Ampeg Portaflex B-15-N question

[Precisionb87]

Hi. I have what I believe to be a 1968 B-15-N-F Portaflex. My question is this: I had the amp open a little while ago, and noticed an extra yellow wire coming out of the output transformer which did not seem to be hooked up to anything for some reason. Is this a tap for a different speaker impedance? If so, what impedance does it provide? What impedance is currently being used now?

[Precisionb87]

bump

[Febs]

Shortly after reading your post, I happened to come across this one which may answer your question:

'66 Ampeg B-15N In New Repair Shop, Getting Concerned

[beans-on-toast]

The color code for the output transformer:

primary
blue plate
red center tap B+
brown plate

secondary
green 16 ohm
yellow 8 ohm
black ground

_____________________________________________

The color code for the power transformer:

white shield ground

primary
black
black

secondary
red high voltage
red/white high voltage center tap 0V
red high voltage

yellow 5 VAC heater for rectifier filament
yellow 5 VAC heater for rectifier filament

green 6.3 VAC heater filament
green 6.3 VAC heater filament

[joshwilkesbooth]

This is a perfect question for the Portaflex thread.

[Precisionb87]

I read that Jess Oliver puts 4 ohm speakers in b-15s he works on because it give you a little bit more head room. Is he really running a 4 ohm speaker with a 16 ohm tap?! Or does he switch it over the the 8 ohm tap for a 4 ohm speaker?

[JimmyM]

Originally Posted by Precisionb87

I read that Jess Oliver puts 4 ohm speakers in b-15s he works on because it give you a little bit more head room. Is he really running a 4 ohm speaker with a 16 ohm tap?! Or does he switch it over the the 8 ohm tap for a 4 ohm speaker?

The speaker out with the wire and 4 pin connector is 8 ohms.

BTW, the late great Mr. Oliver knew his stuff, but I tried the 4 ohm thing, and it made my B-15 a little too tight and a little less tubey sounding for my tastes. I think he got it right the first time...or maybe I guess it was the third time, since mine is a B-15NC