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Bijou All Tube Futterman Headphone Amplifier - Page 264

post #3946 of 4171

no not really, But i figure it would be a nice preamp:) ivegot a grate problem though , both my psus without load they give a nice 250V output however one of them today magicly decided that when it sees load it should drop to 150v. I am so confused i tried everything with no result, any ideas?

post #3947 of 4171

I would suspect the fets since they seem to be most likely to fail.

 

You can try to measure resistance at different places in the circut and compare to your working PS,  I think thats a pretty good way when you don´t know what to do.

 

Im thinking about the possibillity to dubble up the ecc99s and use them in paralell with the original ecc99s, would it be woth a shot?

 

http://imageshack.us/photo/my-images/546/ijoudualver2.gif/

 

In my head this would lower the output impedance and distortion, am I right?

Or would all benefits be lost because of the increased load on the phase splitter?

Do I need to change R9,11 and C3,4?

 

Edit: Im done with my listening test, 6n6p vs ecc99 and I prefer ecc99. They seem more detailed and dynamic.

 


Edited by vlb - 7/17/11 at 12:46pm
post #3948 of 4171

oh boy bad fets. just replaced them with some irf840 to be fair they run hotter but who cares ? they work:) 

post #3949 of 4171

I recently got hold of a perfectly matched pair of 12AU7WA's. Has anybody tried these as a replacement for the ECC99 output stage tubes?

 

Regards,

Snoopy

post #3950 of 4171

I don't believe they will work, as they use 12.6V heaters.

post #3951 of 4171
Quote:
Originally Posted by _Snoopy_ View Post

I recently got hold of a perfectly matched pair of 12AU7WA's. Has anybody tried these as a replacement for the ECC99 output stage tubes?

Regards,

Snoopy

 

The pinouts are the same and many of the specifications are close enough but there are some differences. The maximum cathode current of the ECC99 is 60mA verses 22mA for the 12AU7WA. Also the maximum plate dissipation for the ECC99 is 5W verses 3W for the 12AU7WA. I don't know what the Bijou is drawing and I am not 100% confident (yet!) in the proper equations to compute said values. As such, I would be hesitant to try the 12AU7WA.


Edited by balderon - 7/30/11 at 1:42am
post #3952 of 4171

We use 230V mains here. I wonder if it is desirable/possible to build a version of Bijou that runs without a transformer?

post #3953 of 4171

The output impedance with a 12au7 will be much higher than with the ecc99. The operating points will also need to be changed to fit the tube. 

 

I dont think that matched tubes will make a difference in a Bijou anyways, save them for somewhere where they might.

 

Quote:
Originally Posted by Navyblue View Post

We use 230V mains here. I wonder if it is desirable/possible to build a version of Bijou that runs without a transformer?


It is possible to build all sorts of mains-coupled amps. Dont. It was common practice in older table-top radios to try to save money. They stopped production really quick when they realized how easy it was to electrocute yourself - without opening the case. 

 

post #3954 of 4171

Thanks for the input, folks. So I think I'll stick to the ECC99s.

 

post #3955 of 4171

Guys any shop which sells perfectlu matched tubes?

post #3956 of 4171
What is your definition of "perfectly matched"? With tubes, "close enough" is probably a better target.

Lot's of places will match tubes within a few percentage points. Realize, there is no guarantee they will actually perform identically at your operating point. Matching just means they tested close at a particular test point which is generally not representative of the actual operating conditions the tube will be used at.
post #3957 of 4171

so matching them myself would be the best way right? any easy way of doing it no scope or signal generator here :/

post #3958 of 4171

 

Quote:
Originally Posted by yiancar View Post

so matching them myself would be the best way right? 

 


Forgetting about matched tubes would be the best way.

 

It may sound somewhat generic at first glance, but is the quest for matched tubes on an amp that does not require them any less generic? Its really a generic quest in many amps... something people do for no reason other then that's what they generally do. 


Edited by nikongod - 8/9/11 at 10:19am
post #3959 of 4171
Quote:
Originally Posted by yiancar View Post

so matching them myself would be the best way right? any easy way of doing it no scope or signal generator here :/


So, to pull on the comments from Nikongod a bit farther, why do you believe perfectly matched tubes are important?

You could certainly test with a tube tester. You could also test them in circuit if you want to go through the effort. That would probably be more accurate. One could argue you should also modify the circuit appropriately to find the "sweet spot" for a particular tube or set of tubes rather than search for the perfect tubes for the circuit.

It really depends upon how much work you want to put towards it.
post #3960 of 4171

On a balanced bijou, should the left and right channels be in phase or out of phase? What are the benefits and repercussions of each?

 

Thank you!

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