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Double Bass Bandmates love my...B15N?!?!

#61
Hi Bob, well here is the update. Put in about 10
hours trying to fix this amp head. Still has hum
and without a schematic I dont seem to be able
to find the problem ! One reason is this amp is DC
coupled and it seems to go around in circles so I can
not go any further without some sort of diagram . I
did hook up an outboard power supply and the hum
went away so I did localize the problem but with no
diagram to tell me voltages I am stuck. :crying: It
might in fact be the transformer but Im not sure at this
point. Thanks for your input and suggestions. You were
right on about the futility of repairing this unit but I had
to try. The speaker cabinet is OK and sounds great with
another input source so I am now on the lookout for an
amp head. Best regards, Tom :hmm:
 
#62
bikerbassplayer said:
Hi Bob, well here is the update. Put in about 10
hours trying to fix this amp head. Still has hum
and without a schematic I dont seem to be able
to find the problem ! One reason is this amp is DC
coupled and it seems to go around in circles so I can
not go any further without some sort of diagram . I
did hook up an outboard power supply and the hum
went away so I did localize the problem but with no
diagram to tell me voltages I am stuck. :crying: It
might in fact be the transformer but Im not sure at this
point. Thanks for your input and suggestions. You were
right on about the futility of repairing this unit but I had
to try. The speaker cabinet is OK and sounds great with
another input source so I am now on the lookout for an
amp head. Best regards, Tom :hmm:
Click to expand...

Tom,

I am truly sorry to hear that things didn't work out. Unfortunately, those are diabolical amps to try to repair (not to mention they weren't so great sounding to begin with). There are other amplifiers from the same era, Acoustic for example, that would probably be relatively easy to repair given they hadn't been too terribly abused, but the SS Ampegs from the late 60's just weren't good designs. If it's any consolation, if you had been able to repair your Ampeg, it likely would have just blown up again. :(

Good luck with finding another amp. -bob
 
#63
bikerbassplayer said:
Hi Bob, well here is the update. Put in about 10
hours trying to fix this amp head. Still has hum
and without a schematic I dont seem to be able
to find the problem ! One reason is this amp is DC
coupled and it seems to go around in circles so I can
not go any further without some sort of diagram . I
did hook up an outboard power supply and the hum
went away so I did localize the problem but with no
diagram to tell me voltages I am stuck. Tom :hmm:
Click to expand...

This doesn't sound too hard. The shortest life components in virtually all amplifiers are the power supply filter capacitors--the big cylinders. 30 years is a LONG life for them and when they go bad, you hear loud hum. I'd just replace them based on the ratings that should be written on their cases. Since this is a solid state amp, these should be lower voltage and thus easier to find than those used in tube amps.

If you don't know where to look to find replacements, let me know what value they are and maybe I can find a source.
 
#64
I have a 64 B15N (which is the most recently made member of my Ampeg collection). I wouldn't gig with it for upright, I don't think, but I have gigged it for bass guitar and also have used it as a recording amp for bg and guitar (it's great for clean or mostly clean guitar or some keyboards, which is another reason they are still popular in studios). Mine came with a battered original CTS square back alnico speaker, but I have switched out to another speaker that was a factory option when new, the Altec 418-8H, which is a great, great speaker. These are louder and warmer than the 421, and you don't need the higher power rating of the 421 in that amp anyway. The JBL D140F is also a great choice and was another factory option. Any low wattage 15, preferably alnico, that is designed for bass should work well in a B15; I would avoid modern high power drivers as they sound terrible in that application. 15" drivers that are not designed for bass will likely develop a voice coil rub over time, so I would avoid the Altec 417, JBL D130, and most Jensens for that reason. I actually had that problem with a 418 before but I'm pretty sure it had already started when I got the speaker and just got worse. Now I keep a backup 418 at home just in case.

I like old brown base 6SL7s in the preamp and a red base 5691 in the phase invertor. I think I have a pair of not quite matched RCA 7027 in that amp as far as power tubes, and of course a Mullard or Philips made GZ34, because they almost never die and they put out the requisite high voltage without fail (the tube Sovtek sells as a GZ34 puts out lower voltage than the GZ34 spec).

I don't like the sound of a cranked B15 for bass, but at around half a turn on the volume knob, they are an optimal sound source for bass guitar, IMO. They do sound great cranked for guitar with the right speaker.
 
