N(V)AD - 1967 Ampeg BT-15

[P-oddz]

Just picked this up this evening - '67 Ampeg BT-15. Great price on it, and it's super clean.

Original speaker has been replaced with an Eminence Beta 15A which sounds really good to me so far. Luminescent panel wiring has been disconnected (apparently to noise it introduces - can't confirm) but overall seems to be in great shape minus that it stinks to high hell from staying in a smoking household.

Still trying to find as much as I can about these. Grace me with your knowledge. Especially how to get smoke scent safely off of tolex and inside the speaker cab.

 

[P-oddz]

Also - I know it's kind of a stupid question but none of my other Ampegs have had the 4-input layout, so if anyone can elaborate on the difference between the 2 channels and/or difference on the inputs that would be awesome. Calling all Ampeg guys - obviously starting with @JimmyM , please and thanks!

 

[bobyoung53]

Also - I know it's kind of a stupid question but none of my other Ampegs have had the 4-input layout, so if anyone can elaborate on the difference between the 2 channels and/or difference on the inputs that would be awesome. Calling all Ampeg guys - obviously starting with @JimmyM , please and thanks!

I'm not JimmyM but the top two have a (treble) G clef and the bottom two have a bass clef, on my 70's B-15S and SVT's the top two are for the bright channel and the bottom two are for the normal channel, (the two on the left are for the first channel (bright and normal) and the other two on the right for the 2nd channel) i would imagine yours is the same, remember Everett Hull was still the owner at that time and made them for jazz players who could usually all read music hence the clefs, he hated rock n roll. Nice amp, how's it sound? I love the 1967 style of portaflex amps.

 

[P-oddz]

I'm not JimmyM but the top two have a (treble) G clef and the bottom two have a bass clef, on my 70's B-15S and SVT's the top two are for the bright channel and the bottom two are for the normal channel, (the two on the left are for the first channel (bright and normal) and the other two on the right for the 2nd channel) i would imagine yours is the same, remember Everett Hull was still the owner at that time and made them for jazz players who could usually all read music hence the clefs, he hated rock n roll. Nice amp, how's it sound? I love the 1967 style of portaflex amps.

Thanks for the info! I kind of assumed as much, but was definitely curious if there were huge distinctions between channel 1 and two.

I didn't get a ton of personal time to really fully explore the amp at home (young baby in the house), but my first impressions are very positive. The tone is warm and punchy, or round and tubby depending on settings - kind of exactly what you'd expect from a flip top from that era. It's probably lacking in some mojo from tube compression/sag/drive, but by no means is it a slouch. The Eminence replacement speaker has a nice tone to it with some caveats that I have to sort out. When volume was approaching cranked (around 3 o'clock or so) I was getting really awesome grunt overall, but certain notes on my E string were sending it into "SPLATTY" territory.

I'm not sure if that's a byproduct of the amp hitting its rails in a very unpleasant clip, or if the speaker is achieving some sort of excursion limit? Shy of that, the amp has a real nice mojo and definitely a cool style to it. I'm going to experiment with my SFT pedal this weekend and see if adding a little bit of gain from the pedal yields some nice, throaty results without having to crank volume to the point of splats.

Definitely think it will be a cool amp to jam around at home with and perhaps make its way into some recordings.

 

[JimmyM]

I'm not sure if that's a byproduct of the amp hitting its rails in a very unpleasant clip, or if the speaker is achieving some sort of excursion limit?

A Beta 15a will take a pretty good pounding before it gets splatty, so I'd have to think you were overdriving the amp.

 

[bobyoung53]

Thanks for the info! I kind of assumed as much, but was definitely curious if there were huge distinctions between channel 1 and two.

I'm not sure about that I've never tried one either but if it's like the other B-15's they were be pretty close or identical sounding.

 

[P-oddz]

A Beta 15a will take a pretty good pounding before it gets splatty, so I'd have to think you were overdriving the amp.

On further review, it seems like the amp and the speaker are able to take the beating. What seems to be making the splatty noises seem to be vibrations happening at the grill and perhaps some bracing towards the bottom inside the amp. I'm going to remove the speaker and see if there is anything that looks suspect in front of the grill. In another B-15 repair thread I saw someone mentioning some material in between the speaker and grill that limits vibration that can deteriorate after awhile(?)

I'm not sure about that I've never tried one either but if it's like the other B-15's they were be pretty close or identical sounding.

After playing around for a while, I think that pretty much appears to be the case. They sound nearly identical to my ears.

