Hi,
I bought this marantz 2216b dirt cheap for fixing up, one channel was blown, taking it's pre-driver, power transistor and fuse out with it along with Q706, I removed the 4 main power transistors and powered up using a current limiter, found a bad cap as well, these are all fixed up now, also issue on the other channel on the tone control board, which I have also rebuilt, new caps, and some new c1845 & ksa992 from farnell. The sound is great from the headphones, and I also checked the DC voltages on the output coil & at the base of Q701 & Q702 and its reading 20mA so looks good. Voltages also measure good. I am nearly ready to install the power transistors, I set the bias control resistors to full resistance, I have one question though the Lamps 0.6v VT01 & VT02 one has been replaced with a fuse on the other side of the PCB, I presume these are to limit current spikes and help protect the output transistor, is a fuse ok here? I have looked for suitable replacements in farnell, but 0.6v is impossible to find, what is the best to put in here, I have some fuseable 10ohm resistors, I presume the bulb acts as an inductance. Any advise? What do people use? Thanks.
I bought this marantz 2216b dirt cheap for fixing up, one channel was blown, taking it's pre-driver, power transistor and fuse out with it along with Q706, I removed the 4 main power transistors and powered up using a current limiter, found a bad cap as well, these are all fixed up now, also issue on the other channel on the tone control board, which I have also rebuilt, new caps, and some new c1845 & ksa992 from farnell. The sound is great from the headphones, and I also checked the DC voltages on the output coil & at the base of Q701 & Q702 and its reading 20mA so looks good. Voltages also measure good. I am nearly ready to install the power transistors, I set the bias control resistors to full resistance, I have one question though the Lamps 0.6v VT01 & VT02 one has been replaced with a fuse on the other side of the PCB, I presume these are to limit current spikes and help protect the output transistor, is a fuse ok here? I have looked for suitable replacements in farnell, but 0.6v is impossible to find, what is the best to put in here, I have some fuseable 10ohm resistors, I presume the bulb acts as an inductance. Any advise? What do people use? Thanks.
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As they might be used as fuses and you have trouble locating them the other alternative is to use ---Surface Mount PTC,s --poly-switch reset-able fuses.
They are available in a large number of very low current specs.
Surface Mount PTCs - PolySwitch - Resettable PTCs - Littelfuse
They are available in a large number of very low current specs.
Surface Mount PTCs - PolySwitch - Resettable PTCs - Littelfuse
They might be a combination of clipping indicator, fuse, inductance even... They are only on the PNP output base which is suggestive of correcting for differences between PNP and NPN devices, or of catching thermal runaway. The inductance of a bulb filament isn't very big, I doubt that's the reason unless the output devices were fast.
A ferrite bead could be used if instability is an issue with 10 ohm resistor / polyfuse.
A ferrite bead could be used if instability is an issue with 10 ohm resistor / polyfuse.
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