Stupid Mark C+ question

[supramax]

...Where is the V5 preamp tube slot located? Next to the trafo, or amongst the 3 ?

 

[Platypus]

it's the one furthest out away from the amp (closest to you), next to the tranny.

 

[supramax]

Thanks, Platypus!! Btw, I just brought it back home after sitting half a year at a useless tech with his thumb up in the ***..problem is a hum when standby is on, except it's only in Simul-class mode.

Could it be the power-tubes?

.. and, since you are a C+ man; is there anything wrong with using both 6L6 and EL34 as long as they are balanced?

I have a June 84 original one

 

[Platypus]

Thanks, Platypus!! Btw, I just brought it back home after sitting half a year at a useless tech with his thumb up in the ***..problem is a hum when standby is on, except it's only in Simul-class mode.

Could it be the power-tubes?

.. and, since you are a C+ man; is there anything wrong with using both 6L6 and EL34 as long as they are balanced?

I have a June 84 original one

If you have a simul class amp then yes, you can run EL34's in the outer sockets and 6L6's in the inner sockets. How old are the tubes? When you say standby on, do you mean when the amp is in standby and it goes away when you take it out, or does the hum start only when you put it to 'ON' (both rockers all the way up)?

 

[supramax]

Both the rockers up, yes, the tubes are 50/50% new and old... I don't know how old though. Tech said that he couldn't understand the hybrid powertube thing and put all 4 6L6 in it. Works fine in Class A mode, but still hums in Simul, and I recon there would be no difference to that if I swapped for EL34 in the outer sockets.

I forgot to pick up the new EL34's at the techs, but I guess I'll pick em up and try them tomorrow.

Danm useless tech... he did check that there was nothing wrong with the caps though, at least he said he did check..

Anyway, to isolate the problem, it works ok in Class A, hum in Simul - and the old ones are in the outer sockets

 

[JOEY B.]

Try taking your two inner 6L6's and moving them to the outer sockets. Put nothing in the inner sockets, and switch to Class-A. If the hum is still present, try another pair of known good (low mA draw) 6L6's in the outer sockets. This should isolate wheather it is a tube or amp problem. If you want to run EL-34's in your C+, make sure that pin #1 is connected to ground on the outer sockets. 8)

 

[Boogiebabies]

It sounds like you have a broken tube pin to the heater supply on your 6L6's. On both tubes it is pin 2 and 7. On the left 6L6 you will see two twisted wires coming off these pins to the preamps V1. On the right 6L6, pin 2 is just above, and connected to a brown/black/brown/gold 100 ohm resistor. Just count clockwise to pin 7. If you have a multimeter, you can also test the two 100 Ohm resistors below the speaker jacks for 50 Ohms parallel. The imbalanced heater supply could easily cause hum and it is already isolated to just the simul-class setting. The early to mid production C+ with the brown phenolic sockets are prone to a loosening of the clamps that hold the socket to the base. When the socket gets loose and you wiggle the tube out, you are basically bending the internal pins back and forth where they connect to the circuit board.
Over time they just snap.

 

[JOEY B.]

The early to mid production C+ with the brown phenolic sockets are prone to a loosening of the clamps that hold the socket to the base. When the socket gets loose and you wiggle the tube out, you are basically bending the internal pins back and forth where they connect to the circuit board.
Over time they just snap.

I had to repair a pin#2 solder joint not too long ago. I could kick myself for not upgrading to the ceramic tube sockets when my amp was at MESA a couple of years ago. There goes that hindsight thing again .

 

[supramax]

Thanks for the replys, guys !! You are all truly fantastic !

While I don't seem to be exposed to any of the tube socket-problems you're describing, I did try out the EL34-s in the outer sockets, and it surprisingly sounds absolutly fine to me!
There is a little bit of buzz on the lead channel, but I can't seem to think there's anything other than normal hiss, really.

I'll most certanly be aware of the pin issue, keep it in the back of my head.

Thanks again, and looking forward to spending a bit more time here after I Finally got my baby back and are taking it out gigging. Can't wait.

Cheers !