Cerwin Vega BG-250 amplifier, starving output

[Jazz P Bass]

What voltage can you measure at the Yellow wire?

[thintheherd]

.33 volts on that yellow wire.

[Jazz P Bass]

0.33 is the amps dc offset. That is o/k.
Apparently it is not enough to raise Pin #9 above Pin #8.
You could try to lower R503.
By the way, what I see on this sensitivity board, is it is just a display.
It has nothing to do with the amp function.

[thintheherd]

yeah, that offset should be fine. i realize the sensitivity board is not "necessary" i would just like the amp to be fully functional. in my mind if that offset is ok then there is no reason the board shouldnt work!?! i have tried and lowered that resistor but to no avail. the only thing that works is to untie that input by removing the resistor completely. i dont feel good about leaving it that way.

[Jazz P Bass]

Removing R503 doesn't untie the input.
R 501 & R503 form a voltage divider.
What are the values of R501 & R503?
The comparator Pin #9 must be above the level of Pin #8 to turn off the output.
This is a sensitive input. We are talking millivolts higher on Pin #9.
R504 could be increased to lower the idle voltage of Pin #8.
What are the values of R504 & R505?

[BasicBassVI]

I hate to drag up an old thread, but did anyone ever find a decent manual for this amp? I just picked one up and could use a little knowledge. Also, is there any chance the OP would be willing to re-post the schematics?

[Jazz P Bass]

Here it what I have from the last go round.

[BasicBassVI]

Thankyou thankyou thankyou you beautiful person! As you may or may not remember, documentation for these amps is as scarce as hen's teeth! This will be VERY helpful.

[BasicBassVI]

To further resolve this thread, I contacted Gibson Brands customer support and a very helpful man by the name of Kirk Eberhard e-mailed me with all the information they still had available for this head. It's just specs, but here they are:

"Aaron,



Thanks for your inquiry. Below are specifications for the BG-250 bass amp head and BG-215 speaker cabinet.



*

BG-250 Bass Guitar Amp

With 6 Band 12dB/octave equalizer

POWER OUTPUT 200 Wrms @ 8 ohms

POWER OUTPUT 335 Wrms @ 4 ohms

FREQUENCY BANDS 73, 147, 294, 587, 1174, 2349 Hz.

POWER REQ. 120/240 VAC 50-60Hz



BG-215 Specifications…

Frequency response: 40Hz to 4kHz

Power handling: 300 watts RMS

Sensitivity: 100 dB

Driver : 154EB-16 ohm 15” woofer, 2” voice coil, cast frame

Impedance: 8 ohms

Dimensions: 43” X 27” X 20”

Enclosure: Vented direct radiating

Application: Subwoofer, bass guitar

Weight: 88lbs.

*



Thanks again for contacting Gibson Customer Service, and best regards always.



Kirk Eberhard"

It's nice to know there's still some decent folks on the Gibson support line.