Official Ampeg Portaflex Club

[gmacc]

Hello, I'm new to the group. I just took delivery of a 67 b18x. she's sweet. been playing trhough a friends 15 and my peavy tk115. no comparison. my Miller Jazz juat loves the amp and my upright does as well.
Mine appears to have the origional speaker and horn. the tolex only has a couple of small nicks, no tears, and the grill fabric looks to ne perfect.

I have enjoyed reading all that you have to say out here, its a great learning avenue.

Grant

 

[Barrister]

David:

Thanks for your excellent help. People like you make the world a better place.

I received the B18N and took it directly to my local amp guru. (mathes-amps.com - He just a 1959 bassman clone for Steven Stills.) He was working on a B15N when I showed up. He was going to start the head up on a variac and double check everything, craft a speaker cable for me, switch out the 2 prong for a 3 prong plug, and then build a dummy load for me.

He mentioned the amp/line in serves as a line out as well. I assume this is a pre-amp out before it hits the power stage. Anyone know differently?

I am jazzed about the gear (which is interesting because I gave my USA J deluxe to my son for Christmas - lol).

Thanks again.

Steve

 

[JimmyM]

#104 gmacc

 

[beans-on-toast]

He mentioned the amp/line in serves as a line out as well. I assume this is a pre-amp out before it hits the power stage. Anyone know differently?

Yes. The ext. amp jack serves as either a pre-amp out or a power amp in port.

Ampeg intended it to be used to connect to a second amp. This can be done in one of two ways: 1) connect an instrument cable between the ext amp jack and the input of another amp, or 2) connect the cable between the ext amp jacks of two Ampeg amps. In the latter case, the power amp section of the second amp is acting as a slave with the pre-amp by-passed. The pre-amp of the first amp is fed into the power amps of both amps.


David

 

[anonymous02282011]

Yes. The ext. amp jack serves as either a pre-amp out or a power amp in port.

Ampeg intended it to be used to connect to a second amp. This can be done in one of two ways: 1) connect an instrument cable between the ext amp jack and the input of another amp, or 2) connect the cable between the ext amp jacks of two Ampeg amps. In the latter case, the power amp section of the second amp is acting as a slave with the pre-amp by-passed. The pre-amp of the first amp is fed into the power amps of both amps.


David

David,

Thanks for this useful bit of information.

How do you make sure you don't blow anything up? I would imagine only the second amp, the slave, needs to see a load. Is that correct? Do you get more volume this way?


I just got a 63 double baffle as a backup to my 66 single baffle. I'm going to give this a shot. I'll post up pics soon.

 

[jnewmark]

Yes. The ext. amp jack serves as either a pre-amp out or a power amp in port.

Ampeg intended it to be used to connect to a second amp. This can be done in one of two ways: 1) connect an instrument cable between the ext amp jack and the input of another amp, or 2) connect the cable between the ext amp jacks of two Ampeg amps. In the latter case, the power amp section of the second amp is acting as a slave with the pre-amp by-passed. The pre-amp of the first amp is fed into the power amps of both amps.


David

So if you wanted to use just the preamp of a B15N, you would use this jack, and run it into a poweramp's input? Does it have enough juice to run a power amp?

 

[anonymous02282011]

yea, it should def have enough juice.

 

[anonymous02282011]

I'm just considered about where the load would be connected in order to not blow up the amp . . .


. . . . . by the way, whats the right term for "blow up" when you run a tube amp without a load?

 

[JimmyM]

Infinite ohms, runaway...I still prefer "blowed up," though

 

[beans-on-toast]

So if you wanted to use just the preamp of a B15N, you would use this jack, and run it into a poweramp's input? Does it have enough juice to run a power amp?

Yes. Connect an instrument cable from the EXT AMP jack to the power amp's 1/4" input. The signal from your pre-amp is simply being split, a portion will go to the external power amp, a portion will go to the B15's power stage. If you don't want to use the B15's power section and speaker, one solution would be to use a dummy load.

Whether or not the pre-amp will drive an external power amp to full output will depend on the power amp that you're using. The input requirements vary from one product to the next. It won't hurt to try it.

If the pre-amp signal is lower than you would like, try inserting a patch cord from the second jack of the first channel to the input of the second channel, then turn up the volume controls of both channels. This will combine the signals from both pre-amps and give you a little more juice. If it distorts, turn down the second channel's volume.


david

 

[beans-on-toast]

How do you make sure you don't blow anything up? I would imagine only the second amp, the slave, needs to see a load. Is that correct? Do you get more volume this way?

It's always best to save any explosions for the end of the show.

If you connect two amps, one as a master and the second as a slave, both speaker cabinets are connected and both amps are working. A dummy load is not used. The master amp, the one that you have your bass plugged into, is sending the preamp signal to the power sections of both amps. In doing this, the pre-amp of the slave amp is bypassed. The advantage of this is that you only have to worry about adjusting one set of volume and tone controls.

Yes you will get more volume. Two amps are louder then one. Nothing should blow up.


David

 

[Barrister]

LOL

My local amp genius is building a "magic box" which has an internal load resistor and a DI. This will allow me to run my B18N without a cabinet for studio purposes. I will be able to dial in the tube harmonics, without experiencing the mystical "blowed up" feature. I will keep you updated on progress.

p.s. Mark @ Vintage Blue is also building a nice cabinet for the head. Should be a classic.

p.s.s. You need to hear a 1967 ES-335 played through the B18N head through an AC30 extension cabinet. Our lead guitarist has run it through its paces. Absolutely vintage beauty. Not like my 8-string or Warwick fretless, but for a "guitar" it sounds good.

Hope all are well.

 

[anonymous02282011]

It's always best to save any explosions for the end of the show.

