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 Post subject: 6BX7 amp
PostPosted: Nov Mon 06, 2006 6:21 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2834
Location: Powder Springs,Ga. USA
6BX7 amps were mentioned in another thread and I decided to try one. I found two tubes with good emission but balance left a lot to be desired. Here is the schematic. Note that it may change and will be updated as I experiment.

Schematic drawn using TUBEPAD and Microsoft Paint

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It sounds good but with eight watts has about half the power of the 6L6 predecessor amp . The 6BX7's are running at maximum power dissipation also.
Note that one 6BX7 can be removed and the amp still works. Other tubes to try are 6BL7 and possibly 6SN7.

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Terry, K4TLJ
"Never run out of airspeed, altitude and ideas at the same time"


Last edited by Terry Judkins on Nov Tue 07, 2006 9:08 pm, edited 2 times in total.

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PostPosted: Nov Tue 07, 2006 1:16 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
An excellent tube choice.

I built my stereo 6BX7 amp in 1964, from plans in the Oct. 1960 issue of Electronics World. I'm still using it as my treble amp, crossed over at 500Hz into theater horns.


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PostPosted: Nov Tue 07, 2006 1:35 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2834
Location: Powder Springs,Ga. USA
I really need a good speaker to go with it. I had an RCA center channel but unfortunately it belonged to my son... he took it home last weekend. I just might keep this one and stop experimenting. :)
Frequency response and distortion levels are very good.

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Terry, K4TLJ
"Never run out of airspeed, altitude and ideas at the same time"


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PostPosted: Nov Tue 07, 2006 2:16 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4724
Location: Freehold NJ 07728
Nice job Terry,
I am working on my killer 1 watt tube amp now to get it to sound better. How long did you work on this one?

Regards,
Sal Brisindi

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Need capacitors, resistors and other parts--> http://www.tuberadios.com/capacitors


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 Post subject:
PostPosted: Nov Tue 07, 2006 2:33 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2834
Location: Powder Springs,Ga. USA
Sal Brisindi wrote:
Nice job Terry,
I am working on my killer 1 watt tube amp now to get it to sound better. How long did you work on this one?

Regards,
Sal Brisindi


A couple of days intermittent dabbling... retired you know...

I may fine tune it a bit more. Most of the circuitry was retained from the 6L6 amp that you saw when here last Spring. I installed a 'real' ten Henry choke replacing the power transformer primary choke that was used in the 6L6 amp. That got the ripple down to half a volt to the output tubes. I kept the Hammond organ output transformer though. That is the big open frame transformer in the photo. Considering splitting it up and making a stereo amp.. I have another output transformer.

It drove the RCA speaker to good volume at max power out and can get really too loud when connected to my homemade speaker with the efficient 12 inch speaker.

I have to judge the fidelity with a scope and audio signal generator though. My antique ears have a cutoff around 4 Kc. :) I was using a 10kc sine wave input at maximum power to check when clipping started and could not hear it at all. Bet the dogs in the next county started barking. Most of the old radios sound good to me...

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Terry, K4TLJ
"Never run out of airspeed, altitude and ideas at the same time"


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