Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: scrimpus on September 07, 2012, 05:08:04 pm

Title: Crate BV 120
Post by: scrimpus on September 07, 2012, 05:08:04 pm

I recently picked up a crate blue voodoo 120 head that does not make any sound, If I crank the volume on channel 1 I get no sound from the speaker but I can faintly hear the output transformer buzz when a chord is played. The speaker is good, tubes all light up and I have replaced all the internal fuses, no apparent signs of damage on the circuitry. Does this sound like a bad output transformer or could it be bad tubes?

Title: Re: Crate BV 120
Post by: navdave on September 07, 2012, 11:45:19 pm

I would swap out the preamp tubes first. If you have a spare one handy
swap it out with the others one by one more than likely it a tube. Why did you replace
all the fuses was there a blown one?

Title: Re: Crate BV 120
Post by: Leevi on September 08, 2012, 12:07:32 pm

I would try to check first is the problem in the preamp or in the power amp.
Solder a guitar jack to PI input and plug guitar in it and check if the power amp works.
/Leevi

Title: Re: Crate BV 120
Post by: scrimpus on September 08, 2012, 12:11:24 pm

I swapped out all the tubes and still no sound from the speaker but  I can hear sound comming directly from the output transformer itself. Also if I unplug the guitar and touch the tip of the cable the output trans buzzes loudly but not the speaker.

Title: Re: Crate BV 120
Post by: Leevi on September 08, 2012, 12:31:36 pm

Measure the OT with Ohm meter. TURN OFF the amp first and unplug from mains.

Primary: from CT to Plate and from CT to another plate.
The values should be close to each other

Secondary: Disconnect the speaker and measure.
The value should be pretty low (some Ohms)

Leevi