Jess Oliver's legacy - AMPEG PORTAFLEX CLUB part 9

[Ras Keita]

Been looking high and low, but now I'm a proud owner. I suppose it's to be expected there's some rattle, I'm planning to refurb, might try getting hold of Mark Gandenberger Vintage Blue, he's about three hours away...

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[JimmyM]

Rattles can be a real PITA to get rid of, but you can get rid of them. Just take them one at a time.

[Franklin229]

Originally Posted by JimmyM

Rattles can be a real PITA to get rid of, but you can get rid of them. Just take them one at a time.

Agree-
Sometimes its just simple stuff that comes loose in/on the cabinet-When I got the B-18, there was some rattling-a few of the lock nuts that hold the speaker to the cab were loose. The one on the bottom was completely off and sitting in the bottom of the cab. Tightened them down and it was rattle free. I would think the other thing to look for would be a worn cabinet gasket.

[lowstar]

thanks for the answers, guys ;-)
wow, i´m a talkbass methusalem but this is actually the first club here that i joined. :-D
i´m still torn between leaving the two extra power nodes in or going completely back to original.
i´ll also check if the aforementioned resistors are still in spec - funny that they used carbon comp for the two 22K resistors (R37/R38), i just ran across a gutshot of a b15 just like mine and it had the exact same resistors installed.

cheers,
lowstar

[Ras Keita]

The top pictured cab has a rattle bottom right, if you look at the pic you can see a little hole in the grill cloth, that's near to the source. I going to order a "clutch screw driver" from Fliptops.

[beans-on-toast]

Originally Posted by lowstar

i´m still torn between leaving the two extra power nodes in or going completely back to original.
i´ll also check if the aforementioned resistors are still in spec - funny that they used carbon comp for the two 22K resistors (R37/R38), i just ran across a gut shot of a b15 just like mine and it had the exact same resistors installed.

Whatever caps you decide on, it is fully reversible. Tone wise, it doesn't cost that much to try both. It is the only way that you'll know which topology you prefer.

You see that with the resistors in their other amps like the SVT as well. I see no reason to use carbon composition resistors in those positions other than they fit, or they got a good deal on a truck load of them and wanted to use them up. Sometimes that type of resistor is used in the signal path for its sonic qualities but that isn't the case here.

[beans-on-toast]

Originally Posted by Ras Keita

The top pictured cab has a rattle bottom right, if you look at the pic you can see a little hole in the grill cloth, that's near to the source. I going to order a "clutch screw driver" from Fliptops.

When the cab was built, there was a layer of foam under the grille cloth. The foam breaks down to a powder with time leaving the cloth loose which can be the source of a buzz. The foam was affixed with staples and if one is sticking up a bit, over time it can result in a tear in the grille cloth.

If you remove the grille cloth completely, you can first glue on a layer of thin fabric store felt in place of the foam. This is what Mark at vintage-blue does on his cabs and it's a really good solution. The felt adds a bit of padding under the grille cloth to help cushion it and keep it from flapping.

[beans-on-toast]

Originally Posted by spacebassed

Here are the tube sockets on my late '64/early'65 B15NC (eyelet board). Do we know exactly when the new serial # system began?

I don't know about the new serial numbers but I think that the bottom mounted sockets went with the eyelet board models and the top mounted sockets went with the circuit board models.

As far as I know, they started using the circuit board in 1965 with the NF revision. These amps have a stamped serial number on the back of the chassis under the power cord. If you were lucky, there was a paper tag inside the cabinet with a serial number that matches the one on the chassis.

So my guess would be, the new serial numbers began when the NF was released.

[coreyfyfe]

Originally Posted by beans-on-toast

As far as I know, they started using the circuit board in 1965 with the NF revision. These amps have a stamped serial number on the back of the chassis under the power cord. If you were lucky, there was a paper tag inside the cabinet with a serial number that matches the one on the chassis.

So my guess would be, the new serial numbers began when the NF was released.

Just to throw a wrench in this, my 65 is an NC but it has a printed circuit board. The pots date to late 64/early 65 and it has a serial number under the power cord. I think the serial is like 004011 or 004001 or something like that.

[spacebassed]

Originally Posted by beans-on-toast

I don't know about the new serial numbers but I think that the bottom mounted sockets went with the eyelet board models and the top mounted sockets went with the circuit board models.

As far as I know, they started using the circuit board in 1965 with the NF revision. These amps have a stamped serial number on the back of the chassis under the power cord. If you were lucky, there was a paper tag inside the cabinet with a serial number that matches the one on the chassis.

So my guess would be, the new serial numbers began when the NF was released.

Well David, that would make sense, but it seems like those changes were completely arbitrary - and we know Ampeg loved arbitrary. My NC has an eyelet board and the new serial # system, but the codes are all '64. There are also some NC's with PC boards - like coreyfyfe's. The top mounted sockets do seem to start with the PCB, but I'm sure there's at least one out there that will prove me wrong - it's the Ampeg way. Another change around that time was that the inputs began to be labeled - Guitar. Bass, Inst. - I think that might have started with the NF, but I'm not sure.

Edit: I see that coreyfyfe beat me to it. Does your PCB NC have labels above the input jacks?

