It is currently Mon Mar 16, 2020 6:21 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 9 posts ] 
Author Message
Post subject: CVR on the fritz
Posted: Thu Jun 04, 2015 12:14 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Jan 13, 2014 12:58 pm
Posts: 15
I've recently picked up a barely-used Custom Vibrolux Reverb back in April and I seem to have encountered an issue ... My Normal channel works fine, but as of yesterday, plugging into the Bright channel yields only a sort-of fizzy sound--I can hear a little guitar when I crank it to about 8, but for the most part it's become useless.

A little history: A month or so ago I replaced the 12AX7 in V1 with a 12AU7 to get rid of some of the hiss and increase headroom (with success!). I didn't try the Bright channel at the time, like a twit. I hadn't played the amp again till last night, since it's too loud for my house.

I should note, too, that I am a newbie with tube amps. In trying to get out the V2 tube after struggling with V1--just to see if there was an issue with the V1 tube socket or if it was just me (it was just me)--I might have pulled things a little too hard ... So I wonder: would damaging the V2 tube socket (assuming I did) cause the problem I described? Or is it possible that I have a loose tube somewhere, or something else?

Thanks!


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: CVR on the fritz
Posted: Thu Jun 04, 2015 12:27 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Yeah, try pulling the tubes and putting them back into the same sockets. You may want to use a little contact cleaner to help pulling & inserting. I like Caig Deoxit DN-5 or GN-5.

Good luck! Keep us posted. :D


Top
Profile
Post subject: Re: CVR on the fritz
Posted: Thu Jun 04, 2015 3:20 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Jan 13, 2014 12:58 pm
Posts: 15
BMW2002Ti wrote:
Yeah, try pulling the tubes and putting them back into the same sockets. You may want to use a little contact cleaner to help pulling & inserting. I like Caig Deoxit DN-5 or GN-5.

Good luck! Keep us posted. :D


I tried pulling V2 and replacing it; no luck. I pulled it again and tried replacing it with the AX7 I pulled from V1 in case there was an issue with the tube itself; no luck there, either.

I should mention that with my volume at 0, I'm still getting some sound.

Is it possible that it's because I replaced the V1 with an AU7 and V2 remains an AX7, or is that not at all related? (Again, I'm a tube noob ...).


Top
Profile
Post subject: Re: CVR on the fritz
Posted: Thu Jun 04, 2015 3:34 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Jan 13, 2014 12:58 pm
Posts: 15
Interesting take from TGP user phsyconoodler:

Quote:
Well I had one of those amps and they don't respond kindly to having v1 removed. They share plate resistors and when you pull out v1 it makes v2 unstable and can cause all kinds of issues like oscillations.
...
Even if you use just a lower gain tube in v2 it upsets the balance caused by the shared plate resistor and sometimes the amp won't make any sound at all.


I've done the opposite: put a lower-gain tube in V1 while leaving the higher gain AX in V2. So maybe I'm on to something. I'll try replacing the AX in V1 so they match up once I get back home for the evening.


Top
Profile
Post subject: Re: CVR on the fritz
Posted: Thu Jun 04, 2015 5:43 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Jan 13, 2014 12:58 pm
Posts: 15
Yup, that was it. I replaced the 12AU7 with the original 12AX7 and now both channels work. I lost the headroom I gained and gained back that hiss I lost with the 12AU7, so I'm going to try putting 2 AUs in V1 and V2 and go from there.

Thanks a lot for your reply, and great username, BMW2002ti!


Top
Profile
Post subject: Re: CVR on the fritz
Posted: Thu Jun 04, 2015 6:01 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Hmm... never heard of this issue. In most Fender amps I've worked on, the amp will work with V1 or V2 inputs removed. Provided you are plugging your guitar into the channel with its input tube connected. I have not worked on any of these new '68 Custom amps. So, not sure of input interactions.

But, if the amp works ok now --- that's all that matters. Try a 5751 in V1. These are nice, quiet tubes with a tad less gain (mu) than the 12AX7. But, other electric characteristics is closer to the 12AX7, than the 12AU7.

JJ makes a good model:

https://www.tubedepot.com/products/jj-5751-preamp-tube

The best 5751s are NOS black plate or gray plate dual or triple mica ones. Raytheon, Sylvania, GE, RCA, to name just a few.


Last edited by BMW2002Ti on Thu Jun 04, 2015 6:29 pm, edited 1 time in total.

Top
Profile
Post subject: Re: CVR on the fritz
Posted: Thu Jun 04, 2015 6:13 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
BMW2002Ti wrote:
Try a 5751 in V1. These are nice, quiet tubes with a tad less gain (mu) than the 12AX7. But, other electric characteristics is closer to the 12AX7, than the 12AU7.


+1

A 12AY7 might also work well.

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: CVR on the fritz
Posted: Thu Jun 04, 2015 6:44 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Jan 13, 2014 12:58 pm
Posts: 15
Thanks, all! I actually just ordered another JJ AU7 to match the one I already have--it really took out a lot of that hiss. But I'll check out your recommendations another time.


Top
Profile
Post subject: Re: CVR on the fritz
Posted: Thu Jun 18, 2015 6:59 pm
Offline
Hobbyist
Hobbyist

Joined: Mon Jan 13, 2014 12:58 pm
Posts: 15
Li'l update: I plugged in both AU7s into V1 and V2, and that made the CVR veeeeery angry. Both channels made a sort-of electronic fart when I'd insert or remove a cord, and that's about the only sound they'd make.

I replaced them with the original AX7s for practice, but when I got home, I replaced just V1 with an AU7. It made a god-awful hum. So now I'm thinking, I fried something ... Or, maybe, less dramatically, that that particular AU7 is a dud. So I swapped out one AU7 for the other, and everything is happy again. (Except for the Bright channel, but we already knew that, and I'm cool with it, unless I'm effing something up ...).

So, for now I'm pretty pleased. I have the sound I want, cleaner and with no hiss. I don't need the bright channel, and I'll just plug the AX7 back in if I sell it at some point (again, if I'm not messing something up--can't imagine I am, but I'll have to play the noob card once again).


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 9 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: