Little-Bear B1 modding..

Status
Not open for further replies.
Jump to Latest
#21
I obtained an older power supply (phone) which put out 7 volts out of the circuit and 6.3 installed. I have found that any voltage under 8 to 9 volts will not let the amp work properly. At lower levels it sounds fine but at high volume levels it seems to crackle, especially when much bass is playing. I have come to the conclusion that the twelve volts to the heaters is needed to match the circuit of the amp and allow the tube to function at it's fullest potential. It sounds great at 12 volts. I just purchased two spare 6111's and when it burns one out I will replace them. I did notice that the tube on the most recent amp I purchased is a clearer tube and is of a different shape that most 6111's. Yep, it stills gets hotter than an firecracker.

ie: 5.3 vdc to heater-----horrible sound reproduction
6.3 vdc to heater---acceptable reproduction but distorted at high volume
9.0 vdc to heater---a little better but not acceptable on Audio Technica
M50x's
10, 11, 12vdc to heater--great sound at highest volume on Audio Technica
M50x's
I think we may be expecting too much from a $50 to $70 unit.
 
#22
There is a little amp kit from Fred's Amps in Australia that uses a 12Au7 that sounds great! It is not a rechargable unit as built but I converted mine to recharge using a battery and charging system similar to the B-1. The tube is not included with the kit but are not that expensive and it lends to tube rolling. If I remember correctly the kit is $36.00 plus shipping. He also guarantees the amp even if you screw it up assembling it. I will attempt to post a pic of a couple of completed ones that I have assembled for my grandsons. Just thought I would throw that info out there. I purchased mine through EBay.
 
#23
Mine doesn't crackle at high volumes probably because I am using low impedance headphones at low to moderate volume. I'm pretty satisfied with it, after the modifications 😉 My only concern is the battery, it seems to be three phone lithium batteries in series. After those wear out, and they will, the heat and the somewhat quick discharge cycles don't help, I don't know how I'll find replacements to fit in there.
 
#24
DanManDMC said:
I obtained an older power supply (phone) which put out 7 volts out of the circuit and 6.3 installed. I have found that any voltage under 8 to 9 volts will not let the amp work properly. At lower levels it sounds fine but at high volume levels it seems to crackle, especially when much bass is playing. I have come to the conclusion that the twelve volts to the heaters is needed to match the circuit of the amp and allow the tube to function at it's fullest potential. It sounds great at 12 volts. I just purchased two spare 6111's and when it burns one out I will replace them. I did notice that the tube on the most recent amp I purchased is a clearer tube and is of a different shape that most 6111's. Yep, it stills gets hotter than an firecracker.

ie: 5.3 vdc to heater-----horrible sound reproduction
6.3 vdc to heater---acceptable reproduction but distorted at high volume
9.0 vdc to heater---a little better but not acceptable on Audio Technica
M50x's
10, 11, 12vdc to heater--great sound at highest volume on Audio Technica
M50x's
I think we may be expecting too much from a $50 to $70 unit.
Click to expand...

I dont understand this at all? Are you lowering the voltage for the entire amp ,or just the heater filament?

You need the tube plate voltage, and the supply voltage to the opamp to remain at 12v, then lower the voltage to 6.3v for the tube heater.
 
#25
DanManDMC said:
There is a little amp kit from Fred's Amps in Australia that uses a 12Au7 that sounds great! It is not a rechargable unit as built but I converted mine to recharge using a battery and charging system similar to the B-1.
Click to expand...

That looks like the same circuit, though a 12au7 as its name suggests can run on 12v which makes things a little easier.

redshot said:
Mine doesn't crackle at high volumes probably because I am using low impedance headphones at low to moderate volume. I'm pretty satisfied with it, after the modifications 😉 My only concern is the battery, it seems to be three phone lithium batteries in series. After those wear out, and they will, the heat and the somewhat quick discharge cycles don't help, I don't know how I'll find replacements to fit in there.
Click to expand...

Mine comfortably plays into the too loud territory too. With the voltage regular i am using the only heat source in the amp is the tube itself so the battery doesn't really heat up. You can buy the battery's on there own on eBay should you ever need one.
 
#26
Hey guys, Well I finally got the lIttle Bear running correctly with a cell phone board. It sounds great and functions at all volume levels. The tube that was in the amp had either burnt beyond usuable like or something. I put a new 6111 in it and purchased a $5 car charger at Walgreens and walla! Thanks for all of your help on this project.

P.S. Has anyone noticed that there are no Little Bear B-1s on EBay anymore. There is only one like it and it looks to be a rebranded Muse and they want $109 for it. I was going to get another and mod for my grandson but can't find any. Maybe the Chinese holiday and they are going to wait and list them after it is over.

Anybody out there have one for sale? I would purchase it if so. Just let me know on this forum.
 
#27
I suspect it is due to the holidays as none of the regular sellers are listing anything at the moment.

Dead tube, almost certainly caused by the wrong heater resistor putting 12v across a 6v tube, mine was toast too after a few hours use.
 
#28
I probably wasn't clear on my previous post. I installed a new 6111 tube and a phone charger board inside the amp to get 6 volts to the heater rather than the ridiculous 12vdc. Running great, once I let the tube warm up a minute or so..

I am running a test on another new 6111 now on a 12 volt power supply to see how long it will last before blowing the heaters. It is so hot that you can hear it sizzle when licking your finger and touching the tube. It has been running for 4 hours and still burning, but when I took the power off to look at it the inside of the tube is totally black. Probably would not function correctly in the circuit as it is now. I'll let everyone know how long it will burn.
 
#29
What your going to get is migration from the filament onto the anode, plates, and glass which is the black staining you will see inside everything. I belive its tungsten migration, you will also see it on tubes that have very high hours on them. Result will be the tube emission will drop off to next to to nothing long before the actual filament gives up and breaks. Like i said, after an hour or so running like that, its F'd.
 
#32
Is there some type of adaptor to hook headphones up to a power amp that does not have a headphone jack? I would guess it needs to drop the signal dramaticly as to not blow the hell out of my phones.

I have no idea to begin on the construction of one. Thanks in advance for ya'lls help
 
#34
I know its a bit late, but forgot about this project for about a year and recently dug it up, I`ve installed the traco module and an 20k log alps pot, however the volume is still scratchy and doesn`t seem logarithmic (it doesn`t change for about a third of a turn then rapidly increases, the minimum volume is quite high) and after installing the traco module, there is a large amount of hiss. I burnt off some of the tabs on removing the old potentiometer so the new one might not be grounded properly or something since I`ve just wired it to the component along the path. I can post pictures of the board, any ideas or fixes for this?, thanks in advance.
 
#35
 
#37
Very interesting, i see they added a small boost supply for the heater circuit like we have been doing with the Traco. I wonder if they read this thread..

Price is a bit steep though, especially when you could buy the older version and add a Traco regulator yourself for $10-20.

I also bought one of the v1.2 board models, but there is nothing of any real note that is different inside it. The main difference is they added a huge 6800uf cap to the opamp supply to try and null out the shutdown pop. meh.

KatieandDad said:
I used Obligato PIOs they are very nice and fit the original B1 board very well.
Click to expand...

Link? I've never seen a small Obligato, let alone one that would fit inside a B-1
 
Status
Not open for further replies.
Top Bottom