Mesa Boogie Stiletto Deuce

[lowell]

Customer says the Tight Clean and Fat Clean modes on Channel 1 are much lower volume than the Crunch mode. Looking at the schematic I'd say this is normal, as there is an extra gain stage for the Crunch mode. After said stage, there is only a 30% reduction voltage divider.

I really thought there was a problem when I got it as there IS quite a volume difference. However, I've checked just about every damn thing, including drawing out what relays are on for each mode, confirm continuity in all modes, tested tube voltages, some caps and resistors in-line with signal flow. Every SEEMS fine to me.

There is about 12v p-p at V3A grid on Crunch, and about 4v p-p on the 2 Clean settings.

Anyone have experience with this? I read on another forum someone saying that the series 1 versions had this and that it was inherent to the design.

http://music-electronics-forum.com/a...4-stiletto.pdf

[Jazz P Bass]

Have you tried putting in a call to Mesa?

[lowell]

Sorry shoulda mentioned that...yes. waiting for a reply.

[lowell]

So they said this is normal.

Now, there is a decent hum, definitely too audible. I installed a bias pot, the amp has 6CA7 in it and the customer wants them biased to 70%, which is about 38ma per tube at ~460v. I don't think the hum was there initially, but the amp was also biased as stock with a -38v grid voltage. If I put -38v on the grids with the bias pot, the tubes are at .15ma per tube! So I set it to 38ma (-20v grid), and HUM. So now I'm at that place where I don't know if this is a new problem or was there before the customer changed the tubes or not. The hum goes away if I pull the PI. It does NOT go away if I pull V3, the last tube in the chain before the PI (V4).

I've checked the PI voltages and all biasing resistors - good. If I short either grid to ground with a BFC the hum goes away. Both Ra have ~135v across em so both triodes are conducting. I tried a new .1uf cap on pin2. Also if both grids are shorted together, hum goes away.

I've been here many a time - hum in the PI. It's always a challenge. Any thoughts? Yes, tried 2 different brand new JJ3cc83.

[Pedro Vecino]

Mesa Stiletto have a certain level of hum, audible and annoying at relatively low volume. I tried quartets and sextets perfectly matched in Deuce and Trident and is still there.
My opinion is that a bias adjustment of 70% does not suit well the crunch mode. A lower adjustment helps to a less tense sound, more agile and articulate.

[lowell]

I managed to make the Ch1 Crunch more on par level wise by adding a 68k across the grid leak on pg. 2. It really took changing the 1M to 68k to get the volume down to the other modes.

On Ch2 the Fluid Drive mode is almost inaudible. I've done some troubleshooting on it and haven't found anything. Need to scope the signal path and see where it doesn't look right. These amps are insanely time consuming to troubleshoot and I've had a few in as of late that seem to have PCB issues, like conduction issues. One had a bias issue only on one side of the OT. I exhausted every effort save for replacing the pcb board to fix it.