Jess Oliver's legacy - AMPEG PORTAFLEX CLUB part 9

[kuratacus]

could always carve an M to complete my broken logo, guess i'm ambitious, yet lazy ahahahah

[Vintage-Blue]

Originally Posted by JimmyM

Hey, but it's still $20. I don't care what anyone says, $20 is still $20.

I REALLY wish I had bought a bunch more of those logos back in 2006 when I was purchasing parts through Jess.
They were only $3 and change back then. Heck, even in 2008 they were only $5.94 direct from Loud.

[JimmyM]

Well I was going by the Fliptops price, which is $16, and with shipping it's easily $20. I can't imagine it costing more than a quarter to make them, but you never know...maybe the price for zinc has gone up recently

[beans-on-toast]

When you start looking, you realize that Ampeg had a lot of different logos over the years. They came and went with different amps. The B15 had the two script and the square logo. Maybe there were others variations. Grille cloths also changed.

Back in the 50's they were more old school with silkscreened logos like the one below. The vintage metal script logos like on the early B-15 amps are reminiscent of the type that were used on automobiles. There are a lot of places making repro car emblems. Lucky for them, they are a large consumer base.

[JimmyM]

If Ampeg ever brings back that mid-50's look with the baseball logo (or so they call it), I'm on it!

[beans-on-toast]

Originally Posted by Vintage-Blue

I REALLY wish I had bought a bunch more of those logos back in 2006 when I was purchasing parts through Jess.
They were only $3 and change back then. Heck, even in 2008 they were only $5.94 direct from Loud.

You can never have too many spare parts on hand. Wives may beg to differ.

[Drizzy Way]

Curious if I could join the club?

I pulled this B-15N out of my grandfather's basement last year and am finally on a kick to get it up to working order. It at least has a blown tube, but I suspect there is more wrong than that. So I just want to get the whole thing gone over. Pretty sure it hasn't seen any action since the 80's. I'm currently weighing my options of who to take it to in the Omaha, NE area.

Any advice or questions?

[Franklin229]

I have had a B-15N for a few years (first pic) and just scored a nice B-18N (second pic) that has just been gone through electronically. I am in the process of cleaning it up as it was in a studio/workshop for a long time and is a bit dirty/dusty.

[beans-on-toast]

Originally Posted by Drizzy Way

I'm currently weighing my options of who to take it to in the Omaha, NE area.

Any advice or questions?

Nice amp. Even better when it has some family history associated with it. You might find someone listed here that is in your area.

[beans-on-toast]

Originally Posted by Franklin229

I have had a B-15N for a few years (first pic) and just scored a nice B-18N (second pic) that has just been gone through electronically. I am in the process of cleaning it up as it was in a studio/workshop for a long time and is a bit dirty/dusty.

That B18 looks massive in your pic. It must have a huge tone when you link it together with the B15.

[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 ?):


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

Originally Posted by lowstar

hello everybody,

first, thanks to all the contributions of the knowledgeable people in this thread, i´v been skimming through a lot of posts and learned quite a lot.
now, to my question: i´m in the process of recapping and refurbishing my early 70ies european b15n, and have some questions. this is how mine looks like inside:
Attachment 312182
and here is the schematic to go with this amp:
Attachment 312183
now, as you can see, somebody who worked on this amp before installed an xtra electrolytic can cap inside. the trace that comes from the yellow wire of the 40/40/40 cap (the one going to the preamp tubes) has been cut, and by using this can cap and two 10K resistors, an extra "stiffer" power supply (plus filtering) has been generated for V1 and V2 going to the anode resistors (470K/220K).
has anybody ever seen something like this ? was this a mod that was once considered "good" ? maybe there was excess hum before, and this double r/c filter was installed to get rid of it ? should i leave it like it is, and just change the 40/40/40, the 30µf/600 and the 10/100 pair plus the 25/25v, or convert it to completely original ?

thanks and cheers,
lowstar

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

[christw]

lowstar, forgive me for not addressing your questions but I'm not a tube guru.

