Building Started...

[Grainger49]

Randy,

That is beautiful work.  It is so neat it looks like a military piece of equipment.  It makes my first Bottlehead build look awful. 

I took my time and built my Eros over a week's time.  It got a full treatment of heat shrinked STP ends with different colors for right and left.  I built stock to begin with.  Now I have trouble taking it out of the system to put in some upgrades I bought.  I just love listening to it too much.

 

[rlyach]

Thanks for the compliments on the build. The instructions deserve most of the credit. I just took my time. I also wanted to mention that the voltages came in very close to the expected values. The 2A3 cathodes were both right at 61 volts. The 2A3 plates were both exactly 360V. The B+ was 388V on both left and right channels. I also noticed that the plate voltages of the triodes in the 12AT7 did not match exactly. One was 214V and the other was 207V. I suspect the difference is because the 300K bias resistors in the C4S board did not match exactly. This wont matter though as the flat load line will keep the tubes output swing the same, and since they are AC coupled to the power stage the DC difference will not matter (correct me if I am wrong). It is very gratifying to see that the voltages matched the calculations and the simulations I ran using the published plate curves for the JJ tubes. Thanks again for all the encouragement. I think I may try and build the Toad guitar amp next. I thought about building speakers but I am not much of a wood worker.

 

[Paul Birkeland]

One was 214V and the other was 207V. I suspect the difference is because the 300K bias resistors in the C4S board did not match exactly.

That voltage difference is a matter of different emission from each triode of the 12AT7.

You could alter the 300K resistors to be 250K-350K and you'll still see the same plate voltages you have now.

 

[jrebman]

Randy,

Glad you got it done and  it sounds good so far.  Just wait until you get those Orcas, and by the time the Orcas have their full break-in time, the amp too should be well seasoned and I'm predicting you're going to be amazed at what  you hear.  The JJs are really great tubes and you have to spend a whole lot more to better them, and even then, no telling how much of an improvement it may be to your ears.  Plus they're built like tanks and are run well under their dissipation limits so they should last a very long time.

-- Jim

 

[rlyach]

Thanks for the info on the 12AT7. I wonder if you can get one that has matched triodes? Yes, the JJ's are very nice tubes. The glass is very thick and the tubes look nice as well. One more piece of data. I used the min/max function of my DMM to measure the peak output voltage into my 8 ohm speakers at full volume. I measured 5.93V p-p. That calculates to 4.39 Watts of peak power from this amp. I realize this is a simplistic way of looking at it but it does match my simulation and hand calculations very well. I may get ambitious and hook up a sine wave generator to the input and measure the output for power and distortion. Thanks again for all the help understanding the inner workings of this amp. I have really enjoyed the building process.

 

[jrebman]

Just ask for/look for a tube with matched sections.  That said, I think you'll be very hard pressed to hear a difference with the tube you have.

-- Jim

 

[Paul Birkeland]

"Matched" tubes can mean a whole lot of things.  You can turn the volume knob all the way up, then put 60Hz of tone into the amp input, then measure the AC voltage at 4 and 12 to see how well the tube is gain matched. 

 

[drewh1]

Replying to your earlier post - I want to build some speakers too, likely Full range in a Transmission Lline -  too bad you are not in the Bay area, I am more of a wood worker than analog elec. guy, so I could help you with the speakers and you could help me with all this other stuff. 

There are some kits that let you buy the wood pre-cut, so all you have to do is assemble. At any rate, let me know when you want to get started and I will offer any advice that I can.

drew.

 

[Paul Joppa]

The plate voltages of the 12AT7 are unusually close together already. Normal tubes will vary +/-30% or so - the circuit is designed to accommodate this variation. (Transistors are much worse, the gain of the 2N2907A for instance is between 50 and 300...)

The output tube has some DC feedback in the form of the cathode bias resistor, which more tightly controls its operating point. The bypass capacitor removes teh feedback at audio frequencies.

One of the unique things about SET designs is that they generally do not use negative feedback, at least in the audio band. This makes them more susceptible to parts variations, and to various sources of noise and distortion - but it also makes them sound more natural, at least to the ears of very many observers.

 

[rlyach]

Drew,

I was also looking at building a full range single driver using a fostex 4" driver. I also looked at the available kits but it is hard to find high efficiency drivers. This is why I ordered the Orcas in the first place. The added benefit of the Orcas is that Blumenstein also sells bases for the Stereomour that match the speakers. This helps the wife acceptance factor  ;D.

Paul,

After looking at what is available in balanced 12AT7's, my 3.3% difference is indeed looking pretty good. I am amazed that everything else in my amp matches to less than 1V. I did go to the extra trouble of measuring all my components and using them in the A or B side in order to keep the total DC resistance identical. I got within one ohm through the choke, the hum circuit, and the cathode circuit. I am also glad I purchased the Goldpoint Attenuator. The sound is smooth and matched all the way down to low listening levels. I also do not hear any switch noise while changing the level. This was probably an extravagant upgrade but I am glad I did it.

Randy

 

[rlyach]

My Blumenstein base arrived but I am still waiting for the Speakers. Here is the amp from the top. I really like the dark base contrast with the plate and the polished chokes and transformer bell. 

 

[Doc B]

We got a new carmelized base in from Clark and Molly a couple days ago. It was done to a really nice deep brown too. Looked sexy, wish I had thought to take a pic before shipping it out.

 

[Grainger49]

Randy,

The polishing looks great in these pictures.  I can see the end bell and frames better in these pictures.  Exactly, great contrast!

 

[rlyach]

Just for fun I built this removable pilot light for my amp. I took a 9 pin socket saver, removed the center screw, and placed a 12-16V amber grain of wheat lamp in the hole, soldereing the wires between pins 4 and 5. I can use the adapter if I want the pilot light or remove it if I don't. I haven't heard any difference in the sound yet but I will listen more closely when my Orcas get here tomorrow. Can't wait.

 

[drewh1]

You must be so excited to hear those speakers - just like christmas.  I can't believe my kit hasn't shipped yet, it better ship soon or will have spent all my money on stuff before it even gets here.  I am still looking at drivers, have found a number that are 96db and higher, expensive though.

Hey, let me know if you want to do DIY interconnects. I have built about 6 different versions and really like the fine magnet wire versions.

drew.

 

[rlyach]

Yes, I am really looking forward to finally hearing the system. I ordered the kit and speakers on the same day (1/11/13). I guess Blumenstein has been very busy with a lot of backlog to build. Now the only decision is what song to play first  .

 

[drewh1]

well, I am not a big fan of the idea of electronics "breaking in" but speakers sure do need a break in, so if they sound great right away, just know they will only get better.  Also, if you are like me, you'll spend at least a week moving them around to get just the right listening position and bass response.  All in all, you are going to busy with them for a while!

 

[Grainger49]

  .  .  .    Now the only decision is what song to play first  .

I always go with CS&N the first LP.  I have a Classic Reissue Remastered.  It is better than my first pressing of the LP.

 

[drewh1]

Now available in 24/96 khz remix on HD tracks. 

 

[rlyach]

My Orcas came! WoW. I have never heard anything like what I am hearing from the amp and the Orca speakers, and it keeps on getting better the more I listen. My wife even commented on the sound. Now I really notice the difference in recordings. I guess all recordings are not created equal. I am streaming my music digitally through a tos link cable to a Cambridge audio 24 bit DAC, and then to the Stereomour. I know many of you are cringing because I am streaming digital music, but I can't get over the sound. I am a very happy camper. I have this system in my bedroom and it fits perfectly. It even looks nice.