Electrolytic capacitors in polytone babybrute

[eventide]

I'm trying to buy Electrolytic capacitors to use in polytone babybrute(with distortion version).
please tell me the how many caps and alll the value needed
(both power supply and on the pcb board)
thank you

[Scolohofo]

maybe POLYTONE SERVICE INFO

[SamBooka]

I hope it is only the caps that have the issue.. it is almost impossible to find proper replacement MegaBrains these days.

[Franz 1997]

I think you need the schematic for your particular amp- the baby brute from the 80s is a little different from the Megabrute circuit shown on the Murch site info. The power supply caps will be the same though - screw-fit 4700 uf caps, which can be a little difficult to find these days. You can sub modern caps by fitting cap clamps to the chassis.

The schematic will tell you all the cap values.

There are 2 pcb boards on the Babybrute; recapping everything is quite an undertaking, I've done it.

[Engine Swap]

There are 2 pcb boards on the Babybrute; recapping everything is quite an undertaking, I've done it.

Is there a particular problem you're experiencing? Filter caps should be replaced due to age. The electrolytics in the signal path can probably stay - you won't hear a difference.

I've done a few of these as well. Pictures and description here.

You can probably find the schematics you need in the "Polytone" section here: Amplifier Schematics

[Greentone]

Are you sure that the caps need replacing? It is routine to swap caps in a tube amp after 5-10 years (the 'lytics, anyway). In a solid-state amp, however, the power supply doesn't take the brutal beating that it does in a tube amp. The voltages being demanded by the finals in a tube amp are in excess of 400 volts. The electrolytic capacitors are frequently being operated right at their practical limits in tube amp power supplies. This is not the case in solid state rigs. Honestly, I haven't had caps malfunction even in quite old solid state amps.

If you are just replacing capacitors to freshen up the amplifier, or to make it more reliable...you might consider that many of us are operating old, to very old Polytones on their original capacitors without problem. I would simply never do this with a tube amp out of fear of wiping out the transformers--this gets expensive.

GT

[Greentone]

FWIW, I can post the cap values in a couple of days. When the painter gets done, I will unpack my Baby Brute and take a look. I will post the cap values in the amp for the electrolytics. However, you are probably ok with what's inside now.

[Greentone]

I found the Baby Brute without having to open many boxes and crates. Here is the list of electrolytic capacitors in an 80s Baby Brute with distortion:

Preamp Section:
2 each: 470 mf @ 35 volts
2 each: 10 mf @ 10 volts
2 each: 10 mf @ 35 volts

Poweramp Section:
2 each: 4000 mf @ 40 volts (Mepco/Centralab clamped can capacitors)--main filter capacitors
2 each: 47 mf @ 50 volts
1 each: 10 mf @ 50 volts

That's not many capacitors, but the Polytone--a copy of the late-60s "Tiger Amp" from Popular Electronics, I think--is a dead simple circuit. (Although this one has the infamous distortion circuit)

[Engine Swap]

That's not many capacitors, but the Polytone--a copy of the late-60s "Tiger Amp" from Popular Electronics, I think--is a dead simple circuit. (Although this one has the infamous distortion circuit)

Power section resembles the Doug Self "blameless" circuit.

Couldn't agree more on the simplicity of the circuits. In spite of what is posted all over the web by so-called "techs", I find Polytones very easy to work on and troubleshoot. Preamp and power amp are modular, quick connectors are used, all the ICs and power transistors are mounted in sockets - what more do you want?

[Greentone]

I have serviced my own Polytones for years...doesn't get easier. And, of course, they sound great. The Molex plugs simplify things, but are a source of oxidation issues. Keep their contacts clean. Except for the odd IC, the components last and last. Speakers can get roached out though.

[eventide]

The amp hum and hiss a bit.
i just opened it last night to see the in side but cannot pull out the top chasis. There are hex screws under the top chasisis. Do i have to remove that? Or
Do i have to remove a speaker to be able to remove the the top and bottom chasis?
Thank you everyone for answer my question.
sincerely

[SamBooka]

Power section resembles the Doug Self "blameless" circuit.

Couldn't agree more on the simplicity of the circuits. In spite of what is posted all over the web by so-called "techs", I find Polytones very easy to work on and troubleshoot. Preamp and power amp are modular, quick connectors are used, all the ICs and power transistors are mounted in sockets - what more do you want?

