15 inch 4 ohm Speaker for Polytone Mini-brute IV

[fatz]

Hello,

it's been discussed a couple of times already in the past but I still have a few questions regarding replacing the speaker in my old polytone mini brute IV amp (15" speaker). I got it used a few months back for a good deal but the speaker sounds a "muddy", especially the low mids. I checked the speaker today and I see marks of repair (glue) on it. The tear is about 3 inches long coming from the border of the cone towards the center.

I was thinking of replacing it, there's not much information on it expect a number on the back "15-0053 / 137-8042". Also there's a sticker on it that says "Feb 27th 1981". No brand.

I've measured 3.8 ohms impedance.

I'm ok with a bit of power loss, so I'm thinking of installing a 8 ohm speaker.

- Most of the 15" speakers are labeled as "bass speaker" or "subwoofer"... I guess that translates into a different response to the higher frequency and I'm not sure how this relates to the guitar sound ?
- I think the Eminence Legend 1518 can be a good match, but it's labeled as 150W whereas the Polytone has an output of 160W... given that I increase the impedance, can I assume that the wattage will be reduced and this will be ok ? or should I just avoid pushing it ? or is it an absolute no-go ?

If I remember correctly from my physics courses... P = UI and U = RI gives us P = U^2/R.. so with U constant and R doubling, I'm about to turn my 160W amp into a 80W which would easily be handled by the 150W speaker ?

Also when opened I notice the reverb tank wasn't correctly fixed, that could explain a bit of noise that I got when trying to set the reverb even at low levels, will try to fix this first before changing the speaker.

Thanks for your help on this! great forum by the way

[Herbie]

Hi fatz and welcome to the forum and to the Mini Brute IV Club!

Legend 1518 is great (!) speaker but considering that most common replacement speaker to the Polytone amps is Beta A-series speaker I would recommend Eminence Beta 15A.

BETA-15A - Loudspeakers | Eminence Speaker

I don’t have experience with it but I have used the 12” and 10” versions and they work fine with Polytones.

If You live in the US You can contact Eminence Custom Shop and order a 4 ohm version of it.

Good luck in Your quest!

[deacon Mark]

I like polytones but the typical issues are repairing them and getting all the old parts to not make noises of different types. I put an eminence in my babybrute used 8inch 8 ohm for the 4ohm rating. It works fine but no more thinking polytones are good. Too many other things that are better now and can do the same thing with much better reliability.

[fatz]

Thanks! I've seen the recommendations about the Beta, but it's also recommended as woofer/bass and I wonder if that would be fine for guitar (the frequency range is lower...).

But I see the Beta 12A has almost the same range as the Beta 15A, so if you're happy with it, I'll have a look around. I'm in Switzerland, so custom order may be complicated.

[medblues]

These look promising and very light:

Faital Pro 15PR400 Bass Guitar Speakers - Faital Pro 15PR400 bass guitar and PA speaker that has a lightweight neodymium magnet - Faital Pro 15PR400 800 watt high efficiency of 100dB SPL woofer for all mid-bass and bass applications. Faital Pro 15PR4

Eminence Delta 15A speaker. The Eminence Delta 15A is a 15" 8 ohm speaker. Delta-15A is a 400 watt RMS 12" woofer.

[fatz]

hey would be nice to spare some weight in the process a bit pricy though.

But just for info, this is also labeled as a bass guitar speaker... like the Beta. So is it really ok to consider bass/woofer speakers ? I really thought this would have a big impact on the sound, when played with a guitar. But it looks like I'm wrong ?

[medblues]

hey would be nice to spare some weight in the process a bit pricy though.

But just for info, this is also labeled as a bass guitar speaker... like the Beta. So is it really ok to consider bass/woofer speakers ? I really thought this would have a big impact on the sound, when played with a guitar. But it looks like I'm wrong ?

Many people used Polytone Mini Brutes as bass amps safely and liked how they performed.

[old tube]

Just FYI, the codes on your current speaker are decipherable: 15-0053 / 137-8042

15-0053 will be the model number
137 is the EIA Manufacturers code for CTS (Chicago Telephone Supply)
8042 means the item was manufactured by CTS 42nd week of 1980.

