Hi Folks. I acquired a Forte Model 3 amplifier, in apparently good working order except for one of the RCA input jacks that would not grip the center post of an RCA plug. To make a long story short when trying to remove the RCA jacks for inspection/replacement I broke off the red wire right where it comes out of the gray sheath that insulates the two conductor cable (one conductor shielded) from the board to the jacks (it looked like maybe the wire had been nicked there at some point prior to me). I am a rank amateur, so in trying to deal with a shorter wire I really messed up the shielded wire, too, and barely had enough length left on both wires to make a connection - although it seems to work.
Realizing that the way the amp sounds is the most important thing, the ugliness of my "work" nonetheless bothers me greatly. So, I Google searched extensively trying to find replacement two conductor cable of the same type, preferably gray so it would look original, but I could not find anything that seemed to match (the only thing remotely close was a cable sold by guitar shops that's for connecting a guitarist's foot pedal). Do you folks know where I could find such cable?
I figured that if I was going to replace the gray cable, which apparently requires removal of the board, I might as well replace the trim pots since I seem to get a lot of voltage/heat sink temp drift with the current ones. I've read up on that, and my only question there is what kind of "goop" I need to put on some of the transistor parts so they will conduct heat properly to the heat sink when putting the board back.
Thank you!
Realizing that the way the amp sounds is the most important thing, the ugliness of my "work" nonetheless bothers me greatly. So, I Google searched extensively trying to find replacement two conductor cable of the same type, preferably gray so it would look original, but I could not find anything that seemed to match (the only thing remotely close was a cable sold by guitar shops that's for connecting a guitarist's foot pedal). Do you folks know where I could find such cable?
I figured that if I was going to replace the gray cable, which apparently requires removal of the board, I might as well replace the trim pots since I seem to get a lot of voltage/heat sink temp drift with the current ones. I've read up on that, and my only question there is what kind of "goop" I need to put on some of the transistor parts so they will conduct heat properly to the heat sink when putting the board back.
Thank you!
My sincere apologies; I made an assumption that Model 3 owners would know without a photo. However, a photo is now attached, with arrows pointing to said gray cable, although it is a photo that someone else took of how the cable/wiring/soldering of the shield is supposed to look. Mine is the same but my gray cable seemed to be shorter to begin with and now has zero slack. I'd be happy to take a photo of mine, but will need to unhook it and take the lid off.
The gray cable contains an unshielded red wire, and a black wire with a braided shield around it. I don't know whether, at the board, the shield is soldered to anything, or whether instead only the black wire is soldered there. As shown, though not super well, in the photo, the black wire is soldered to the negative terminal of the RCA jack, but the shield from both the right and left channel is soldered together between the RCA jacks.
The gray cable contains an unshielded red wire, and a black wire with a braided shield around it. I don't know whether, at the board, the shield is soldered to anything, or whether instead only the black wire is soldered there. As shown, though not super well, in the photo, the black wire is soldered to the negative terminal of the RCA jack, but the shield from both the right and left channel is soldered together between the RCA jacks.
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for transistors - buy Keratherm 86/82 here in Store then you'll not need any goop, replace all old thermal pads
be sure to include bigger washer under output transistors screw heads, same as split washer; if needed, replace screws with longer ones
coaxial cable is generic coaxial, with two (red and black) multistrand central conductors, shield around; you can buy something similar pretty much everywhere ...... Digikey, Mouser, TME
just example of selection: https://www.tme.eu/rs/en/katalog/mi...17;1335:1543113,1598011,1598012;2517:1450993;
trimpots - if you're going to change them, think of replacing them with multiturn
depending on their physical orientation on pcb , choose proper position of trimpot screw ( it can be on top or on side)
be sure to include bigger washer under output transistors screw heads, same as split washer; if needed, replace screws with longer ones
coaxial cable is generic coaxial, with two (red and black) multistrand central conductors, shield around; you can buy something similar pretty much everywhere ...... Digikey, Mouser, TME
just example of selection: https://www.tme.eu/rs/en/katalog/mi...17;1335:1543113,1598011,1598012;2517:1450993;
trimpots - if you're going to change them, think of replacing them with multiturn
depending on their physical orientation on pcb , choose proper position of trimpot screw ( it can be on top or on side)
Thank you very much. Re the cable, as I look at the photo I posted it kind of looks like the original there is a two conductor with what is think is called a braided "drain" that doesn't surround the black wire, but I'm almost sure that mine looked more like the arrangement in the attached (which is the foot pedal cable I mentioned) where the braid actually surrounded one wire. Hmm, I may be mistaken or maybe it doesn't matter. I've also attached someone else's photo of their Model 3 in case it clarifies anything.
