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PostPosted: Wed Mar 08, 2017 1:47 am 
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Mark I

Joined: Wed Jun 18, 2008 11:51 pm
Posts: 23
Hello, I have a Roadster head I bought used about 2 years ago. I believe it was one of the first built as it has a low serial number.

I run on Bold with all channels at 100 watts during band sessions, 50 watts at home. Tube rectification on channels 1-3, diode channel 4.

I have a TC Gmajor 2 in the effects loop. Ch. 1-3 fx loop toggle is On, ch. 4 is Off.

The amp has worked rather flawlessly and I've loved it since day 1.. a big upgrade over the Rectoverb I was using.

However, in the last couple weeks I've noticed an issue when using channel 3 (modern), the volume is noticeably lower than channel 4 (also modern) even though the volume and eq settings for both channels are nearly identical.

When I engage the effects loop on channel 4 to test, the volume is consistent.

When I toggle channel 3 to diode rectifier, the issue seems to go away and switching between channel 3 and 4, volume is consistent.

My question is, is this the normal function of tube rectification or are the tubes in need of replacement?

How long do rectifier tubes typically last and do they wear down like power tubes or do they work until they don't?

I retubed power and preamp tubes when I bought the amp and again recently in December 2016. The rectifier tubes I last replaced with new when I bought the amp in July 2015.

I'm using 6L6 preferred series (tube store), Mesa 5U4GB rectifiers and the following 12ax7's:
V1 - tung-sol
V2 - mullard cv4004
V3 - gold lion ecc83 standard (china?)
V4 - preferred series (tube store)
V5 - shuguang B
V6 - sovtek lps

Last night I replaced the gold lion in V3 with a spare Shuguang and the volume difference between ch. 3 and 4 seems not as bad as before, but still not as consistent as when using diode rectification on both channels.

I'm guessing that even though the gold lion tube is manufactured in China, it still wore down prematurely in V3.

My last question is, are current production Mesa tubes (not labeled Chinese or Russian) susceptible to wearing down faster in the cathode follower positions v3 and v5? I have a few Mesa 12ax7 I could try in those spots to see if they alleviate the issue.

Thank you for reading and any feedback is appreciated.


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PostPosted: Wed Mar 08, 2017 5:55 am 
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Joined: Mon Jan 01, 2007 6:52 am
Posts: 3046
Location: New Haven, CT U.S.A.
the.rev wrote:
Hello, I have a Roadster head I bought used about 2 years ago. I believe it was one of the first built as it has a low serial number.

I run on Bold with all channels at 100 watts during band sessions, 50 watts at home. Tube rectification on channels 1-3, diode channel 4.

I have a TC Gmajor 2 in the effects loop. Ch. 1-3 fx loop toggle is On, ch. 4 is Off.

The amp has worked rather flawlessly and I've loved it since day 1.. a big upgrade over the Rectoverb I was using.

However, in the last couple weeks I've noticed an issue when using channel 3 (modern), the volume is noticeably lower than channel 4 (also modern) even though the volume and eq settings for both channels are nearly identical.

When I engage the effects loop on channel 4 to test, the volume is consistent.

When I toggle channel 3 to diode rectifier, the issue seems to go away and switching between channel 3 and 4, volume is consistent.

My question is, is this the normal function of tube rectification or are the tubes in need of replacement?

How long do rectifier tubes typically last and do they wear down like power tubes or do they work until they don't?

I retubed power and preamp tubes when I bought the amp and again recently in December 2016. The rectifier tubes I last replaced with new when I bought the amp in July 2015.

I'm using 6L6 preferred series (tube store), Mesa 5U4GB rectifiers and the following 12ax7's:
V1 - tung-sol
V2 - mullard cv4004
V3 - gold lion ecc83 standard (china?)
V4 - preferred series (tube store)
V5 - shuguang B
V6 - sovtek lps

Last night I replaced the gold lion in V3 with a spare Shuguang and the volume difference between ch. 3 and 4 seems not as bad as before, but still not as consistent as when using diode rectification on both channels.

I'm guessing that even though the gold lion tube is manufactured in China, it still wore down prematurely in V3.

My last question is, are current production Mesa tubes (not labeled Chinese or Russian) susceptible to wearing down faster in the cathode follower positions v3 and v5? I have a few Mesa 12ax7 I could try in those spots to see if they alleviate the issue.

Thank you for reading and any feedback is appreciated.

The current Mesa 12AX7 is a JJ ECC83, and is fine for cathode follower use.

Has this 'volume cut issue' just started, or has it been this way for the past 2 years you have owned the amp.
[EDIT] I just saw that you mention you noticed this over the past few weeks [/EDIT]

On my Roadster, ch 3's master is always a bit higher than ch 4's, even with identical modes/rectification. When using the tube rectifier, I find I need to turn up the amp ever so slightly, not as much as when in Spongy power mode, but the B+ voltage drop when using just the 5U4GB's is noticeable. If I change a channel to tube rectification I usually need to goose the master a bit to bring that channel's level up to match the others.

Those knobs are put on by hand, you can't expect them to all be in the same identical position when tightened to the pot shaft, and the pots themselves, as well as other parts of the circuit have value tolerances that can cause slight differences between settings. I EQ my amps with my ears, not my eyes, especially with my Mesa's.

Rectifier tubes usually either work, or don't. I don't think I have ever experienced a 'starting to fail' rectifier tube.... they usually just stop working, often taking the mains fuse with them when they do die.

If this is an issue that has just started I would try a good cleaning of all the jacks, and maybe even the tube sockets.

Dom

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PostPosted: Wed Mar 08, 2017 9:30 pm 
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Mark I

Joined: Wed Jun 18, 2008 11:51 pm
Posts: 23
Thanks for the reply.

I suppose I've always noticed it, but not to the extent that it has been the last couple of weeks.

For the most part mine has behaved similar to how you describe your amp.

Swapping out the tube in V3 seemed to help considerably and it's back to what I'm used to.

Is there anyway to tell if this tube would not survive long in a cathode follower: http://www.thetubestore.com/Tubes/12AX7-ECC83-Tube-Types/Genalex-Gold-Lion-ECC83-12AX7-Standard-Version

When both channels are using diodes, there is no difference in volume to my ears, which made me start to wonder if the rectifier tubes wear down or if that was always just "normal" when using a tube rectifier.

I pulled it out of the chassis the other day because I just recently came across the Roadster service notice from several years ago and wanted to see if I could tell if it was ever done to my amp. My serial is VH-000084.

The amp appears to be in great condition, I don't see any dirty or burnt components.. the board, components and sockets look to be what I would consider brand new state... although I am not an EE. I know it's always a roll of the dice buying used, but it seems the guy who had it before me was honest when he said he hardly used it and preferred his Marshall. It appears to have just sat at his house given the lack of any visual wear and tear.


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PostPosted: Thu Mar 09, 2017 12:35 am 
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Joined: Mon Jan 24, 2005 4:57 pm
Posts: 4448
Location: South of Heaven
I'm the same as domct203. Switching a channel to the tube rectifier drops the volume a touch and they need to be goosed a bit to bring the volume back up.

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| Les Paul | McCarty | Custom 24 | CE 22 |
| D800 | Dual Rectifier | Electra Dyne | Rectoverb:25 | Strategy 8:88 |
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PostPosted: Sun Mar 26, 2017 6:45 pm 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
Posts: 2236
Location: North Carolina
I would agree about the drop in volume when using the tube rectification.

However, I found CH4 to be much louder than CH3 using identical settings and rectification.

Also, voice settings: Modern is definitely the loudest, vintage and raw require adjustments of the master if using one channel on Modern.

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