[Pickersditch]

Originally Posted by lowstar

hello everybody,

maybe my post got lost in the discussion about the logos before, maybe the question was too special (don´t think so, some of you guys seem to be very knowledgeable about anything portaflex), or maybe you felt it was not polite enough to ask questions without properly introducing myself, so i´ll try to properly introduce myself

here is my b-15n, production between 77 and 79 (got to date the pot codes today or tomorrow when i get into my lab), european model (magnavox aera ?):
Attachment 312600

now i got some questions for the gurus, they were in my post #933. i´ll quote myself here:



forget about the "early 70ies" part, the schematic on the inside dates from at least 77, so it must have been between 77 and 79, i´m new to all this dating stuff hehe

thanks and cheers,
lowstar

Hi Lowstar, if you are in Europe it may be worth contacting this guy as the one he has on eBay is a dead ringer for yours.
You may be able to compare as it's European voltage, too.
http://www.ebay.co.uk/itm/1210501223...84.m1438.l2648

[ddbassGA]

Originally Posted by coreyfyfe

Just to throw a wrench in this, my 65 is an NC but it has a printed circuit board. The pots date to late 64/early 65 and it has a serial number under the power cord. I think the serial is like 004011 or 004001 or something like that.

I would argue yours is an NF but they used up old NC labels.

[beans-on-toast]

I have an NF schematic dated 4-65. The power supply capacitors are 30/40/40/40uF (node 1 to 4, power amp to preamp). I look at NC schematics and the power supply caps are 40/40/20/20uF. If an amp has the 30/40/40/40uF configuration and has a circuit board, I would be inclined to call it an NF and override pot codes as the primary identifier.

Another big change in the NC to NF circuit was how they implemented the speaker safety interlock. In the NF, they disabled the amp at the phase inverter. Only a couple of volts were run through the speaker cable and it was much safer. In the NC and earlier, the B+ high voltage was run out through the speaker cable. If a wire from the speaker cable connects to the standby switch, this is the NC scheme. This change was requested by a safety agency and, according to Jess, it was a priority for Ampeg to change this. Yet another thing to look at in determining what revision the amp is.

In terms of the circuit diagrams, they would revise them when necessary but used whatever was on hand in the amp. If they made small changes to the amp, it wasn't always reflected in the circuit diagram. Mark has NC schematics dated 1-64, 9-64, and 11-64. I mentioned the NF dated 4-65. I haven't seen one with a date between November 64 and April 65.

When dating an amp, you have to look at the newest parts and base the estimate on that. If you have 64 and 65 parts, there is a good chance it is a 65. Although with Ampeg there were always transitional amps. They used whatever was on hand. For instance, if they had circuit boards ready for the next revision in late 64, they might have used them and manufactured and sold the amp in 64. In this case, it would be a 64 but based on the 65 NF spec. Stranger things have happened.

[coreyfyfe]

Originally Posted by ddbassGA

I would argue yours is an NF but they used up old NC labels.

It's an NC circuit. Has a 40/40 cap can, two 20uf (well 22) caps, and assuming I'm looking at the right parts/schematis is cathode biased (see the 50uf/50V cap and 250/10W resistor on pin 8 of the power tubes).

There is printing on the right that says B12/B15, but I can't recall what else it says there. I'll take a look tonight.

[lowstar]

hey guys, had a look at my pot codes today and they are from the 42nd week of 78, so it was prolly produced at the end of 78 or the start of 79 ;-)

@beans on toast: i also thought it is weird to have carbon comp in that part of the circuit, maybe they had them lying around as you said :-D

and yes, the one on ebay looks exactly like mine, but is in better condition as far as i can see.

cheers,
lowstar

[Vintage-Blue]

Originally Posted by coreyfyfe

There is printing on the right that says B12/B15, but I can't recall what else it says there. I'll take a look tonight.

Could you also take a look at the date in the corner? The last NC schematic I have is dated 3/65 and my first NF is dated 4/65. I'm curious what yours is.

[coreyfyfe]

Originally Posted by Vintage-Blue

Could you also take a look at the date in the corner? The last NC schematic I have is dated 3/65 and my first NF is dated 4/65. I'm curious what yours is.

No such luck. This schematic is pretty beat up, whatever happened inside this amp (looks like a cap blew) before I got it did some damage - there are some burns on the board as well.

Either way, the printing on the board says "B-12-N/B-15-N-5" and has the ampeg logo. You can see a little better if you view the pictures full size.

[beans-on-toast]

The glued on schematic is interesting. They took an early B-15N schematic and added the C by hand. When they went to the B-15NA and B, they changed the way that the plug was drawn as in the image below. When it came to redo the NC schematic, they didn't modify the NB they went back to the N. THe last model that had a tube rectifier.

That label inside Corey's 1964 cab is very clean.

Been looking through my files. I found an NC schematic dated 1-64. I found your 3-65 schematic Mark. I missed that one earlier.

Below is how they drew the cab connector on the NA and NB schematics. Also the capacitor values look like they were hand lettered in with each schematic revision. They are always darker on the schematics. Maybe they had a generic schematic in the early days and would fill in values with each revision.

[JimmyM]

Whoa...only one more post left in the thread before we open a new one.

[JimmyM]

And here it is....