Help with matching speaker impedance to old tube amp - 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 9th April 2010, 02:26 PM   #1
idebb is offline idebb  Sweden
diyAudio Member
 
Join Date: Apr 2010
Default Help with matching speaker impedance to old tube amp

Hi!


I have an old tube amp that Id like to connect to an 8 ohm guitar speaker. The amp has four speaker output jacks. Two of them are labeled 8 ohms and the other two are 4 and 16 ohms.

Its a Dynacord MV17 from the sixties, and doesnt have a user manual, obviously.

In the past I have connected the 8ohm speaker to one of the 8ohm outputs, leaving the second 8ohm output alone. But Im beginning to worry that this will cause an impedance mismatch if I dont use two 8ohm speakers connected at the same time to each of the outputs.

When opening the amp up it seems that the two outputs positive terminals are connected and so are the grounds. This means that they are connected in parallel, right? If so does this mean that they are in fact are 16ohms together?

If anyone could shed some light on this it would be much appreciated!

Thanks alot!

PS Ive attached the schematic if it helps
Attached Files
File Type: pdf MV17_cir.PDF (53.5 KB, 51 views)
  Reply With Quote
Old 9th April 2010, 03:04 PM   #2
rknize is offline rknize  United States
diyAudio Member
 
rknize's Avatar
 
Join Date: Feb 2009
Location: Chicagoland
Send a message via AIM to rknize Send a message via Yahoo to rknize
Boy...I see your confusion. Ignoring the wiring and just comparing the test voltage levels on the schematic at each of the OPT taps, what they label as an 8 ohm tap does indeed appear to be an 8 ohm tap. Why they have two of them? Good question. Maybe so you can hook up two 16 ohm speakers in parallel? Maybe they got a good deal on quad terminal boards? Who knows.
  Reply With Quote
Old 9th April 2010, 05:17 PM   #3
diyAudio Member
 
Join Date: Mar 2010
It appears that it's just two wires going to the same place. Eight Ohms, either one, but maybe there is some flexibility desired.
  Reply With Quote
Old 10th April 2010, 10:59 AM   #4
idebb is offline idebb  Sweden
diyAudio Member
 
Join Date: Apr 2010
Good thoughts! It seems a bit clearer to me now! Thanks!

rknize...Im curious how you see the impedances by comparing the test voltage levels...(you mean the 16000mV 11000mV and 8000mV readings right?) How did you translate that into Ohms?
  Reply With Quote
Old 10th April 2010, 12:15 PM   #5
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Quote:
Originally Posted by idebb View Post
Good thoughts! It seems a bit clearer to me now! Thanks!

rknize...Im curious how you see the impedances by comparing the test voltage levels...(you mean the 16000mV 11000mV and 8000mV readings right?) How did you translate that into Ohms?

THE Law, specifically Ohm's, "connects the dots". V = IR
__________________
Eli D.
  Reply With Quote
Old 10th April 2010, 04:51 PM   #6
idebb is offline idebb  Sweden
diyAudio Member
 
Join Date: Apr 2010
Ok but there are two unknown factors, impedance and current. How should I get impedance knowing only voltage.

Im quite new to electronics so sorry if Ive missed something obvious...
  Reply With Quote
Old 10th April 2010, 06:27 PM   #7
Hi_Q is offline Hi_Q  England
diyAudio Member
 
Hi_Q's Avatar
 
Join Date: Oct 2007
I think the circuit is a bad copy and the outputs are 4, 6, 8 and 16 Ohms. They have connected the 6 and 8 ohms to the same tapping as this can drive both impedances.
So you are safe just to connect to the 8 Ohm tap with your 8 Ohm speaker.
Les
  Reply With Quote
Old 11th April 2010, 03:09 AM   #8
diyAudio Member
 
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
Quote:
Originally Posted by Hi-Q View Post
I think the circuit is a bad copy and the outputs are 4, 6, 8 and 16 Ohms. They have connected the 6 and 8 ohms to the same tapping as this can drive both impedances.
So you are safe just to connect to the 8 Ohm tap with your 8 Ohm speaker.
Les
I'm inclined to agree.. looks like a blurry '6' to me.
  Reply With Quote
Old 11th April 2010, 04:18 AM   #9
rknize is offline rknize  United States
diyAudio Member
 
rknize's Avatar
 
Join Date: Feb 2009
Location: Chicagoland
Send a message via AIM to rknize Send a message via Yahoo to rknize
Quote:
Originally Posted by idebb View Post
Good thoughts! It seems a bit clearer to me now! Thanks!

rknize...Im curious how you see the impedances by comparing the test voltage levels...(you mean the 16000mV 11000mV and 8000mV readings right?) How did you translate that into Ohms?
Impedance ratio is the square of the turns ratio and the turns ratio of each secondary tap relative to each other is given by those voltages. So the 16 ohm tap has 4x the impedance of the 4 ohm tap but only double the voltage (turns ratio).
  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 power Amp matching with SAE Mark M pre amp and AR18 speaker or MS 25i soultribe Tubes / Valves 1 13th August 2006 11:08 AM
question about coupling & impedance matching tabooes Parts 3 13th July 2006 05:07 PM
impedance matching to a pro amp... MyNameIsJake Solid State 2 4th June 2006 05:32 PM
Need help understanding transformer impedance ratios and impedance matching percy Tubes / Valves 5 28th February 2005 08:35 PM
Impedance Matching & Crossover network query Redhatter Multi-Way 0 6th January 2004 07:59 AM


New To Site? Need Help?

All times are GMT. The time now is 04:10 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