Connecting amp to two 1x12 16 ohm cabs

freefrog

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I'm so confused . At first he had 2 16ohm speaker cabs . Daisy chained them and plugged into 8 ohm amp plug as ya'll advised .


Amp overheated . Then he tested speakers in each cab and they were 8 ohms a piece .

So did he at first have it plugged into the 4 ohm or 8 ohm plug . If he did it as as you all advised him to do , based on 16 ohm speakers , then he was plugged into 8 ohm and overloading the amp . When unplugging one cab , problem went away .
So, what's your conclusion?

Without repeating my previous posts: I'll just state that I've 5 tube amps here (Marshall, Fender, Mesa, Vox, VHT) and that three of them (and not the cheapest) have developed overheating problems at least once in their life with me... albeit they still work fine and have all been used on stage during hours without issues.

Tube amps run hot then get cold repeatitively and are carried like luggages. So, sometimes, a faulty contact or short cut appears for chemical reasons (oxydation) or mechanical reasons (when a contact has been hurt or displaced by a shock)...

And there's the nature of tubes... Even a sane tube can go mad because of how tubes work, AFAIK.
EDIT - Was thinking to this: https://music-electronics-forum.com...itar-amps/theory-design/28478-thermal-runaway
[...to take in account, knowing that Picoman uses a "VHT special 6, BUT with 6L6 tube, instead of the stock 6V6 tube", as he said somewhere above. The MEF topic precisely evokes 6L6's as more prone to "thermal runaway" than 6V6's]

Ironically, my two tube amps without overheating issues until now are the Vox and... my VHT Special 6.

Now, if you ever open a Special 6 and inspect the components, maybe you'll see that the stock power tube socket, for example, is a bit flimsy: the pins of a tube can almost displace the prongs meant to host them. And solders in such cheap devices are sometimes "discussible", as are their other components.

I had posted above an answer edited out in the meantime for whatever reason and that I won't post again but that I can sum up: it contained a link towards an interview in which the designer of the Special 6, Terry Buddingh, was evoking the output transformer of his single ended design as oversized, suggesting that it could stand some impedance mismatching without burning or exploding.

It doesn't deny the possibility of some intermittent issue - potentially due in this case to jack plugs with cold solders adding randomly parasitic resistance, for instance, rather than to the power tube, its socket, or anything else. But who knows?

FOOTNOTE - Actually, the output transformer of a Special 6 is almost too good for this small amp: It gives a rather wide range and a crisp attack without sag. With the diodes rectifier, it contributes to make the amp more hi-fi and less musical than a Fender Champ (which is the basis of the VHT, schematic wise).

FWIW - Indifferent rambilng of a sunday morning.... :)
 
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picoman

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Ok.
We mesured the impendance of the two speaker cabinet connected.
One cabinet has Celestion Classic Lead 80, 8 ohms
Second one has Celeston G12H Aniversary , 8 ohms.
Connected they gave 4 ohms, which is where I connected them to the back side of the amp.

But as I sadi, the amp was getting realy, realy hot.
Can this maybe be an issue couse the Special 6 has only 6 watts, and the speaker have more?....or something like that.......
At this point in time, Ive rplaced the 6L6 with an 6V6 tube.
 

syco

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So, what's your conclusion?


FWIW - Indifferent rambilng of a sunday morning....

Thank you for long explanation that didn't cover anything I asked . So I will condense it down . OP asked How to connect 2 - 16 ohm speaker cabs to amp . Someone posted a diagram showing how to do it . OP then said that he did it exactly how diagram showed and amp got damn hot !!!! . Unhooked one of the cabs and amp didn't get hot anymore . Was asked if he was sure each cab had 16 ohm speakers . OP said yep . 2 days later , OP said the speakers in each cab were 8 ohms a piece and measured 4 ohms combined and that's were he connected to the amp . SO !!!!! Hence my confusion . Did he connect to 8 ohm output as diagram suggested ? If so ......... the 4 ohm load of the speakers would cause the amp to get hot . Or did he connect to 4 ohm ? OP's facts changed several times ..... so just trying to get some clarity to the actual events that transpired . Then not sure what kind of cables he was using .
 

freefrog

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Thank you for long explanation that didn't cover anything I asked . So I will condense it down . OP asked How to connect 2 - 16 ohm speaker cabs to amp . Someone posted a diagram showing how to do it . OP then said that he did it exactly how diagram showed and amp got damn hot !!!! . Unhooked one of the cabs and amp didn't get hot anymore . Was asked if he was sure each cab had 16 ohm speakers . OP said yep . 2 days later , OP said the speakers in each cab were 8 ohms a piece and measured 4 ohms combined and that's were he connected to the amp . SO !!!!! Hence my confusion . Did he connect to 8 ohm output as diagram suggested ? If so ......... the 4 ohm load of the speakers would cause the amp to get hot . Or did he connect to 4 ohm ? OP's facts changed several times ..... so just trying to get some clarity to the actual events that transpired . Then not sure what kind of cables he was using .
OK.

