Jess Oliver's legacy - AMPEG PORTAFLEX CLUB part 9

[christw]

I really like the stock CTS speakers in the B-15 for that buttery flatwound tone. I still have the D130 in my B-15 but I haven't powered it on since swapping speakers. I still need to fix a flappy bit of tolex in the port.

[jnewmark]

Originally Posted by coreyfyfe

There were versions - the B-15NC and B-15ND which were 50 watt, but they were basically a B-18 head (they used a 7199 PI and 7027 power tubes) on either a 2x15 column (NC) or a 1x15 with a 1x15 extension cab (ND). The change over with the high/low boosts was still only 30 watts as far as I know, it used the same power amp as the B-15N(f) revision. There were also B-12 and B-18X models, but I don't know if I've seen schematics or pictures of a B-15X that is referenced in this article as 50 watts.

" 1966 Solid-state 50-watt BT-15 introduced, followed by BT-15C (2x15 cab, 85 watts), and BT-15D (100 watts); B-15NF raised to 30 watts; B-15X raised to 50 watts
1967 B-15NC “second version” (C for “column”) has 50 watts and a 2x15 cabinet with CTS or Altec speakers; B-15ND has 50 watts, 1x15 and a 1x15 extension cabinet; blue check covering on all models replaced by black covering and chrome trim
1968 Completely revamped B-15N “second version” introduced, 50-watt, two-channel head with new preamp, ultra-hi and ultra-lo inputs for each channel, and Thiele porting design"

It seems like, according to this article, those models you mentioned came out in 1966, or 1967. In 1968, according to this article, the B15N was bumped to 50 watts.



"

[coreyfyfe]

Originally Posted by jnewmark

It seems like, according to this article, those models you mentioned came out in 1966, or 1967. In 1968, according to this article, the B15N was bumped to 50 watts.

Yeah I'm saying the article is probably wrong. This page is from a 1967 ampeg catalog, detailing the bass amp series:



And this page is from the 1972 ampeg catalog. It lists the 60 watt B15S and the 30 watt B15N:



Though, to be honest, ampeg is a bit notorious for releasing small variations on their amps for very limited time frames. If I had a 68, 69, or 70 catalog handy that would be helpful to the discussion, but I don't; though I believe information about the various models is available in the ampeg behind the sound book. I'll check it when I get home.

[beans-on-toast]

I have seen at least one other reference that has claimed that the B-15N was bumped up to 50W in 1968. I've always thought that that was a typo. They did introduce a new output transformer for the B-15 in 68, the OT-214. This transformer was used in all the subsequent models.

Below is a copy of the 1970 catalog for the B-15N. They state that it has a 30W output and they have 6L6GC power tubes. The 1971 and 1973 catalogs state the same output power. The schematic, voltages, and transformer set for these later models is the same as the 1968 that I posted above. If you believe the Ampeg catalogs, then it is a 30W amp.

The tube amps that were rated at 50W had 7027A output tubes.

1970 catalog extract:

[jnewmark]

Well, I guess the one I'm getting is'nt 50 watts then. Here's a pic of the back:

[portaflexer]

I believe that model was rated at 30 or 35 W. I can't remember for sure.

EDIT: Oops, I didn't read the ad above... make that 30. Sorry.

[Ric Vice]

Originally Posted by jnewmark

Well, I guess the one I'm getting is'nt 50 watts then. Here's a pic of the back:

I remember playing a lot of different gigs with my 64 B-15N(C) when I was in college and even later. In most circumstances, it did a great job of keeping up. The model you have is voiced a little differently, than mine, but it sounds just great. You might be surprised how well it will keep up. If you have a P.A. handy they work dandy with a mic. Something about it's EQ section that cut's through the mix nicely. Of course, the Double Baffle cabinet, on the earlier ones has the best voicing IME.

Ric

[beans-on-toast]

The volume difference between 30W and 50W isn't that much. I think that you would be better off in terms of volume by adding a second eight ohm 115 cab. Your back might disagree.