The other date is probably Polytone's receipt date.

CTS were key suppliers to Magnavox from the 1920's and also Fender from the mid 60's to mid 70's.

[vintagelove]

Hi, to start, I’ve had a bunch of polytones, swapped speakers, etc.


Don't fall for the “only original poly speakers” Internet myth. Everyone has sounded as good, or maybe even better with a new speaker. I put in a Weber bass 15 in one of mine, and it sounds fabulous.

[Herbie]

I suppose that a bass speaker is a part of the Polytone sound.

I had the 10” Delta and some version of Faitals but according to my ears they did not have that Polytone feeling. Someone else’s ears might tell different story.

The difference between 4 and 8 ohms is not crucial – until You have the volume in 10 and still miss more (if Your speaker handles the watts).

[rolijen]

My Mini Brute IV was a decent bass amp. But for guitar, it was mud city and had weird overtones kinda like a very faint ring modulator (for those old farts like me who remember what that was). And watch out for the dreaded buzzing Boost/Cut switch. I shoved bits of business card under the plastic shield thingy to stop the incessant buzzing. I giggled with it for a year or so but just could not bond with it. Now, I'm wondering if it was just a really bad stock speaker. Good luck! Hoping you get it sorted.

Roli

[Cunamara]

I would think a 150w speaker in a 160w amp should be fine unless you run it wide open a lot. I would look for a 4 ohm speaker, myself. The Betas seem to be a common replacement for the old nominally 3 ohm stock speakers.

[0zoro]

Hej fatz I would discuss the technical end of your delemma with Eminence directly ei the watts ohms etc. I have done the same and they offer quick and helpful information.

[fatz]

thanks for all your replies ! I opened it again yesterday to flip the reverb tank (less hum now) and while I was cleaning it up I noticed a couple of caps and wires that may need to be changed, so I'm thinking of going to a music store get it looked at and maybe then get their input on the speaker as well (if they have some in store and possible to swap/test a few, that'd be great).

But with the current restrictions all music stores in town are closed... will have to wait.

Thanks again

[oldane]

thanks for all your replies ! I opened it again yesterday to flip the reverb tank (less hum now) and while I was cleaning it up I noticed a couple of caps and wires that may need to be changed, so I'm thinking of going to a music store get it looked at and maybe then get their input on the speaker as well (if they have some in store and possible to swap/test a few, that'd be great).

But with the current restrictions all music stores in town are closed... will have to wait.

Thanks again

IMHO, the reason for Polytones fame is that it was one of the few decent sounding solid state amps in its day for those who got tired of carrying around and maintaining a heavy tube amp. Most other solid state amps back then sounded like a donkey farting in a tin can. As said by others, solid state amp technology has evolved a lot and these days there's a lot on the market (both heads and combos) which will meet or exceed Polytone sound quality with greater reliability and at affordable prices - maybe even cheaper than a repair of your Polytone. In addition present day amps often has more options such as outputs for recording/PA systems and more than one (analog) tone stack to choose from. So be sure to factor in both material and labour costs and compare with prices of new and contemporary amps before heading into a repair.

A few examples out of many (more could be mentioned):

Quilter amps, both heads and combos are quite popular with jazz guitarists at present. The Tone Block 202 head seems to be very versatile for a jazz guitarist, so if you have an idle speaker cabinet in the basement, it may be an affordable option. I have one in order to use with my idle Redstone 10 speaker cabinet.

Roland Cube amps have - for good reasons - been popular since the 1980s and have been steadily improved through the years. They are affordable, sound good and are rugged. Many fine jazz guitarists use them.

Mambo amps are basically sound wise out of the polytone mold - but are not exactly cheap, especially not for those outside the EU who has to factor in customs and VAT (they are made in and shipped from UK). The combo versions with 8" or 10" speaker are very small and light and they are very convenient as a grab and go amp. Despite their small size, they sound great. The "wedge" version has a cabinet shape which allows it to be tilted with the speaker 45 degrees up, thus a separate amp stand is redundant. I have a Mambo 8 wedge and am very pleased with it

Acoustic Image heads are extremely versatile with a lot of options and applications. Many guitarists prefer to use some kind of tone shaping preamp in front of it (at least with the earlier versions). Some years ago I used one with a SansAmp Paradriver DI for tone shaping and the mentioned Redstone cabinet and could dial in almost any tone I wanted.

