Repair bench test speaker... whatchu got?

[Garydean]

I was just wondering what sort of speaker arrangement everyone has on/under their bench for testing amps under repair. It's the one thing I'm missing because there are so many options. I have a dummy load covering 4-16 ohms 50-400W.

I need to build something that will work for all occasions, if that's possible.
I have a few ideas......but, it's always nice to hear about other options.

Thanks,

Gary

[drewl]

I have an old Celestion G12T75 from a JCM800 cab.
16ohms, I use it in conjunction with either a 5ohm or 8ohm load resistor so I can see how something sounds without going deaf!
My THD Hotplate also comes in handy for abusing amps to make sure they will continue to work at full output.

[Marc]

I use a single 12T75 in a 2-12 cab so that it's de-tuned. It is fed through a power soak so I can dial it down to keep the wife happy.

MArc

[Enzo]

I have a number of speakers, but the bench has two 2x12 cabs under it, each with a pair or EMinence 12s. I don't know what speaker it is, it is hte one Seymour Duncan used in the COnvertible 100 amps. Each cab is 4 ohms. They run to a path panel on the bench riser.

The cabs themselves are very early SOvteks. Pale gray carpet, the plywood is incredibly thick. CLosed back

[Old Tele man]

...I used a JBL/D130F (before putting it into a VibroClone) with one of Ted Weber's Z-Matching transformers, so I could "match" the speakers' 8-ohm impednace to ANY amplifiers' OT rating, from 2-ohms up to 32-ohms.

[Alex R]

- a 1x12 with a G12T75, and a 2x10 with an Eminence Beta and some kind of celestion guitar speaker, both 8ohm.

The 2x10 is nice and compact, it used to be a ported 1x12 keyboard cab. I bought it cheap off the brother of a keyboard guy. I said why are you selling it, like you do. He said because his brother had died from an o.d. a few years previously and he'd just got over it enough to sell his gear. Didn't really believe this as I was meeting him in a storage warehouse, there was loads of stuff in there, he tried to sell me a Fender Rhodes for a grand, and naturally I thought it was probably all stolen... but no, when I took it apart to put the two 10s in, the port was stuffed up with a little bag containing half an ounce of dried-up dope and some little pills. Myself I think the death by overdose story fits the evidence best, but I offer it to you as a Christmas mystery.

Anyhow... I put the two 10s in there and wired up a two-switch household light switch so you can get 4 or 16 ohms, with the two in series or parallel, or either one on its own for 8 ohms. It is possible to wire such a switch in such a way. I do not remember how, but guys, you can work it out can't you.

My dummy load is a frightful thing with alu-clad resistors all white-goo'd to some mismatched bits of heatsink all bolted to a fan housing with no fan in it. I got it in a garage sale from someone who looked like he'd never touched anything stronger than paracetamol I am glad to say. I put clips on it in certain places to get certain loads. I get a kind of disappointed feeling every time I look at it.

[Joe Bee]

Wow, why are you guys all toasting perfectly good guitar speakers for testing duty? Myself, I use a little 3" speaker that came out of a TV, and it is perfect for all kinds of testing, except cranking the amp up, which I couldn't do in my flat/workshop anyway. In fact it might be able to reproduce some high-ish frequency osscillations that are out of the range of a guitar speaker, but that has not happened so far.

[Steve Conner]

Well, if you work with tube amps, it's quite hard to actually roast a test speaker. It's not like solid-state gear where if you slip with one your test probes, you can put the full rail voltage across the speaker, and more or less shoot the flaming cone halfway across the room. This has actually happened to me when servicing an old Mission stereo amp, and I was glad I had it hooked up to old speakers from a dead boom box.

For testing I used to use an Eminence Beta 8 just in the cardboard carton it came in, but I put that in one of my other amps. I now just use the only two cabinets that I own, a Hiwatt reissue 2x12 with some unknown speakers in it, and a Trace Elliot green carpet 2x10.

