Official Ampeg Portaflex Club

[beans-on-toast]

Ric and Roberto, you are both making points that make a lot of sense to me.

I think the my desire to restore an SB-12 down the road stems from a few things:

I don't expect it to be the same as a B-15. It's a similar design but has tweaks that make it different. It has a unique voice.

The B-15 has a larger power transformer which means that the power supply will handle the low end well. The bass is going to be deeper and the low end lower than an SB-12. Output transformer design is always an exercise in compromise. Having a lot of iron translates into a more present bass and less distortion in low end affording a richer sound. In that respect the SB-12 is different, it can't do low like a B-15 can.

What an SB-12 will do is provide a nice low midrange. As Roberto said, it will reflect and enhance the natural qualities of the electric bass. I agree with both your comments about the need for the right speaker. This is an interesting area where some experimentation can be done. That JBL looks interesting.

The SB-12 is also a good guitar amp for low volume work with clean tones. This is a plus for me.

I'm up in the air as to which SB-12 model would best suit my needs. There is the choice of 7868 or 6L6GC output tubes, early or later amp designs, a later Thiel based cabinet or an earlier ported model. There are a few options to choose from.

 

[Ric Vice]

Ric and Roberto, you are both making points that make a lot of sense to me.

What an SB-12 will do is provide a nice low midrange. As Roberto said, it will reflect and enhance the natural qualities of the electric bass. I agree with both your comments about the need for the right speaker. This is an interesting area where some experimentation can be done. That JBL looks interesting.

The SB-12 is also a good guitar amp for low volume work with clean tones. This is a plus for me.

I'm up in the air as to which SB-12 model would best suit my needs. There is the choice of 7868 or 6L6GC output tubes, early or later amp designs, a later Thiel based cabinet or an earlier ported model. There are a few options to choose from.

I remember that my SB-12 had to have the 6L6GC replaced in my SB-12, the technician didn't get the right sized replacement( were there short and tall 6L6's?) so he had to raise the tube cage with 4 rubber washers. It worked fine, but it looked ridiculous. When it comes to Ampeg's I like blue check. Either amp sounds great, especially if you scored a B-12.

Ric

 

[JimmyM]

Bob Nyswonger sounded great on a clip he did using his SB-12 mic'ed:



Unfortunately, that's my only experience with one

 

[Woodstockz]

Is this Ampaholics Anonymous?

Hello, my name is David and I'm an Ampaholic
I have uncontrollable GAS
Some call me an Ampig

I joined the Portaflex Club for support
There I'm encouraged to indulge
I dream of extension cabinets

Now I've got my eye on an SB-12
What can I do
I've got the Ampaholic's blues

Ampaholic's blues - I built my first Dynakit 40 years ago. I've been hooked ever since. Didn't know that I had a chronic condition. Is there group therapy?

 

[beans-on-toast]

Ampaholic's blues - I built my first Dynakit 40 years ago. I've been hooked ever since. Didn't know that I had a chronic condition. Is there group therapy?

We have meetings here whenever necessary.

 

[59Pan]

I figured that while I'm in a lull, waiting until I have the time to troubleshoot my G-300 further, I'll post some pictures of my '60/'65 B-15-N. It was purchased as a non-working '60 year model, which I was some excited to get my hands on:







Confirmed the year by the serial number inside the cabinet. However, when I removed the chassis, to begin the troubleshooting, there was a vintage circuit board, like used in later models, instead of the expected eyelet/tag board. And, the schematic on the bottom panel stated 1965. Handwritten on this schematic was an April '68 repair date and a business stamp from the music store that made the repairs. The whole chassis had been replaced with a later one, which began to grow on me after looking it over thoroughly. This one has a Guitar channel as well as a Bass channel.

So, I proceeded to replace the power transformer, after determining that this one was bad. I had a spare on hand, as I'm beginning to think that these amps will continue to follow me home. And, PT's are the most dominant issue with the ones that I've had my hand on.

I purchased this one out of New York state, and the music store that made the repairs was only a short distance away from the owner. He is an active Bass player, who has owned it since the very early 70's. The amp finally died on him, and so he parked it after finding out that the expense of repairs could buy him a lighter solid state amp, and money left over. It apparently set for quite a while, before he decided to sell. I didn't deal with him directly, but through his buddy, who is a guitar player. Both of these guys are on up in years, and still very active.

Anyway, the amp turned out fine, and I took it to Church to leave, as I'm running out of room to store these old pieces of equipment that just seem to keep following me home. It's not active there, as our Bass player moved to Australia to take a job. He's a Nuclear Physicist, and killer Bassman. But, I'm hoping we will have the good fortune to have another musician take his place. Then, this amp will really make him shine. Especially, in our small Church.

And hopefully, I'll have something to report on the G-300, by this weekend. Sorry for straying again, away from my original post.

Jack

 

[Jack-Jack]

Noob-question-warning

I have a 1966 fixed bias B-15NF. My question is

[Invalid or Expired Link Removed]

If I buy a matched pair of these (which are said to be reproducing the sound of phillips/RCA vintage tubes), will I have to adjust the bias by soldering some resistors, or do I just take the old tubes out and put the new ones in?

 

[beans-on-toast]

In general, the cathode current will have to be checked and the bias adjusted if necessary when you change the power tubes in you amp. It is the only way to know how the tubes are performing in the amp.

