Official Ampeg Portaflex Club

Discussion in 'Amps and Cabs [BG]' started by JimmyM, May 25, 2008.


  1. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    The problem with PCB amps is that there is very little room to mount a capacitor board.

    Something to consider if you ever get into this with another amp. Looking at how it is mounted, You might be able to lower any hum even more by mounting the SDS board upside down, that is solder joints facing up. In the image below, there is layer of insulating board material (G10) on the bottom. The side facing the cap tops can carry an aluminum shield, as long as the caps do not come in contact with the metal.


    This was a prototype cap board for an SVT that I did years ago. I intended to design a PCB after this prototype stage but haven't had the time to get back to it. It works pretty well as is.
    cap board 1.JPG cap board 2.JPG

    The bottom screws can be plastic.
    cap board 3.JPG cap board 4.JPG cap board 5.JPG
     
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  2. gtmalone

    gtmalone

    Sep 30, 2015
    Allen, TX
    Lack of space was the reason for the SDS board. I knew it would fit since I have one in the Dynaco. That chassis has even less space than the B15.

    Here are pics of the mods/fixes so far. Click the "full screen" icon in the lower right so the filmstrip bands don't overlay the pics.

    Mods-fixes Slideshow by Gordon M
     
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  3. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Thanks for posting the images. Always nice to look at amp guts. You also have a premium speaker in the cab.
     
  4. gtmalone

    gtmalone

    Sep 30, 2015
    Allen, TX
    That's the Altec 421A. I alternate with a JBL D140F. The Altec has a little more definition but both sound great.

    Might get a second cab to make the choice easy or both together.
     
    Last edited: Apr 4, 2018
    JimmyM and beans-on-toast like this.
  5. rust_preacher

    rust_preacher

    Dec 17, 2009
    Finland
    What is striking in the gut shots is that there are metal foil resistors. They must be replacements. Am I right?
     
  6. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    The 1/2W resistors in these amps are very stable and it is rare to change them. The coated resistors are original in many examples..

    The larger sized wire wound resistors run hot and are often changed because they drift with time. One resistor in the fixed bias circuit is also often changed because of drift. Other than that the originals are kept.

    The green coupling caps are very stable. Electrolytics are often changed.
     
    Last edited: Apr 5, 2018
  7. gtmalone

    gtmalone

    Sep 30, 2015
    Allen, TX
    I replaced all of the 1/2 watt and signal caps on the board plus all the electrolytics. I kept the larger resistors since they were in spec at the time. The 100K feeder to the bias supply has since changed significantly. It will be replaced. The 1K wirewound in the power supply is still good at 997 ohms. I kept the resistors on the input jacks. They were in spec and would be a chore to replace.
     
  8. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    Had my first up close and personal with the legendary navy random flair today. Took some stuff in to get worked on, and the shop owner had taken in a 60 Jet. I freaked! But as I looked at it, not cleaned and kind of dinged up, I wasn't as impressed as I'd been looking at it in pictures. Looked kind of dull and lumpy. Then I took a look at the back...it was much cleaner there and almost looked like new for the most part. Yep, it's legendary for a reason. A gorgeous shade of navy with little sparkles all through it shining brightly in the sunlight, ready to reflect the colors of whatever was shining on it on the stage. I thought I heard trumpets when I saw it, but it was just a car alarm in the parking lot.

    This story would have been a lot better with pictures but I forgot my phone.
     
  9. Ric Vice

    Ric Vice Supporting Member

    Jul 2, 2005
    Olivette, Missouri
    I have a Altec 421 8H (Series II) they are very nice sounding speakers. It's in my B-15N(C)Ampeg didn't use them until
    the "helmet head" B-15N's with the Thiel cabinets were introduced, so the JBL D140F's (actually D-130F's) were used in the "upscale" B-15NL's. They also sound great. The Altec's are a bit brighter than the JBL's
     
    Last edited: Apr 5, 2018
  10. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If Loud was smart, they’d reissue some amps with random speckled basket weave. Like stars twinkling against a dark sky.

