Tube Locations

[duffrouillard]

Hey guys I am replacing my 12ax7 in my rm100 and just wondering if the is a diagram to show me what/where the v1 2 3 positons are so I can make sure and get the right tube in the right spot. Thanks in advance

 

[BigBrewtus]

V1 is close to the input jack and the Phase Inverter is farthest from V1.

 

[tuna141]

If I remember correctly, the preamp tube locations in an RM100 head are as follows:

Locations are described as looking at the head from the back:

V1 = right-most socket (closest to the input jack) {1st gain stage after preamps}
V2 = middle socket {effects loop?}
V3= left-most socket (closest to the power tubes) {phase inverter}

 

[JKMV12]

If I remember correctly, the preamp tube locations in an RM100 head are as follows:

Locations are described as looking at the head from the back:

V1 = right-most socket (closest to the input jack) {1st gain stage after preamps}
V2 = middle socket {effects loop?}
V3= left-most socket (closest to the power tubes) {phase inverter}

V2 is the effects loop buffer...though i believe that V1 is actually before the preamp modules. It is the first gain stage (technically first 2 gain stages b/c 12AX7's are dual triodes). Typically in most amps this is where high frequencies are attenuated so that you don't pick up radio stations. The order goes like this:

Input < Amp V1 < Module V1 < Module V2 < Tonestack < Effect Loop Buffer < Phase Inverter < Power Amp < Output Transformer < Speaker Load

For the phase inverter most people including myself suggest a Jan Phillips 5751 because it adds clarity and cleans up the noise (at least in my case). Mine has been going strong for about two years now. It is a great tube. It has similar characteristics to a 12AX7 except it has a slightly lower amplification factor (i think 70 instead of 100). I highly recommend this tube. For the V1 in the amp i have been using a Tungsol 12AX7 and i haven't found any reason to change it. The tubes i usually swap are the module V1 and V2. For high gain i usually keep a Ruby 12AX7AC5 HG in the V2 and change the V1 until i find my favorite combination.

 

[nomad100]

I was suppressed how much i liked the ruby tubes in the modules. I still have a JJ in the V1 but with everything else Ruby except the phase inverter it sounds so much better.

 

[tuna141]

Thanks for the "1st gain" correction JKMV.

I use a 5751 in PI too, and it works well. I actually had a 12AY7 in there for a short time, but found it reduced the gain too much. The 5751 sounded better/more alive.

 

[Kapo_Polenton]

What do you guys make of using balanced/matched preamp tube for the phase inverter? Right now I've got a chinese in there... crunch city.

 

[tuna141]

I've read conflicting reports regarding the use of a balanced PI tube. Some say it matters and others say that it actually sounds better if they are unbalanced/unmatched.

I tried the balanced route a few years ago and did not notice any difference in my amps (tried with a few of my Mesa Mark series amps).

So now-a-days, I usually just try a lower gain tube in the PI of my amps and don't care if it is balanced or not. I find the 5751 works great and allows you to turn-up the power tubes a little more for a slightly thicker/richer power tube generated tone.

 

[JKMV12]

What do you guys make of using balanced/matched preamp tube for the phase inverter? Right now I've got a chinese in there... crunch city.

balanced triodes and matched preamps tubes are two different things, though the tests can be purchased together.

If a tube has balanced triodes then that means that both triodes in the tube have the same or extremely similar characteristics (i.e. amplification factor, anode resistance, transconductance). This reason some people use this for phase inverters is due to its functionality. The phase inverter is designed to take the ouput signal of the entire preamp (amp V1, module, and effect loop) and make two copies of it that are 180 degress out of phase with each other (they are opposite). They do this because in the power amp there are essentially two power tube sections in parallel and each one needs a signal that is opposite to the other. This is called a push-pull power amp. So having a preamp tube in the phase inverter that has balanced triodes is theoretically more effective. I am not suggesting it but simply state the facts. I personally don't get balanced triodes but i may try it in the future.

Now matched preamp tubes is exactly what you think...two or more preamp tubes that are specifically chosen because their characteristics are the same or very close. I personally don't see any point in this because there is no real advantage to it. The differences among preamp tube of the same kind (i.e. 12AX7) cannot be that significant that it can improve or ruin an amps performance. The tone and performance of the amp is determine by the design of the gain stages which are usually based on the ideal 12AX7 tube. A slight change in the specs of the tube will not cause a serious change. If anything it will add that subtle tonal characteristic that you either like or dislike. So having all your preamp tubes essentially identical is not worth the money imo. The idea behind it is that all gain stages are designed for the ideal preamp tube. Though i think that having preamp tubes with slightly different characteristics would be more desirable because it can make your tone more unique.

Summery:
Balanced Triodes: a logical test that can theoretically improve the performance of the power amp.
Matched Preamp Tubes: based on a logical concept but is not practical.