Guess what guys? I can almost understand Jimmy's use of B-15 for most everything. I managed to get through half of an open mic rock/blues night with my B-15 and SVT loaded 410. I had my volume at noon for the first two hours with a slight boost at 120/400/500 Hz on my GEB-7 for louder periods. I was getting a bit of OD but I was happy with my tone and levels. We ended up using the ext amp out to run it to the PA for a 5 string & Big Muff guy who wanted to borrow it during the fifth set. It was just enough for that bar but nothing more. Next time I'll be using the B-12XTC with 6550's and really be pushing that baby SVT vibe.

Oh yeah! Copper cap guys... do we even have enough room in B-15 to drop in 6550's or KT88? I could have checked last night but was in a rush to get out the door.

[coreyfyfe]

Originally Posted by christw

Oh yeah! Copper cap guys... do we even have enough room in B-15 to drop in 6550's or KT88? I could have checked last night but was in a rush to get out the door.

Doubtful. The 6L6GCs seem a bit of a tight fit already, couldn't imagine trying to fit a wider/taller 6550 or 7027 in there. I can check when I get home if you want?

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

Probably just lost in the chatter, most of us non-tech-types clog up the bandwidth with our discussions on broad issues, so specific questions get buried sometimes.

[beans-on-toast]

Originally Posted by lowstar

now i got some questions...

I did miss your question so my apologies and thanks for reposting.

There were a number of revisions to the B-15N design over the years. One of those involved changes to the power supply. I'm not aware of any particular power supply mods that were applied to your model. I'm wondering of someone modified the amp to make it perform in a way that an earlier B-15 model did. Sometimes it comes down to trying a mod and the owner liked it so that's what they went with. Sometimes, if pressed for time, a tech will simply stick whatever parts in the amp that they have on hand.

It all comes down to personal taste. More often the first node capacitance is increased to provide a better low end response. Too much capacitance and not enough power supply ripple can make an amp dull and sterile sounding. It can change the character of the amp. Finding the correct balance is important.

What to do? I would restore it to the original design and see if you are happy with the way it sounds. In terns of noise, these amps are very quiet. I can't see why they would want to increase the filtering to make it quieter. In general 40uF on the pre-amp is already high. Some amps have a 30uF or even 20uF in the pre-amp power supply nodes but 40uF is the most popular choice.

While you are re-capping, it would be a good idea to check out the resistors in the power supply, including plate resistors, and the bias circuit. In particular, any of the power resistors over 1/2W that run hot. Look for any discolouration or cracks in the components but test them to see if they are still within the specifications.


David

[spacebassed]

Originally Posted by christw

Oh yeah! Copper cap guys... do we even have enough room in B-15 to drop in 6550's or KT88? I could have checked last night but was in a rush to get out the door.

The socket spacing in a B15 should be the same as a B18 and ppl have definitely used KT88/6550's in a B18 (Jess used to do/recommend it). It's definitely a snug fit but they should fit - plus you won't have the heat from the 5ar4 with the copper cap.

edit: I've had KT66's in a B15 and I believe they're the same size bottles as KT88/6550's.

[Farfetched]

Is there a good place for an on/off switch for the mid 60s b15?

[JimmyM]

Originally Posted by Farfetched

Is there a good place for an on/off switch for the mid 60s b15?

How about where the on-off switch is originally located?



New members, I'll be updating shortly. A little too fried from flying at the moment to go looking them all up now, but I'll get it later.

[Vintage-Blue]

Originally Posted by Farfetched

Is there a good place for an on/off switch for the mid 60s b15?

If you're looking for a replacement switch Fliptops.net carries them, although they don't specify whose make they carry.

I use Carling switches, model #0930R for the on-off and standby switches. (10A @ 250VAC / 15A@ 125VAC)

I think I got mine from Allied Elctronics.

[JimmyM]

#330 lowstar
#331 Drizzy Way
#332 Franklin229

[JimmyM]

Nice! Used to have one just like yours and lowstar's. You're #329, BTW.