#65
Thanks for the input . The caps are not the original
as someone has worked on this amp before I got it.
There are 3 groups of 3-1000uf at 100 volts in the
power supply ( in parrallel ). As I said, without a
schematic I dont know the value's of the components
or the voltage readings at a particular test point.
These caps are obviously not the originals . The cap
holders on the PC board are large and look to have held
a large value/voltage of electrolytic. ( 1" to 1 1/2" dia. )
The final output transistors are not all the same so
are probably also not the originals. The PC board has
been worked on in the past so it is impossible to know
what the original parts and values were anywhere in the
amp. I am told that the schematic was printed on the
bottom cover of the amp housing. If you are able , or
know where I could find one or get a copy I would be
very gratefull and of course I am willing to buy it.
Thanks again for all the input and help from everyone.
Tom
 
#66
So are there 9 caps, in groups of 3X1000uF each, all marked at 100V? If so and if they were rated about right by whoever installed them, it sounds like you could substitute three ~3000uF/100V caps if you can find a place to mount them, no? A voltmeter could tell you what voltage is there, but I'm not sure that matters if you know 100V is a safe rating. (It's probably close to 75V on each of the three rails.) Polarity is of course critical.

Re a schematic, it seems there is a solid state Ampeg schematic in the Pittman Tube Amp book, but I can't locate my copy and I don't know whether it's the same model or series. I'll keep looking.

I wouldn't give up yet.

P.S. Then again, I did google this .

Teleharmonium, you're after my heart. I used to love those classic drivers and the fire bottles. :D Just kind of got over most of that stuff, I guess. :hmm:

Charles
 
#67
OK , let me start from here:
The EASY simple stuff is ALREADY done.
Caps have been bypassed with new, rectifier
has been changed, all simple techie tests
have been done already. Now I need to know
the ORIGINAL values of the parts or a schematic
to trouble shoot farthur down the line. I have
repaired electronic equipment both tube and
transister for 30 + years and beleive I can figure
out what is needed to fix the amp if I had
documentation. Hope you can find your book .
I have tried every source available , even the
Vintage Ampeg site and nobody has any BT-15c
or similiar amp documentation, none.
Thanks for the input.
 
#68
bikerbassplayer said:
The final output transistors are not all the same so
are probably also not the originals.
Click to expand...

Hi Tom, this remark puzzles me. You wouldn't expect all of your output transistors to be the same, would you? I mean, wouldn't there be an equal number of two different types so that they complement each other in a push-pull circuit?

Unless you mean there are similar trannies but from different manufacturers, of course...
 
#70
Hi Doug and thanks for the question. What I meant
was : of the 4 output transistors, 1 has been replaced
with a different mfg. and part number. That is part of
my problem, not all parts are original or have part numbers
that can be read ( old worn out numbers ) etc. so trying
to figure out what was there originally is difficult. I know
the output transistors operated push - pull and I assume
the one's that look the same cosmetically are original but
that is only an assumption. Some of the parts were changed
before I got the amp and I dont know if those were replaced
with original values. Caps, transistors, diodes and some of the
resistors have been changed or added. It is obvious that the
person who modified the amp knew what they were doing
and I assume some of the mod's were due to whether parts
were available so I haven't given up totally yet but it is sort
of a spare time project now unless I can come up with a
parts list or diagram. Thanks for your input.
Best regards, Tom
 
#71
Quasi-complementary has been an often used topology that allows all n-type devices to be used in the output stage, the negative half as inverters.

Just my opinion, too, but it's a real good idea to replace outputs transistors in sets, and if possible--matched as closely as possible. JIMHO. YMMV. etc. etc.

Just a simple, 50 yr. old EE trying to making sense of this crazy world with the simple gifts that I have. :hiding:
 
#72
On a similar note, has anyone played through the smaller 12 inch older version of the Ampeg? I saw one at a guitar show here last year, but didn't get a chance to try it. I saw Edgar Meyer play through one at a club here years ago and it seemed to work OK for him. I've tried my upright though an older B-15 I found in a music store recently and it still didn't blow my skirt up, and wondered if the 12 would work better.

The next thing I'm trying this week is my old RB400 with an Epiphani 15 cab. I played that combination in a music store last year with a BG and it was the best sounding 15 I'd heard in a long time.