 

[JimmyM]

On further review, it seems like the amp and the speaker are able to take the beating. What seems to be making the splatty noises seem to be vibrations happening at the grill and perhaps some bracing towards the bottom inside the amp. I'm going to remove the speaker and see if there is anything that looks suspect in front of the grill. In another B-15 repair thread I saw someone mentioning some material in between the speaker and grill that limits vibration that can deteriorate after awhile(?)

Yep, they put in foam. Nowadays, everyone uses black felt because it won't deteriorate.

 

[BogeyBass]

thats in really good shape. be awesome find a competent tech to check out the illuminated display. its a whole new mystical amp with the panel lighted. i really like the piping and look of these flip tops it looks so classy

 

[Bass 45]

I wonder is this amp can handle a four ohm load - in which case you can get more power by changing the speaker. If there is a separate jack for an extension speaker, you can check to see if it connects to a diffent tap on the transformer - or if the two speakers run parallel for a 4 ohm load. Also, note in the attached image that there is an ultra high function. Did you try pulling the knobs to switch it on?

 

[two fingers]

As far as the odor goes, the only thing I have found thay works permanently is sunlight.

Pop out the speaker. Set the amp, speaker and grill in the sun several times. UV light is incredible in what it can do. It kills germs and somehow gets rid of odors.

If that doesn't work by itself, try steam and then sunlight. On a sunny day, set the amp in a bathroom and run the hot shower until it steams up pretty good. (Sorry, but that will temporarily make your bathroom smell like smoke as it draws that smell out.) Immediately take the three parts out in the sun. I did that once with a plush case that I thought I was going to have to throw away. Worked great.

Do NOT try to "replace" the smell by spraying it with air freshener. You will only end up with smoky flower smell.

Cool amp.

 

[beans-on-toast]

View attachment 2625592 I wonder is this amp can handle a four ohm load - in which case you can get more power by changing the speaker. If there is a separate jack for an extension speaker, you can check to see if it connects to a diffent tap on the transformer - or if the two speakers run parallel for a 4 ohm load. Also, note in the attached image that there is an ultra high function. Did you try pulling the knobs to switch it on?

At least one revision of the BT-15 is rated 65w into 8 ohms, 100W into 4 ohms. So with two 8 ohm cabs it will increase the volume and output power.

They have something different in some BT-15 schematics, the Ext Spkr jack has a 3 ohm resistor in series with it. Which means that if you connect an 8 ohm extension cab, you are connecting 8 ohms + 3 ohms = 11 ohms in parallel with the main 8 ohm speaker. With the two speakers in parallel, this works out to 4.5 ohms. Maybe they are doing this just to be safe.

If I were connecting a second cab, just to be safe, I would do it through the Ext Spkr jack rather than by daisy chaining two cabs and connecting them to the main speaker out.

By the way, the 8 ohm BT-15 extension cab is a BT-15X.

Will post the manual when I can get to my computer.

 

[beans-on-toast]

Here are two BT-15 manuals and a '67 schematic, see attached. They've been added to the schematics section of the Portaflex Wiki found here: BT-15. There are additional files in the Wiki.

 

[dbase]

Pour a can of beer on it and it will then smell like a bar. My gigging amps always had that smell.

 

[P-oddz]

Thanks for all the responses, guys!
I just heard back from Ampeg (Hodgy - whom I believe is a TBer as well, no?) and he sent user and repair manuals my way as well. But all this information is really helpful and I appreciate you guys taking the time.

Also, thanks for the advice on removing smoke scent. I'll definitely see about giving some of those ideas a try.

As far as some of the internal bracing that might be suffering from too much vibration, does anyone have any suggestions. My thoughts would be a once over of a silicone caulk of sorts, but that might totally be the wrong thing(?)
Perhaps that coupled with some sort of dampening material to really tighten everything up?

My brother-in-law works for SKB cases, so maybe I could get some high quality foam?

 

[Bass 45]

Thanks for all the responses, guys!
I just heard back from Ampeg (Hodgy - whom I believe is a TBer as well, no?) and he sent user and repair manuals my way.

Also, thanks for the advice on removing smoke scent. I'll definitely see about giving some of those ideas a try.

As far as some of the internal bracing that might be suffering from too much vibration, does anyone have any suggestions. My thoughts would be a once over of a silicone caulk of sorts, but that might totally be the wrong thing(?)
Perhaps that coupled with some sort of dampening material to really tighten everything up?

My brother-in-law works for SKB cases, so maybe I could get some high quality foam?

