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B15 Rattle and hum.

Vin_MM_Sabre_79

Vin_MM_Sabre_79

Apr 14, 2007
1,116
12
Ballaarat Australia
#1
I connected up a new 230V transformer last night and finally got my B15 cranking over on Aussie mains today. :p ... Love the sound but definitely needs cleaning up- I'll have a bit of work to get it to a state fit for recording. First to tighten up all rattles or buzzes. Iv'e read that Jess Oliver relines his baffle with carpet underlay. When I removed the cloth you could see that whatever was there before had disintegrated to dust.Here's my attempt...

Link Removed

Better- but I think it needs to be thicker- mine's only a couple of mm thick. It dampens the sound but I think it needs to be thick enough to actually mute the vibration.

The other thing I have is a bit of hum. I've grounded the chassis with the mains earth- Apparently this means I should change the caps but I dont want to go marching in to changing the circuit around till I've researched it up.

What have other Fliptoppers done to clean up their sound?
 
#3
As for the hum, did you adjust the hum pot? This can have a great effect on the amount of hum. Also make sure your preamp tubes are good - bad 6SL7's can create some serious hum.

I also found that if the four pin speaker cable is replaced with a standard metal 1/4" receptacle, it can create a ground loop. Replacing it with one that doesn't ground on the chassis will alleviate the problem.
 
#4
The speaker cable has four cores for a reason. Two are for the speaker and the other pair are shorted by the cabinet socket to complete the ground from the power supply. This is to prevent the amp running without a speaker attached. The extension speaker socket is insulated from the chassis deliberately. When you use an external speaker it is wired in SERIES with the one in the cabinet and should be a 8Ω unit. This same socket changes taps to the 16Ω tap from the output transformer.

Most amps of this vintage will need a recap job. The primary filter is a 30µF 600V unit and the multi cap is IIRC 40+40+40+40µF at 500V. Antique Electronics (Invalid Link Removed) have the multicap and 16µF and 20µF at 800V electrolytics. They also have a 33µF Solen plastic cap that would be ideal for the primary filter.

Paul
 
#5
Great advice. Thanks guys.
I actually have a caps kit from fliptops.net to install but I want to get used to the 'before' sound first so I know what difference the new caps make.

The Speaker had been modded at some point to a 1/4" jack so yeah I'll have to look into that. I'll be taking it to a guy in Australia who knows WAY more about tube amps than I do, so I'll be getting him to check this out, get his input on the condition of the tubes and install the caps.

Meanwhile- I'm putting my furniture building experience to good use tightening up the cab. The glue on the inner baffle had come loose with vibration so I've opened it up and reglued and clamped.

2219389801_31330395ce.jpg
 
#7
After what I just discovered, I'm really surprised that noone else has had issues with B15N cabinet noise.

Even after installing the santas beard I still had that ticky-buzzy grill cloth noise. Finally found the problem- the original tolex partially covered the ports on the inner baffle which rattles at high volume. (...questioning 1965 Ampeg quality control? :eek: :D)

2223588555_afdcdc5146.jpg


I trimmed it back ... noise gone.

2224378218_37915c9ed7.jpg
 
#8
Finally- the latches on mine had a little bit of movement which were mostly fine- but at high volume made a bit of noise.

I highly recommend this quick and easy addition...
By putting a bit of weather stripping around the rim the lid the old latches are now totally silent. The lid is still flush with the cab when closed but now pushes up against the latches.

2223588781_4af81875b5.jpg
 
#9
Vin_MM_Sabre_79 said:
I highly recommend this quick and easy addition...
By putting a bit of weather stripping around the rim the lid the old latches are now totally silent. The lid is still flush with the cab when closed but now pushes up against the latches.
Click to expand...

I would add, be careful to get open cell foam (light gray, not the darker stuff). If you get the stiffer foam, you run the risk of bending the latches. Mine actually bent where they meet up with the square head screw on the lid.
 
#10
This thread is awesome!

I'm repairing an old B15 "homemade" bottom for a friend. He has a blue diamond b15 head and this dubious cabinet that he's using with it. It's built all sorts of wrong but he needs it to be working in his studio next week. I've had to build new baffle for it. I'm just gonna make this one a single baffle and make it sealed instead of spacer ported... the thing just has to many buzzes to fiddle with porting.

But I would love to see more pictures of these double baffle B-15n cabs.

Also, can anybody point me in the direction of the plans for the original double baffle box? I think I'm gonna try to build one to replace this POS.
 
#11
#12
Wow thanks!

should be super easy to build one of these... would be cool to build it out of some nice baltic birch and make it a stand alone cab for the recording studio.

I'm collecting all of the measurements from the threads on here. should be able to triangulate.

what kind of wood is yours? It's hard to tell from the photos... but it looks like regular "old-style" birch ply with poplar strips for the front fram and top brackets...

cheers,
David
 
#14
Hey Trono. I'm probably going to do the same thing. I'd love to build a twin sister of this cab as an extension cab.

I'd recommend you do the double ported version as it doesn't add any noise in itself and is pretty easy to build. Most of the noise comes from the grill cloth, latches, loose tolex flaps and as Jimmy pointed out the other day- the handle.

As an update to this I've fixed and tightened the handle and also replaced the power capacitors. Sounds squeaky clean now even at high volumes.
 
#15
Yeah. The crappy copy cab I have here I'm just trying to make "work" without too much fuss... but I've already had to make a new baffle and back panel so I'm gonna quit while I'm ahead :)

I'm ordering a bunch of baltic birch for some other projects and I will order enough to make one or two of these guys. One stock for a fliptop head and one a stand-alone for use with whatever.

incedentally the same guy gave me to fix a B-15S cab that is worse-for-wear as well. Seems there was some flooding in his studio a while back. Both of his cabs have mildew and some warping/rot issues. the B15S cab had a dead 421-8H that I get to keep for my self... I plan to have this reconed and put into my B-15S... but after I fix his cab I'm putting a older Magic Parts cast frame 15" in there that I have kicking around... he'll probably be using this cab with different heads...Bassman, SVT, Ampeg SS stuff, etc...
 

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