Acoustic was mentioned here, I think; one of the best amps I played through in a concert was a smaller version of the 360. It had the separate amp/speaker system with a folded 15 and the amp had the graphic EQ. It may have been a 160, not sure. Maybe somebody knows what it was.

Ike
 
#73
Ike,
What you saw was (if it was a tube ampilfier) was an Ampeg
SB-12. I actually owned one. Well, that's not entirely true, my wife owned it. It was a smaller bass amp that was supposedly for
"String Bass" thus the SB prefix. A reall nice little amplifier,
it had a tilt back peg and the blue check covering.
The Ampeg Book has pictures of the amp. I believe that it was Everett Hulls brain child since he really wanted a more portable
amp for Double Bass. It was a 15 watt unit. amazing isn't it.

Ric Vice
 
#74
Ike Harris wrote: "On a similar note, has anyone played through the smaller 12 inch older version of the Ampeg? I saw one at a guitar show here last year, but didn't get a chance to try it. I saw Edgar Meyer play through one at a club here years ago and it seemed to work OK for him. I've tried my upright though an older B-15 I found in a music store recently and it still didn't blow my skirt up, and wondered if the 12 would work better.:

I've played a couple of the portaflex version (the single channel one, with no tremelo) with 7591 power tubes. They tend to fart out in the deep bass at anything resembling giggable volumes, but they work great for recording and are especially great for guitar. There are also B12X and B12XT amps that are great guitar amps but not really suitable for bass, and older "Bassamp" models that came with 12" speakers that I have not heard. Those go back to the late 40s when they used field coil speakers. I doubt they got very loud and clean but they sure look great and they would not have needed to get as loud back in those days.

Eric Jackson wrote: "Re voice coil rub, I was always in the habit of rotating speakers in their mounting every few months or whenever I thought of it. "

That makes a lot of sense, especially for 15s. I think I will take up this policy. I bet my old 418 with a rub could have been saved if I had done that, because it didn't start rubbing due to any particular high volume event or trauma. I still have it, maybe I'll mount it upside down from the way it used to be for a couple of years and retest it.

Aleph5 wrote: "Teleharmonium, you're after my heart. I used to love those classic drivers and the fire bottles. Just kind of got over most of that stuff, I guess. "

right on. There's always ebay...
 
#75
Aleph5 said:
Quasi-complementary has been an often used topology that allows all n-type devices to be used in the output stage, the negative half as inverters.

Aleph, I thought that might be the case for more modern amps, but aren't we talking here about the early days of solid state circuits when you used to have to pair a silicon with a germanium?

Doug (also born '54 - same year as the Fender Strat...)
Click to expand...
 
#76
I don't know when the quasi-comp. was invented, but a quick google refers to its early use precisely because P devices were so poor. Don't know about the amount of germanium in that series either. I do remember the 2nd gen. of s.s. products from Ampeg, Sunn, Fender, et. al. were generally touted as using "all silicon."
 
#77
I happen to have an old SB-12.
It sounds very good for URB at low to medium volumes, but will get a bit farty once it is turned up too much. Has just one channel, two inputs, which each sound very different. A volume control, and bass and treble controls, that's all, simple and perfect. It's allways been my understanding that the amp puts out 25 watts, but I could be wrong.
A very good tube amp guy that used to be in LA, Ray Blackenship gave it a good going over in 1999 and once finished, proclaimed it to be one of the finest ones he'd ever seen. Unfortunatly, it sees little use. I'm on the road all the time, in fact I'm still in China for the time being. The last time I gigged with it was August, 2004 when I was home for a minute. It sounded wonderful on a piano trio gig in a small club. It's heavy, at least 50 lbs. Sure sounds good, great with Fender too. Not for loud playing at all but loud enough for many gigs in smaller venues. When I was a kid I saw Cedar Walton, Bob Burg and Billy Higgins at Donte's with David Williams on bass. He was playing his URB thru one, it was perched on a folding metal chair. This was 30 years ago, the sight of it, with the glowing tubes and all, the sound, the band, the club, was the coolest thing I'd ever seen or heard. As one might imagine, I was very thrilled when I was able to get my SB-12. My amp dosn't make me play better or anything, but every time I fire it up it brings a very pleasent vibe to my heart, bringing to mind this wonderful memory. I have no plans to sell it, the amp, like my family, is something I cherish and miss greatly when I'm out of town.
 

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