Pop is heard then volume cuts out, returns seconds later, recurs

sounds like a bad tube or your transformers shot

I bought a 3rd B212D unit that powers on, has white noise, no music. I took the 8 screws off and discovered that the solder connection at the woofer had broken off. I surmise that either the unit was dropped or the speaker wire had gotten hot over the years. Since the amp had an open output from the break, the high output burned up as I heard a pop when I turned the volume up. . If your volume wasn't maxed out, you could check the wiring and make sure it is connected & save yourself some change!!!

Sounds like output valve, if the amp is more than few hundred hours then suspect this for sure. I don't know much about this amp specifically but does the sound fade/return suddenly or over a few seconds? Try running it with the back off and fan on the valves etc. Then play at loudness where problem occurs and see if any improvement. Remember that at band practice you always play much louder than you think and put a lot of stress on it.

You had best get a second opinion! When somebody says "there is something wrong" means they don't really know the details enough to give you an estimate even. If the amp cuts out sharply I would suspect that: 1. Bad volume control 2. Cracked circuit board 3. Bad solder joint on circuit board 4. Bad jack. These are in order from least to most likely.

I have answered some of this before, however I have reveiwed the schematic and as an electrical engineer I want you to do a couple tests.

First, plug in a set of headphones into the preamp out jack. Note that due to the impedance mismatch what you hear will not be very loud. Now change the state of the clean OD. Did you hear a faint pop?

Next plug a LOW impedance device OR even an instrument cable into the power amp "input" jack. Do this with the power off then warm amp up.
Now, change the state of the clean OD. Did you hear a faint pop?

Now for the analysis. If you did hear one in the first test and NOT in the second, the pop you are hearing is the "NATURE OF THE BEAST".

I can tell you from the design that the pop you hear is from coupling within the clean and OD relays within the unit. There is no cure for this within the unit other than find another brand...

I would recommend that you use an EXTERNAL pedal for the effects you want rather than trying to use the clean OD in this amp. I suspect it was never intended to be shifted during playing as I can guarantee it will pop when you shift while having anything other than dead silence (not even a bit of hum from your guitar). There is also statistical noise in the preamp that the laws of physics will not let us get around that may be enough to create a bit of a pop.

You could also use a volume pedal between the preamp output and the power amp in to throttle the volume to zero before shifting to OD.

In general I think you will find that what you are hearing is the nature of this beast.

Not likely preamp tubes. If they cut out they would fade slowly then come back slowly...

First check for marginal input jack. These take a beating and get loose and poor contacts. The vibration can cause the contact to be lost.

Also volume controls can get marginal...

Try to catch it in the act and tweek things to find someting that is affected.

Another common problem is contacts on jacks meant for effects inserting. These pass the signal through switch contacts when nothing plugged in and those contacts are "junky" to say the least.

It is unlikely that your actions with the plug strip caused any permanent damage to your unit.

If you unit has a digital effects unit, probably the setting for that got disturbed and you need to reset it to your desired setting.

You have a broken solder joint. You'll have to disassemble the amp enough to get at the soldered side of the circuit board that the controls are mounted to and touch up any suspect solder joints. Just be sure to resolder only the joints that were originally soldered or need to be soldered. Hope this helps.

try cleaning the send and return sockets with switch cleaner or WD40

90 % of these types of problems are caused by faulty leads .... make sure that you have correct speaker cables and not just a regular guitar cable