Polytone power supply rehab..can u help?

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Hi, I am new to the group and love the sound of my Polytone baby Taurus with 8 inch speaker. This thing is old now (like me) so I would think its not too hard to make a "Polyclone' of this thing. I have some electronics background, but never built an amp before...not great at translating the schematic to a PCB. Can anyone recommend a starting point? A book or something to get started with cleaning up this power supply? Its now full of pops and buzzes...probably needs new filter caps...i dont even know which things on the board are the filter caps...or what they do. So..thats where im at. Anybody ?
 
Here are some pics!

GREAT idea! I didnt know you can upload pics here.
This is the amp and the power supply only...I just want to rebuild the power section for now...not sure where to start or where to get supplies..etc...i need some guru mentoring....i would be willing to pay for some one on one tutoring. I have the power transistors out...waiting for replacements.
On this you can see that the large yellow (cap?) is just flappin in the breeze. Well..i have another amp of exact same model..that works perfect, so I opened it up to see where that lead is supposed to connect to. The 'good' amp has the SAME cap just hangin there! but it works!! I do not see where it could have been attached, but there is solder on the end of it..also, it may connect to the nearby resistor...but I cant make that out on the schematic on murch which is blurry..i can post the schmatic if you dont have it...but its here: http://www.murchmusic.com/Polytone Info/schem2.JPG but its posted online upside down.
Im hoping that fixes it..but something tells me its not that easy. Please feel free to contact me on this! Chas
 

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Well , Changing The transistors will only help if the old transistors are burnt out or you are upgrading the transistors to newer types ...... Transistors generally work or they don"t work with nothing in between , new transistors and old but working transistors will generally sound the same and dont gradually deteriorate with time ......

It looks like that big cap with one end just hanging connects to one of the 2 holes right underneath it , I suspect that trace with the 2 holes in it is where it connects , the other hole probably connects to a wire that probably goes to ground .......
Those types if caps (electrolytics , there looks to be 5 of them) do deteriorate gradually with time which can cause crackling and increased hum , i would suggest you replace those with new ones ........

The ceramic caps (The brown disk looking caps) can be replaced with newer film caps , the ceramic caps that are in there won"t go bad from time but ceramics in the audio path can sound a little brittle ......

The blue caps are probably fine where they are .......

looks like a cool little project ......

PS: the Schematic you posted isn"t the schematic for your amp .....

:D

Cheers
 
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wow..thats not the schematic? The layout is very close..but i guess where it says CR1...well..i dont have a CR1.
Any idea where i can find the schematic? Polytone does not exist as far as parts or customer support....I think Murch is the only poly guy around. So, without the sch..how would I know which value new caps to buy? THanks for the response!!
 
Hopefully you did not bend the wire on the end of the cap that is broken off. It’s position, angle etc will give big clues to were it should go.

If your camera has macro ability take a high resolution close up picture of the area you think it came from. Take the pictures from many angles with good lighting. Then crop out everything but about 2 sq inches around were you think it connected. This way you can upload high resolution pics without having large file sizes. If you get the lighting and angle right we should be able to see down those holes and be able to inspect that resistor for any connection.

The pic i uploaded is an example of what can be done with good lighting and a macro camera. This is a automotive relay about 1 inch square in it’s case. I wanted to know the condition of the contacts and could not see between the contacts very well. I took about 15 pictures from different angles and one of them caught the light just right.

BTW, this super close up after being cropped is only 167KB
 

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thanks! but..i dont have such macro power on my camera. The lead that is dangeling has not been touched...and it does not correspond to any connection...this is true in both amps.
I went to 'musicparts.com and bought the polytone baby taurus lead schematic...1987...
All the components on the layout match the physical amp...except CR1...no schem shows a cap there...i dont know how to read the CR1 part...is that a rectifier section? Anyway..thanks for the response...still waiting for the new parts..I may be able to replace the caps as noted above. ...soon as i figure out what to order as replacements. THANKS AGAIN ALL!
 
Im 99% sure that the end of that cap goes to the Pad with 2 holes that is right underneath the cap ......
Putting a trace there with nothing connected to it is just not a logical thing for any designer to do and the cap does nothing without both ends hooked up ......
 
Yea..sounds logical...but when you place the cap down onto the board, those holes are really no where near the lead that is dangling...the lead actually looks like it was soldered to the resistor that is there..anyway..that is where it lines up when you hold the cap in place. When i replace the transistors, i will pull off the board and look at the other side to see if there are clues...a friend of mine has the same exact amp ...im trying to get him to open his up to see if he has the same thing goin on...but he's a afraid to pull it out...
 
Your schematic did not post.

It looks to me like there is solder rosin by the resistor lead and hard to see but the solder looks flat on the end of the cap like it was spread out on the pcb next to the resistor. So the cap was probably tacked to the side of the resistor lead.
 
I think you are correct...it lines up almost perfectly. There is some solder on the resistor lead also....i could see that falling off...just wish one of these schematics showed this...they all show CR1 and give no data on it. I tried to upload the schem again...maybe its being filtered out?
 
Hi, I am new to the group and love the sound of my Polytone baby Taurus with 8 inch speaker. This thing is old now (like me) so I would think its not too hard to make a "Polyclone' of this thing. I have some electronics background, but never built an amp before...not great at translating the schematic to a PCB. Can anyone recommend a starting point? A book or something to get started with cleaning up this power supply? Its now full of pops and buzzes...probably needs new filter caps...i dont even know which things on the board are the filter caps...or what they do. So..thats where im at. Anybody ?

Well actually, if you are hearing buzz, especially 120 cycle, there is a pretty fair chance you do have a bad transistor, or diode, not that changing the old electrolytic capacitors will help also...
pops can be dirty controls and jacks, or bad solder connections.
The transistors in these amps need to be changed fairly frequently, I suppose they run hot and there is a lack of thermal management.
You can add some better heat sinks, newer packages, or use insulators to mount the new transistors / packages to the chassis...
or just change them now and again, anyhow they blow.
I have no idea what to change them to, as far as substitutions, there have not been many of these Polytones around for a number of years.
There "should " be some substitute matched pairs that you could use...
anyhow, when they do work, they sound good for a clean sound. I never liked the built in distortion on these amps.
 
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