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Ampeg flip top B15 series


Ghost Rider
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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
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7 minutes ago, 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!

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 

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On 28/08/2021 at 20:36, 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.

 

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.

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16 minutes ago, 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 

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.

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On 05/09/2021 at 08:46, 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.

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
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14 minutes ago, 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.

 

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.

 

1 minute ago, BassmanPaul said:

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

 

Thanks, I might get some of those.

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8 hours ago, 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.

 

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

 

 

 

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

Edited by beans-on-toast
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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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