If you connect two amps, one as a master and the second as a slave, both speaker cabinets are connected and both amps are working. A dummy load is not used. The master amp, the one that you have your bass plugged into, is sending the preamp signal to the power sections of both amps. In doing this, the pre-amp of the slave amp is bypassed. The advantage of this is that you only have to worry about adjusting one set of volume and tone controls.

Yes you will get more volume. Two amps are louder then one. Nothing should blow up.


David

David,

Thank you for the detailed explanation. One of my B15s still has the two prong plug, so when they are both plugged into the my power strip I get a little electrocuted. I finally bit the bullet and am taking my amps to a tech next weekend to fix that and a number of other things.

 

[JimmyM]

LOL

My local amp genius is building a "magic box" which has an internal load resistor and a DI. This will allow me to run my B18N without a cabinet for studio purposes. I will be able to dial in the tube harmonics, without experiencing the mystical "blowed up" feature. I will keep you updated on progress.

p.s. Mark @ Vintage Blue is also building a nice cabinet for the head. Should be a classic.

p.s.s. You need to hear a 1967 ES-335 played through the B18N head through an AC30 extension cabinet. Our lead guitarist has run it through its paces. Absolutely vintage beauty. Not like my 8-string or Warwick fretless, but for a "guitar" it sounds good.

Heck yeah. Not only for the guitar, but for Mark's work. He is a real artist with those cabs.

 

[beans-on-toast]

Jazz guitarists have always liked the B15.

There are some YouTube clips of Jimi Hendrix playing through a B15 on the Dick Cavett Show. Here's one ().

He seems to be able to get a nice tone out of it.


David

 

[jnewmark]

Yes. Connect an instrument cable from the EXT AMP jack to the power amp's 1/4" input. The signal from your pre-amp is simply being split, a portion will go to the external power amp, a portion will go to the B15's power stage. If you don't want to use the B15's power section and speaker, one solution would be to use a dummy load.

Whether or not the pre-amp will drive an external power amp to full output will depend on the power amp that you're using. The input requirements vary from one product to the next. It won't hurt to try it.

If the pre-amp signal is lower than you would like, try inserting a patch cord from the second jack of the first channel to the input of the second channel, then turn up the volume controls of both channels. This will combine the signals from both pre-amps and give you a little more juice. If it distorts, turn down the second channel's volume.


david

Thanks. What exactly is a dummy load? My intention was to use the B15N's, preamp only to a power amp to a cab. I assume the speaker cable from the B15 has to be connected to something, thus the " dummy " load?

 

[beans-on-toast]

Thanks. What exactly is a dummy load? My intention was to use the B15N's, preamp only to a power amp to a cab. I assume the speaker cable from the B15 has to be connected to something, thus the " dummy " load?

You are correct, if you want to use the pre-amp only, you will need to unplug the speaker and connect a dummy load instead of the speaker. A dummy load is used as a substitute for the speaker in the circuit. It acts as a load without producing any sound. The energy from the amp is dissipated as heat. It allows the output of the power tubes to see a proper load at the primary of the output transformer. Without this, the power tubes, output transformer and other parts could be seriously damaged.

As usual, things are usually more complicated than you think they're going to be. If you have a 4 pin XLR connector on your B-15, you will need to short pin-2 to pin-3 (the inner two pins) and connect an 8 ohm 50W load resistor across pin-1 and pin-4. Here is a link on how to build an 8 ohm 200W, or if you short the two halves together, a 4 ohm 400W dummy load for an SVT (Link Removed). In the case of a B-15, you would only need one resistor. If you want to spend more money on parts, you can use the 200W version without any problems. Spreading the heat out over a number of resistors is better. To be safe, it is best to mount the resistor in a small steel box with a connector like the type on your speaker cabinet (Switchcraft C4M)(Invalid Link Removed). Here is an example of the type of resistor you can use (Invalid Link Removed ). These type of resistors have to mounted onto a metal surface such as a chassis or box with heat sink compound (aids with heat transfer) so that they won't burn up.

There are other alternatives that don't require connecting a dummy load. For example, some people simply pull out the power tubes. On the plus side, you are not expending the power tubes and you are reducing the load on the heater circuit. On the negative side, pulling and plugging the tubes often will wear out the sockets and there is a greater chance that you're going to drop a tube and break it. Another negative, this changes the load on the power supply and could affect the performance of the pre-amp. You can give it a try and see how you like the sound. Cheaper than building a dummy load. If you pull the power tubes, you will still need to short pin-2 to pin-3 for your amp to work.


David

 

[jnewmark]

Thanks, David. You're right, it is more complicated than I thought! I can see right nowI will have to have my tech guy build me this dummy load. Makes me wonder why somebody has'nt built a stand alone preamp based on the B15? Or have they?

 

[Barrister]

My local amp genius is working on a box for me. I want mine though to have true DI / balanced out capabilities so I can capture the harmonics from the output tubes. You might follow up with him. mathes-amps.com

Disclaimer: I have no financial interest in Chuck's enterprise. I do know him to be a man of very good character.

Keep us informed on your progress.

p.s. Thanks David for great info.

Steve

 

[beans-on-toast]

Thanks, David. You're right, it is more complicated than I thought! I can see right nowI will have to have my tech guy build me this dummy load. Makes me wonder why somebody has'nt built a stand alone preamp based on the B15? Or have they?

I've seen B-15 based pre's from time to time sold by boutique amp makers. I'm not aware of any currently being marketed but I'm sure that any boutique amp company would be willing to build one.

It would probably be more cost effective to buy a junker B-15 head, have a tech rip out the power amp section, and rewire it to function only as a pre-amp.



David