Nothing wrong with using tape. If the lining gets mucked up, it's a lot easier to change. It's a lot better than the tons of staples that are often used. When the batting is glued in place it makes it even harder to replace.
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Official Ampeg Portaflex Club
- Thread starter JimmyM
- Start date
The blue line graphics were only used until 1972, so that would put it between 68-72. From what I've experienced in the past, the only way to get a more accurate date is to look for the manufacturing codes on the internal components (make sure you look at multiple components because some wear out and get replaced over time). My SB-12 Portaflex is the same series. Last time I had it serviced, the tech guessed it to be a 1970 based on date codes on the pots.
If anyone knows a more accurate way to date them, please let me know. I also have a blue line GU-12 from the same era. That particular model wasn't made until 1970, so it's a little bit of a smaller window. It would be really cool if they were both 1970 models.
If anyone knows a more accurate way to date them, please let me know. I also have a blue line GU-12 from the same era. That particular model wasn't made until 1970, so it's a little bit of a smaller window. It would be really cool if they were both 1970 models.
Anyone else use their b15 for vocals? Ive been using mine for about two months as a vocal monitor because my zeppelin tribute band has been rehearsing in a large warehouse and we don't own a PA. So far it keeps up well against a loud drummer, and the guitarist and my half stacks. It starts to distort some after about an hour so if I really push it but thats normal I guess. One of those times I also ran one of my ibanez fender copies with flats and I got awesome grinding tone even though the drummer and guitarist had to turn down.
I also just got a couple of months ago a second b15 that I haven't had a chance to fix or get the other parts for. 150USD for the cab with a destroyed and modded head... Can't remember If I posted pics or not so here they go...
Looks like it'll be a fun project. The amp has had some mods to say the least. It looks like all the guts were removed. Are you planning to use a turret board or do a circuit board? THe cab looks like it will clean up nicely.
The nice thing about that model is that the chassis can be painted and it can look as good as new. Can't do that with chrome. I've done a number of the front gray panels and they turned out well after I figured out to use a zinc chromate primer.
Very nice j! It looks like it has been well cared for. Always a good sign. Yes, the design change was in 1968.
The easiest way to estimate the manufacturing date is to look under the chassis at the date codes on the pots. They used CTS pots, so code starts with 137. For your era, the following two digits indicate the year, the next two are the week. So 1376824 would indicate a CTS pot manufactured on the 24th week of 1968.
There can be date codes on the larger wire wound resistors.
The capacitor mounted on top of the chassis may have a date code.
If you remove the transformers, there is sometimes a paper label with a date code. This is rare to see.
The four shock mounts that the amp tray is mounted on also have a date code.
You can also check out the speaker for a date code.
There is also a serial number on the chassis of that B-15 revision:
Serial Number Range Year
000001 to 020000 1965
020000 to 049000 1966
049000 to 075000 1967
075000 to 080000 1968
080000 to 092000 1969
Finally, here is an ecopy of the 1968 schematic:
Thanks for the info, much appreciated. Was this revision also the change to 50 watts ?
J Newmark,
To the best of my recollection, the helmet head logo B-15N's were never bumped to 50 watts. The B15-S amps did have that output. The Solid State BT-15's were 50 watts, and in 1967 the they built a B-15ND that used
the B-18N head atop a pair of B-15N Cabinets. Both of those amplifiers precede the redesign of the amp in 1968.
Ric
All the guts were removed... Any idea if that stock speaker on this battered one will sound better than the jensen I have for my almost stock working 70s b15? I'm thinking about trying it out but its at my techs shop which is a very long drive and he doesn't normally answer the phone or have one most of the time.
Here's an article from Bass player mag about the B15N. Scroll down to a brief history to 1968, where it says the B15N was bumped up to 50 watts. I'm wondering if this is accurate info or not.
Invalid Link Removed
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.
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 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.
" 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 trim1968 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.
"
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.
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:
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:
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.
EDIT: Oops, I didn't read the ad above... make that 30. Sorry.
