SOme different resistors or caps going to the heaters is my guess what you need.
The voltages in you MAC are out of control when any sort of surge.
Some preamps eat tubes. Most d onot.
IMO usually unless a design flaw, eating tubes is a (as I mentioned) some sort of error in the resistors/caps feeding your tubes.
This is entirely hearsay, as I am not a tube maven.
That's the way it is. Tubes are best when they are new and they are slowly wearing as they accumulate hours. Some brands of tubes can be hardier than others in situations where they are driven hard, but which brands will hold up better in your preamp may be a matter of trial and error. However, you may find a tube that lasts longer, but there is no guarantee you will like the sound as well as the tubes you are using now. Mullard CV4004 (12AX7) are about as good as it gets, but supplies are running out, so don't wait.
I think Liz is on to something,low level signal tubes in my own experience have maintained sound quality for 'many years' before needing replacement. A good tube should`nt wear out that early.
Did you speak to the manufacturer about this problem? It clearly spells the design flow of using maximum bias to the tube for the maximum gain. That's why I tend to like more solid state phononstages. If you like sound of your Mac preamp, you can get an outboard SS phonostage(Pass X-Ono or similar), you'll still be able to benefit from valve preamplification.
Personally, I would have called Mcintosh with the second incident. Mullard is a quality tube and my experience is that they do last beyond 10,000 hours. You might also get some good feedback by redirecting this post to Audiogoners that own a MAC C220. Good Luck!!
A line disruption should not affect the tubes at all.
OTOH, it is normal for signal tubes to start out quiet and slowly built up noise as they age. In the old days there were some tubes that were rated for 10,000 hours but no-one does that today. So you may just have to replace tubes every 2000 hours or so.
If you run a high output cartridge the tubes will seem to last much longer! 10,000 hours might be quite reasonable then.
If you leave the preamp on 24/7 you are wearing out the tubes needlessly. Its best to start up the preamp about an hour or so before listening.
Time for a pre evaluation with mac. Jallen
If your C220 is blowing tubes consistently what about the internal fuses?
Sorry to intermit, but OP is just changing tubes once they become noisy and not necessary bad or blown.
According to Atmasphere it's the usual nature of signal tubes to build up noise and I tend to agree with him.
JFET phonostages are substantially better than valve especially if tube noise is of any consern.
Did this also happen prior to your acquisiton of the MEN220? I'd take the MEN220 out of the loop and see what happens over a period of time. How old is the MEN220? If fairly new (within last 6-9 months or thereabouts), the issue has been resolved.
The early MEN220's caused MC501's to run extremely hot on one side of the heat sinks because of a design issue. There were reports of this design issue also affecting other McIntosh amps like the MK1.2's (IIRC) & not sure if the MC402 was also included since it's a stereo amp vs. a mono.
Tubes should last along with the guidelines you expect & certainly longer than you've experienced.
Just my 2 cents.
You folks have been great and I do appreciate the time you've all taken. In response to one query, the MEN220 is new, and I had had three of these tube replacement occasions before I installed the unit between the C220 and the MC402.
One other thing came up this afternoon. As I'd mentioned, I had had a "trigger" cable connecting the C220 to the MC402 but not one connecting the MEN220 to the two other components. When I had previously powered up the C220, the MC402 powered up without incident. Now I have added another cable to get the MEN220 into that trigger chain (and have ascertained that the connection sequence is proper) but NOW there is an audible pop in the speakers within three seconds of powering up. There might be no connection between the two issues but I bring it up in case it provides any sort of usable evidence/information.
It should first be established if there is in fact a problem with the preamp. We do not know what quality tubes are being used and if the OP is buying the tubes from a reputable dealer. I had a similar problem with a Quicksilver Full Function preamp. The input tube is run very hard and the preamp was eating Golden Dragon tubes for lunch. Looking for a more reliable tube I tried an Amperex tube and never had another problem.
Contact McIntosh and find out of your tube wear/noise is typical. The head of the service dept. is a very nice.
Did you buy the preamp new or used? If used, I would be getting this into an authorized repair center. I bought an Art Audio PX-25 amp used and when it arrived it didn't sound to what my expectation was. I sent it back to Art Audio and they found someone had jacked with it and changed out a number of resistors and caps. They restored it to factory spec and all was good.
I agree with Atmasphere. It may just be time after 2000 or so hours to replace the tubes. However, you can also take the unit to an authorized McIntosh labs service technician for evaluation. But first, do a little math. How many hours do you feel you have on the tubes? if close to or more than 2000 hours, they need to go.
Curious, what voltage do you have coming out of the wall?
If you are using Chinese signal tubes the life may be less than 2000 hours if you are using LOMC and need low noise. They can be very quiet but can go downhill in only 1000 hours.
Had you considered a step up transformer for the phono section? You will get a much longer service life out of your tubes and IME is preferable to going solid state.
I had a couple of brand new Sovtek 12ax7lps tubes fail in my preamp after less than 9 months of use. So I googled "what would make sovtek 12ax7lps fail" and got this:
I don't know what design your preamp employs, but this may help explain. BTW, I have switched to NOS by RCA, Sylvania, Telefunken because I have been so disappointed by modern tubes. Also, you really should have your gear checked by a pro on a bench, you're just postponing the inevitable here.
Onemug, It's a dedicated line and there's 116v reading right now (11:35 a.m.) at the wall. I am also reading 116v at the Brickwall.