Polytone Mini 12L ICs...

[jazzbass1]

Hi,
Several years ago I picked up a 1985 Polytone Mini 12L that wasn't working properly. This has an onboard modulation circuit, sort of like a Uni-Vibe wannabe thing.
Polytone removed the numbers from some of the chips, I guess to safeguard their new design that they hoped would set the world on fire.
Naturally, the first thing I did was call Polytone and get a schematic. THis proved to be a frustrating experience, they sent the srong schematic TWICE. It's seemingly impossible to contact anyone there that has a clue.
Next, I laid out $20.00 to download a service manual from musicparts.com.The chip numbers WERE NOT ON THE SCHEMATIC! AAAARRRGGGHHH!!!
So I'm out another twenty bucks and still at square one.
I was able to examine a standalone wersion of the phase shifter effect and it was the same, no numbers on the ICs.
Does anyone out there know what ICs are in this thing?
Any help would be greatly appreciated!

Bill Cherensky

[52 Bill]

Does anyone out there know what ICs are in this thing?

I'm not sure which ICs you are talking about. The common 14 pin dip that they used in the preamps was the 4739, dual op-amp.

[jazzbass1]

Polytone Mini 12L ICs...

Thanks for the reply.
No, these are the ICs in the modulation circuit. I should've been more specific, sorry.

Bill

[oc disorder]

I found this circuit a friend brought back when he was at Berkely when he
bought one of the Polytone series way back in the 70's.
They must put something in the water as he hasn't touched a valve amp since! I digress........
In his amp this section was not populated and as it was called "harmonic divider" I assumed it was some kinda octave device...He was told they were not fitted as they didn't work satisfactorily but who knows ..also the
salesman???? mentioned that they do break down but usually once they are fixed they should give no more problems....
My mate got a photocopy from the salesman preparing for the inevitable
and sure enough it did "blow up" and took both the speakers !
Im digressing but thats the history of this schematic which is looking
rather tattered around the edges.My usb scanner stopped working
(anyone know any fixes?) so I had to take a photo with a camera.
I looked at the schematic again and it appears to have a "speed pot"
sounds like the latest club drug but I'm digressing again so just maybe
keeping this for 30 odd years may have proved worthwhile.
U9 is a CD4520 a Dual Binary Up Counter and U11 is a CD4023 a Triple 3-Input NAND Gate.
I hope this is of some use particuarly after reading all my rubbish!

[jazzbass1]

Polytone Mini 12L

I found this circuit a friend brought back when he was at Berkely when he
bought one of the Polytone series way back in the 70's.
They must put something in the water as he hasn't touched a valve amp since! I digress........
In his amp this section was not populated and as it was called "harmonic divider" I assumed it was some kinda octave device...He was told they were not fitted as they didn't work satisfactorily but who knows ..also the
salesman???? mentioned that they do break down but usually once they are fixed they should give no more problems....
My mate got a photocopy from the salesman preparing for the inevitable
and sure enough it did "blow up" and took both the speakers !
Im digressing but thats the history of this schematic which is looking
rather tattered around the edges.My usb scanner stopped working
(anyone know any fixes?) so I had to take a photo with a camera.
I looked at the schematic again and it appears to have a "speed pot"
sounds like the latest club drug but I'm digressing again so just maybe
keeping this for 30 odd years may have proved worthwhile.
U9 is a CD4520 a Dual Binary Up Counter and U11 is a CD4023 a Triple 3-Input NAND Gate.
I hope this is of some use particuarly after reading all my rubbish!

I think that's a different amp...mine is from '85 and has a phase shifer type circuit, not an octave divider.
Thanks for taking the trouble to respond, though. I'll forward the info to my tesh anyway just in case.

Bill

[oc disorder]

Actually I'm suggesting because of the clock circuit and the "speed control"
I think its more likely to be some type of chorus with a misleading name.
Also it has 2 x VT811 L.DR.'s photocells which are more likely found in a
chorus or similar rather than an octave divider.
Perhaps some genius would like to comment on the workings of this circuit.
Anyway CMOS chips often fail and are cheap to replace.
The modern ones are probably more stable.
Some times I have found a reference number under the chip .
With some that have had the number scrubbed, wetting it and getting the right viewing angle using a magnifier, I can sometimes see enough part numbers to work it out.

[Enzo]

I too was thinking ther might be a number on the underside of the ICs.