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Stupid 5w SET Amp

My SEXy SET
sexknob.jpg
 
What is the life expectancy of the tubes in the amps we have been talking about? The tubes that normally go in the Olson amp?

These: EL84/6BQ5 output tubes, a 12AX7 driver, and EZ81

I love the pictures of the amps you guys have been putting up!!
 
I have an Almarro A205, like the one that Urizen posted, and the current tube complement has about 3500 hours of gentle use on it, with no problems. Fisher-branded Mullard 12AX7, and Matushita EL84s.

No EZ81, though, so I can't comment on that.
 
luvvinvinyl said:
I have an Almarro A205, like the one that Urizen posted, and the current tube complement has about 3500 hours of gentle use on it, with no problems. Fisher-branded Mullard 12AX7, and Matushita EL84s.

No EZ81, though, so I can't comment on that.
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Thanks, just trying to learn all I can about these things.
 
Tube lifetimes can be very long. Small signal tubes may last for decades; power output tubes should last years depending on how conservatively the circuit they're in is designed.

As I recall, the Western Electric 300B was designed for 10,000 hour MTBF.
 
What he said!

If the tubes are run conservative you should get many many years of trouble free and full
service from any tube, output tubes "generally" not as long as inputs but circuit dependant.
 
For those of you who were asking about the 71a. It is an earlier tube than the 45. Lots of radios used them in both class A and Class AB. The class a uses would normally be in low output for battery radios but higher output than a 201a or a 10 could deliver. An example of a radio that used a 71a as a class A output tube would be a Radiola 17 which was made around 1927. Most A/C sets would have had a pair of 71a's in Push Pull. Interestingly enough the 71a like I said was actually developed for DC operation in Battery sets, but it heavy filament allowed it to perform satisfactorily in A/C filament circuits.

Now "in the day" no self respecting "hi fi" set would be caught dead using any of these tubes in class A operation. Not saying that to stir the pot just an interesting point.

The 45's didn't come out till around 1930 and were a true A/C filament tube.

For even less power and further "fleaness" go for a 12a or 10 even less power than a 71a.

Steve


http://www.radiolaguy.com/Showcase/Radiola17.htm
 
Here is the latest incarnation ( I think ) of Nate's Dolly SE 6BQ5. Good things do come in small packages :thmbsp:

RC
 

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I've heard one...

Cut-Throat said:
Well I was referring to current production amps, I just digressed on the old table radios and juke boxes. I did not realize that the 71A was used them also. In fact tonight is the first time I've heard of a 71a.
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Chiming in a little late on this thread, but I've heard a 71A amp on my M19's and IIRC, my Simplex VOTT's. I'd like to compare it again to my 45 SET amp, because as I recall, it was making some of the sweetest sounds I could remember hearing at the time....:thmbsp:
 
analog addict said:
Chiming in a little late on this thread, but I've heard a 71A amp on my M19's and IIRC, my Simplex VOTT's. I'd like to compare it again to my 45 SET amp, because as I recall, it was making some of the sweetest sounds I could remember hearing at the time....:thmbsp:
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How about 76s driving 71As?:scratch2:
 
jaymanaa said:
How about 76s driving 71As?:scratch2:
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Now you're thinking....:thmbsp:

I can get more of the 76's if necessary. Helps to have a huge antique radio collector as a co-worker/friend....:yes:

So Jay if you get something like that up and running, be sure and send me a copy of the schematics....:scratch2:
 
analog addict said:
Now you're thinking....:thmbsp:

I can get more of the 76's if necessary. Helps to have a huge antique radio collector as a co-worker/friend....:yes:

So Jay if you get something like that up and running, be sure and send me a copy of the schematics....:scratch2:
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You bet.:thmbsp: I haven't even looked up the specs on the 71A, but I think someone said .8 watts. I would "assume" it would like about the same load (meaning OPT Pri. Z) as a 45, but I'll have to take a look.
 
76 is essentially a 6J5 (half of a 6SN7) so it should work well. If you have a 7A4 in your loctal stash, though would be a suitable substitute, as well.

5k for the opt is probably where you want to be. There are a few schematics on the net for 71As, one uses transformer coupled 01As driving the 71A.
 
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