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Discussion Starter #1
Hey. So I understand Ohm matching and all that. I'm having a problem getting my head around my amplifier head and cab connections. I might be over thinking it or something, but I want to know if this particular connection is "OK". First I'll post the pics, which I really cannot find anywhere in my searches for the particular amp and cab (BS HT-20H head and BS HTV212 cab):




So the way I'm reading it is that my normally used 8 ohm (or 2 x 16 ohm) from amp can either be connected to the 8 Ohm Mono cab in or by connecting the 2nd out from amp to the other (16 ohm Right) to effectively cut the normally 160W in half and using each 16 ohm speaker (V30's) in stereo "within the cabinet". I realize it isn't true stereo as there is very insignificant space between the 2 16 ohm speakers, but for the sound I want with the cut in Wattage it works nicely. I only tested it very briefly because I want to ensure I'm not gonna blow the Tranny. The cab instructions also seem to indicate this is possible, but the wording is not quite specific.

This is all the instruction manual includes:

"HTV-212 Extension Cabinet Power Rating (RMS): 160 Watts Impedance: Stereo – 2 x 16 Ohms. Mono - 8 Ohms. Selectable by input jack Speakers: 2 x 12˝ Celestion Weight (kg): 21.9 Dimensions (mm): 715 x 556 x 278"


Any suggestions?
 

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Run from your 8ohm out on the head to the 8ohm mono input on the cab. You only need one speaker cable.
 

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Discussion Starter #3 (Edited)
Run from your 8ohm out on the head to the 8ohm mono input on the cab. You only need one speaker cable.
That's what I usually do. It's the correct way to use both speakers at 8 ohms. I want to use each 16ohm separately as stereo in this case. I know it's not a typical application, but I'm not your typical guitar geek. Or maybe I am. Yeah. I am. I want to cut the overall 160W to 80RMS. I don't care if it's practical or not. But if it's possible.......;)
 

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You need two amps to run in stereo. If you are using one amp, just run mono.
 

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Discussion Starter #5
@Budda thanks. I see see where amy thinking on the wording on the amp went wrong. I suppose I could try mismatching my 8 Ohm Fender BJ to the other 16 Ohm 212 input. I go into these weird testing different things phases just to see if it will work. I have an ABY already, which I've been using to good effect. But I'm just trying to use each 16 ohm speaker in the cab individually. Thanks for your input man.
 

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Just to clarify, the rating on the cab for stereo is 80W per channel (side). So if you run both sides it's still a total of 160W for the cab.
And the cab wattage is only the max. power it can handle, it does not determine the power from the head.
 

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Discussion Starter #7
Yeah...I think I have the idea now. I just wanted to try using each individual sides with the head to see if I could get a different sound or feel from the amp. I like experimenting once in a while.
 

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I’m new to this so sorry if this is dumb but could you run a 16 ohm head into one of the 16 ohm inputs of the cab shown in the pics? I have the same rig and want to know if I can put a 16 ohm head into it.

Thanks,

Dan
 

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I’m new to this so sorry if this is dumb but could you run a 16 ohm head into one of the 16 ohm inputs of the cab shown in the pics? I have the same rig and want to know if I can put a 16 ohm head into it.

Thanks,

Dan
Yes, but you will only be using a single speaker vs both. You'd have to use the Right input jack on the cab vs Left (because it will assume mono @8 ohms if you do that).
 

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Discussion Starter #10
Yes, but you will only be using a single speaker vs both. You'd have to use the Right input jack on the cab vs Left (because it will assume mono @8 ohms if you do that).
On that note, I'll take it that I can use the 16 Ohm out on the BS head to the 16 Ohm right. It's been discussed before, but I also fairly briefly connected my Fender BJ (8 Ohm) to the Left 16Ohm for a "safe" mismatch, using the Radial ABY. I know you're really experienced with the tech side, so have you seen or heard of any big issues with the mismatch up (vs down). There's a lot of discussion and different ideas on too many forums to consider any mismatch safe with a knwn commodity like yourself setting it straight....or many other on here. Yes, I just called you a commodity @Granny Gremlin :D
 

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The main thing you will notice is a halving of the wattage (which is just 3db less volume; litterally barely noticable). I dunno what the safe limits are for tube amps (I have heard conflicting things and have not had an OT I was willing to risk to find out the truth). With solid state amps, go over the amp rating as much as you want (you just lose half the power for each step above the amp out - so down to quarter power if using a 4Ohm out to feed a 16 ohm speaker); just never go lower then the output rating. I take it going a step down with a tube amp is not a problem, and then even crazier things, but I stand by none of it as I have not verified this myself.
 

