Originally Posted by fender3x
You're actually correct, one of the original speakers from my 410TX cab has a little white sticker stuck to the frame that reads Peavey Model 121 Imp. 8 Ohms.
You're actually correct, one of the original speakers from my 410TX cab has a little white sticker stuck to the frame that reads Peavey Model 121 Imp. 8 Ohms.
Update:
The glue I used to glue the dust caps back on the speakers seems to have dried, so all the speakers are ready to go back in the cab, on Tuesday this coming week, I'll pay a visit to my local Jaycar Electronics store and see if they have any acoustic dampening material in stock, and I'll buy as many rolls of it I can, next stop will be to my local Bunnings store for a set of new castors, and some nuts, bolts, and washers for attaching them to the cab, will also buy a new cordless drill while I'm at it.
Update:
Just spent what seemed like two hours trying to remove the four mounting screws for the tweeter speaker so I could test it to see if it still works, only to find that it doesn't, so I'm going to have to buy a replacement one, Jaycar stock a 100W 8 Ohm piezoelectric tweeter that I think may work fine as a replacement, it only costs about Au$12.00 or so, the speaker has a rotary attenuator knob for the tweeter mounted on the back panel, so I can adjust the tweeter level if need be, hopefully the attenuator rheostat isn't burnt-out.
Update:
I managed to make quite a bit of progress on the repair/restoration work on my Peavey 410TX bass cab, you should have seen the ton of dirt and detritus I had to clean-out of the cab along with the foul-smelling acoustic dampening material, just as well that I was wearing a pair of rubber dishwashing gloves at the time, amongst the dirt and detritus I "evicted" from the cab was a rodent skeleton of some kind, I kid you not, the cab still needs a good vacuuming-out to remove the last vestiges of dirt and detritus from it, the post office on Cavenagh St happens to have cordless vacuum cleaners in stock, so next fortnight I'm buying myself one.
I have managed to get all the new castors installed on the cab this afternoon, so that's one less thing for me to do.
Update:
I decided to give the interior of my Peavey 410TX bass cab a good clean-out with a scouring sponge soaked in some water and pine-o-clean, it was still pretty grotty after giving it a good sweep-out, but it looks clean enough inside now, this bass cab actually had a crossover circuit built onto a pcb, which had the original input socket soldered onto it, since the new NL4 Speakon socket I'm going to be using as the new input socket, is going to create some clearance issues, I have elected to re-build the crossover circuit using an old-school breadboard point-to-point style method of construction which involves using a suitably-sized piece of 12mm thick pine wood to mount some 8-way tagstrips which will be used for mounting all the components used in building the crossover circuit.
I have made some drawings of the crossover circuit and also a drawing of the new breadboard layout which I think should work perfect, for those interested, I will post pics of my hand-drawn crossover circuit as well as the breadboard layout if you're interested in building one for yourself, I will also include component values too.
And as promised, here are my hand-drawn versions of the crossover schematic in my bass cab, as well as a breadboard layout:
As you can see, the schematic for the crossover is really simple, it consists of what looks to me to be a High-Pass LC T-Filter formed by a 3u3/250V Polypropylene Cap, a 15uF/100V Polypropylene cap, and a 200uH air-cored inductor, the output of the High-Pass LC T-Filter goes to a constant impedance rheostat, there's also that 1.0mH iron-cored inductor going to four bass speakers wired in series-parallel, that's there to stop high frequencies going to the bass speakers.
Here's my theory of how the crossover works.......
For frequencies from say 1Hz up to the cutoff frequency of the LC High-Pass Filter, the 3u3/250V Polypropylene capacitor will appear to be an open-circuit, remember a non-polarized capacitor is nothing more than two conductors separated by an insulator, now for a capacitor the resistance at pure DC should ideally be infinite, as you increase the frequency the resistance to AC decreases and more of the signal flows through the capacitor, in electronics AC resistance is also known as impedance.
At some frequency the AC impedance of the 3u3/250uF capacitor is going to be low enough to allow the maximum signal level through to the 200uH air cored inductor, but, inductors behave in the opposite way to capacitors, as frequency goes up so does the AC resistance or impedance of an inductor, the 200uH inductor is there to stop ac signals going to circuit-ground so the signals are left with only one other path to take, and that's through the 15uF/100V polypropylene capacitor.
Now, if the high frequencies try to go through the bass speakers to ground, they will be stopped by the 1.0mH iron-cored inductor since the AC resistance of an inductor increases with frequency.
As a side-note the letter H is used in electronics for the unit of Inductance known as the Henry, a 1 Henry inductor is a very large unit of inductance and you're more likely to see inductors in the mH (milli-Henry) or uH (micro-Henry) range, but 1H and larger values of inductors do exist.
Sidenote two, I deliberately kept maths to a bare-minimum in my theory of how the crossover works, because the maths gets quite complex, and I wanted to keep the explanation as simple as possible, of course, I could go ahead and calculate the cutoff frequency of the LC High-Pass T-Filter if I wanted to.
Last edited by DrNomis_44; 15-03-2023 at 10:51 AM.
I think you probably know way more than I do about this, but I am not sure that it would be a good trade to use a piezo tweeter. I found a manual for this cab:
https://assets.peavey.com/literature...s/80301559.pdf
Attenuater knobs don't work too well with piezos. Also, particularly in a bass cab, they would not need a crossover. At least that is my understanding. Unfortunately the manual doesn't tell you much about what sort of tweeter it came with, just that the crossover frequency is 3.5 kHz.
...so I did a little more digging, and I think the OEM tweeter is a Fostex 024H27 ... These seem to have been rather widely used in bass cabs. I found them listed as used in your 410TX cab, as well as in SWR cabs. Usually these seem to be in the neighborhood of $15 USD. I mean...as long as you are rebuilding the crossover...in for a pound... ;-)
You may well be right too, well, if I can find one of those Fostex 024H27 tweeters going for something like Us$15.00 or the equivalent in Au$ then yeah, I will seriously consider buying one, cheers for that mate, I'll see if there are any on eBay, to be honest, I really didn't know what make/model number the original tweeter was so I ended up buying the Piezo tweeter from my local Jaycar Electronics store as a last resort, I didn't even know if the original tweeters were still available.
I don't know if Fostex makes them anymore, but they seem relatively common. I found a bunch on ebay...but I am in the US so YMMV ;-)
Yeah, it can't hurt to have a look, you never know, I might score myself a good bargain.
I just posted pics of my hand-drawn crossover schematic and breadboard layout, tomorrow I might see if I can get my printer/scanner/copier up and running and make scans of them that are clearer.
Update:
Popped-by my local Jaycar Electronics store yesterday to buy some bits and pieces I needed to build the new crossover for my Peavey 410TX bass cab, I found that Jaycar did not have any 15uF/100V polypropylene caps in stock, so I had a bit of a think to myself about how I could solve the problem, and then remembered I could put two lower value caps in parallel to make up the needed capacitance value, I did a quick calculation and found that if I put an 8u2/250V cap in parallel with a 6u8/250V I would effectively get a 15uF/250V cap which would be perfect, Jaycar did have some 3u3/250V polypropylene caps in stock though, so I bought two 8u2/250V caps, two 6u8/250V caps, and two 3u3/250V caps, I also bought eight 8-way tagstrips, and some self tapping screws and washers while I was at it, next week I will be paying a visit to my local Bunnings store for some suitably sized 12mm thick pine wood for the breadboard, as well as some other things I'll need and hopefully the bass cab should be working by the end of next week.
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