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Reverb Gremlins [message #12641]

Tue, 05 January 2010 21:36

thekid
Messages: 25
Registered: August 2008
Location: Cape Cod, Massachusetts

Junior Member

Ok I need a techie for this one. I had my Frankie head repaired not long ago and among other things, the guy replaced my reverb tank. Now when I have the reverb turned up I lose volume on that channel. The tank he replaced it with is an accutronics 4AB3C1B. After reading a few posts I have realized that the correct pan is a 4FB3D1B. My question is if the symptom with the volume loss is a result of the wrong pan. When I dont use reverb, the amp is great, but I hope I havent hurt anything by using this pan. so I havent been using my reverb, but I miss it!!!! Crying or Very Sad

The main diff between the two pans is that the input impedance for the pan I have currently is only 8 ohms while the correct pan is rated at 1400 and change for the input side. also the output is grounded on my current pan and not on the correct one. Any advice? will buying the 4fb3d1b correct my symptoms? Thanks guys/gals.

Rockin , Tuckin & Rollin!
Gold L795RV Frankie
2x15 JBL D130F Kustom cab
'86 Ibanez Roadstar II
'67 Crucianelli PANaramic Hollowbody
'82 Westone heelless set neck ThunderII
'70 Sekova double cutaway Hollowbody

[Updated on: Fri, 05 February 2010 16:52]

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Re: Rever pan question [message #12642 is a reply to message #12641]

Wed, 06 January 2010 08:29

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Hi, as you have found out you got jerked off with the wrong pan, that pan with a 8 ohm input is for a fender black/ silver face amp. The DC measured input resistance for a frank pan is 182 ohms,so a pan with around 1.7 to 1.85k input IMPEADANCE is whats needed.
Also you do not need the factory ground wire from the pan to the rear of the chassie, as I have found it to only sever to add hum when the reverb is turned up it creats a unneeded ground loop.
The pan does need to have a ground from one of its rca jacks to the pan though.
Also replacing those cheap factory rca cables with better sheilded fat type Hi Fi ones will kill off some hum.
also on that reverb board the original black paper cased 500mfd at 50volt cap needs get replaced and stepped up to a 75 volt cap.

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Re: Rever pan question [message #12643 is a reply to message #12642]

Wed, 06 January 2010 17:23

thekid
Messages: 25
Registered: August 2008
Location: Cape Cod, Massachusetts

Junior Member

So do you think it is the pan thats causing the volume loss symptom? Or the cap that you mentioned on the effects board? Im not really getting any "hum" just severe loss of volume when i turn up the reverb.

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Re: Rever pan question [message #12645 is a reply to message #12641]

Thu, 07 January 2010 06:05

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

No, its the pan.
Those Fender amps and others that use that low input impeadnace pan have a tube/gain stage followed by a small 1 watt output transfomer to drive the signal thru the pan. You just have a transistor/gain stage in the Frank head.
If you get the right pan installed all should be well. but if from that point on you find the reverb level changing and going down hill, than that cap( 500mfd at 50 volt) should get changed out.
In fact there is another more important one of the same type and value/spec on the preamp regulator/output stage driver board mounted on the rear of the amp.
If that goes you will have posssibly no output at all no less no reverb if the first one mentioned fails.

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Re: Rever pan question [message #12646 is a reply to message #12645]

Thu, 07 January 2010 16:40

thekid
Messages: 25
Registered: August 2008
Location: Cape Cod, Massachusetts

Junior Member

well thanks! I assume this is something I could do myself. I can use a soldering iron, at least. Where do you reccomend I get the two caps? Nothing wrong with a little preventative maintenance I suppose. As far as the pan goes, Im goin back to the guy and demanding a swap out.

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Re: Rever pan question [message #12649 is a reply to message #12641]

Thu, 07 January 2010 17:41

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

The reverb control will act like a balance control. Full counter clockwise is all straight signal with no reverb, and full clockwise is all reverb with no straight signal. So what you describe is actually normal.

The wrong input transducer on the tank will cause the reverb to be weaker than it should be.

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Re: Rever pan question [message #12650 is a reply to message #12641]

Thu, 07 January 2010 21:39

thekid
Messages: 25
Registered: August 2008
Location: Cape Cod, Massachusetts

Junior Member

Aha. So theoretically I could just change the transducer on the pan I have and it would be fine?

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Re: Rever pan question [message #12651 is a reply to message #12641]

Fri, 08 January 2010 06:44

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Yes, Acutronics the maker of the pans do sell parts to do that but its not worth the work to drill out the hold down rivet and fight with the springs to get them back hooked onto the thing as you stand a real good chance of snapping off those fine brass wires that the spring retaining hooks are crimped onto!
A whole new pan from Antique Electronics is less than 30 dollars so I can not see spending two hours or more to swap out the transducer.
Cap wise what you need you can order from www.Newark.com.
To replace two big cased 500mdf caps, you will need part number 18C4463. One for the reverb board and one for the regulator board.
Note that the regulator board is held onto the rear of the amp with 4 machine nuts, and I think they are 8/32 so you will need a nut driver or a 1/4" drive socket set to get them off.Then the board will slid off of the 4 pins of the two regulator transistors that it loads onto.
Also the reverb board must be unbolted fron the chassie to get good access to the bottom nuts.

While you have the amp opened up it has 16 more white cased caps that should get changed out also as on the preamp board in these amps I always find one cap that has already started to leak at one end, in which case it will be a short time before that channel goes dead.
To replace all of these if the amp has no vibrato/reverb board you will need QT7 17M9377 caps
QT7 95C1181
QT4 95c1177
QT1 14M6654
I would also pick up some 01F195 de-soldering braid with the order to help you get the old caps out with out killing the circuit traces.
A good tip would be to use a fine tipped marker to make a plus sign on the board that will note to you where the plus end of the replacement cap goes. With some of these caps the orientation does not matter, but with others it does if you do not want them to blow up, so do the marker thing!

[Updated on: Fri, 08 January 2010 06:49]

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Re: Rever pan question [message #12848 is a reply to message #12651]

Tue, 02 February 2010 20:35

thekid
Messages: 25
Registered: August 2008
Location: Cape Cod, Massachusetts

Junior Member

Okay, so I got my amp tech to replace the reverb tank he gave me by mistake with the "right" one which is the 4fb3d1b. I put it in myself and now, as soon as I power up my amp it lets out the most heinous squeal I have ever heard. The noise does not respond to volume knobs. It is loud no matter what the volume is set at. What is wrong with my amp?!?

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