Amp is whistling, is it likely a preamp tube?

[blackba]

I was playing my '66 Vox AC50 tonight and it started whistling, does this especially when I play an A bar chord on both channels. I assuming its a preamp tube, but I am not sure, never had a whistling amp before. The only tube the channels share is the Phase Inverter. Each channel uses a half of V1 too.

Anyone delt with a whistling amp before?

 

[Bad Brad]

That's what it sounds like to me, when was the last time you swapped out tubes? Oh by the way what part of Michigan are you from, I have family in Bay City that we visit every year.

 

[blackba]

I just swapped out some of the tubes last month. I checked them all too

I am on the west side of Michigan. I am actually closer to Chicago than Bay City or Detroit.

 

[guitarslinger]

I just had a NEW, whistling Groove Tubes Sovtek 12AX7WA show up.

So much for tube-quality-screening

 

[D-Rock]

Could also be a poweramp tube.

 

[blackba]

It was the RCA 12AU7 in V1, the old pencil tap test showed that one pretty easily. I don't have another 12AU7, so I put a GE 5751 in V1....

 

[JTyson]

It was the RCA 12AU7 in V1, the old pencil tap test showed that one pretty easily. I don't have another 12AU7, so I put a GE 5751 in V1....

Did it solve the problem?

 

[megamike]

i had a whistling preamp tube in my STILETTO a few weeks ago,a new tube fixed it

 

[blackba]

It was the RCA 12AU7 in V1, the old pencil tap test showed that one pretty easily. I don't have another 12AU7, so I put a GE 5751 in V1....

Did it solve the problem?

Yep the 12AU7 was the issue. That tube was supposed to be NOS but it only lasted a month of so

 

[JTyson]

PM sent - Jim

 

[blackba]

The 5751 sure makes the amp more gainy, more marshally. I think I liked the 12AU7 better, I got more chime and could control the volume alot easier.

 

[King Crimson]

Anyone delt with a whistling amp before?

Yeah, try to determine what key the whistling is in and write some originals to it. You may have stumbled onto something big...

 

[blackba]

Anyone delt with a whistling amp before?

Yeah, try to determine what key the whistling is in and write some originals to it. You may have stumbled onto something big...

When I had that tube in there the amp would whistle more when I played an 'A' bar chord. Time to write a song in the key of 'A'

 

[Drkorey]

I'm having a pre amp tube issue I think - please remind me of teh pencil tap check method.

I get a loud scratchy feedback noise issue on my Peters cruch channel that started half way through practice last night. The clean channel sounds fine but when I switch it's pretty bad.

I remember the test being either tapping on the tube with lead or eraser side and listening for pings or something?

 

[blackba]

I'm having a pre amp tube issue I think - please remind me of teh pencil tap check method.

I get a loud scratchy feedback noise issue on my Peters cruch channel that started half way through practice last night. The clean channel sounds fine but when I switch it's pretty bad.

I remember the test being either tapping on the tube with lead or eraser side and listening for pings or something?

I used the eraser side of the pencil and tapped all the preamp tubes lightly. They should have a small thud when you tap them. When I tapped the bad tube it sounded like clanking glass (like you are doing a toast with glasses)