Some companies supply tube matching information on the set of tubes that you buy. For example, you may see two numbers on each tube, these are cathode current and transconductance. The numbers relate to the tube's performance. The numbers for each tube in a matched set should be close to each other.

You bias your amp with the new tubes. The next time you buy tubes from the same company and specify that you want that same cathode current and transconductance. The new tubes can be used without adjusting the bias. It is a good idea to check the cathode current in the amp once these new tubes are installed, just to be sure. If they sold you what you requested, then you should not need to adjust the bias.

Mesa Boogie has a different system. They apply small colored dots on the tube base. If you buy an amp with green dots on the power tubes, then when you change tubes, you specify green dot tubes. There should be no need to adjust the bias.

 

[59Pan]

Update on the G-300.

Referring to my schematic (if you'd like), I lifted one leg of C14. I then took a resistance reading across R32, which is supposed to be 1M ohm. It is open on any resistance scale on my meter. So, if time permits tomorrow (Wed), I will finish removing C14 (even though it may be good) and remove R32. The cap that I removed is rated for 400vDC, and my last reading was 436vDC on the B+ side. My replacement is rated for 600vDC, and happens to be a bit smaller. I have a 1/2 Watt metal film resistor to go back in place of the original R32.

So, if all goes well, I'll have those in tomorrow, and give the amp another test. More to come. Have a good one.

Jack

 

[beans-on-toast]

Update on the G-300.

Good progress Jack. I would expect some drift on the 1M but a reading of open is rare.

Nice amp images.

 

[59Pan]

I would expect some drift on the 1M but a reading of open is rare.

At times, when I'm salvaging fine old components like very old and cool looking resistors, I have found where one leg will be burned open inside the resistor. Or, just fall off with no signs of burns. But, this one is tiny compared to those. I'll take another reading when I get it out and on the bench. I feeling a bit confident that a fix is in sight. Not overly, though. Just a good feeling.

Jack

 

[jbd5015]

Havent checked in for quite some time! Been giggin 2 nights a week at this point with the B15 2x15 without fail for the entire summer. Im simply blown away by the reliability of this amp.

When i bought it, i had to invest a lot (twice what i paid for it) to get it to a point that i was happy with it and it was worth every penny. Anyone else gigging their B15 weekly? Mine wasnt perfect from the get-go, so im not too ashamed of gettin it dented or puttin tears in the tolex, as long as it sounds right, its gonna get used!!!

cheers!!!

 

[JimmyM]

I wish I could sill gig with it, but it struggles a bit with cleans since bumping up our volume, so the V4B is the better choice for me these days. May take it to our next gig just to see what happens, though.

 

[slobake]

Is this Ampaholics Anonymous?

Hello, my name is David and I'm an Ampaholic
I have uncontrollable GAS
Some call me an Ampig

I joined the Portaflex Club for support
There I'm encouraged to indulge
I dream of extension cabinets

Now I've got my eye on an SB-12
What can I do
I've got the Ampaholic's blues

There is only one cure, you have to go cold turkey and send all your amps to me.

 

[beans-on-toast]

There is only one cure, you have to go cold turkey and send all your amps to me.

I enjoy my addiction too much. I could use some more space though.

 

[slobake]

I enjoy my addiction too much. I could use some more space though.

Would you like to store them at my house?

 

[beans-on-toast]

Havent checked in for quite some time! Been giggin 2 nights a week at this point with the B15 2x15 without fail for the entire summer. Im simply blown away by the reliability of this amp.

When i bought it, i had to invest a lot (twice what i paid for it) to get it to a point that i was happy with it and it was worth every penny. Anyone else gigging their B15 weekly? Mine wasnt perfect from the get-go, so im not too ashamed of gettin it dented or puttin tears in the tolex, as long as it sounds right, its gonna get used!!!

cheers!!!

A healthy vintage amp is more road worthy than any new amp. Getting it into a healthy state can be the hard part and that can get expensive as you found. Having a good tech makes all the difference. New amps tend to be of modular construction with connectors joining the modules. These can be a source of failure. Vintage amps have hard wiring which helps make them able to take a punch and keep on working.

 

[beans-on-toast]

Would you like to store them at my house?

People ask me that but the waiting list is way too long at this point.

 

[beans-on-toast]

At times, when I'm salvaging fine old components like very old and cool looking resistors, I have found where one leg will be burned open inside the resistor. Or, just fall off with no signs of burns. But, this one is tiny compared to those.

With old parts things can happen, especially when subjected to extreme temperature cycles. This resistor might have had too much heat applied when soldering. That can cause an immediate failure or hasten one down the road.

 

[59Pan]

With old parts things can happen, especially when subjected to extreme temperature cycles. This resistor might have had too much heat applied when soldering. That can cause an immediate failure or hasten one down the road.

True. Either way, it's getting two new components today or tomorrow. I'm thinking today.

If this is the fix, I'll give it some cook time for a little while, before slipping it back into the cab. Then, I'll try to snap some closeups, front and rear.

It has one foot missing. Oliver used some hard plastic feet on his amps. My PA-100X (next one on the bench) had three shattered feet, leaving only one good one. I will use that one to replace the missing one on this amp, and I already have some taller rubber ones of the same diameter, to go back on the 100X. Those are tall enough to straddle a handle, if the speaker cab has one on top.

Jack