Dickerson Lap Steele Amp Troubleshoot

[SilverFox]

I'm working on my first amp job and before I spend too much time trying to determine the exact source of the problems, I could use some opinions on a source of noise and distortion in the amp.

Can't find the exact schematic but the one below is close. Exceptions are: 6L6 instead of a 6V6 and the coupling caps that were in the amp are slightly different value than the schematic, (.002 and .02 instead of .005 and .05). I suspect the bias resistor is a different value also but haven't measured that yet.

Here is what I've done and the outcome:

Replaced all caps. Removed the cap going from the line to chassis- Death cap? The first person to work on the amp replaced the power cord but did not add a grounded cord. Cleaned the volume pot. I also tried adding a temporary ground wire to see if that would reduce the hum present in the amp but to no avail.

The preamp tube was dead so upon installing a new one the amp seemed to work fine. Customer liked sound However, at that point I replaced the filter caps including the cathode bias cap. Upon filter cap replacement the amp seems to have picked up a very soft distortion that fades in and out as the sustain levels drop off. There is also a small amount of distortion that is now present in the tone at all levels and the distortion is not pleasant. It appears too that the power level has dropped since replacing the caps but that doesn't seem to add up. I've read it could be the voice coil. I have not replaced the rectifier tube.

In the end I put the amp back to it's original state regarding the cathode bias caps and filter caps that were still working but this did not clear up the problem. No one seems to have noticed the distortion until after I replaced the filter caps but again, I've put the amp back to it's original state and the noise is still there.

Any suggestions? I wonder also what amp this may be model after?

Regards,

silverfox.

[Stevem]

I have had many a preamp tube make that issue, so swap that out first with a known good tube!

[Structo]

What model amp is this?

Does it have a single ended 6L6?

They started making these amps in 1938!

There were many such amps and lap steel guitars made in the '40's
because of the popularity of Hawaiian music and slide guitars.

[SilverFox]

6L6 SE. There is also a lot of corrosion. I'm going to inform the purchaser of the decisions here. Do you want Nostalgia or function. I don't have another 6SJ7 and this one came from Tubesandmore. It didn't seem to make any noise at first but as I mentioned, everything is back to the way it was regarding the power supply caps. I seemed to have begun after installing new filter caps but didn't resolve upon going back the the originals.

I'll try the 6L6 swap as it 's one of those metal envelope tubes so perhaps it's bad too.

After I talk to the owner I may post pics of the internals.

silverfox.

[SilverFox]

Last night I checked the amp out and initially it worked fine. After about 10 mins the problem appeared. I'm thinking the cathode resistor needs changed. At first I thought the amp was not worth continuing with. However if that is all that's wrong I'll correct it.

Do rectifier tubes cause AC buzz? I wouldn't think so but there is a high level of hum. More likely related to the layout.

silverfox.