I never post to argue nor to prove others wrong but I'll peacefully share my perspective (one more rambling. LOL).

In post 1, Picoman has posted a pic showing the backplate on one of his VHT cabs: it clearly mentions "16 Ohm", on par with the drivers theoretically mounted in VHT cabs for Special 6 (ChromeBack VHT loudspeakers, normally rated each @ 16 Ohm: https://www.vhtamp.com/avsp212vht ).

In post 9, Picoman was still sure that each of his cabs was 16 Ohm .

The two 8 Ohm drivers that he mentioned in post 14 are Celestion (Classic Lead, G12H) and not VHT's.

He didn't say that these Celestion are in his VHT cabs... which could suggest that VHT cabs were not the same than those with Celestion.

But granted, his wording in post 9 suggested it. So, let's suppose that his VHT cabs are fitted with unexpected 8 Ohm Celestion drivers....

It still doesn't explain what Picoman wrote about these Celestion's: "Connected they gave 4 ohms, which is where I connected them to the back side of the amp.
But as I sadi, the amp was getting realy, realy hot" (from the horse's mouth, albeit I know you're not a horse, Picoman).

In post 25, he added: "Theres somethng very wrong with my amp.
I wet to play it yesterday, al of a sudden like there sis no power?!...like the amp has half of its volume.
I tried changing tubes...tried different guitar cables......but no differece...
WTF?!"

BUT after that, he explained in post 33 that according to the tech, there was no problem with the amp...

Hence my rambling about possible explanations including those of the post 41: with post 33 to put it in perspective, the post 25 effecitvely suggests to me an intermittent issue (maybe due for example to a cable or jack plug hurt by vibrations and working accidentally like a resistive load, limiting the output level for one cab.... a bit like when a cab is plugged in parallel with an attenuator, halving the perceived volume).

...


@picoman: in fact, the post 41 was largely if not mostly for you. Not that my rambling has any value in my mind... but it doesn't harm either to share my subjective experience with amps, including the same model than yours.
EDIT - Related ideas: using Deoxit to clean the tube socket(s), changing the socket of the power tube for a ceramic one, reflowing the solder on loudspeakers jack plugs (those of the amp, those of the cables and cabs used)... Non limitative list. Feel free to PM me if I can help you.
 
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syco

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He didn't say that these Celestion are in his VHT cabs...
Ok.
We mesured the impendance of the two speaker cabinet connected.
One cabinet has Celestion Classic Lead 80, 8 ohms
Second one has Celeston G12H Aniversary , 8 ohms.
Connected they gave 4 ohms, which is where I connected them to the back side of the amp.

But as I sadi, the amp was getting realy, realy hot.
Can this maybe be an issue couse the Special 6 has only 6 watts, and the speaker have more?....or something like that.......
Regardless of new or used , you should always verify you have what you say . Comes in handy when you are seeking advice . Looking for answers when everyone else wants to argue . Hope you have a pleasant day / night .
 
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freefrog

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He didn't say that these Celestion are in his VHT cabs... which could suggest that VHT cabs were not the same than those with Celestion.

But granted, his wording in post 9 suggested it. So, let's suppose that his VHT cabs are fitted with unexpected 8 Ohm Celestion drivers....
BTW, Picoman, are your VHT cabs externally rated @ 16 Ohm those hosting 8 Ohm Celestion drivers? Or are these four different cabs?
 

picoman

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So, let's suppose that his VHT cabs are fitted with unexpected 8 Ohm Celestion drivers....
CORRECT! :)

To clear thing a bit more.
I have 2 VHT cabs. Both are 1x12 and both have VHT creamback speakeras wich are rated 16ohms.
I removed the stock speakers and put Celestion speaker in each of the VHT 1x12 cabinet. Both Celestions are 8 ohms speakers.
I connected the cabs wich gave me an 4ohm load (we made an reading). And this is where I pluged the cabinet cabel in the back of my amp.
The rest of the story you know
 
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freefrog

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CORRECT! :)

To clear thing a bit more.
I have 2 VHT cabs. Both are 1x12 and both have VHT creamback speakeras wich are rated 16ohms.
I removed the stock speakers and put Celestion speaker in each of the VHT 1x12 cabinet. Both Celestions are 8 ohms speakers.
I connected the cabs wich gave me an 4ohm load (we made an reading). And this is where I pluged the cabinet cabel in the back of my amp.
The rest of the story you know
Ok, thx!

So and to sum up the situation as I (mis)understand it, you've got two successive configurations (one with 16 Ohm speakers, the other with 8 Ohm drivers) and in each case, the presence of a second cab caused some issues - overheat or volume drop.

Out of the ideas already developed above by all of us , I hope that one of the links between cabs hasn't been wired accidentally for a series operation...

Human error happen even in factories, where QC is not always optimal. For the record, I've repaired once a brand new attenuator (Harley Benton, made in China) in which the 16 Ohm plug was actually measuring... 150 Ohm (!). Just because of a botched solder job on a defective cheap jack plug. I've changed the plug, redone the solder job and the problem was solved. But it would have hurt any OT.
 
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