As for the tororid, I'm afraid I can't tell who made it since it has no indicia.
As for the tororid, I'm afraid I can't tell who made it since it has no indicia.
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you're mistaken, and it really doesn't matter
now, only when you dismantle at least one cable from RCA and pcb, you'll see how it is actually connected
having RCA on back, you really need one wire with screen
now, only when you dismantle at least one cable from RCA and pcb, you'll see how it is actually connected
having RCA on back, you really need one wire with screen
Understood. Thanks again. Apologies for the typos, was working on the phone in a waiting room while waiting on a doctor for the yearly exam (turn head and cough).
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I remember seeing gray cables from computer CDR units for analog audio. They usually have two inner conductors and a braid like mic cable.
In case anyone is interested, I found some printing on the gray cable in my Forte Model 3, and it says E87D4 (or maybe it's E8704) 2 CDR 22 AWG Type CL2 but unfortunately the manufacturer name is cut off. Yet I could not find any cable via Google that has/had an E87D4 (or E8704) number.
At some point when I'm up to replacing it I'll cut through my cable to see whether the braid just surrounds the black wire, or both wires, or whether it's kind of like an extra wire that surrounds neither the red or black. I could swear, though, that per my recollection the braid surrounded the black wire only. Cable that has such an arrangement is elusive, and what I instead found available was braid around both wires, or a foil around both wires, or a braid around none of the wires and instead kind of a stranded element of bare wire that ran parallel to the red and black wires - the exception being the Fender foot pedal wire mentioned (and shown in the photo) earlier.
FWIW, I'm attaching yet another person's photo that again shows how the gray cable wires / braid are connected to the RCA jacks.
At some point when I'm up to replacing it I'll cut through my cable to see whether the braid just surrounds the black wire, or both wires, or whether it's kind of like an extra wire that surrounds neither the red or black. I could swear, though, that per my recollection the braid surrounded the black wire only. Cable that has such an arrangement is elusive, and what I instead found available was braid around both wires, or a foil around both wires, or a braid around none of the wires and instead kind of a stranded element of bare wire that ran parallel to the red and black wires - the exception being the Fender foot pedal wire mentioned (and shown in the photo) earlier.
FWIW, I'm attaching yet another person's photo that again shows how the gray cable wires / braid are connected to the RCA jacks.
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1987 date code?
It is 22 AWG Class 2 wire, possibly lower than mains rated in voltage, good enough for RCA jacks.
Stereo headphone wire is two inside a shield, that or CAT 5 shielded wire will work. Use two pairs if needed.
Even mono single inner shielded wire should work.
I would put new jacks if the old ones are corroded, or plating is damaged.
It is 22 AWG Class 2 wire, possibly lower than mains rated in voltage, good enough for RCA jacks.
Stereo headphone wire is two inside a shield, that or CAT 5 shielded wire will work. Use two pairs if needed.
Even mono single inner shielded wire should work.
I would put new jacks if the old ones are corroded, or plating is damaged.
With only a small bit of obsessing, I cut some insulation off one of my gray cables in the Forte and found that my recollection was incorrect. They are simply foil-shielded two-conductor with a bare/stranded so-called drain (grounding?) wire running parallel to the red and black wires. NareshBrd is probably correct that the indicia on the original cable was just a date code. The jacks are gold plated and look new, and I was able to tighten their grip on the RCA plug center post by prying up the inner contact with a sewing needle (I purposely broke off the needle tip under the contact to provide kind of a shim).
Re Zen Mod, I am going to start a new more-appropriately-titled thread to seek a bit of clarity on the bolts / washers for re-mounting the transistors to the heat sinks after I take off and reinstall the PCBoards. I just ordered Keratherm from the Store.
Re Zen Mod, I am going to start a new more-appropriately-titled thread to seek a bit of clarity on the bolts / washers for re-mounting the transistors to the heat sinks after I take off and reinstall the PCBoards. I just ordered Keratherm from the Store.