Can You Damage a 1 Watt Amp Mismatching Speaker Impedance?

Cadorman

Cadorman

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Here's the situation. I have 2 16 ohm cabs that I want to run off my DSL1HR. The head only has a single 16 ohm output jack. I can daisy chain the pine cab through the OR112. Will running this puny thing with a 12AU7 power tube damage the output transformer at 8 ohms instead of 16 ohms? I'm probably stupid enough to try it, but figured I'd see if anyone that stayed at a Holiday Inn Express last night knew.
 
syscokid said:
View attachment 72286

Z-Matcher 100w Impedance Matcher – Weber Speakers

www.tedweber.com www.tedweber.com

Your welcome... :cheers:
Click to expand...
Yep thats one of those genie boxes that unlocks the power of beating a bad mismatch! Very cool they came up with these. I thought about getting one of these or the Radial Cab Link to run the Marshall Mode Four into its 2 400w cabinets safely ( currently it can only safely run one MF400 cab at its full 350w power at 8ohms, a single 280w 16ohm cab at 245w or a full stack at 350w into 2 280w cabs at 16ohms each)
 
And to answer the question, yeah like @gball said: never go under the rating. You can go higher to degree but if its asking for 16ohms, dont run a 4ohm or 8ohm cab into it. Itll burn up parts, most likely screen resistors and transformers, sometimes way worse.

You can however, run like an 8ohm cab into a 4 ohm input or 16ohm cab into an 8ohm input more often than not on valve amps. Speakers wont be pushing like they should and volume will choke down but it usually wont hurt the amplifier. Too far however, can cause issues too, like a 16ohm cab into a 4ohm input
 
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The underbelly of the beast.
So the red, blue and brown wires in a row on the back right edge of the board go directly to the output transformer. Coming out of the other side of the tranny is a white, black and orange wire. The black and orange wires go to the back board by the single 16 ohm speaker jack. The white wire is taped off.
 
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Here's where the black and orange wire connect. There doesn't appear to be a trace connecting R110 to R107 or R108 on the top side. So, you have the output jack, 3 resistors and the 1 watt/.1 watt switch. This is a two sided board.
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Here's the back. I don't see traces for the orange wire on either side. In this pic the orange wire is the two solder lugs top left going nowhere. The black wire ties into the R108 resistor with traces going to R110 and the switch. All 3 of the bottom lugs are tied together and go to the switch. I guess I don't care about all that. I just want to figure out what that white wire is for.
 
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Output transformer sticker. I'm going to see if I can find anything about this thing online.
 
Cadorman said:
View attachment 72289
The underbelly of the beast.
So the red, blue and brown wires in a row on the back right edge of the board go directly to the output transformer. Coming out of the other side of the tranny is a white, black and orange wire. The black and orange wires go to the back board by the single 16 ohm speaker jack. The white wire is taped off.
Click to expand...
That white is actually 8ohm capable according to what i pulled up here online. Ill PM it you
 
Cadorman said:
The white wire is taped off.
Click to expand...
I would guess that the white wire COULD be the 8 Ohm tap. But before ANY experimenting figure out!!! (BTW: an OT with just a 16 Ohm secondary would be pretty unusual). At first i would try to read the labels on the OT. Maybe try to measur the DCR of the OT secondary (i know, difficult becaus of tiny values. What You should observed if it is really an 8 Ohms tap: it should be between ground and the 16 ohms tap, and DCR should be half.
 
All the important stuff has already been covered, like only mismatch high (like 8 ohm output into 16 ohm cabinet etc), but it's also a good idea not to mismatch more than 100% (4 into 8 or 8 into 16).
Doing the opposite & mismatching lower may hurt/overstress your 12AU7.

I have read of people hooking up & using the OT's white secondary wire as an 8 ohm tap (maybe Marshall forum). IIRC, some thought it sounded great, others not so much.
As @bea has said, your ohm meter will help decipher what it is. Cheers
 
You could replace your output transformer to 4/8/16

www.mojotone.com

Clone of the Wright 1580 10K to 4-8-16 - 12BH7/12AU7 PP Output Transformer

Mojo Clone of the Wright 1580 10K to 4-8-16 - 12BH7/12AU7 PP Output TransformerThe Mojo 1580 is actually from a tear down of a Wright 1580 output transformer that was brought to us by Carl Williams of Anchovy amps. Carl has been working with 12bh7 output sections and other low wattage output...
www.mojotone.com www.mojotone.com
 
So, if I want to add a SPDT toggle switch to keep it a single jack and choose between 8 and 16 ohms what kind of rating would I need on the switch?
 
But with those switches there is a danger to accidentally switch the output (during transporttation, e.g.) IMO a rotary switch is preferable (and has been preferred with the Hiwatts). I would prefer something with 2 positions and (hence) 6 switches and, of course, use only one of them.
 
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