[garmenteros]

Originally Posted by beans-on-toast

I can't say which will sound better. Probably a good idea to try them both in that cab and see. Sometimes you'll be surprised by the outcome. I have a Jensen Concert that I really like.

I've got a visit to the tech tomorrow and I will let you guys know.

Also anyone care to comment on EMINENCE LEGEND CB158 15", 8 OHM ,300W SPEAKER sold at fliptops.net? I want to gig my b15 someday like a small room at a bar im doing friday and dont think the stock speaker or jensen would cut it.

[beans-on-toast]

Originally Posted by jnewmark

Here's a pic of the back.

Amazing condition!

The 5AR4 is made by Mullard. The 6SL7's are made by Sylvania. GE power tubes. All very good to have. I also see the orange sticker issued by the City of Los Angeles.

[JimmyM]

Originally Posted by garmenteros

Also anyone care to comment on EMINENCE LEGEND CB158 15", 8 OHM ,300W SPEAKER sold at fliptops.net? I want to gig my b15 someday like a small room at a bar im doing friday and dont think the stock speaker or jensen would cut it.

Only goes to 3k. Sorry, not high enough for me. I've got Delta 15a's in mine, which are quite badass and sound just like the old CTS speakers, but if I had to do it over again, I'd probably go with Beta 15a's because they're $20 cheaper, sound about the same (maybe a little brighter), and take a bit more power, despite what the thermal rating tells you...Beta has more xmax so it can take more volume. Like that matters in a B-15

If you go with neos, I might give one of those Faital 15PR400's a shot. Even brighter than the Betas, and they work in small cabs.

[ddbassGA]

Originally Posted by beans-on-toast

The volume difference between 30W and 50W isn't that much. I think that you would be better off in terms of volume by adding a second eight ohm 115 cab. Your back might disagree.

I have a 50 watt b-18 head and a couple of B-15's. The 50 watt head has significantly more usable volume than either the 25 watt cathode bias '64 or the fixed bias '66. Or the '71 B15N for that matter. The 50 watter really shines driving 2 B15 cabs. The difference has to be in the OT, cause there's no real reason to think a pair of 7027a would be louder than 6L6's.

I tried a B25 thinking it would be like the B-18 head, but very different: farts out way early -- well mine did. I had more usable volume with a B15.

[esselbass]

Hey guys,

Long-time reader, first-time poster.

I picked this guy up yesterday and thought I'd better bring it before the experts for you to look at, and I have a few questions:











I think, from my research, the fact that it's a B-15NB means it's a 1963?

When I took it home there was some bad rattle, but I quickly figured it out it was that the second baffle was loose, so a few new nuts and it was good to go.

I had to learn some new tunes this afternoon so I ran it for a few hours, then played it for a few more hours tonight at a rehearsal. The amp is dead quiet, no hum. ...and it sounds INCREDIBLE. I'm really, really happy with it. Warm, round, even, full. Love it.

Had a few other questions for you guys:

I know those side handles aren't original, but what about that speaker with the square magnet? The foam on the inside of the cab? The knobs?

Also, is that tolex original? I don't recognize this style from any other fliptops I've seen. If it's original, I'll leave it, but if it's not, I may have it redone.

Last question, maybe the most important: I'm thinking of taking this guy out on the road with me (on tour), is that a really stupid idea?
The band I play with uses in-ears, and we bring a really hefty PA, so the volume is a non-issue.
Is it a foolish idea to take such an old amp around? I'd be getting a road case made for it if I did. Would it be smarter to get two so that the head and cab travel separately?

Any advice would be appreciated... Thanks guys!

Steve

[JimmyM]

#320 esselbass

Very little in that B-15 looks original, but who cares? Yours looks a lot like mine used to before I had it restored. Fortunately, you can still get everything you need to restore it if you're thinking about doing it, although I might hop on the blue diamond tolex as there was a shortage last year.

OK, here's what's not original for sure...

