Hi all, & hope all's well.. Here's a pic of the back panel of my Bell & Howell 12643, aka model 138, & the associated schematic (in 2 parts), & not wanting to remove that jack, can anywhere help me make heads or tails of it?
Many thanks in advance for any assistance.
Kenny
Many thanks in advance for any assistance.
Kenny
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I think this amplifier has the output transformer in the speaker case. So it's not possible to 'just' connect a loudspeaker. Part of the smoothing of B+ is also done in the speaker case. Furthermore the bias voltage for the outputstage is formed in the speaker case. It also seems to have some form of protection but I'm not quite sure (see the relais in the speaker case; in the 'make' position it puts a 1K resistor from B+ to ground).
The connections (of the female plug on the amplifier):
1 = connects the amplifier (except for the output stage) to the B+ when the plug is inserted (the male plug connects 1 to 3)
2 = anode 1 (to anode connection 1 on opt)
3 = raw B+ (only rectified)
4 = ground
5 = anode 2 (to anode connection 2 on opt)
6 = bias voltage for output stage (the negative voltage is formed over the 100 Ohm coil and the 15 Ohm relais coil in the speaker case).
The connections (of the female plug on the amplifier):
1 = connects the amplifier (except for the output stage) to the B+ when the plug is inserted (the male plug connects 1 to 3)
2 = anode 1 (to anode connection 1 on opt)
3 = raw B+ (only rectified)
4 = ground
5 = anode 2 (to anode connection 2 on opt)
6 = bias voltage for output stage (the negative voltage is formed over the 100 Ohm coil and the 15 Ohm relais coil in the speaker case).
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True,you definitely can not "just connect a speaker there"
As pcl200 said, the OT is in the case, the +B filtering too, but most important: the speaker is a field coil type, so case and main unit can´t be used separated from each other.
It´s very reasonable to have a +B emptying resistor, since main amp connector is female, case one is male, carrying hundreds of volts on its exposed pins.
As pcl200 said, the OT is in the case, the +B filtering too, but most important: the speaker is a field coil type, so case and main unit can´t be used separated from each other.
It´s very reasonable to have a +B emptying resistor, since main amp connector is female, case one is male, carrying hundreds of volts on its exposed pins.
Yes, PCL200, I have a tech, and a rather experienced old chap who has been able to circumvent any amp issues I bring him, but I just wanted to get a better understanding of what I'm bringing him, and so I can add any appropriate jacks on my own. Yes, he's an amp guy, but not a musician, as much as I'm not a tech, & the more info I have about what I'm dropping off, the better I can present it. From the git-go, assuming there is an electronic fix to this, would it be appropriate for me to prep this amp w/a 1/4" speaker out?
Thanks so much!!
Kenny
Thanks so much!!
Kenny
Oh, we'll get this thing working, by hook or by crook. Any load or tranny needed can probably be electrically worked out. Yes, it will require some thinking out of the box, or outside the cabinet, but nuclear fission it ain't, but believe me, all of you know better than me,,, but I will keep you advised~
Thanks all & stay safe, Kenny
Thanks all & stay safe, Kenny
Well, here's the bottom side of the power tranny, & I'm not quite sure what that thing below it is, but there's wires going in & out, & it's fastened down pretty well.. ,,??
Yes, in a previous B&H refurb, much of the guts related to the projector was removed, but some still remain.
Thnx
Yes, in a previous B&H refurb, much of the guts related to the projector was removed, but some still remain.
Thnx
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