Polytone mini brute II

[pipposalsiccia]

happy thanksgiving everybody!
Need an expert tech..
I have a poly mini brute ii from 1980.
I noticed a distortion at the tail end of notes (not all notes but mostly trebles)
what’s your opinion about it?
I would like to fix it, I bet you guys know more
than me!

regards

[J M Fahey]

It might be crossover distortion due to poor biasing but equally possible dirt in or deformtion of your speaker voice coil, which now "scratches".

Open amplifier, disconnect wires from speaker and connect them to any spare speaker you have around, in this low power test impedance is not critical.

Play a full chord (into the new speaker) and let it die naturally.

Typically distortion at higher volume wonīt be that bad, but increase togeher with decaying chord.

If new speaker also distorts, itīs an amplifier problem; if not, itīs the original speaker one.

EDIT: now I see you posted the exact same question twice, with 10 minutes difference.
No need for that, once is enough, twice is confusing.
Thanks.

[pipposalsiccia]

ok sorry for the double post.
I’ve tried another speaker (very shitty 8” 8ohm).
the distortion seems 95% reduced. I bet there’s something wrong on the speaker.
As you know, poly has a synthetic cover glued on the speaker front, do I open it?
how about replace well the synthetic cover?
I’m not an expert, just a little bit scared to damage the cover
regards

[52 Bill]

I would suggest that you double check your test by using a decent speaker to test for the distortion. That way you can be certain that the speaker is in fact the problem and then you won't waste time or money by replacing the original one for no reason.

I'm not certain that I understand what cover you are referring to, a carved foam grille panel or the round foam disc that covers the front of the speaker.

In either case, the foam is held on by Velcro strips. There is a protective black scrim fabric glued to the front of the speaker, which can be removed by carefully sliding a thin putty knife along the edge of the cardboard speaker gasket. Sometimes the gasket will de-laminate and leave a thin layer of cardboard on the edge of the fabric, but this can be scraped off after it has been removed from the speaker frame.

The original speakers are 4 ohm and should be replaced with another 4 ohm unit or the amp will not put out the correct wattage.

[pipposalsiccia]

I would suggest that you double check your test by using a decent speaker to test for the distortion. That way you can be certain that the speaker is in fact the problem and then you won't waste time or money by replacing the original one for no reason.

I'm not certain that I understand what cover you are referring to, a carved foam grille panel or the round foam disc that covers the front of the speaker.

In either case, the foam is held on by Velcro strips. There is a protective black scrim fabric glued to the front of the speaker, which can be removed by carefully sliding a thin putty knife along the edge of the cardboard speaker gasket. Sometimes the gasket will de-laminate and leave a thin layer of cardboard on the edge of the fabric, but this can be scraped off after it has been removed from the speaker frame.

The original speakers are 4 ohm and should be replaced with another 4 ohm unit or the amp will not put out the correct wattage.

yes I mean the round synthetic cover around the speaker.
I will looking for another 4ohm to try best.
thanks , I will post the solution.
anyway, polytone’s one of the best sounding amp for jazz

[pipposalsiccia]

yes I mean the round synthetic cover around the speaker.
I will looking for another 4ohm to try best.
thanks , I will post the solution.
anyway, polytone’s one of the best sounding amp for jazz

ps: it has the old cts, I like a lot.
It’s almost impossible to find the same replacement

[J M Fahey]

If you are talking about the speaker, when CTS failed (money wise) one former employee started his own Company, doing basically the same because thatīs what he had learnt.
Such company is Eminence, and browsing its catalog you can find whatīs basically the same sounding.
Only slight problem is that 4 ohm versions are relatively rare.

If hard to find, ask whether you can get Jensen C12K in 4 ohm. Or worst case C12N.
Those are "old style" speakers and quite compatible with your amp.

What Country are you writing from?

[pipposalsiccia]

If you are talking about the speaker, when CTS failed (money wise) one former employee started his own Company, doing basically the same because thatīs what he had learnt.
Such company is Eminence, and browsing its catalog you can find whatīs basically the same sounding.
Only slight problem is that 4 ohm versions are relatively rare.

If hard to find, ask whether you can get Jensen C12K in 4 ohm. Or worst case C12N.
Those are "old style" speakers and quite compatible with your amp.

What Country are you writing from?

Eminence..wow!
thank you.
I’m from switzerland

[pipposalsiccia]

If you are talking about the speaker, when CTS failed (money wise) one former employee started his own Company, doing basically the same because thatīs what he had learnt.
Such company is Eminence, and browsing its catalog you can find whatīs basically the same sounding.
Only slight problem is that 4 ohm versions are relatively rare.

If hard to find, ask whether you can get Jensen C12K in 4 ohm. Or worst case C12N.
Those are "old style" speakers and quite compatible with your amp.

What Country are you writing from?

i’ve found those models 4 ohms:
texas heat
beta 12c
delta 12 lfc
eps 12c
delta pro 12
koppalite 12
eminator 12
k1071

which is the best suitable for poly on your opinion?

[J M Fahey]

Closest to original is Texas Heat, but are you sure itīs available in 4 ohm?
Some user comments showing itīs not the typical "Rock" speaker:

Very natural, un-colored tone with a higher db rating so it's louder too, a win, win

a replacement for the stock speaker in my Fender Blues Junior. I liked the way the way the amp sounded before replacing the speaker, but this speaker truly brought new life to my blues junior. The bass response, previously non-existant, is very strong. Highs are tight; they just sing. Mids are great, but I like to back them off. Besides the added bass, the best thing about this speaker is how warm, fat, and smooth the sound is.

The first sound that came at me was full-bodied, fat, gutsy, with just enough brightness to cut through, and without that Celestion shrillness...bloody PERFECT!! After ripping out some crunchy stuff I played with a clean sound with a little stereo chorus. It was warm, bright, full, and thanks to the chorus, swirling & shimmery too. I could not be happier with my cabs! They can handle ungodly amounts of power, (150 watts rms per speaker, so 300 per cab), and the tone is fantastic! I kinda hate to admit it, but I'm never going back to British speakers. These Eminence Texas Heats OWN all! If you want your guitar tone warm, full and fat with just a little shimmer on top, these are for you!

The other Eminence you mention are excellent but more PA type than Guitar ones.

Very good buy way more "polite", if that word means sonmething to you.

If Texas Heat is not available in 4 ohms, Jensen C12K is about the same.

I donīt care much about "brand" or "image" but how they are built inside, and the speakers I suggest are built very much the same, give about the same sound..

[pipposalsiccia]

Closest to original is Texas Heat, but are you sure itīs available in 4 ohm?
Some user comments showing itīs not the typical "Rock" speaker:


The other Eminence you mention are excellent but more PA type than Guitar ones.

Very good buy way more "polite", if that word means sonmething to you.

If Texas Heat is not available in 4 ohms, Jensen C12K is about the same.

I donīt care much about "brand" or "image" but how they are built inside, and the speakers I suggest are built very much the same, give about the same sound..

eminence texas heat is avaliable in 4 ohms, but I suppose it has boomy bass on poly.
I’m reading good feedbacks about eminence beta c.
eminence guitar legend is not avaliable in 4 ohms.
Anyway tomorrow i’ll try to contact a tech, first of all repair mine voice coil CTS.
Then I’ll find some of your suggestions.

eminence speaker is 4.4 kg vs jensen 3 kg.
I’ll keep also in consideration the weight, Polytone wooden 80’s cabs seems weak than modern amplifiers.
My polytone seems an old nebulizer machine, but is
sexy!!

[glebert]

Polytones should have a smooth sound IMHO. Both of mine have 15" PA type speakers. I think the Mini Brute IV would be the same amp circuit as the II but with a 15" speaker, which I would guess would be more PA than guitarlike.

[DrGonz78]

I had a late 90's mini brute ii for a little while. The speaker was great sounding and very much part of the design of the amp. As I recall it was 12" 3 ohm speaker. The lady who owned it before me played a keyboard through the amp. Definitely good for jazz and for a full clean sound. Definitely more PA speaker and it worked wonders in those amps. Still I am curious to know how well the amp sounds with a more guitar based speaker.

[pipposalsiccia]

I had a late 90's mini brute ii for a little while. The speaker was great sounding and very much part of the design of the amp. As I recall it was 12" 3 ohm speaker. The lady who owned it before me played a keyboard through the amp. Definitely good for jazz and for a full clean sound. Definitely more PA speaker and it worked wonders in those amps. Still I am curious to know how well the amp sounds with a more guitar based speaker.

absolutely amazing for jazz guitar.
especially the diamond early 80’s.

[pipposalsiccia]

It might be crossover distortion due to poor biasing but equally possible dirt in or deformtion of your speaker voice coil, which now "scratches".

Open amplifier, disconnect wires from speaker and connect them to any spare speaker you have around, in this low power test impedance is not critical.

Play a full chord (into the new speaker) and let it die naturally.

Typically distortion at higher volume wonīt be that bad, but increase togeher with decaying chord.

If new speaker also distorts, itīs an amplifier problem; if not, itīs the original speaker one.

EDIT: now I see you posted the exact same question twice, with 10 minutes difference.
No need for that, once is enough, twice is confusing.
Thanks.

Hello
I’ve tried a better test with 8ohm jensen ck12
the distortion is still there, like a parasite.
I suspect something is wrong on power supply
what do you guys think?