HEAD:

Knobs (stove top knobs were stock)

Tolex on chassis tray (really not sure what they used back then but pretty sure that's not original)

Light up plate is missing

CAB:

Tolex (blue diamond was stock from 63-67)

Grillcloth (stock is gray/silver with black horizontal lines)

Foam (they used fiberglass insulation on the back wall only, but I recommend breaking tradition here...I used a sheet of 1" Nu-Foam poly-fil on the back wall of my cabs, but it looks like what you have in there should work, although a bit of overkill)

Speaker (not sure about that...B-15NB's came stock with either a Jensen C15N, a JBL D130F, or a Cleveland. Definitely not a Jensen or JBL, not sure what the Cleveland looks like, but it looks more like a CTS to me, which were used in B-15's but not until 64).

Side handles (for wussies only)

Logo is missing

Tilt back rod is missing (I guess he covered it up with the tolex)

As for whether it'll hold up taking it out on the road with you...I take my 64 out all the time. Would have posted some pics, but I can't get on the site they're stored. I only bring it in my own personal van or car so I just use soft covers for it and flip the head inside. If you're taking it out in a trailer, you should definitely consider using a case with some cush padding, and I would likely take them separately. But it'll hold up to road use. They're pretty much tanks. Throw a mic on it, too!

[christw]

B-12 local to me for $1000. I can pick it up and ship it for you guys if needed. http://dayton.craigslist.org/msg/3490693692.html

[jnewmark]

Originally Posted by beans-on-toast

Amazing condition!

The 5AR4 is made by Mullard. The 6SL7's are made by Sylvania. GE power tubes. All very good to have. I also see the orange sticker issued by the City of Los Angeles.

Why would there be such a sticker ? And , as far as adding another cab, does that mean it can take a 4 ohm load ? I was wondering if I could use the head alone with my 4 ohm 212 cab.

[beans-on-toast]

The sticker was applied to amps used in LA to certify that it is safe to use. A manufacturer would pay to have a product "certified".

There's an ext. spkr. jack on the back of the amp. It is intended to use with an 8 ohm speaker cab. When you plug in, the main cab's speaker is connected in series with the external cab and is switched internally to a 16 ohm tap on the transformer.

People run these amps with a 4 ohm cab connected to the 8 ohm tap that the main speaker is normally connected to. Jess Oliver, the designer, used to re-cone the standard 8 ohm speaker with a 4 ohm speaker coil. This makes the power tubes run harder which wears them out faster. It also changes the character of the amp a bit because there is an impedance mismatch which allows more current to run through the output circuit. It seems that they amp can handle it. Fender used to do this with some of there amps. You can do this with some amps without any ill effects.

It isn't going to hurt to try your 210 cab. If you do, keep in mind that it is an old amp. My concern is that if the transformer is pushed and it overheats it could lead to a breakdown in the coating on the transformer's coil wires. This could cause a short and lead to a failure. Try it at low volume, keep an eye on the temperature of the output transformer. If it seems to work, go for it. If you had a new transformer in there, I wouldn't be so concerned. It all depends on what kind of shape your vintage transformer is in.

[jnewmark]

Originally Posted by beans-on-toast

The sticker was applied to amps used in LA to certify that it is safe to use. A manufacturer would pay to have a product "certified".

There's an ext. spkr. jack on the back of the amp. It is intended to use with an 8 ohm speaker cab. When you plug in, the main cab's speaker is connected in series with the external cab and is switched internally to a 16 ohm tap on the transformer.

People run these amps with a 4 ohm cab connected to the 8 ohm tap that the main speaker is normally connected to. Jess Oliver, the designer, used to re-cone the standard 8 ohm speaker with a 4 ohm speaker coil. This makes the power tubes run harder which wears them out faster. It also changes the character of the amp a bit because there is an impedance mismatch which allows more current to run through the output circuit. It seems that they amp can handle it. Fender used to do this with some of there amps. You can do this with some amps without any ill effects.

It isn't going to hurt to try your 210 cab. If you do, keep in mind that it is an old amp. My concern is that if the transformer is pushed and it overheats it could lead to a breakdown in the coating on the transformer's coil wires. This could cause a short and lead to a failure. Try it at low volume, keep an eye on the temperature of the output transformer. If it seems to work, go for it. If you had a new transformer in there, I wouldn't be so concerned. It all depends on what kind of shape your vintage transformer is in.

So, if I'm understanding you correctly, using an extension, 8 ohm cab, WITH the internal speaker connected also, still gives an 8 ohm load ? I always thought that, with tube amps, you could go lower in loads, but not higher ?

[beans-on-toast]

Originally Posted by ddbassGA

I have a 50 watt b-18 head and a couple of B-15's. The 50 watt head has significantly more usable volume than either the 25 watt cathode bias '64 or the fixed bias '66. Or the '71 B15N for that matter. The 50 watter really shines driving 2 B15 cabs. The difference has to be in the OT, cause there's no real reason to think a pair of 7027a would be louder than 6L6's.

I tried a B25 thinking it would be like the B-18 head, but very different: farts out way early -- well mine did. I had more usable volume with a B15.

I know what you mean, there is a volume difference. I've found that at loud levels, that extra volume didn't make that much of a difference.

I find that different speakers will also make a difference in how much you can get out of an amp. You can take the same amp with two different cabs and one can cut though better or have a nicer tone. The capacitors in the power supply will make a difference in usable volume and headroom. If the caps are performing below spec the usable volume will be lower. Just saying that it is a factor. If the amp is optimally biased, it also makes a difference in what you can get out of it. I guess I'm saying that a lot of factors come into play when it comes to an amp delivering an optimal musical output.

There is a difference between the 7027A and the 6L6GC. The 7027A can be run at higher plate voltage levels (600V vs 500V of the 6L6GC) and it can dissipate an extra 5 watts of heat on the plate. This means that you can run the tube at a higher voltage which allows you to squeeze more output wattage from the tube.

This is exactly what Ampeg did in their 7027A based amps. The plate voltage of the 68 B-15N with 6L6GC's is 450V. This is in contrast to 7027A based amps like the B18N (and B-15ND) that had a plate voltage of 505V, the B15S was run at 575V. As you mentioned, the output transformer used also makes a difference. The 50W 7027A based amps had a different transformer than the 30W amps. I don't know if it was simply a beefier transformer to take the higher wattage or if there was an impedance difference that helped them get more power as well. I don't have the specs on the one that they used. The point is, the higher voltage allowed them to bias the power tubes into a region that allowed more power out of the tubes.

It is true that some manufacturers were selling 7027A tubes labeled as 6L6GC and these were interchangeable. If you take an amp designed for the 7027A spec and install a 6L6GC, you might be pushing the tube. You can sometimes get away with doing this because many of the NOS tubes could be pushed beyond their published data sheet limits. The data sheet specs were intended to provide optimal service life. Some manufacturers like Fender would design amps with voltages higher than the published specs. Back then, tubes were of good quality, they were cheap and the designers knew that they could take the extra stress so they took advantage of this.

[beans-on-toast]

Originally Posted by jnewmark

So, if I'm understanding you correctly, using an extension, 8 ohm cab, WITH the internal speaker connected also, still gives an 8 ohm load ? I always thought that, with tube amps, you could go lower in loads, but not higher ?

Not quite, with the 8 ohm extension cab connected you have a 16 ohm load.

The amp has both 8 ohm and 16 ohms taps on the transformer. You don't have access to these at the back of the amp. When the 8 ohm internal speaker is connected, it is connected to the 8 ohm transformer tap. The impedance is matched. When you plug an external 8 ohm cab into the ext. spkr. jack on the back of the amp, the wiring is shuch that the internal speaker is connected in series with the external cab (8 ohms + 8 ohms = 16 ohms) and this is switched to the 16 ohms transformer tap. This switching is done internally when you plug into the ext spkr jack. So now your speaker load totals 16 ohms and is connected to the 16 ohm transformer tap. Again the impedance is matched.

You are correct, with tube loads it is better to go to lower impedances than it is to go to higher impedances. Either way there is a price to pay in doing so and matching loads is optimal.