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Good to hear that things are normal. How is the hum. Did it go away. If it did you may have some sort of intermittent connection. If the hum comes back check again for red plating. Also did the poping when going from standby to on stop. The poping could be a sign of arcing. You can check for...

One other thing to check is the fuse particularly since this is a new amp for you. Check to make sure it is the proper current which is 3 amp slow blow for the Mark IV. I have seen people put in large fuses so they can play their amps. This does defeat the purpose of the fuse, i.e. the amp fails...

Well your one inner tube going out twice could be coincidence but I doubt it. The hum and the tube could be related. Try switching to class A mode and see if this helps the hum. Class A basically disables the inner two power tubes. This will also allow you to use the amp without compromising...

Basically the problem you are having is pin 1 of the XLR connector (the connector to the footswitch) is stuck in a logic low condition. The problem can be in either the amp or the footswitch. It is easier to start with the amp. To check if there is an issue in the head do the following...

Ok the first thing to try is switching using the mode switch on the back of the amplifier. Looking at the back of the amplifier you will find this switch on the right side. It is round, has five positions (it is marked footswitch, rhythm 2, rhythm 1, lead and ext). Use this to switch the...

Found this evaluation of 12ax7 tube performance. fyi. http://thetubestore.com/12ax7review.html

Good luck. Let the group knows how this turns out. It is how we all learn.

Ok a couple of comments here. First having the guitar pick up the more 60 hertz sort of noise (more of the buzz sort of noise) and having it position/location dependent is normal. Single coil pickups (Fender Strats, Teles, etc) are more susceptible than double coil Humbucker pickups (Gibsons)...

If shorting the input cable killed the noise it would suggest that the amp is ok. That leaves the guitar as the culpret. Have you tried the guitar and cable in another amp to make sure that one of these items is not the cause of your noise. Also is the noise more of a buzz (60 hertz pickup) or...

Nice score. I am assuming that the noise you are hearing is 60 hertz type of noise (buzz as opposed to static). First thing to try is a different guitar cable or try the cable and guitar into another amp and make sure as a unit they are ok. Next thing you can try is the ground switch on the back...

I can't answer most of your questions directly but below is a way to figure out what is what. 1. The tubes that are on when in 60 watt mode are the outside tubes. 2. Refer to the schematic at the link below for the pre-amp-out/power-amp-in question. I am assuming the schematic labeled Mark II...

One other thing to note is that the volume control goes straight into the grid of V1B. If the grid goes positive relative to the cathod the grid will pull current. This could account for the "weird" voltage readings you encountered when you varied the volume control. Removing the wire between...

Good to hear that you located the problem. Measuring dc from leaking caps can be tricky. It is a good place to use a VTVM (vacuum tube volt meter) which has a very high input impedance. More conventional meters can have an input impedance that will sufficiently load the circuit which will lower...

So what ever happened with this amp. Did you locate the problem. Just curious.

Recently I did have a weird problem concerning the volume/tone stack. Tracked it down to a leaky cap in the tone stack. Not a bad thing to check for. Look for any dc on the tone control pots and the volume control with no input. Make readings relative to ground. An interaction with getting into...

Another good reason to leave the reverb tank connected and turn the control off. Disconnecting the reverb tank will leave the transformer unterminated. It is like not connecting a speaker to the output. It will produce a mismatch and could compromise the transformer. I have had Fender amps...

You can disconnect the reverb tank without any ill effects. The circuit that drives the reverb tank derives it signal from the preamp path, sends it through the reverb tank, then adds it back into the preamp path. So the reverb path is parallel to the preamp path not inline with it. Rather than...

Well your experience seems to support what I remember about Boogies being on the cold side. You should let the group know how your biasing experiments turn out and how you go about it. We are all interested in improving our tone and how to go about it.

I think we are in total agreement (read above). Like I said my advise to glawk was more of a judgement call for a point of diminishing returns for putting in a bias control on a simulclass. However you do have my curiosity. What sort of improvement did you get and under what conditions. How did...

I agree with dodger916 on this issue and said as much in a previous post. A counter agrument to this is that you can at least optimize one or the other set of tubes with a single bias control. This is a legitimate point of view and in principle could be done. To me it isn't worth the effort...