Very Cool Vintage Ampeg B-15-N rolled in for some TLC... Pic Heavy!!!

syscokid

syscokid

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So... This guy that I know from the occasional jamfests that at I have participated in, asked me if I can take a look at his friend's vintage 1976 Ampeg B-15-N that has recently developed a problem. First of all, I didn't know anything about this amp and its history until three days ago. The problem, or at least part of the problem, was one of the power tubes was bad. Currently I don't know if the tube was used a lot, or maybe something else caused the tube to fail. Anywayz... This is one of the coolest amps I've had the pleasure to fondle... AND THIS IS A FRICKING BASS AMP!!!! Ok, it's time for pics...

The Beginning...:
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Oh feces, look what popped up...:
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Very complicated...:
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Plenty ventilation for our precious glass:


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The two Svetlana Winged C 6L6GC's are mine, and they will always be mine. 6SL7's for the preamp and phase inverter. V1 and V2 are Magnavox USA, and V3 is a Sylvania. Rectrumfier is a Magnavox (Great Britain?) 5AR4:
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syscokid said:
Ampeg should have built tanks for our military... :whistle:
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You may never be able to get an Ampeg to break up, but..... You can bury one in your back yard for ten years, unbury it, plug it in, and it will sound as good as the day you buried it. My '65 Gemini II has the original tubes in it. When I had it serviced a couple of years ago for the first time since I bought it '77, Bob said it needed nothing. He just cleaned it, replaced the power cable, and got rid of the death cap. It still sounds like it always did. With a killer spring reverb too.
 
ivan H said:
Here's a bit of a write-up on the two types. The Difference Between a 5881 and a 6L6GC Valve? | ampvalves.co.uk
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The above quote and info was submitted at jtcnj’s recent thread on his Silkyn amp problems. After reading the article on the difference between a 5881 and a 6L6GC, it got me thinking…:
The Ampeg B15N is fixed bias and designed around the 30 watt 6L6GC. And just like my old Ampeg VT-22, these amps do not have a bias trimpot to adjust the bias. The bias is set with a fixed resistor. I’ve yet to measure this B15N’s set bias, but if the Ampeg factory bias settings is aimed at a medium-ish 60% dissipation of a 30 watt tube, the same bias setting with the Sovtek 5881/6L6WGC’s 20.5 watt rating means that this tube is operating at 88% max dissipation… way too hot! This might be a logical reason why one of this amp’s Sovtek 5881 power tubes met a premature death… :unsure:
 
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