Question for you experienced guys

[Masterof1angel]

is it common to blow out preamp tubes by pushing them too hard on a mark iic+
I like high gain settings like 9.5 pulled, 9 pulled, 4 in, 7, 2 pulled, 8 pulled, 7 in, and I get a great crunch with my black shadow ev speaker, but i find myself nearly maxing the 80 hz slider since the (mine at least) shadow speaker has less boom than say a gt-75 or such. Invariably, when I turn up my master volume past 1.5 or 2, there comes a low wobble and one of my preamp tubes blows out (3 times now) is this cool?

 

[zodiac272]

Hey,

I don't think that's common. which preamp tube is burning up? same one every time? Either the tubes are bad or they are getting too much signal, but it seems hard to think you would keep blowing tubes by cranking it, unless there was a problem.

I love high gain too, but your settings seem to be a bit over the top. Yeah the EV is a bright speaker, but with the bass at 4 and the 80hz slider nearly maxed you should have plenty of low end. Maybe needs a cap job? Are the caps bleeding the low end signal?

have you tried pushing V1 and pulling the lead master? that will give it more gain. Your lead master seems really cranked. is that not insane loud? Seems like the sweet spot there is between 3.5 and 5.5 on the lead master

I love high gain, and I use something like this:

7 (7) 2.5 5 (2) (9) (4) GEQ medium scooped V shape. presence about 2.5

that has tons of gain with great clarity, and I can turn V1 up if needed

you might get it looked at, especially if it hasn't been serviced in 25 years

any pics? hehe

scott

 

[Masterof1angel]

Thanks Scott, I had the filter caps replaced here when i first got it so they should be ok. the tubes blew 3rd, then the 2nd, and 1. Some of them were microphonic. I have el-34's in it that i'm not sure are the right bias, could that cause it? The amp is fine until i turn it up a bit on the master, then the 80 hz starts distorting (in a flubby way) and I know the tubes are going to blow out. Kinda like on the mark V if you turn the bass knob up real high. But the kicker is that this is past the preamp circuit so I don't know why it would effect preamp tubes. (duh?) also sometimes just cuts out, then i have to turn the master down and back up and it comes back on. I tried it on my 4x12 gt-75 there is almost too much bass when i turn it up like that but it's flubby. I'll try what you said. I have a really light touch so I like lotsa gain. Maybe I'll put some pics up later. thanks for the help.

 

[chipaudette]

This is not meant to be insulting...but your comment about the EL-34 has me worried. Is your amp simul-class?

If not, your amp can't take EL-34 at all. It might throw off all of the voltages within the amp and, perhaps, cause problems with the pre-amp tubes.

If your amp is simul-class, only two of the power tubes can be EL-34, and it has to be the correct ones (the outer tubes?).

Given that you likely know what you're doing with the power tubes, this probably isn't the problem. I've never heard of consistently blowing pre-amp tubes without there being a problem with the amp. The settings on the front shouldn't matter for the pre-amp tubes. To me, it sounds you either got a batch of bad pre-amp tubes (were they all bought from the same batch) or that the amp's pre-amp supply voltage is too high...a bad cap job or something.

How do the tubes look when the amp is running? Are they glowing super-brightly?

Chip

 

[Masterof1angel]

Yeah, Chip it's a simulclass and it's the outer two tubes, I tried 6l6's and it helped the bass a bit but when i turned it up, it still cut out and blew a preamp tube. so I put in some tubes in that I had in my mark IV that I knew worked and would chug for me along a high quality mesa russian v1 preamp tube that made the bass deep and strong like I want it.
It sounded a lot less flubby and deeper but then when I turned up to a good volume it still popped and cut out to silence. I had to turn the master down, then back up past where it was before it came back on. too bad this tube blew out because it was high quality. now it scratches and crackles a bit. I don't know why it does this.
Before that, I had a different tube in the v1 and there were two rods glowing pretty brightly. all of these tubes have bright orange glowing spots on them but I'm not sure what would constitute them glowing brightly to you. They are different tubes, from different sets. Two of them were chinese ones in v1 and 3 that i liked the sound of but they were microphonic, one was a jj from a set selected from eurotubes, and this one was a really good one my amp tech gave me. also, i blew a gold plated tung sol in v2 the other day that one actualy turned blue. the chinese went scratchy/howly and so is the russian now. Tubes only blow out when i turn the master volume up to a bit and they blow out faster if I Play the low notes.
I can put the bass all the way up and have it on high gain all day at bedroom levels but once you turn the master volume up to a certain point on the amp, she cuts out and you get total silence, and you can turn down the master volume and she stays quiet untill you turn it past the point you were on before, where the amp comes screaming back on and the tubes are shown to be blown.

 

[chipaudette]

This amp definitely has a problem. It needs to go to a tech. You have a string of blown tubes and it sounds like it is repeatable. Once on his work bench, a decent tech ought to be able to quickly find the cause of repeatable problem like this.

Chip