Anyone know what some of these Bogen preamp modules are for? Oddball modules for oddball amps!

[sean sweeney]

This thing sucks! deletes entire posts if you take to long and type A LOT and put a TON of pics...
Anyway... sorry,
I was curious about these preamp modules that came along with these Bogen amps I got today...
What was the reason for these things? They don't seem to do much that the amp isn't already doing! Found all of these amps earlier today and was pretty amazed at the luck! Two MO60s and TWO MO100's... the 60 uses the 7027 tubes, and the 100 the 6550 or KT88's... they had a bunch of WRONG tubes in them... so I ordered all the ones I will need, plus a bunch of caps and supplies in case they need a lot of worn... the odd unit appears to be another Bogen from the early 50's?

But just curious about the modules and what they were used for... seems with the transformers they have, these could be easily converted to a nice XLR tube mic pre... anyway... pretty jazzed about these and they have some SERIOUS iron... the best amp I ever had was a Bogen... a BP60 I believe... and it was totally rare... couldn't find an example anywhere, much less an asking price... so I put it up for high... about 2500... and it sold in FIVE MINUTES... DOH! When that happens, it's not usually a good sign... lol anyway... here's the pics if it lets me post this time... copying and pasting this message!! lol

 

[Ohighway]

Hmm. I always thought that the correct tubes for a MO100 were 8417.

Sorry can't help with information on those modules

 

[gadget73]

The MO-100a uses a quad of 8417. The original MO-100 uses a pair of 6550. The MO-100 circuit-wise is basically the same as the DS-265 hifi amp. If the transformer is capable, it should be a good performer. I have a pair of MO-100a's using stock iron and @dcgillespie's modified circuit to let it run a 6550 or KT88. They're excellent amps. I don't think the transformers are the same though.

Not really sure on the modules. Seems they would have had to plug into a backplane or something. Looks like 4 modules and the power supply? Guessing its used as a preamp or mixer unit. Feed in signal from your music source or a phone patch for paging purposes, set the levels where needed. The transformers are probably impedance matchers.

 

[sean sweeney]

The MO-100a uses a quad of 8417. The original MO-100 uses a pair of 6550. The MO-100 circuit-wise is basically the same as the DS-265 hifi amp. If the transformer is capable, it should be a good performer. I have a pair of MO-100a's using stock iron and @dcgillespie's modified circuit to let it run a 6550 or KT88. They're excellent amps. I don't think the transformers are the same though.

Not really sure on the modules. Seems they would have had to plug into a backplane or something. Looks like 4 modules and the power supply? Guessing its used as a preamp or mixer unit. Feed in signal from your music source or a phone patch for paging purposes, set the levels where needed. The transformers are probably impedance matchers.

Yes! You definitely nailed that! I have the original 6550 version of that, two identical mono blocks, and on the chassis it says to use the "PDR" version of the preamp, which I have one of here. The pre's are without power supplies themselves, and that one has a 12ax7 and 12at7, with two matching transformers... again, not sure why there's two, but I guess it's to have one coming in and one going out? There is an 11 pin output for the preamps and the same in female version on the amp... there's no cable, but the amps provides power for those. I was wondering if I didn't need them, if they would serve as a good and possibly valuable all tube mic pre... and if i could get a good enough tone from them to use here in the studio...
And do these preamps ever split the phase on XLR mic inputs? For years I thought that XLR's split their phase and that's why they were able to sent them over long distances... thinking there was more to it than just a high impedance wth a ground shield... But for some reason I always thought that in higher end studios that the preamps split the phase and preamplified the signals that way, for some reason. I have a tendency to overcomensate! lol... I guess I'm going to either make or try to hunt up a few of these cables. There's a preamp box for all five chassis, interestingly. The older one that uses all the 40s era tubes should be interesting too! I had to order a pair of 6J7's today, as no one of my tech friends or the vintage stores here had one. lol

I did a ton of work on the 6550 amp yesterday... about 14 hours. What a tank!! There was some bad caps and some arcing inside the chassis... all better now and sounds pretty amazing!

 

[trainbuftony]

Cant help on the modules. But that triple rectified 7027 amp, I don't even know what to say. Wow! 250 miliamps of B+ per 5ar4, means they were anticipating pulling more than half an amp, through that transformer.
That's going to sound very real.
You sound like you know what you're doing too!
Godspeed.

 

[sean sweeney]

yea, I found a date code on the MO100 that puts it from 1961... I knew it was pretty old, as the original power cord was literally the texture of a pretzel stick! I put a grounded one in and the other one will I guess need one too... I ordered a bunch more parts today... gonna be a fun restoration, and fun listening! I just spent about three hours trying to make a *!(T)(EW& 11 pin molex cable and wound up running out side and stomping it to little bits... but I have four more on order... just REALLY wanted to hear one of those modules... ARRGH...

 

[gadget73]

XLR is usually a balanced signal. Might be using one transformer as a BALUN and the second for impedance matching. Usually stuff like this has to have something plugged in, so if it wasn't the transformer it would have a dummy plug with jumpers to complete the circuit.


I think I've seen that older one with the top cap tubes. DO-20 maybe? What output tubes, 807 ?

 

[paart]

These Bogen amplifiers were not designed with home audio use in mind. The expected use was primarily in commercial sound systems such as paging systems. Examples: school systems, hospital systems, and a variety of other "distributed sound " applications such as churches, sports stadiums, amusement parks, etc. For that reason, a number of modules were made available to connect to everything from juke-boxes, to to telephone systems, and intercom systems. I'm guessing the modules you have may be for these applications.

 

[sean sweeney]

XLR is usually a balanced signal. Might be using one transformer as a BALUN and the second for impedance matching. Usually stuff like this has to have something plugged in, so if it wasn't the transformer it would have a dummy plug with jumpers to complete the circuit.


I think I've seen that older one with the top cap tubes. DO-20 maybe? What output tubes, 807 ?

Yes, the older one has 6J7 tubes with the pigtails... it has the old 6L6 tubes with the balloon style... I have the 6J7 tubes on order. I had some until recently.

 

[sean sweeney]

These Bogen amplifiers were not designed with home audio use in mind. The expected use was primarily in commercial sound systems such as paging systems. Examples: school systems, hospital systems, and a variety of other "distributed sound " applications such as churches, sports stadiums, amusement parks, etc. For that reason, a number of modules were made available to connect to everything from juke-boxes, to to telephone systems, and intercom systems. I'm guessing the modules you have may be for these applications.

yes. I was thinking that, just curious what they were used for... and if they could be converted to XLR, which I believe they can... just have to research how to convert properly. thanks!

 

[sean sweeney]

I ordered a bunch of molex connectors for the modules, and then realized that the things have 11 pins (which i ordered) but the connectors for them on the amp have 9 pins!!! I'm thinking that two two extra pins are going to be an audio output of some sort... but not sure about that either... I'm going through a few different routes, to find a manual and schematic for them so I can get them hooked up... I have a PDR preamp, which is what is used on the early MO100 and MO200 amps... (there was a MO200!!??) and TWO LA1 preamp modules for the MO60 amps... (the triple rectified ones!!) and a PSR power amp or power supply which i think is also to power these somehow, but I only have one, so I may have to create MORE... and one final one called a POT-1 which appears to be an oscillator to create dings and various noises for industrial purposes... I read one post a while back that the MO200 was used for a SHAKER TABLE... whatever that is... I have reason to believe it's a TABLE that SHAKES and probably uses some kind of speaker coil type of induction to do the shaking... lol... I wouldnt mind having one of those! lol

 

[gadget73]

I know there was an MO-200A, which was a pair of 100A's on one chassis. Mono technically, the input and output were paralleled to get a 200 watt single channel amp. In hifi use, you split that to get a stereo amp. @dcgillespie did a thread on re-working the MO-200A. I have a pair of 100A amps built to the same design. Much less difficult to move around.

The 100A and 200A were sometimes used in shaker table duty. They have a 115v output, and I don't know of any industrial speaker system that runs that. 70v and 25v are typical, and it did have those. Shaker tables are pretty much what you think they are. Its designed for vibration testing of equipment. basically shake the thing until it fails or doesn't. Using a big amp lets things be vibrated at different frequencies depending on what needs to be tested.

 

[sean sweeney]

I know there was an MO-200A, which was a pair of 100A's on one chassis. Mono technically, the input and output were paralleled to get a 200 watt single channel amp. In hifi use, you split that to get a stereo amp. @dcgillespie did a thread on re-working the MO-200A. I have a pair of 100A amps built to the same design. Much less difficult to move around.

The 100A and 200A were sometimes used in shaker table duty. They have a 115v output, and I don't know of any industrial speaker system that runs that. 70v and 25v are typical, and it did have those. Shaker tables are pretty much what you think they are. Its designed for vibration testing of equipment. basically shake the thing until it fails or doesn't. Using a big amp lets things be vibrated at different frequencies depending on what needs to be tested.

I'm dying to find out how to hook up these preamp modules! I bought some molex connectors, before i really had a look at the amp, because while the modules have 11 pins out, the amp hookup for them has 9 pins in... something tells me that the RED RCA on the back of these has something to do with the pre modules... since it says "see instructions before using" but i've seen the instructions and have them downloaded... doesn't say anything about them!