I think silicone might help if what you are are hearing an air leak - but probably wouldn't help if you have vibrations due to structural issues.

 

[beans-on-toast]

You have to identify, for sure, what the vibration issue is. It could be loose joints, it could be delamination with loose bits inside the ply, it could be the tray that the amp sits on, the baffle might be loose, the lid might be warped, loose latches, overly compressed gasket, the speaker could be loose, the speaker gasket might need to be replaced,..... The list of possibilities is long.

You have to carefully check out the cabinet, one detail at a time. You can narrow down the problem by separating the head and the cabinet. That allows you to determine if the noise is coming from the head or the cab or both.

If the problem is with the cab, narrow it down by applying pressure on the surfaces while playing can help isolate the vibration. Push or sit on the cab, rotate it around and apply pressure on those surfaces. Narrow it down. Tapping on surfaces can help identify delamination. If you find this, glue can be injected with a syringe. If joints are loose, adhesive can be injected into the joints. Sometimes bracing or turnbuckles are required.

It comes down to being creative and figuring out what the problem is and how to resolve it. Debugging noises can drive you nuts.

 

[P-oddz]

You have to identify, for sure, what the vibration issue is. It could be loose joints, it could be delamination with loose bits inside the ply, it could be the tray that the amp sits on, the baffle might be loose, the lid might be warped, loose latches, overly compressed gasket, the speaker could be loose, the speaker gasket might need to be replaced,..... The list of possibilities is long.

You have to carefully check out the cabinet, one detail at a time. You can narrow down the problem by separating the head and the cabinet. That allows you to determine if the noise is coming from the head or the cab or both.

If the problem is with the cab, narrow it down by applying pressure on the surfaces while playing can help isolate the vibration. Push or sit on the cab, rotate it around and apply pressure on those surfaces. Narrow it down. Tapping on surfaces can help identify delamination. If you find this, glue can be injected with a syringe. If joints are loose, adhesive can be injected into the joints. Sometimes bracing or turnbuckles are required.

It comes down to being creative and figuring out what the problem is and how to resolve it. Debugging noises can drive you nuts.

Again, thank you for the very solid advice, Beans!
I was doing this the other day, and that's how I narrowed down at least two problem areas. Definitely getting some flap at the grill, so I'm going to look at what is happening in front of the speaker and if I need to replace some foam/felt between the two. I can place pressure on the grill and definitely lessen the vibrations, so it might be a combination of some things. Second problem area seems to be (the best way I can describe it) in the baffle that sits below the speaker inside the cabinet. I can put weight on it and stop it from vibrating so intensely, so I definitely think there are issues with joints there.

 

[beans-on-toast]

It isn't unusual for the cloth to loosen. Sometimes all you have to do to fix the flapping is to heat it evenly with a hair dryer. Ampeg used to recommend this in their manuals.

To do the job properly, I would remove the grille cloth, clean up the dust inside, glue on some felt, cut out arou d the speaker hole, wash and replace the grille cloth. The grille cloth has to be installed with even tension so that it looks uniform. You'll need a hardware store Arrow type of stapler. Use staples with ¼" legs. Then shrink the cloth with a hair dryer (not a heat gun) if necessary. While the grille cloth is off, inspect the speaker cutout hole. Sometimes there are loose bits in there that need cleaning out. Actually this is pretty common. A CA glue or wood glue can stabilize the wood. Loose wood here can be a source of buzzing. Then use wood filler or epoxy to fill any voids. A lot more work.

The bottom plate that you described (over the port if I am understanding you correctly) is screwed on in some cabs. The screws simply need tightning. If not, it needs to be tightened down, glue or like you said silicone can work.

 

[DougA]

for smoke smell: Here's something that sounds crazy. I thought it was nuts until I tried it and it worked on my '86 BMW which had been a smoker's car for decades (and of course, exposure to sunlight wasn't doing anything...) I saw this on a car forum: every day I put a pie tin of frito corn chips and a banana peel in the floorboard. (This shouldn't be my first post on a forum, but it is..) I did this for a week or two and it removed the cigarette smell. Later I got a '69 Kustom K-100 head and 1x15 cab that had been in the possession of an inside smoker for 35 years.. It was so bad that I couldn't have the amp in my house. I quarantined it to the garage and did the same thing with the cabinet in giant garbage bag, fritos and banana peels. later did it to the head. You'd never know it today that it was ever a smoker's amp.

beans-on-toast, thanks for posting the manual. I just got a BT-15 and I'm happy to find this thread.