The Amp Garage Forum Index The Amp Garage
A tube amp builder's community
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Carr Rambler oscillations on certain notes
Goto page 1, 2  Next
 
Post new topic   Reply to topic    The Amp Garage Forum Index -> Technical Discussion
View previous topic :: View next topic  
Author Message
SFMUSICMAN



Joined: 02 Aug 2011
Posts: 20

PostPosted: Tue Aug 02, 2011 2:00 am    Post subject: Carr Rambler oscillations on certain notes Reply with quote

Hey tube gurus,

I have a Carr rambler that sounds wierd oscillations on certain notes and I really hear them more clearly when I play my new CS '51 Nocaster.

Someone told me I need to get rid of the Sovtek tubes and go with some NOS ones by say, Sylvania i.e. 12AX7WA for the preamps

I have Sovteks in the 6L6's and this guy says my amp is really capable of way more attitude if I get rid of the tubes. And of course, I want the oscillations to go away.

Can someone suggest which tubes would be a good fit for this 1x12 amp?

thank you
Back to top
View user's profile Send private message
Structo



Joined: 17 Oct 2007
Posts: 14143
Location: Oregon

PostPosted: Tue Aug 02, 2011 2:39 pm    Post subject: Reply with quote

Since the guitar is new to you, does the amp do this same thing with a different guitar plugged in?

If not then I would look at the nocaster and how close the pickups are to the strings.

_________________
Moderator

Don't let that smoke out!
Back to top
View user's profile Send private message
David Root



Joined: 04 Aug 2006
Posts: 3018
Location: Lower Mainland BC

PostPosted: Tue Aug 02, 2011 2:48 pm    Post subject: Reply with quote

If the tubes are the usual Sovtek WA/WB crap, dump 'em. If they are the Sovtek LPS, maybe not. This refers only to the main signal path, not reverb or tremelo circuits.

The amp is well designed and built so I would not expect any issues intrinsic to the amp. Mr. Carr knows his ass from his elbow, electronically speaking.

Sylvanias tend to be on the bright side and this amp derives largely from the Blackface Fenders, which are also on the bright side, so I would try either GE, RCA or Raytheon 12AX7s in NOS.

Look in the For Sale section of TAG right now and you'll find a bunch of NOS RCA and Raytheon (and Sylvania) 12AX&s at way below dealer prices. For the first stage my choice would be the long (17mm) blackplate RCA or the long blackplate Raytheon. If you're on a tight budget, the RCA short plate (14mm) 12AX7, but they are relatively one-dimensional compared with the blackplates, which have more harmonic content. Compared with the basic Sovteks, even the short plate RCAs will be a night & day improvement. Those are what most BF amps shipped with anyway.

Use longplates only in the first gain stage, the second and third should both be short plates. This will minimize microphonics.

Your friend mentioned Sylvania WA 12AX7s. WAs are all short plates. The GE 12AX7WA would be worth a try, but NOT the '80s Philips ECG version--overpriced and not in the same class. Or older JG-12AX7WA, same tube. The older ones have white labels that smudge easily, the later ones have green labels that don't. All have the date code on them and older is better.

Don't pay more than $20 max. for anything out of the '80s by anyone.

In European tubes "real" Amperex from the Heerlen Holland factory are very nice and in used condition relatively affordable. Vacuum Tubes Inc. in Orlando often have used '60s Heerlen 12AX7s for $30-$40 each, which is fair for a dealer.


I don't have a schematic of the Rambler, but if it uses a 12AT7 for the PI, the above advice translates to 12AT7s too, except there are no longplate 12AT7s, only (very) short plates. 12AT7WAs are good too, I got three '57s on fleabay for $11 when no-one was looking. One of 'em has perfect balance, good for the PI.


Last edited by David Root on Tue Aug 02, 2011 3:01 pm; edited 3 times in total
Back to top
View user's profile Send private message
sixstringer



Joined: 03 Feb 2010
Posts: 111
Location: SoCal

PostPosted: Tue Aug 02, 2011 2:55 pm    Post subject: Reply with quote

NOS tubes can be great, but perhaps changing out the preamp tubes with known good, current manufacture tubes, say JJ's (they work well and are inexpensive), would prove that the issue really is a tube and not something else. did you try trading the 12AX7s around to see if it changes the situation?

If the filter caps aren't doing their job, there could be a ripple current that could allow out of tune sounding sub notes, a bad grid resistor can allow instability too. There are a lot of things that could cause oscillation, poor lead dress, poor grounding, etc. but Carr amps are well built and highly regarded so that is unlikely. Any amp can have a component failure, did Carr suggest that it might be a bad tube?
Back to top
View user's profile Send private message
SFMUSICMAN



Joined: 02 Aug 2011
Posts: 20

PostPosted: Tue Aug 02, 2011 5:51 pm    Post subject: Reply with quote

wow these are really generous replies thank you all.

I did have a conversation with Steve two years ago when I first heard this issue with another guitar. Happens to various degrees with different guitars.

