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Motorola Table Radio B100

jeffsod

jeffsod

Active Member
Anyone have any information or experience with a Motorola Table Radio Model B100W? I am considering purchasing this and am told by the current owner it is a tube style Am/Fm radio. This would be my first vintage tube radio since having a tube philco console growing up. Never knew what I had back then but definetly liked the warm sound of that old unit. Any way any advice appreciated.
 
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I got one of those ! Got it for $40 at a junk store...Decent performer, prolly needs to go see Terry to REALLY sing. Not overly sensitive, but I never have bothered to hook up an antenna, either.. Don't think you'll be disappointed..
 
Service info is in Sams Photofact folder 693-9. Not in my my collection, but check your local library...
 
Sandy G thanks for the tip to have Terry check out the radio but being new to the forum I have to ask who is Terry?
 
Something about these B100W's makes them great audio from the golden age of tube gear, simple modern design...solid and simple. I'm a bit confused why they get passed over and sell so low....found mine at a show and it went unsold at $25., so at show's end made a $10. offer and became the new owner. I recommend finding a better pair of speakers then the ones which came with it. Any smaller decent 2-way speaker with make a big difference, the B100W has enough power.

A Motorola ad from 1962 really sold the 'Stereo' sound aspect of these, as well as it being point to point hand wired, plus high fidelity sound. At $129. they were not cheap...thats $500. in todays dollars !

If you're looking for a tube reciever and refuse to pay the foolish high prices that folks seem to be paying for untested examples by other makers....search out the Motorola, it's a classic - yet unsdiscovered!
 
Hi ten years ago at the Cluttered Closet in Denver I found a really cool portable (30lb) Motorola Am/FM radio in a beautiful wood cabinet with brass hinges and handles. Its vacuum tubes and looks very similar to your B100W. My model says B1000M and I have not been able to find any information for it. If you have info where I can find info for these radios please send my way. regards DM
 
Old thread I know, but does someone know how to set bias on this? Got mine for 29 bucks about 6yrs ago. Very cool radio. Just going through it now.
 
There is a 150 ohm resistor connected from the cathodes (pin 2) of the 6BM8 power tubes to ground, that sets the bias of those tubes. There is also a 50uF cap from cathodes to ground which, if faulty, can affect the bias. The same is true of the .1 coupling caps that lead to the grids (pin 3) which, if leaky, will affect the bias by causing the tube to draw more current than it should.
 
Sorry, took awhile. I did replace three electrolytic caps. Tubes are Ok...mostly around 60%. This little radio sounds very nice tonally. It has one 12ax7. I put a pigtail iec connector on it, so I could switch powercords.
I put my HFC Ultimate powercord on it for two days burn in, along with an MC0.5 helix+ in the same outlet. These HFC. products focus magnetic conduction energy...it takes a while to saturate.
Then I switched out the HFC powercords to a Blacksands Violet Mk Ii. Left the .05 helix+ in the outlet.
To my delight, I found the Blacksands had the better tone, but minus the magnetic induction strengthening.of the HFC poercord. The .05 and Blacksands retain enough energy to elevate the sound of this table top. Really it has no right sounding this good. I have swapped the 12axc7 from Tell long smoothplate, to Tell ribbed shortplate, to Bugle boy shortplate. Decided on ribbed shortplate ( for her pleasure!) Tele.
Anyway, there is a bias trimpot on top of unit. The only problem I have is tise.stereo indicator light does not stay lit, only momentary. I have not changed out the the multi- section electrolytic canister yet, which I believe is contributing to less than desirable bass. I am open to suggestions on how to resolve these issues.
 
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On the second 6bm8 is there also supposed to be a 150 ohm resistor to ground? Appears to be remains of a broken off lead there!
 
RWood said:
There is a 150 ohm resistor connected from the cathodes (pin 2) of the 6BM8 power tubes to ground, that sets the bias of those tubes. There is also a 50uF cap from cathodes to ground which, if faulty, can affect the bias. The same is true of the .1 coupling caps that lead to the grids (pin 3) which, if leaky, will affect the bias by causing the tube to draw more current than it should.
Click to expand...
I found a broken off lead on the 2nd 6BM8, #2pin. Is there supposed to be another 150 ohm resistor to ground there?
 
No, the power tube cathodes are joined together by a single wire and then there is a single 150 ohm cathode to ground. The cathode bypass cap is handled in the same way (although the cap might be located in one of the original cans). This cap is typically replaced with a low voltage e-cap.
 
So this is an split load/cathodyne driven design? I can see where the coupling cap, can make a major difference.
 
No, it is a pair of single ended power amplifiers, cap coupled to audio frequency amplifiers, where both stages for each channel reside in that channel's one tube. 6BM8 is a signal triode + power pentode.

And the two power tubes are biased with a common resistor.
 
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