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Discussion Starter #12 (Edited)
The main thing you will notice is a halving of the wattage (which is just 3db less volume; litterally barely noticable). I dunno what the safe limits are for tube amps (I have heard conflicting things and have not had an OT I was willing to risk to find out the truth). With solid state amps, go over the amp rating as much as you want (you just lose half the power for each step above the amp out - so down to quarter power if using a 4Ohm out to feed a 16 ohm speaker); just never go lower then the output rating. I take it going a step down with a tube amp is not a problem, and then even crazier things, but I stand by none of it as I have not verified this myself.
Sorry for the late response. Yeah, the word out there (for Tube amps) is that you can go up or down 1. With a caveat. Most people don't recommend going form 8 Ohms to 4 Ohms, as it apparently is harder on the Output Transformer, which can also lead to other "burnt components" as well. If you go from 8 Ohms out to a 16 Ohm speaker connector, I believe it's harder on the tubes. All depends on the situation, but I typically try to keep it the same if possible.
 

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Sorry for the late response. Yeah, the word out there (for Tube amps) is that you can go up or down 1. With a caveat. Most people don't recomend going form 8 Ohms to 4 Ohms, as it apparently is harder on the Output Transformer, which can also lead to other "burnt components" as well. If you go from 8 Ohms out to a 16 Ohm speaker connector, I believe it's harder on the tubes. All depends on the situation, but I typically try to keep it the same if possible.
Ive run a 2 ohm amp into a 8 ohm speaker many times. It basically turns the output transformer into an attenuator
 

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Ive run a 2 ohm amp into a 8 ohm speaker many times. It basically turns the output transformer into an attenuator
It is my understanding that volume level(s) and duration are the important factors (re: the risk of damage to the OT and tubes) when running an impedance mismatch of that extreme.

How loud and for how long did you run the above mismatch?
 

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Discussion Starter #15
Would it also not depends on the OT's overall specs? I wish I'd understood the OP AMP section of the Electronics Engineering program I took back in '95. Unfortunately I'm one of those "learners" that depends on a certain type of teacher style to get across what's actually going on. It kinda sucks actually because I'm rather abstract at times.
 

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Sorry for the late response. Yeah, the word out there (for Tube amps) is that you can go up or down 1. With a caveat. Most people don't recomend going form 8 Ohms to 4 Ohms, as it apparently is harder on the Output Transformer, which can also lead to other "burnt components" as well. If you go from 8 Ohms out to a 16 Ohm speaker connector, I believe it's harder on the tubes. All depends on the situation, but I typically try to keep it the same if possible.
Other way around. Too high of a load impedance (8 ohm output to 16 ohm speaker) will cause voltage flyback (reflections back to the amp, if you will), possibly causing breakdown in the insulation of an output transformer. Too low of a load impedance will work the tubes a bit harder, trying to produce more current to supply the load.

I think this topic is drastically overrated and over-discussed. Amps are built with a certain amount of component 'safety factor', or the manufacturer would be dealing with way too many returns. So the components of any reputable builder are over-rated for the job. They will tolerate some abuse. That said, if you run an amp full out for hours upon hours with a significant mismatch, sure, you risk of doing damage.

But for the 99.999% of the rest of us that don't run the amp full out for extended periods of time, significant impedance mismatches wouldn't be a problem. A good safety rule of thumb though, is as you said: "2:1 either way". If the amp can't take that, it wasn't spec'd very well.
 

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Would it also not depends on the OT's overall specs?
Yes, I'm quite sure you are correct about this. The 'hefty' OT's being able to withstand more. How 'hefty' it would have to be and how much punishment it could withstand is the next question.

Electronics is a hobby for me and I'm never totally confident in trusting some of what I know.

@High/Deaf and I were typing at the same time and I didn't see his post. He explained everything in detail.
 

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Discussion Starter #18
Thanks for straightening that out for me @High/Deaf , I was thinking after I posted I might have got it ass backwards.

So "safe" is 16 to 8 and "be careful" is 8 to 16 on the internet, but realistically amps are built for normal gigging and playing use....it would probably be tough to exceed the limits (unless you're Angus). Angus just blows everything up!
 

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It is my understanding that volume level(s) and duration are the important factors (re: the risk of damage to the OT and tubes) when running an impedance mismatch of that extreme.

How loud and for how long did you run the above mismatch?
Louder and longer than I care to admit, although not at the same time.

Cranked to 10 for a half hour or so once. And on 4 for 3 hours or so on stage. The OT got rather warm from that. I've since bought a Weber Z-matcher, so I don't worry about impedence anymore.
 

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I took a lunch box head to a rental jam space one night for band practice. Plugged in to the provided 412 using my 16 ohm tap, because that's what was dymo-labeled on the cab. After about 35 minutes of playing near full out (fairly big room with mic'd drums), I noticed I couldn't touch the head, it was too hot. Turns out the cab was actually 4 ohms, so I was running a 4:1 mismatch. I let the amp cool a bit (and worried that I cooked the PT or OT to death), switched the 8 ohm tap and finished the night with no problems. Ten years later that amp still works great.

I wouldn't recommend doing that, but it does show that these 'old tech' things will take a lot of stupidity, because hardly anyone understood any of this when these things were state-of-the-art. I imagine there were lots of mismatch / misuse scenarios even worse than this that a good tube amp just tolerated. SS is much less tolerant of these mistakes - which makes sense considering how much more dense, say, a power transistor is than a power tube.
 
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