    Sales would have them dansing in the moonlight.

     
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  11. Ric Vice

    Ric Vice Supporting Member

    Jul 2, 2005
    Olivette, Missouri
    While their at it, how about
    a run of Diamond Blue Check Vinyl
    that’s a exact reproduction of the
    original, so it would match with vintage amps.

    Ric
     
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  12. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Mark at Vintage Blue has had some made and has it on offer.
     
  13. gtmalone

    gtmalone

    Sep 30, 2015
    Allen, TX
    Thought you guys might like a chuckle. I had to go to Fry's in Plano to get a part for the amp. I'm sitting in a traffic jam practicing my cursing skills, then looked over and saw this:
    blinky%20thing.jpg
     
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  14. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    You have to be able to read to understand.

    Is that a temporary license on your window?
     
  15. gtmalone

    gtmalone

    Sep 30, 2015
    Allen, TX
    That's the registration sticker. Looks larger than it is.
     
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  16. gtmalone

    gtmalone

    Sep 30, 2015
    Allen, TX
    And the Sencore meter is working again. Don't know what happened. Touched up the calibration on DC a little and seems okay except for the still burned out 1v range. AC and ohms are spot on. Cool!
     
  17. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Maybe it needs some deoxit on a contact inside.
     
  18. el murdoque

    el murdoque

    Mar 10, 2013
    Germany
    An Info for the European userst of the PF20/50T:
    Somewhere in the depths of this thread, the Rigid 22" Tool box is mentioned as a good inexpensive case for the amp.
    You do get the same one over here, but the companies' name is not Rigid, but Keter. I got mine off amazon for €35.
    I added some foam inserts and the amp is housed properly now. This feels like it is roadworthy. We often get help loading and unloading the van and I always have a bad feeling when someone else stuffs my gear in there, especially when other stuff gets stacked on top in a game of gear Tetris. With the Keter box, I'm fine with that.

    And a question for the users of the PF20/50T:
    When playing live, what signal do you guys send to FOH and do you go straight from the amp's output or do you use something to tame the signal?

    The last time I played in rehearsal, I had the problem that when I played low notes (B-G) I had a sizzling sound on the attack of each note on the IEM, but not on the cab. I did not bring a laptop so I could not access the settings of the behringer X-Air that is used. At home, I tried the same thing with my cheap home mixer and realized that when I used the transformer output XLR into an XLR input (on the cheap mixer the XLR inputs are mic level with a gain pot and the 1/4" are line level) with the master at max, the bass at 2 o'clock and the gain around 9 o'clock (clean sound with gain to spare until it reaches saturation), the low notes would send my board into clipping on the low notes, even with the gain on the mixer dialed to minimum which _should_ mean line level. Once i dialed back on the bass pot until I sounded clanky with no bottom, the sizzle was gone and the signal strength was ok.
    How can I remedy that?
     
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  19. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    I use the transformer output and I've never had a problem like that. Makes me think there's a setting on your mixers that's causing an overload. Have you tried an alternate DI source or plugging directly into the mixer? If it's not clipping into the cab, it shouldn't clip into the board as long as your gain stages aren't grossly boosting the signal into the board unknowingly.
     
  20. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    The lower notes have the most power. Those are the ones that bring on the distortion that are overloading the mixer. You signal is too hot.

    Adjusting your EQ to cut the bass will help. If the mixer has an input pad, you can try that. There are also XLR inline pads. Here is an example: AP-DB | XLR In-line Signal Pad. They are used to lower XLR signals that are too hot for the receiving amp.


    8173CA24-0773-412C-A2D9-584260D8B67A.jpeg


    Search for “Neutrik in-line XLR balanced attenuator”, you may find pads like this locally.
     
    Last edited: Apr 9, 2018
    lowplaces likes this.
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    Jun 15, 2021

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