I had preamp tubes from a '55 Gibson GA-20 and a Holland 4x10 MagmaGibb to test with, as well as swapping tunes within the Carr itself. Was able to still hear the issue but perhaps I'll do again.

I am concerend though that the Sovteks aren't doing the amp justice anyways so think I should just go tube hunting and at least bring this amp to snuff in that regard.

Thanks, very interesting feedback from you all
Back to top
View user's profile Send private message
SFMUSICMAN



Joined: 02 Aug 2011
Posts: 20

PostPosted: Tue Aug 02, 2011 6:02 pm    Post subject: Reply with quote

David Root wrote:
Use longplates only in the first gain stage, the second and third should both be short plates. This will minimize microphonics.


David, how do I tell which of the 3 preamp tunes are "first, second or third" gain stages?
Back to top
View user's profile Send private message
SFMUSICMAN



Joined: 02 Aug 2011
Posts: 20

PostPosted: Tue Aug 02, 2011 6:18 pm    Post subject: Reply with quote

David Root wrote:
I don't have a schematic of the Rambler, but if it uses a 12AT7 for the PI, the above advice translates to 12AT7s too, except there are no longplate 12AT7s, only (very) short plates. 12AT7WAs are good too, I got three '57s on fleabay for $11 when no-one was looking. One of 'em has perfect balance, good for the PI.


All 3 preamps are 12AX7's FYI
Back to top
View user's profile Send private message
SFMUSICMAN



Joined: 02 Aug 2011
Posts: 20

PostPosted: Tue Aug 02, 2011 6:25 pm    Post subject: Reply with quote

The 6L6's are Sovteks' too.

What should I consider for replacement for this 1x12 amp?
Back to top
View user's profile Send private message
pdf64



Joined: 12 Mar 2011
Posts: 371
Location: Staffordshire, UK

PostPosted: Tue Aug 02, 2011 7:04 pm    Post subject: Reply with quote

Any difference in triode or pentode mode? Triode mode will make your amp much more prone to power supply ripple modulating the signal, creating weird out of tune sub harmonics, at high signal levels. Pete.
Back to top
View user's profile Send private message
T Wilcox



Joined: 11 Feb 2011
Posts: 225
Location: Sacramento, CA

PostPosted: Tue Aug 02, 2011 7:45 pm    Post subject: Reply with quote

SFMUSICMAN wrote:
David Root wrote:
Use longplates only in the first gain stage, the second and third should both be short plates. This will minimize microphonics.


David, how do I tell which of the 3 preamp tunes are "first, second or third" gain stages?


first stage is V1 furthest preamp tube from the 6l6's.
next preamp tube is V2 2nd gain stage.
Next will be the PI phase inverter V3

then the next 2 V4&5 will be your 6l6's.

This holds true for most tube amps as long as tubes are lined in one row.

Todd
Back to top
View user's profile Send private message
SFMUSICMAN



Joined: 02 Aug 2011
Posts: 20

PostPosted: Tue Aug 02, 2011 7:52 pm    Post subject: Reply with quote

pdf64 wrote:
Any difference in triode or pentode mode? Triode mode will make your amp much more prone to power supply ripple modulating the signal, creating weird out of tune sub harmonics, at high signal levels. Pete.


Ooo good one! Let me try that and see what happens.
thank you
Back to top
View user's profile Send private message
SFMUSICMAN



Joined: 02 Aug 2011
Posts: 20

PostPosted: Tue Aug 02, 2011 7:53 pm    Post subject: Reply with quote

David Root wrote:
This holds true for most tube amps as long as tubes are lined in one row.


This is true for this amp as well, thanks David
Back to top
View user's profile Send private message
T Wilcox



Joined: 11 Feb 2011
Posts: 225
Location: Sacramento, CA

PostPosted: Tue Aug 02, 2011 8:06 pm    Post subject: Reply with quote

Well if my name was David I would say your welcome Laughing

Sorry didn't notice you were asking him specifically

Todd
Back to top
View user's profile Send private message
SFMUSICMAN



Joined: 02 Aug 2011
Posts: 20

PostPosted: Tue Aug 02, 2011 8:14 pm    Post subject: Reply with quote

T Wilcox wrote:
Well if my name was David I would say your welcome Laughing


Absolutely you too Todd! Laughing
Back to top
View user's profile Send private message
SFMUSICMAN



Joined: 02 Aug 2011
Posts: 20

PostPosted: Wed Aug 03, 2011 3:42 am    Post subject: link to small sound file of issue Reply with quote

I recorded this issue and attached here. It's 585K file mp3

It does it in both Triode and Pentode modes

I am playing some double bends and holding the bend when you can clearly hear the sound Evil or Very Mad

I play two E bends (hear the issue)
then one F bend (hear the issue)
two G bends (no issue!)
back to E and F bends (hear the issue)

What's wierd too is on the F bend it only does it during the bend, not on the held diad, but it does do it random all over

STRANGE
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    The Amp Garage Forum Index -> Technical Discussion All times are GMT
Goto page 1, 2  Next
Page 1 of 2

 
Jump to:  
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
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum


Powered by phpBB © 2001, 2005 phpBB Group