I dont know how I missed your original rebuild post but it is great!!!!

[Jazz_175]

I found the Baby Brute without having to open many boxes and crates. Here is the list of electrolytic capacitors in an 80s Baby Brute with distortion:

Preamp Section:
2 each: 470 mf @ 35 volts
2 each: 10 mf @ 10 volts
2 each: 10 mf @ 35 volts

Poweramp Section:
2 each: 4000 mf @ 40 volts (Mepco/Centralab clamped can capacitors)--main filter capacitors
2 each: 47 mf @ 50 volts
1 each: 10 mf @ 50 volts

That's not many capacitors, but the Polytone--a copy of the late-60s "Tiger Amp" from Popular Electronics, I think--is a dead simple circuit. (Although this one has the infamous distortion circuit)

Excuse my ignorance but what does "mf" stand for?: microfarad or millifarad?

[Greentone]

Sorry...I don't have a "mu" letter on my keyboard. mf means micro-farad, not milli-farad. 47, 470, and 4700 are common values. 4000 is a little unusual. 10 is easy to find.

There are four screws--two on each end of the preamp chassis on the top to unsecure it. You don't have to remove the speaker, just the back panel--8 screws, IIRC--to get things out. However, removing the speaker facilitates things.

[eventide]

Here is the picture i took last night.

[Greentone]

Undo those two white Molex plugs, pull out the preamp chassis (the picture is of it), then you can lift out the power amp chassis (after removing a few screws at the bottom of the amp). This will be easier with the speaker out. Most of the electrolytic caps are in the power amp section, but you can see four of them in the preamp chassis in your picture--they are the light blue cylinders.

[Engine Swap]

Sorry...I don't have a "mu" letter on my keyboard. mf means micro-farad, not milli-farad. 47, 470, and 4700 are common values. 4000 is a little unusual. 10 is easy to find.

The filter caps on the power amp should be 4000uF for the 55w version and 7300uF for the 100w version. Best to visually check and replace with the same uF/voltage rating. You'll need the screw terminal type of connector. Pay attention to the diameter as well.

[Greentone]

Your version is the low power version. ..can tell from picture.
100 watt came out later...I have it too.

[eventide]

It' s 75 watts
the biggest two electrolytics caps are 40v4000uf
I have a recone to 4 ohm with new voice coil jbl d208 should i tried with the amp ?
Or it's not polytone sound anymore

[eventide]

Voice coil former is bekelite not paper
coils is eminence copper 8ohms cut in half so it's 4ohm
I told the reconer to use paper dust cap but he forgot and put alumenium dome on the cone.

[HCarlH]

Are you sure that the caps need replacing? It is routine to swap caps in a tube amp after 5-10 years (the 'lytics, anyway). In a solid-state amp, however, the power supply doesn't take the brutal beating that it does in a tube amp. The voltages being demanded by the finals in a tube amp are in excess of 400 volts. The electrolytic capacitors are frequently being operated right at their practical limits in tube amp power supplies. This is not the case in solid state rigs. Honestly, I haven't had caps malfunction even in quite old solid state amps.

If you are just replacing capacitors to freshen up the amplifier, or to make it more reliable...you might consider that many of us are operating old, to very old Polytones on their original capacitors without problem. I would simply never do this with a tube amp out of fear of wiping out the transformers--this gets expensive.

GT

I pulled my 1977 (new at the time...I'm the only owner) 102D out of storage a couple of years ago after not being used since the mid 80s. After a minute of being turned on, white smoke started to poor out of the ventilation slots and it died.

Wouldn't that be caps that have exploded? I'd love to get this thing fixed, but not sure if that's possible. The wiring inside is a mess.....spaghetti everywhere. It looks like an amateur wired it.

[Greentone]

The JBL should work just fine. I have used that speaker in the Baby Brute before with pleasing results--I actually thought the sound was improved (heresy).

HcarlH: your amp problem is probably a smoked capacitor. The amp is reparable. There _are_ wires running not everywhere, but from the preamp chassis to the amp chassis. It looks like a mess. Your amp is more modern than this old 104, but the idea is the same--preamp chassis above, power amp chassis below, speakers between. It is actually pretty easy to work on.

[eventide]

Thank you again greentone and everyone