Servicing a model 15 amplifier. Q113 and Q112 need replacements. Marantz part numbers DTM13 and DTM11 for these parts.
Any idea what these are in terms of industry standard part numbers?
Any idea what these are in terms of industry standard part numbers?
Could you post a circuit diagram ?
The advertisement for this amp boast complete protection of the output devices , if they are blown is the protection still working ?
The advertisement for this amp boast complete protection of the output devices , if they are blown is the protection still working ?
Here's the schematic that I have. There are a pair of 6 volt lamps in series with the output devices. One of these had also failed in a peculiar manner, being that the post that supports the filament was completely melted down to the glass on one side.
Q112/113 are bad. I tried subbing a couple of NPN devices I had in the shop, but the channel oscillates. I don't know what the hfe of the original device is because I can't look it up.
Told the customer of the complications. It's likely he's going to abort the repair due to the low budget and the degree of complexity of the problem.
Q112/113 are bad. I tried subbing a couple of NPN devices I had in the shop, but the channel oscillates. I don't know what the hfe of the original device is because I can't look it up.
Told the customer of the complications. It's likely he's going to abort the repair due to the low budget and the degree of complexity of the problem.
Attachments
Oh, wow, 1966 model. Everything was slow then. 400 khz ft on the outputs. The factory that made those old homotaxial products is now a parking lot or an amusement park or something. there is no minimum ft on the 2n3055 mj2955 replacements.
IF the outputs are modern Ft >2 mhz, you need to put 10 ohm 1 w resistors between emitters of drivers and the base of the outputs.
plus, the c9 and c13 could be more profitably used between b&c, not b&E. More like 50 pf disks too, instead of .033 uf film caps. Most later designers sped up the drivers to avoid current crossover, not slow them down.
Probably your drivers are TO5, which ebc pattern is unobtainable except from houses that leave out all the specs like NTE. They will give you Vcesat every time, wow. Twisted TO126 or TO220 has given me broken legs after 5 years. I'm thinking TO39 ebc 10 w (with heat sinks) transistors that are still available in the farnell house brand may be the thing, but haven't tried them out yet.
Definitely a job for a hobbyiest, too many mods required to be profitable to a pro.
With <50 v rails (rail capacitor specification) you might be able to get away with shotgunning the whole board with a LM3886 board. This can't be more than about a 60 W /ch amp.
IF the outputs are modern Ft >2 mhz, you need to put 10 ohm 1 w resistors between emitters of drivers and the base of the outputs.
plus, the c9 and c13 could be more profitably used between b&c, not b&E. More like 50 pf disks too, instead of .033 uf film caps. Most later designers sped up the drivers to avoid current crossover, not slow them down.
Probably your drivers are TO5, which ebc pattern is unobtainable except from houses that leave out all the specs like NTE. They will give you Vcesat every time, wow. Twisted TO126 or TO220 has given me broken legs after 5 years. I'm thinking TO39 ebc 10 w (with heat sinks) transistors that are still available in the farnell house brand may be the thing, but haven't tried them out yet.
Definitely a job for a hobbyiest, too many mods required to be profitable to a pro.
With <50 v rails (rail capacitor specification) you might be able to get away with shotgunning the whole board with a LM3886 board. This can't be more than about a 60 W /ch amp.
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Indianajo has a point substitute them with old school BJT,s of VERY low ft/gain not high gain/ high ft BJT,s
Yeah, the whole amp would have to be re-engineered to make modern parts work. It motorboats with the TO-66 replacement driver I tried. Definitely not worth the time and money that the customer is willing to spend.