[Enzo]

Joe, it all depends on what you are doing. I fix amps for a living, so I need to hear what an amp sounds like. The tiny 3" speaker would tell me that the amp functions to some extent, but little more. I use real guitar speakers so it sounds like a real guitar amp when I play through them. And there are often times when an amp won't exhibit a symptom at low levels, but will at high level. The first time I would strum a big loud chord on a Marshall 100 watt, that little guy would be in shreds.

[Old Tele man]

...the question asked about "test speaker" not "dummy load"...for all my "how much power" testing, I use four 200W non-inductive 4-ohm ceramic resistors and use "jumper cables" to configure their combinations into the proper "ohms" load, 2-16 ohms...although I could just use one 4-ohm resistor and the Z-matcher (old habits are hard to break).

...P.S. they're supposed to be 5% resistors but, that's only when ambient, when "heated" they all tend to thermally drift "high" in value, so I actually take digital VOM readings immediately after shutting down power, while they're still "hot", and use those values, which are often 5-10% higher than spec's at 72-deg. F.

[petemoore]

Whatever junk with say >10w rating, 'junk' 12'' or car 6x9 types.
I start with volume low, then if the amp seems close, I move to one of my nice cabs.
Junk anything that sounds is enough to tell if it's 'working', beyond that, to tweek the amp...best done with the speaker and guitar it'll be seeing alot or most of I think.
Other than a very unlikely scenario such as connect PT Secondary to speaker, speaker damages seemed to be a lot more common, haven't read about them so much lately, must be the users understand the 'required' information.
Having blown a few...the speaker [if it's worth beans] will generally sound good at a certain volume, more makes it sound worse, more yet loosens the voice coil...Recommended to not make it sound worse and blow by not applying so much pressure to it, get another speaker or add one to it.
Blowing speakers cause they don't get loud enough is for the uninitiated and kids.
A 'good' guitar speaker sounds funny at super low volumes, sounds great at medium to high volumes, starts sounding wierd again at very high 'pressure levels' [but doesn't really get 'louder' just worse sounding]...play it at medium to high volumes, forego subjecting coil to extremely high pressure levels for more than very short life.

[drewl]

Wow, why are you guys all toasting perfectly good guitar speakers for testing duty? .

Compared to my other cabs and speakers a G12T75 isn't a perfectly good speaker
If I liked it, it would be in a good cab getting used on stage.

[petemoore]

Wow, losing lots of edits and posts...gotta remember to copy then submit !
I haven't read of toasted speakers lately, must be people understand them better...heat the voice coil for most effecient destruction.
I figured it this way...
1 dont blow nice speakers = overrate power handling or use junk.
2 2x10'' cabinet with radio salvage sounded pretty good, medium volumes
3 any 6x9, 6'', 8'', 10'', 12'' or 15'' junk tells me enough about the general acitivties of an amp to do the other tests that should be done, enough to decide if it's fit for applying 'carefully' to the intended 'performance' speakers.
I figure testing on nice speakers is low risk/why risk it.
Huge power handling probably wouldn't handle a PT Secondary anyway, something [almost unpeakable] like that is what it'd take for a small amp to blow an over-rated speaker..possible but very unlikely scenario/ why I use whatever junk to get started on.
We're building lots of amps, but not reading about blown speakers [poll]?
Generally, attempting to loosen coils on speakers by applying greater pressure and heat than they can withstand doesn't sound good, you haven't lived until you can hear a cheap speaker start to sound bad before the coil separates././valueable lesson for smallwatt speaker users. If it starts sounding bad and breaking up wierd at high volumes, back off, help should be sought for it.

[sportster4eva]

I have a big ported cab with a 100w eminence 12", and a couple of 250w 8ohm Dale resistors mounted on an aluminum plate. Parallel them for 4ohm test, series them for 16ohm test. I fire up the amp with the scope on the load first, and if all is well hook up the eminence and have a listen. Tweak it with the speaker you intend to use it with.

[Euthymia]

Yeah, I'll go with the "gotta hear what it sounds like with a real speaker" replies.

A pair of high-power 12" (Eminence and Electro-Voice) in EV TL806 cabinets.

Gotta be careful using good speakers with SS amp repairs, as Steve said. Have yet to have a tube amp throw DC.