bogen mo-200 modded for stereo
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century tek
Addicted Member
Those 200's are excellent for stereo as they are originally a 200 watt mono amp with eight 8417 tubes.
As battradio mentioned, photos are a must. Look at the output transformers. They should have been seperated if it has been indeed modded for stereo along with the seperation of four 8417 tubes and two individual input jacks.
As battradio mentioned, photos are a must. Look at the output transformers. They should have been seperated if it has been indeed modded for stereo along with the seperation of four 8417 tubes and two individual input jacks.
century tek
Addicted Member
If you can, turn off your flash but have plenty of overhead light. The speaker hook-up looks simple enough. You have four wires where 2 are the negative and 2 are the positive. Connect one of the red wires to one lug on the speaker and the other red wire to one lug on the other speaker. The black wires are common ground so it doesn't matter which speaker you connect them to.
century tek
Addicted Member
Nope! It's a mono amp where the two output transformers are wired in parallel and only has one input jack. Here is a web refference:
The amplifier consists of two almost separate amplifiers, each with its own output transformer and push-pull-parallel set of 8417 tubes, and a 7247 driver. The inputs to the 7247 grids and the secondaries of the output transfomers are connected in parallel. Needless to say, an octet of matched 8417's, and a pair of matched 7247's would be essential for maximum performance.
If the input sections and output wiring are separated, the unit can be modified to be used as a dual channel power amplifier. Each channel of course has its own output transformer and push-pull-parallel set of 8417 tubes, and a 7247 driver. In such a case, each channel will have about 100 watts output. Both share the power supply. The impedance conversions are shown below:
radioactive
tube gear fanatic
nope dave your wrong it is indeed a mono amp that can be run in stereo .im still searching the net for info as i almosst bought one a few years back
It will depend on what connections have been brought out from the OP Transformers. The MO-200A essentially uses two MO-100A OPTs in parallel, so when separated you should end up with the equivalent of two sets of MO-100A output terminals... but the person doing the mod might not have made them all available.
The schematics for the MO-200A and MO-100A are here:
MO-200A: http://makearadio.com/schematics/images/bogen-mo200a-7.jpg
MO-100A: http://makearadio.com/schematics/images/bogen-mo100a-7.jpg
The most useful connections from each OP trans would be the 16 Ohm and the 25V CT (6.2 Ohm). On the MO-200A mono version these are paralelled for 8 Ohm and 3.1 Ohm.
The schematics for the MO-200A and MO-100A are here:
MO-200A: http://makearadio.com/schematics/images/bogen-mo200a-7.jpg
MO-100A: http://makearadio.com/schematics/images/bogen-mo100a-7.jpg
The most useful connections from each OP trans would be the 16 Ohm and the 25V CT (6.2 Ohm). On the MO-200A mono version these are paralelled for 8 Ohm and 3.1 Ohm.
century tek
Addicted Member
Dnewma04 found the one site I got my info from!
century tek
Addicted Member
If that is the case then it has not been seperated to run in stereo mode. It is still factory wired in mono and the guy just added two more wires to run another speaker for a total of two speakers to be run in mono.
Exactly my point mono with 2 speakers wired together, I told the owner but swears it's been modified for stereo. but someone marked switches stereo/mono and it has what i thought were two volume pots . So i gave him the benefit of a doubt, and they also marked stereo input on the jacks?:scratch2:
century tek
Addicted Member
What kind of camera are you using? Have you figured out how to get us some half way decent pics?
Have you looked underneath it yet to see if the two output transformers have been seperated?
Have you looked underneath it yet to see if the two output transformers have been seperated?
jwalker
Well-Known Member
Based on the tap arrangement on the secondaries of the two output transformers, you'll need to remove all the connections that go to the secondary taps of the opposite side.
In this "stereo" configuration there's no true 4-ohm tap on each transformer. There's a real 16ohm tap and a 25VCT taps on the same winding. The 25VCT will give you a little over 6ohms. And if you take the center tap from this to the common tap you get around 1.5ohms.
For you 4ohms speakers I would just connect to the 6ohm taps and the common tap. This is not a perfect match, but your speakers aren't a 4ohm impedance across their frequency response anyways (unless they're full range crossoverless ribbons.)
The schematics I saw say the 25V(6ohm) tap is yellow and the common is black. Good luck.
