audio lecture 53, 12AU7 vs 12BH7, simple theory and real application test 

Mr. Ahn, I appreciate your attention to detail. Reliability (confidence) is often overlooked by those seeking momentary, fleeting or imaginary performance gains. It's refreshing to see truth in such a subjective topic.

Some good info here but a few things not mentioned or not clear. Yes you can use a 12BH7 in place of a 12Au7 with Caution. You can't just put them in because the current draw is much higher. I have a preamp and an Amp that use 12AU7s a conrad johnson PV-10A, I can't put 12BH7s in because the power circuit for the heater voltage can not handle the current draw. I also have a VAC PA 100/100 Amp that is designed to use either 12AU7 or 12BH7. So you can't just interchange these tubes unless you really look and the specks on the Preamp or Amp. Also you said why would we use a 12BH7 instead of a 12AU7 the main reason should be sound. The 12BH7 leans toward a richer sound in most circumstances, than it comes down to personal taste on if you like the sound better and than every manufacture sounds a touch or a lot different so it makes Tube rolling much more open to find the best tube and sound for your system. That should be the main reason you would use a 12BH7 over a 12AU7.

what about 12BH7 driving parallel pushed pull EL84 ? theortically 4 el84 power requirement is similar to 300b, so it seems 12BH7 would be a suitable driver in this situation

What is the heater current? In a guitar amp repair shop, we had to be careful when swapping a 12ax7 with a 12au7 that we didn't exceed the heater power supply ratings, and wreck the power transformer.

大変に参考になりました。

Hello Young Ahn, You seem to be knowledgeable about preamp tubes, power tubes, circuitry and Hi-Fi amplifiers. Perhaps you would engage in a RU-vid conversation with me about something I am doing at present. I have a headphone amplifier that uses the 12AU7 in the power output section. I have not measured the output but it should be around 1 watt. It is a stereo unit, but I believe I am only using one side connected to the guitar speaker(s). I have installed in series a preamp using the 12AX7 to drive the 12AU7 headphone amplifier. I can actually drive a 12" 16 ohm guitar speaker or a speaker cab with (4) 10" 8 ohm speakers for my guitar playing. For clean I set the 12AU7 at about 1/2 volume and it is clean, just not annoying loud. Nothing wrong with that. For distorted tones I set the 12AU7 headphone amplifier for above 1/2 to max volume and also set the 12AX7 preamp module to above 1/2 volume to full volume. The Behringer Tube Ultragain MIC100 module using a 12AX7 preamp has a gain control that I adjust to taste, as well as limiters. A nice uint for only $39. This cobbled together guitar amplifier can be annoying loud on the hi-gain settings. I played for over 1-1/2 hours last night and when I stopped, to my surprise my ears told me that they had been abused a little. On a 1 watt amplifier I asked myself, yes is the correct answer. As I understand it, the purpose for the very existence of a 1 watt guitar amplifier is to prevent hearing damages while still obtaining hi-gain guitar tones. I must admit I was also using an Ibanez Tube screamer at times and also a ProCo "Rat" guitar pedal to smooth out the clean volume and to add more gain for my hi-gain tones and also to increase the volume. Maybe that's why my ears suffered. The cobbled together guitar amplifier will not hurt/annoy my ears without these distortion/volume increasing guitar pedals. They call the Ibanez pedal a "Tube Screamer" no less and the name aptly applies. The ProCo "Rat" is even more powerful. Marshall Amplification has just come out with a new 2018 DSL1H guitar amplifier head in 16 ohms that is a 1 watt head for guitar. It has two seperate channels and both use the 12AX7 (each with a 100% gain factor), it has a power section which uses a 12AU7 (16% gain factor). This is what gave me the idea to cobble together the $29 Behringer Tube Ultragain MIC100 (microphone and line preamp) in front of the $79 Bravo by Audi (Chinese ) headphone amp. I wanted to try a low output guitar amp. My question is do you think that if I substituted a 12BH7 would I get more output watts/volume from the headphone amplifier that is at present using a 12AU7? I have a concern that the headphone amplifier may not be able to withstand the 12BH7 tube. However, before this I had substituted a 12AX7 and also a 12AT7 in the headphone amplifier and used it in series (in front of) the Tube Ultragain MIC100 preamp just to add tube preamplification to all my existing SS/Digital Guitar amplifiers. This worked with no problems. BTW yesterday, when I substituted a 12AT7 into the headphone amp when I was using the cobbled together rig as a guitar amplifier the output was so very hi-gain that it was completely unusable as a guitar amplifier. It was actually the sound of the proverbial "Bees in a jar" sound! So I learned that a low output / low gain factor tube works best in that particular design. In truth I have no valid reason for more power in my cobbled together guitar amplifier as the existing rig can be very loud (with guitar pedal), but like so many selfish, greedy individuals on our planet I seek "More". Well, I am also curious asking myself is there a difference between 12AU7 and 12BH7. I have found experimenting with different tubes can yield positive results sometimes. Not always though. I put a 12AT7 in V1 of my Fender Hot Rod DeVille 410 III and the amplifier was limited to a volume setting of less than 5 out of 10 otherwise it made unmusical sounds. yest people say that is one way to lower the gain/output volume in these guitar amplifiers. I just shrugged it off, thinking the tubes were no good. But then why do they work in my headphone amplifier-I ask myself. I have another question. The specification of the Bravo by Audi headphone amplifier did not indicate the output or minimum ohm output required to not damage the unit. So I first tried it on a 16 ohm speaker and it was fine. Then the same day I tried it on 3 different 8 ohm speaker cabs and it was very good. I have a 2x12 Jensen speaker cab reated at 4 ohms which would allow for more power/volume. I hesitate to even connect them because I know most typical home stereos use 8 ohm speakers so I guessed that the unit is designed for an 8 ohm load. Confusingly, I am aware that a typical home true stereo speaker system should be using (2) of the 8 ohm speakers which is a total load of 4 ohms. So maybe I am safe. I am a little short of cash right not and could not replace the unit. I would not wish to damage my Bravo Headphone amplifier because it is sounding so good as I am using it now at 8 ohms to a single guitar cabinet. EDIT: I just looked up the specifications and output impedance: Input Power: DC24V, Input Sensitivity: 100mV, Input Impedance: 100KOhm, Out-Put Impedance: 20~600 Ohm, Gain: 30dB, Frequency response: 10Hz-60KHz +/- 0.25dB, Signal/Noise Ratio: >90dB So Out-put impedance is 20~600 Ohms! Yet it works well at 16 Ohms and even 8 Ohms. I think I well be safer using my 16 Ohm speaker cabinet. That's close enough to 20 Ohms -Peter

Please let me Audio output transformer winding formula

Lose the music and talk about what were seeing in the video. Maybe its just me but its would be nice to have this explained