Fender Tonemaster amps - for those who like blackface sounds. They are one trick ponies - but do the trick very well - designed to be modern solid state reincarnations of the good old Deluxe Reverb and Twin Reverb amps, but with no intentions of or options for sounding like anything else.

[zizala]

When I had my Polytone MiniBrute it was quite awhile ago....got it cheap because but it needed a speaker at the time.

Had great sounding success with a regular Eminence Legend 15" (8 ohms).
Later I found another MiniBrute on Craigslist with electrical problems, took out the chassis and turned it into a matching extension speaker cab.
So I put another 8 ohm Legend 15 in that one and had the ability to run the two 15's at 4 ohms.
Quite nice!

Either way I was quite happy with the sound.

I eventually sold all that to a very talented young player, when I moved on to my exploration of old tube amps.
In retrospect I miss it and was probably a bit hasty letting it go.

[BBGuitar]

Hello,


I've measured 3.8 ohms impedance.

Did you measure with a dc ohm meter?
DC resistance does not give you impedance, common misconception.

Did you consider having it re-coned?

[mad dog]

I would put in the Emi Legend 151. If you're a guitarist rather than basis. Have used that guitar in several 1x15 amps and cabs. It's often the best choice, if not, always near the top.

[timjgbeun]

The best 15" replacement for Polytone 15 mini brutes, etc is the Eminence DeltaLite 2515 neo speaker. Super smooth, huge low end, takes tons more power and headroom at 300W RMS (600W peak) fits most brutes perfect AND is super light being neo, about 5 lbs.

It is 8 ohm so slight power loss BUT since super efficient at 99.2 which I'm sure is way higher the originals, will be as loud or louder. And being an 8 will allow proper use of the EXT speaker jacks for the brute amps that have them, as adding another ext 8 ohm spk in parallel will be 4 ohm total that the brute amps can handle. Just perfect all around for jazz guitar and jazz bass, I have used it for both. Smooth full tone very similar to the original...better actually. Cost about $200 usd.

[Cavalier]

I often use the Deltalite 2515 in my modified Twin. It has a completely flat response and does not color the sound. Eminence also makes neo 15s in 4 ohms for pedal steel that work great too, I use one from time to time, they have a bit of chime.

[timjgbeun]

Good to hear someone else tried and found this speaker a worthy contender. Yeah very smoky tone on guitar, and big deep bass. Yeah they make other neos in 4 ohms but those I think are higher level series more expensive being even higher power, but also not as flat, as you say having more chime or whatnot. That is why I stuck with this 8 model, as at $200 it is already very costly, and as I said efficient enough at 99dB to prob not be lower output at 8 ohm compared to the probably less efficient stock ceramic 4 ohm. And the tone is as you say, thanks for the reply

[Cavalier]

Yes it is a great speaker, I use the neo pedal steel for bigger groups needing more cut, it does handle more power and lists for more too! I sourced one used.

[Timpicks]

This thread has some great information—maybe too much for my non-technical brain. I recently picked up a ‘90s Mini Brute III on CL cheap but didn’t notice a speaker tear. D’oh!

I had brought it to my repair guy for another issue—the input jacks were cutting out intermittently—and he tried to replace with a 4ohm 15” speaker (300 watt rated) that he had laying around that was originally for a Leslie. No bueno, horrific buzz on low guitar notes. Interestingly, with the back off, no buzz, so his theory is that the closed back is interfering with the cone’s need to move air freely.

So might the solution be to install a 150 watt speaker that moves less air? Drill holes in the cab back to let it breath? Reconing doesn’t seem to makes $ense based on the info here. Some of the recommended replacements here are either 8 ohm or higher wattage so not sure they would work. But then I am pig ignorant about this stuff, so any gentle nudges in the right direction would be greatly appreciated.