Mark V - Barely Audible w/Loop Engaged

SonVolt · Feb 16, 2019

All of a sudden the volume level across all 3 channels is very, very low. The loop send knob is set at 12 noon like it always is. If I hard-bypass the loop on the back everything seems to work fine. Once I engage the loop most of the volume disappears. This effects all channels in 10, 45 and 90 watt modes.

Any ideas what to do? Is it a bad tube?

Not sure if this is related, but the amp was working fine this morning. I was using the V as a slave power amp for my Mark IV and panned the delay signal hard right to the IV. When I panned back - Boom, no volume on the left side coming from the V. This has to be coincidence, surely, but I found it unusually odd. Surely the FX8 didn't kill my Mark V.

Eevil · Feb 16, 2019

Hi.

Please test with jumper cable from fx send to return. On occasions I also have intermittent signal loss if fx loop is on and no jumper in place.. cleaning the connectors did not cure the prob so the jumper stays there in my amp. :shock:

SonVolt · Feb 16, 2019

I tried a jumper cable but it didn't seem to help.

mace · Feb 16, 2019

is the SOLO engaged and the solo dial set low? (probably not, but just checking).

Otherwise, V6 pre-amp tube has the SEND return. Not sure what tube does the send (maybe it just gets sent from the channel masters).

Seems like an odd problem, and like you said, odd as to when it first occured.

SonVolt · Feb 17, 2019

mace said:
is the SOLO engaged and the solo dial set low? (probably not, but just checking).

Otherwise, V6 pre-amp tube has the SEND return. Not sure what tube does the send (maybe it just gets sent from the channel masters).

Seems like an odd problem, and like you said, odd as to when it first occured.

Surely it's got to be the SEND return tube... I just look at the back of the amp and there's a cage AND a row of power tubes in the way. This is going to be fun...

mace · Feb 17, 2019

It ain’t so bad. Cage snaps off at the little plastic holders. Remove the two right side power tubes and you can access all pre-amp tubes. Set the amp in 10W mode for all channels and you can even test the pre-amp tube swap with the two right side power tubes still removed (10W mode only uses the left teo power tubes).

There should be a video online somewhere about how to remove the pre-amp cans (slight turn) and power tubes (open the butterfly clips).

Hope the tube swap helps.