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Ampeg flip top B15 series

Ghost Rider

By Ghost Rider,
in Amps and Cabs

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BassmanPaul Mentor

BassmanPaul

Posted
Posted (edited)

A change I did make to my unit was to remove the "Polarity' switch and it's capacitor. I then relocated the 'Standby' from the rear apron  to where the 'Polarity' switch was. 

 

I tried a couple of different drivers in the cabinet, JBL Altec, but liked the original square magnet the best. It's what's in there now.

 

Another change was to wire a fast recovery silicon rectifier in series with the plates/anodes of the GZ34/5AR4. This eliminated a flash over problem that reared it's ugly head. I'd recommend anyone with an original B15 to do the same mod. It increases the PIV of the rectifier system.

Edited by BassmanPaul
  • Like 1
Reggaebass Grand Master

Reggaebass

Posted
Posted
  On 05/09/2021 at 11:55, skychaserhigh said:

Mainly passive Jazz bass , sometimes P bass , and I have a  Jazz that's active/passive but I usually use on active. Everything sounds great through it , the Fender/Ampeg combination is a classic sound!

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Thanks, I got one yesterday and  im just trying it out with different basses, the jazz and bb1024 sound superb , my Hohner B2A has an active/passive switch and I just wondered if it’s ok to play active through the 0 dB input 

JapanAxe Grand Master

JapanAxe

Posted
Posted
  On 28/08/2021 at 19:36, BassmanPaul said:

A change I did make to my unit was to remove the "Polarity' switch and it's capacitor. I then relocated the 'Standby' from the rear apron  to where the 'Polarity' switch was. 

 

I tried a couple of different drivers in the cabinet, JBL Altec, but liked the original square magnet the best. It's what's in there now.

 

Another change was to wire a fast recovery silicon rectifier in series with the plates/anodes of the GZ34/5AR4. This eliminated a flash over problem that reared it's ugly head. I'd recommend anyone with an original B15 to do the same mod. It increases the PIV of the rectifier system.

Expand  

 

What silicon diodes did you use? On my recent B15-inspired build I had a GZ34 that was arcing. I fitted a new GZ34 and then tried a UF4007 before each anode on the GZ34, but the amp didn't work with the silicon diodes fitted.

skychaserhigh Proficient

skychaserhigh

Posted
Posted
  On 05/09/2021 at 12:35, Reggaebass said:

It’s a really great amp and the sound is superb, I’m just finding my way around it, I’ll probably have more questions for you 😁, what cab do you use 

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I have the Ampeg SVT212 av cab which is a perfect match. I tend to keep the ultra low and hi off, mid select at 800 and just a touch of bass and mid boost for fingerstyle. Ultra low on with some mid cut is great for pick playing. I usually have the master high and use the gain to set overall volume , I prefer that to having the gain high and master low.

  • Like 1
BassmanPaul Mentor

BassmanPaul

Posted
Posted (edited)
  On 05/09/2021 at 12:46, JapanAxe said:

 

What silicon diodes did you use? On my recent B15-inspired build I had a GZ34 that was arcing. I fitted a new GZ34 and then tried a UF4007 before each anode on the GZ34, but the amp didn't work with the silicon diodes fitted.

Expand  

Did you put them in the right way around?  :D Positive of the diode to each anode of the GZ34. I can't remember which device I used but I'll try to find out for you.

 

Edited by BassmanPaul
JapanAxe Grand Master

JapanAxe

Posted
Posted
  On 05/09/2021 at 20:35, BassmanPaul said:

Did you pay them in the right way around?  :D Positive of the diode to each anode of the GZ34. I can't remember which device I used but I'll try to find out for you.

 

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Ha ha, yes I know how diodes are oriented! I recently rebuilt a modern Princeton Reverb and it had BYD33V diodes fitted to the rectifier valve in exactly this way.

 

  On 05/09/2021 at 20:51, BassmanPaul said:

Diodes I used were UF5408. A 4007 should have worked too but maybe not as well.

 

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Thanks, I might get some of those.

beans-on-toast Enthusiast

beans-on-toast

Posted
Posted (edited)
  On 05/09/2021 at 12:46, JapanAxe said:

 

What silicon diodes did you use? On my recent B15-inspired build I had a GZ34 that was arcing. I fitted a new GZ34 and then tried a UF4007 before each anode on the GZ34, but the amp didn't work with the silicon diodes fitted.

Expand  

 

The uF4007 is fine. UF5408 will work but are harder to fit because of their size. The diode must be located after the bias tap if there is one. 

 

I describe it here:

 

https://www.talkbass.com/wiki/technical-amplifier/#39-protecting-the-rectifier-tube-from-flashover

 

 

 

55F75648-02C9-4B19-89F7-B29AF5958989.jpeg

5B9D9F0B-EAF2-4B05-B9D0-7C50F3FC2D29.jpeg

Edited by beans-on-toast
d
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beans-on-toast Enthusiast

beans-on-toast

Posted
Posted

Cathode bias eliminates one possibility. Something odd is going on then. Carefully recheck the wiring. When soldering on the socket, the rectifier tube should be removed. Check the socket tension, the tube should slip in and out with some resistance. It helps to have a scope to examine what is going on. Test the high voltage AC secondary with the tube removed. Check for the presence of the 5VAC heater. Then check the rectified voltage with the other tubes removed.

 

Be patient. It requires logically checking each step along the pathway. 

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