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Official Ampeg Portaflex Club

#9,623
garmenteros said:
I tried both heads with both speakers, and with the same sets of tubes in both, all ampeg branded with the italic type lettering which look like the originals that came with the blueline I purchased... The jensen sounded brighter with both heads, and the blueline fliptop headed sounded rounder and fuller with both speakers. My tech told me that he thinks it might have something to do with the circuit boards which are different. Both amps sound awesome though.
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Hmmm...and to think I thought I liked my 77 B-15N ;) But it had a CTS from 71 in it and not the Eminence that they started using in 74.
 
#9,624
JimmyM said:
Hmmm...and to think I thought I liked my 77 B-15N ;) But it had a CTS from 71 in it and not the Eminence that they started using in 74.
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Any b15 is an awesome b15, but the square magnet speaker is really something else. I can't wait to get the 60s head up and running, maybe by this weekend and I can give a good comparison of several eras and make a video...
 
#9,625
garmenteros said:
My tech told me that he thinks it might have something to do with the circuit boards which are different. Both amps sound awesome though.
Click to expand...

There are a lot of things that can make two amps sound different. Even when new, every resistor and capacitor has a tolerance such as +/- 10% or 20%. So the actual value of a 0.022uF capacitor might be higher in one amp and lower in another. This applies to all the components. Add up all these differences and the tone is affected.

The circuit board vs an eyelet board can make a difference as well. Often when you look inside an amp you see pools of solder flux around solder joints or between traces. This flux attracts dirt and other things. This allows very small levels of current to flow between traces or eyelets, creating circuits that shouldn't be there. Even the circuit board material can be conductive. This affects how the amp sounds. So at the very least, remove that flux, or if the amp sounds great, leave it there. :p
 
#9,627
So what do you think, too much porting? :D

cab_0018.jpg



cab_0019.jpg


I was reading something a couple of weeks ago about speaker clearance when the B15N head is inverted and I got this idea. I modified an old double baffle cabinet so I could see how things looked inside the cabinet. Right now I don't have a decent selection of speakers but here are some photos showing the clearances with a JBL D140F. There is quite a bit of room around it.

cab_0020.jpg



cab_0021.jpg



cab_0022.jpg



cab_0023.jpg
 
#9,630
Still working on Cataldo's B15. New power tranny is working fine, thanks FT. Was replacing plate resistors to cure an intermittent noise issue, and noticed that the plate Rs in the phase inverter were not ala the schema, schema says 47k, what is actually installed is 120k. Hmmmmmm What value should I replace?

While 47k would put a lot less gain in the PI, it would cause you to run the preamps hotter, not necessarily a bad thing. And it is all inside the FB loop, so you are mainly reducing the open loop gain.

So what is the net.wisdom on this? Any preference?

Thanks!
 
#9,631
In the earlier amps with the 47K plate resistor like the NA to the NC revisions, they ran 310V (300 on the NC?) on the plates which is pushing the 6SL7GT. The data sheet says 275V max but the tube can take more.

With the NF they used the 120K plate resistor and lowered the plate voltage. If you download the Heritage B-15 user's manual from the Ampeg site, you will see the plate voltage in that amp is around 200V and they also use a 120K plate resistor. BUT, it depends on the power supply voltages. What it comes down to is they are biasing the PI tube differently. This will affect the voltage swing, headroom, distortion, plate current and other stuff.

I like the way it sounds with the 47K plate resistor. Just my preference.
 
#9,632
Mark, I don't even want to see what a Delta does! I ended up having to put pieces of felt on the Delta to keep it from banging into the transformers. Doesn't bang into the magnet...more on the frame. But it bangs. And yet I still carry it flipped.
 
#9,634
JimmyM said:
Mark, I don't even want to see what a Delta does! I ended up having to put pieces of felt on the Delta to keep it from banging into the transformers. Doesn't bang into the magnet...more on the frame. But it bangs. And yet I still carry it flipped.
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I've never tried a Delta. I'll need to check this weekend and see if I still have a Beta floating around to try.
 
#9,637
Apex_speed said:
Hey Mark...thanks for doing that! It is really great to see exactly what the clearance is flipped and not have to guess.
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You're welcome Carl! Since I typically use a Beta-15a in my cabinets I'm curious to check one of them out, especially after reading Corey's comment.
 
#9,640
BlueLine1 said:
No experience with a 410hlf, but my 610hlf sounds great with my SVT. Does a different amp sound any different with your 410hlf? That cab should handle anything your Classic can throw at it... Odd.....

Alan
Click to expand...
The 610hlf doesn't go quite as low as the 410hlf. Never heard many cabs go lower than the 410hlf that didn't have "subwoofer" written on them.
 

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