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Topic: Session 400 and Ltd 400 reverb issues |
Ken Fox
From:
Nashville GA USA
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Posted 29 Apr 2021 4:12 am |
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The original LTD400 and Session 400 did not have a reverb bag. Installing one is always a good upgrade. Best to slide a piece of cardboard between the tank bottom and the bag
You might check and make sure the connections are cleaned. Check and make sure the reverb springs are clean. Some of the older tanks had some foam weather stripping above the springs to help dampen external vibrations. Often the foam rubber would rot and fall into the springs
Best bet then is a new reverb tank. The original was a 2 spring tank, 4EB2C1B by Accutronics. The 9EB2C1B is a three spring upgrade for deeper sounding reverb
Also the tank's connection cables are often plugged in backwards at the amp chassis. Works but will add hum and not as good a reverb sound. Also tanks jacks face the speaker
The two RCA jacks up under the amp are not identified, thus making it difficult for someone to know which plug goes where
To identify easily just unplug the tank and lay the cable out the back of the amp. Turn the amp on and turn the reverb knob up a bit. Then ID which cable tip makes noise when you touch it. That cable goes to the reverb tank output side.
The reverb drive in the amp is a two push pull transistor circuit, not tubes |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 29 Apr 2021 4:37 am
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| Great info, Mr. Fox. Thank you for sharing. I plan to check the crappy sounding 'verb on my LTD and make the suggested changes if necessary. The 'verb on my Session sounds alright as is, so I'm hesitant to diddle with it. |
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Colin Keyworth
From:
Derbyshire, England
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Posted 29 Apr 2021 2:25 pm
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Thanks for the info Ken, I'm still having trouble with mine,I replaced the tank which was shot & I now have reverb however I have a really bad hum when I turn up the reverb control. I've done all the checks with the moldex connector and even tried reflowing the solder on the modex pins on the circuit board but no better,I think it's a bit out of my area now so I'm probably going to take it to a tech
_________________
Sho-Bud LDG,Fender vintage 52 Telecaster, Fender Strat plus,Gibson Les Paul, Peavey session 400 limited, Line 6 Helix |
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Ken Fox
From:
Nashville GA USA
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Posted 30 Apr 2021 4:33 am Hum
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| Colin, does the hum go away if you unplug the tank from the chassis? |
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Ken Fox
From:
Nashville GA USA
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Posted 30 Apr 2021 4:35 am
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| Colin, if you have Molex connectors then I would think this is a Session 400 LTD, not an early small cabinet Ltd 400 |
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Colin Keyworth
From:
Derbyshire, England
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Posted 30 Apr 2021 5:33 am
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Thanks Ken,I'm only just learning that there is a difference, this is the one I have
_________________
Sho-Bud LDG,Fender vintage 52 Telecaster, Fender Strat plus,Gibson Les Paul, Peavey session 400 limited, Line 6 Helix |
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Ken Fox
From:
Nashville GA USA
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Posted 30 Apr 2021 8:41 am
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| Colin, does the hum go away if you unplug the tank from the chassis? |
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Ken Fox
From:
Nashville GA USA
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Posted 30 Apr 2021 8:42 am
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| Colin, does the hum go away if you unplug the tank from the chassis? |
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Colin Keyworth
From:
Derbyshire, England
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Posted 30 Apr 2021 11:35 am
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Just tried it Ken ,yes it does
_________________
Sho-Bud LDG,Fender vintage 52 Telecaster, Fender Strat plus,Gibson Les Paul, Peavey session 400 limited, Line 6 Helix |
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Ken Fox
From:
Nashville GA USA
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Posted 30 Apr 2021 12:12 pm
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Ok. So the problem is not the tank and cables. Likely a bad IC that operated both the reverb return and reverb send.
