United States
diyAudio Member
Join Date: Aug 2004
Location: New York
Default Dynaco Stereo 70 Output Transformer

One of the channels on my st70 only plays with the 16 ohm taps being used. The 4 & 8 ohm taps play extremely low. All the voltages are what they should be at the output tubes. Has anyone ever heard of a problem like this? Maybe 4 & 8 shorted?
  Reply With Quote
Old 17th April 2007, 04:34 PM   #2
BudP is offline BudP  United States
diyAudio Member
BudP's Avatar
Join Date: Feb 2007
Location: upper left crust, united snakes

What are the voltages at the 4.8 & 16 ohm taps on the "bad" transformer Vs what they are on the good one? To do this properly you should have a dummy resistor for each tap but that is not a likely thing to have laying around.

So, keep the 16 ohm tap on both transformers loaded with a 16 ohm speaker and measure relative voltages of all three impedance taps. It is pretty unusual, when a winding goes bad, not to have a power loss on all three, as they are usually series connected internally, each tap using the preceding winding for part of it's turns.

It is possible that Dyanco wound the 16 ohm winding as a completely separate winding, they did every other kind of strange thing to these outputs. If your measurements show a voltage drop on 4 & 8 ohm taps you will need to replace the output. Your choices there can be interesting. It is unlikely that even the Dynaclone transformers will be a perfectly matched audible replacement So you may need to budget for two new transformers. Tell us what you find.

  Reply With Quote
Old 19th April 2007, 12:25 AM   #3
diyAudio Member
Join Date: Jul 2003
Location: Ann Arbor, MI
Hey Bud,
The St.70's output, the A470 is a single secondary design, Common-4-8-16
the Tnuctipun will return
  Reply With Quote
Old 22nd April 2007, 10:39 PM   #4
rudy129 is offline rudy129  United States
diyAudio Member
Join Date: Aug 2004
Location: New York
This is weird. I took an output transformer from another st70 and replaced the one with the low 4 & 8 ohm taps and this one does the same thing. Obviously the transformers are good so what could be causing only the 4 & 8 ohm taps not to play on one channel?
  Reply With Quote
Old 22nd April 2007, 11:07 PM   #5
SY is offline SY  United States
diyAudio Moderator
SY's Avatar
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 2
Well, then there's either a miswiring or unintentional short at the output terminal strip. You can confirm by connecting the speaker and the feedback loop directly to the transformer wires pulled away from the terminal strip.
A philosopher is a blind man in a dark room looking for a black cat that isn't there. A theologian is the man who finds it. - Mencken
  Reply With Quote
Old 22nd April 2007, 11:42 PM   #6
rudy129 is offline rudy129  United States
diyAudio Member
Join Date: Aug 2004
Location: New York
Thanks, found it!! Positive was touching chassis.
  Reply With Quote


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
Dynaco Stereo 400 Amp andrew01 Solid State 5 19th June 2011 03:33 PM
Dynaco Stereo 70 amplifier Burnedfingers Tubes / Valves 231 30th December 2009 02:45 AM
Dynaco stereo 416 for sale ShoNuff Swap Meet 0 21st October 2008 12:41 PM
Dynaco Stereo 400 mods XaQ Solid State 2 21st November 2005 07:13 AM
Need Help: Dynaco Stereo 120 amp jainbaby Solid State 4 18th December 2002 02:03 PM

New To Site? Need Help?

All times are GMT. The time now is 07:13 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2