"Dumble" Deluxe Reverb wierdness

[AcePepper]

Hi All,
I just built a "Dumble-style" Deluxe Reverb. Mostly AB763 w/ 'verb channel turned into a switchable OD channel. Still has 'verb and 6G6-style trem. Everything is working, mostly. A couple quirks.

1) Normal volume (also known as clean channel volume) won't go all the way to zero. All the way down some guitar signal still coming thru AND a loud "hissss" is present. Much louder than normal. Amp gets very loud very quickly. At 10 o'clock volume comes on all at once and sounds 1/2way up. Clean tone at this point, but starts overdriving the amp very soon after. 1/2 way up on the knob is full volume and overdriving like crazy. Other pots, including O/D controls seem to work normally. I thought about bad grounds, but other pots are fine. Changed 1M volume pot, no change in sound. Ideas?

2) 6G6-style trem works well but does not go all the way to zero. Speed and Depth all the way down, still seeing the bias go up and down. Just a few milliamps +/-, not audible, but still worrysome.

3) Power tranny running hot. Has eaten a couple fuses, but not right away like a burnt tranny. May have something to do with my relay power supply, tapped off the 6.3v.

I didn't use a brass ground plate. Instead I ran a "ground buss", connecting all the pot grounds with a wire, grounded to a screw in the chassis, near the input jacks. Also connected all the circuit board grounds and grounded them at this "preamp ground" spot. Preamp filters are also grounded here. All power grounds are grounded to a PT mounting screw. No 60Hz hum issues. Amp is built an a DR chassis from Mojo. I may need to change some grounding, but not sure what to change as so much is working correctly.
Suggestions? Ideas? Thanx!!!

[loudthud]

Does the power transformer have a center tap on the heater winding? Usually you can't ground the CT AND ground one side of the DC you rectified with a full wave bridge. It creates a low quality short that won't always blow a fuse, just make the transformer run hot. Does the winding produce a good 6.3 to 6.9 VAC?

Check this thread: http://music-electronics-forum.com/t3934/

[AcePepper]

Yes, it does have a CT for the filaments. I am using a bridge rec for the relay p/s, but it's "floated" a few ohms above ground. I did it like the "ac to dc.gif" from blueguitar.org. It's possible that's not happenin';-) I'll try isolating the whole relay-thing, that's worked on other builds.

Any ideas about the extra-hot volume pot deal? Fixin' to try some other tubes, as per another post I read.
Thanx!

[Steve A.]

Yes, it does have a CT for the filaments. I am using a bridge rec for the relay p/s, but it's "floated" a few ohms above ground. I did it like the "ac to dc.gif" from blueguitar.org. It's possible that's not happenin';-) I'll try isolating the whole relay-thing, that's worked on other builds.

Any ideas about the extra-hot volume pot deal? Fixin' to try some other tubes, as per another post I read.
Thanx!

Mr. Pepper

I knew your brother, Sargeant, very well.

One suggestion regarding the pot: check to see if there is any coupling going on (either parasitic or through a common ground, etc.)

As loudthud suggested make sure that the filament windings do not have the center tap connected if you are using my AC-to-DC drawing.

I am not sure what you meant by floating the ground. On my drawing the ground lug goes directly to ground, and you are supposed to keep + and - completely isolated from ground (using an isolated 1/4" jack for a footswitch). If you are using a two button footswitch for channel switching and tremelo you need to keep the two grounds separated.

So does your build use the HRM or non-HRM design (that would be the trim pots after the OD stages)?

When using my AC-to-DC drawing you probably need to drop the voltage a bit when using relays instead of tube filaments. You need to pick out a series resistor so that the voltage is acceptable when the relay is activated. I think I was using something like 1 ohm or even smaller. I suppose that it would make more sense to use a 6 volt zener but I am not familiar with using them in that application.

Good luck!

Steve Ahola

[AcePepper]

Hi Steve,
Thanx for the reply!
I'm not sure what you mean about the coupling, parasitic or otherwise. What should I be looking for?

I'll disconnect the filament CT as suggested. I do have the footswitch jack isolated w/shoulder washers. Drilled an extra hole for it. I had the sleeve wired to ground (but isolated the jack anyway in case that wasn't right;-). Where should I connect the footswitch/relay ground/negative?

I am using a 2-button f/s for the 'verb and trem, old fender-style w/RCA jacks. That's workin' fine. No hum issues, etc.

I'm getting about 3.6vdc on the relay now from the bridge rec. I kinda expected more than that. Hmmm...

My build is the non-HRM. O/D channel seems fine. Matter of fact, it works better than the "clean" channel. The O/D controls DO go all the way to zero, and they're connected to the same ground buss as all the other controls, including my "clean" volume that won't go to zero. Could it be a problem w/my input wiring?

Tried a couple different tubes. No change.

Man, I did a Twin like this a couple months ago and it worked fine. It's killin' me tryin' to figure out what's different/wrong with this one. Thank you all very much for the help!

[bloom]

It seems like your 1M Clean pot might be a linear taper instead of an Audio (log) taper.