With the tank out that just leave the reverb return circuit to troubleshoot that would be IC4. A common 4558 chip. It amplifies the return from the tank. There are a few other components in the reverb return that could be suspect as well. IC4 is cheap and is a plug in chip. |
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Colin Keyworth
From:
Derbyshire, England
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Posted 30 Apr 2021 12:20 pm
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Great stuff thank you, there is a component shop locally so I'll give them a call tomorrow and see if they have a coupleand replace them both and see if that cures it. With the original tank there was no reverb at all and when you turned it right up it squealed so I got a new tank and that seems to have eliminated that. I bought the amp really cheap so I don't mind spending a bit
_________________
Sho-Bud LDG,Fender vintage 52 Telecaster, Fender Strat plus,Gibson Les Paul, Peavey session 400 limited, Line 6 Helix |
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Ken Fox
From:
Nashville GA USA
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Posted 1 May 2021 6:25 am
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Like the original Session 400 the Session 400 limited used a push pull transistor circuit to drive the reverb tank. Bit unlike the older Session it did use 1/2 of a 4558 to recover the tank signal
Later amps used both halves (two amps in there) of the 4558 to drive and recover the tank signal |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 3 May 2021 8:13 am Re: Session 400 and Ltd 400 reverb issues
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| Ken Fox wrote: |
| The original LTD400 and Session 400 did not have a reverb bag. Installing one is always a good upgrade. |
Is there any advantage whatsoever in installing a reverb tank liner inside a reverb bag? Are two bags better than one? The outfit in Arizona that goes by at least three different monikers offers both:
Reverb tank bag
Reverb tank liner |
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Ken Fox
From:
Nashville GA USA
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Posted 3 May 2021 9:04 am Bags
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| It offers more physical protection. The tank floats more in the bag as opposed to being screwed down to the cabinet bottom. Less sensitive to stage vibrations as well |
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Peter Siegel
From:
Belmont, CA, USA
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Posted 3 May 2021 2:28 pm
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Ken,
Perhaps an obvious question but...
How do you recommend fastening the bag to the bottom of the amp?
4 wood screws?
TIA |
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Ken Fox
From:
Nashville GA USA
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Posted 4 May 2021 10:58 am
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| Fender used a wood screw and cup washer on each end of the bag. Works pretty good |
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Ken Fox
From:
Nashville GA USA
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Posted 4 May 2021 10:59 am
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| Best to place a piece of cardboard under the reverb unit to prevent the bag from touching the springs |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 13 May 2021 5:13 pm
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| Jack Hanson wrote: |
| I plan to check the crappy sounding 'verb on my LTD and make the suggested changes if necessary. |
Changed out the tank, installed new bag and liner (with cardboard) to Ken's specs, verified the cables were correctly attached, and the once-noisy reverb on my old LTD 400 works fine and is quiet as a church mouse.
Thank you, Mister Fox! |
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Ken Fox
From:
Nashville GA USA
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Posted 2 Jun 2021 5:54 am
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| Bump |
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Kenny Davis
From:
Great State of Oklahoma
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Posted 7 Nov 2021 7:04 pm
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I bought my Session 400 new in '74 or '75 and I don't recall ever replacing the reverb unit. While troubleshooting a problem with the reverb in my Nashville 112, I opened the Session up and found the following: Accutronics #4FB2B1A
This number isn't what I've seen on this thread for the Session 400. According to the number, it's supposed to be mounted open side up?
A year and a half ago I replaced the original unit in the 112 with a 9EB2C1B and it has recently developed a minor feedback sound that progressively gets louder. I don't use hardly any reverb (3-3.5) so I don't know if I gain anything from a 3 spring.
What was the original Accutronics model number that my vintage Session 400 should have had? I don't see any cross reference for the number I have.
_________________
Best lyric in a country song: "...One more, Moon..." |
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Ken Fox
From:
Nashville GA USA
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Posted 8 Nov 2021 2:49 am Tanks
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The tank you have is for the older Webb amps that used a long tank
Your tank would have been a 4EB2C1B
Picture file |
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Jerry Overstreet
From:
Louisville Ky
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Posted 8 Nov 2021 4:28 am
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It is not unusual to see different models of tanks in Peavey amps. Maybe that's why the reverb might vary so much among amps of the same model.
F.I., one of my 1989 NV400s had a model number 9FB3C1B unit. I know it was original to the amp because I bought it brand new in the box. |
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Kenny Davis
From:
Great State of Oklahoma
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Posted 8 Nov 2021 2:46 pm
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I mentioned that I discovered evidently the wrong tank in my Session 400 while diagnosing my Nashville 112...
I am experiencing the same symptoms that Karl Paulsen has (see https://bb.steelguitarforum.com/viewtopic.php?t=375279) with his Vegas 400 except I don't have to dial the reverb that high before I get the same sound.
Last year I replaced the original 2 spring with the 9EB2C1B by MOD. It doesn't seem to make the noise in my Session 400, nor does the Accutronics 4FB2B1A while in the Nashville 112. All connections appear to be in good shape and correctly connected.
Any ideas? I'm thinking I'll maybe order a two spring like originally installed, but by MOD.
_________________
Best lyric in a country song: "...One more, Moon..." |
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