HELP! New Power tubes for an Ampeg B-15N

What is your amp doing that makes you think its tubes are bad? BTW, a B15N is cathode biased not fixed.

 

Also BTW, I see you're from Birmingham. My B15N and Wizard Bass 500 came from Highland Music.

 

It's a 37 yr old amp. If it hasn't been maintained regularly it's more than likely that the power supply caps will be on their last legs, and quite possible that valves/tubes are on the way out, although these tend to get changed more often.

I think it would be worth taking to a tech to get checked out, with a view to getting capacitors replaced, and checking the idle currents because resistors do change in value, particularly old ones. Valves may need to be replaced as well. But at the end you should have a great sounding amp which will go for another 30 yrs (but not without the odd service...).

 

Does it say B15NF on the top? Mine is a '65 and is fixed biased. A lot of people just leave off the F designation when talking about the B15N. I didn't think the later 60's B15's were anything but fixed biased and the early 60's models were cathode biased.

Tapp

 

It means the output tubes pretty much bias themselves and the amp will have significantly more spongy feel and put out less power than the same amp in fixed bias.

Fliptops has the entire cap kits, IIRC. A good tech can do the job in an hour or two barring any unforseen problems.

Good question. According to this schematic, identified as a 68 B15N, it's cathode biased, but this schematic shows it as fixed bias. A good tech can tell you which yours is with one look at the output tube socket wiring. FWIW, I have a late 70's B15N and it's cathode biased!