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Official Ampeg Portaflex Club

#8,121
ddbassGA said:
I have a 50 watt b-18 head and a couple of B-15's. The 50 watt head has significantly more usable volume than either the 25 watt cathode bias '64 or the fixed bias '66. Or the '71 B15N for that matter. The 50 watter really shines driving 2 B15 cabs. The difference has to be in the OT, cause there's no real reason to think a pair of 7027a would be louder than 6L6's.

I tried a B25 thinking it would be like the B-18 head, but very different: farts out way early -- well mine did. I had more usable volume with a B15.
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I know what you mean, there is a volume difference. I've found that at loud levels, that extra volume didn't make that much of a difference.

I find that different speakers will also make a difference in how much you can get out of an amp. You can take the same amp with two different cabs and one can cut though better or have a nicer tone. The capacitors in the power supply will make a difference in usable volume and headroom. If the caps are performing below spec the usable volume will be lower. Just saying that it is a factor. If the amp is optimally biased, it also makes a difference in what you can get out of it. I guess I'm saying that a lot of factors come into play when it comes to an amp delivering an optimal musical output.

There is a difference between the 7027A and the 6L6GC. The 7027A can be run at higher plate voltage levels (600V vs 500V of the 6L6GC) and it can dissipate an extra 5 watts of heat on the plate. This means that you can run the tube at a higher voltage which allows you to squeeze more output wattage from the tube.

This is exactly what Ampeg did in their 7027A based amps. The plate voltage of the 68 B-15N with 6L6GC's is 450V. This is in contrast to 7027A based amps like the B18N (and B-15ND) that had a plate voltage of 505V, the B15S was run at 575V. As you mentioned, the output transformer used also makes a difference. The 50W 7027A based amps had a different transformer than the 30W amps. I don't know if it was simply a beefier transformer to take the higher wattage or if there was an impedance difference that helped them get more power as well. I don't have the specs on the one that they used. The point is, the higher voltage allowed them to bias the power tubes into a region that allowed more power out of the tubes.

It is true that some manufacturers were selling 7027A tubes labeled as 6L6GC and these were interchangeable. If you take an amp designed for the 7027A spec and install a 6L6GC, you might be pushing the tube. You can sometimes get away with doing this because many of the NOS tubes could be pushed beyond their published data sheet limits. The data sheet specs were intended to provide optimal service life. Some manufacturers like Fender would design amps with voltages higher than the published specs. Back then, tubes were of good quality, they were cheap and the designers knew that they could take the extra stress so they took advantage of this.
 
#8,122
jnewmark said:
So, if I'm understanding you correctly, using an extension, 8 ohm cab, WITH the internal speaker connected also, still gives an 8 ohm load ? I always thought that, with tube amps, you could go lower in loads, but not higher ?
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Not quite, with the 8 ohm extension cab connected you have a 16 ohm load.

The amp has both 8 ohm and 16 ohms taps on the transformer. You don't have access to these at the back of the amp. When the 8 ohm internal speaker is connected, it is connected to the 8 ohm transformer tap. The impedance is matched. When you plug an external 8 ohm cab into the ext. spkr. jack on the back of the amp, the wiring is shuch that the internal speaker is connected in series with the external cab (8 ohms + 8 ohms = 16 ohms) and this is switched to the 16 ohms transformer tap. This switching is done internally when you plug into the ext spkr jack. So now your speaker load totals 16 ohms and is connected to the 16 ohm transformer tap. Again the impedance is matched.

You are correct, with tube loads it is better to go to lower impedances than it is to go to higher impedances. Either way there is a price to pay in doing so and matching loads is optimal.
 
#8,123
beans-on-toast said:
Not quite, with the 8 ohm extension cab connected you have a 16 ohm load.

The amp has both 8 ohm and 16 ohms taps on the transformer. You don't have access to these at the back of the amp. When the 8 ohm internal speaker is connected, it is connected to the 8 ohm transformer tap. The impedance is matched. When you plug an external 8 ohm cab into the ext. spkr. jack on the back of the amp, the wiring is shuch that the internal speaker is connected in series with the external cab (8 ohms + 8 ohms = 16 ohms) and this is switched to the 16 ohms transformer tap. This switching is done internally when you plug into the ext spkr jack. So now your speaker load totals 16 ohms and is connected to the 16 ohm transformer tap. Again the impedance is matched.

You are correct, with tube loads it is better to go to lower impedances than it is to go to higher impedances. Either way there is a price to pay in doing so and matching loads is optimal.
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Got'cha, thanks. Here is a shot of the speaker mag. Does the " 69 " indicate the year ?
 

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#8,125
Yes as portaflexer said, the 4327150 looks like an EIA speaker code: 432 is Long Engineering, Inc., Waveland, IN, 71 is the year, 50 is the week.

Sometimes CTS would subcontract another manufacturer to help fulfill their orders. Long Engineering made speakers and, like CTS, was also located in Indiana. The speaker would have the same specs as the CTS, sometimes even assembled with the same parts, just produced at a different site.

If the resistor codes turn out to be earlier, perhaps it is a replacement speaker. Other B-15's have turned up with drivers from Long Engineering though so it could be original.

There may be other numbers on the rim where the mounting screws are located. A CTS speaker would start with a 137 code.
 
#8,126
The 69300090 number is the ampeg part number for those speakers. 432 is the EIA code for Long Engineering as [Invalid or Expired Link Removed] (pdf) and 71 50 would be 50th week of 71 as said above. I've seen speakers with a few different codes conforming to the same CTS look in the early 70s amps. Either ampeg or CTS would contract out to other vendors to make the speaker to the same spec when speaker production output couldn't keep up with amp production demands.
 
#8,127
coreyfyfe said:
The 69300090 number is the ampeg part number for those speakers. 432 is the EIA code for Long Engineering as [Invalid or Expired Link Removed] (pdf) and 71 50 would be 50th week of 71 as said above. I've seen speakers with a few different codes conforming to the same CTS look in the early 70s amps. Either ampeg or CTS would contract out to other vendors to make the speaker to the same spec when speaker production output couldn't keep up with amp production demands.
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Thanks. Next time I'm in Boston, I'll buy ya a clam roll ! :D
 
#8,129
JvN said:
Thanx Stiles - so going from the Ext Amp on the SVT/V-4B to your XLR extension cord or a high end passive DI box would give the pre-amp's sound, right?
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Forget that! Here's what you do if you REALLY want badass DI sound out of an SVT that includes everything, including the power amp sound...buy a REDDI ;)

Failing that, take a DI that does speaker level DI such as the Countryman or some of the Radials and hook it up with speaker cables between your SVT and cab. Then you get the entire amp as opposed to just the preamp. The big drawback to doing this, though, and why I use a REDDI instead of doing this, is that tonal or volume changes you make on the fly tend to get magnified in a PA and can make it difficult for some soundmen to deal with. However, if you can keep your mitts off the controls for the most part, it works great.

Have to add that it doesn't work so well if you're cranking into more than a light distorto-ville because it can blow tweeters in the PA, but Radial and Palmer make DI boxes that have speaker sims in them that will work better for distortion. Not sure if the Palmer works for bass, but Radial has an ad in the new BP for it that says it works on bass. I know the H&K Red Box definitely doesn't work for bass, though.
 
#8,132
JimmyM said:
Forget that! Here's what you do if you REALLY want badass DI sound out of an SVT that includes everything, including the power amp sound...buy a REDDI ;)
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Of course, I have been thinking about that (or the UA Solo/610). And then connect it to the Ext Amp - not between your instrument and the amp? SVT/V-4B pre- and poweramp sound minus volume? I know you're a REDDI addict, and given how you changed my life talking me into the Heil mike, I should really try. But I also like the sound and idea of the UA, which even has 2 tubes in it, plus the corresponding controls, which make it a bit more versatile, if at the price of some $300 more. How B-15-ish is the REDDI actually, soundwise? If I would buy a high end DI, it must be able to come as close to the SVT/V-4B sound as possible. And maybe that can be done through the Ext Amp, as you say. Never thought about it that way :-D.

JimmyM said:
Failing that, take a DI that does speaker level DI such as the Countryman or some of the Radials and hook it up with speaker cables between your SVT and cab. Then you get the entire amp as opposed to just the preamp. (...) Have to add that it doesn't work so well if you're cranking into more than a light distorto-ville because it can blow tweeters in the PA, but Radial and Palmer make DI boxes that have speaker sims in them that will work better for distortion. Not sure if the Palmer works for bass, but Radial has an ad in the new BP for it that says it works on bass. I know the H&K Red Box definitely doesn't work for bass, though.
Click to expand...

I have a Palmer PDI-09 which works perfectly fine with bass, but I don't like the speaker emulation and volume problems... which is why I am looking for something else.
 
#8,134
JvN said:
Of course, I have been thinking about that (or the UA Solo/610). And then connect it to the Ext Amp - not between your instrument and the amp? SVT/V-4B pre- and poweramp sound minus volume? I know you're a REDDI addict, and given how you changed my life talking me into the Heil mike, I should really try. But I also like the sound and idea of the UA, which even has 2 tubes in it, plus the corresponding controls, which make it a bit more versatile, if at the price of some $300 more. How B-15-ish is the REDDI actually, soundwise? If I would buy a high end DI, it must be able to come as close to the SVT/V-4B sound as possible. And maybe that can be done through the Ext Amp, as you say. Never thought about it that way :-D.
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The REDDI sounds identical to a clean running B-15 running speaker level DI, except with a relatively flat response and less noise. The noise in my B-15 was slight running it that way, and likely nobody'd ever notice it, but the REDDI's a touch quieter. Having said that, there ain't nothing wrong with that Heil micing your rig, either! As for the UA, I don't know much about it. All I know is that in comparison clips I've heard, I liked it but I liked the REDDI more. Never thought to try it in the ext amp out of my tube amps, though. Didn't think it needed it.

I have a Palmer PDI-09 which works perfectly fine with bass, but I don't like the speaker emulation and volume problems... which is why I am looking for something else.
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Well the volume problems are pretty difficult to overcome, but with a regular DI that does speaker level, you can overcome the speaker sim problem easily enough.
 
#8,137
I don't think so. The newer cabs have extra internal bracing that would also have to be removed. At least in the 2x10, I'd have to look at a picture of a 1x15 to know if they have the same setup inside. Try stalking ebay and craigslist, sometimes orphaned cabs do pop up.

For example, this is not exactly what you want, it's a copy of an ampeg cab with a CTS speaker, but it could do the trick for less than the cost of a VB or fliptops cab for now.

http://www.ebay.com/itm/Bass-Speake...554?pt=LH_DefaultDomain_0&hash=item35c2bb1662
 
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#8,138
I should have specified that I was referring to the PF115HE only. I am pretty sure that would work with the horn removed. There is no internal cross brace like the 210 has.

I cannot verify for sure though. I have been selling off some of my stuff (including the Ebay listing you showed)as I am moving into a smaller place and my PF115's are gone:(
 
#8,139
I have not tried flipping my B-15 head into my PF115he, but aside from the tweeter, you have to consider that the speaker is mounted to one side, and that will likely cause the output tranny to bang into the speaker frame.
 

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