diezel vh4 feedback problems

[guitarbastard]

chanel 1 and 2 work great. on chanel 3 if i have volume on 11clock and gain on 1 feedback starts. if i add a boost it's already quite irritating and hard to controll. on chanel 4 i got serious fb problems with gain set on only 12 - 1- its all setup nicely in a rack. i controll my analogpedals (built in aswell) with midi. master is only set at about 8 clock. i play sg's or flying V. with humbuckers. with my lp junior and p90's i cant play the amp at all on chanel 3, 4.
a friend of mine has the same amp and never has fb problems even with max gain on chanel 4.
any ideas what could be wrong??

 

[Sigma.Xiria]

I would say it has to be a bad preamp tube. Which one, though, I am not sure. I will see if I can get some info for you

 

[FourT6and2]

lol welcome to Rig-Talk! Like I said over at TheGearPage:

Bad preamp tube. Replace with Ruby 12AX7 HG or HG+. If feedback only on channel 3 and 4, it's most likely V2 or V3. But maybe there just isn't enough gain in channel 1 and 2 for you to notice that there's an issue with those as well. So I would recommend replacing V1, V2, V3, V4, and V7 unless you can single out the one bad tube.

V1 Used by all channels
V2 Used by channel 4
V3 Used by channel 2/3/4
V4 Used by all channels
V5 Mixer and Send buffer
V6 Return driver
V7 Phase Inverter

 

[guitarbastard]

thanks alot!! i will check them. or let them get checked and replaced. but do i get i right: with master at 8 clock i shouldnt get feedback even if cranking the gain up to 3 or max?

 

[Sigma.Xiria]

thanks alot!! i will check them. or let them get checked and replaced. but do i get i right: with master at 8 clock i shouldnt get feedback even if cranking the gain up to 3 or max?

Your best bet is to replace them all, if you can afford to.

It shouldn't like you are talking about. I do this all the time with my master at 10-11 and my channels at 11-12 to show my buddies just how much gain the amp has while still retaining definition. Of course it will feedback, if you want it to, but not horribly or uncontrollably.

 

[FourT6and2]

thanks alot!! i will check them. or let them get checked and replaced. but do i get i right: with master at 8 clock i shouldnt get feedback even if cranking the gain up to 3 or max?

Nah, you shouldn't get feedback with the master at 8:00. Sounds like a microphonic preamp tube. Like Sigma said, I would probably just replace them all. The Ruby/Chinese 12AX7AC5 tubes are fairly reliable and low-noise. I'd go with those. If you get the Ruby-branded ones, you can order an HG+ for V1 and V2 and HG for the rest. Those are just tested better and rated for less noise.