Deluxe Reverb, one channel, no tremolo

[telentubes]

Made a bunch of changes and the amp is working now. The grounding was changed per Martin Manning's DR suggestions. V3 wiring was flipped around a bit. The first dropping resistor went from 10K to 12K lowering the voltage for B+C and B+D. The 47K resistor that sends some signal to ground before the 220K mixing resistor was reduced to 33K. Most changes were to reduce the gain going into the PI which tamed the hum and hiss and made the amp feel better under the fingers. I may or may not change the Stand By configuration. I like the amp and am going to use it for a while and tweak if needed. But happy at this point. Now I need to build a cab! I'm liking the Eminence Cannabis Rex 12" speaker the best so far.

[Bob-I]

This is a great thread on a great amp. I had a Princeton type chassis with an amp in it I didn’t like, so I decided to use this layout and schematic, I’m glad I did.

I have the same xformers as in the schem. I fabricated the board, and the bias supply board was already in there so it was an easy build. All tone and blocking caps are Mallory 150, resistors are carbon film. Right now I have NOS JAN Phillips 12AT7a on V2 and V4, and new Mallory 12AX7s in V1 and V3, EH 6V6s and JJ GZ34. I’ll be rolling tubes over the next few days. I have JJ and TAD 6V6s to try, and a bunch of 12..7s to try, but overall, it’s a great sounding little amp.

2 mistakes I found in these files.

1) the bass pot needs a connection from C to CCW, and 2, the reverb driver plate should not cross the cathode/grid leads, very noisy. I wrapped it around the tube socket and the noise floor was lowered dramatically. Sloppy edits, but you get the point.

Single Channel AB768 Layout edit.jpeg

Thx for this, great amp that I’ll get a ton of use from!

[maxkracht]

2 mistakes I found in these files.

1) the bass pot needs a connection from C to CCW, and 2, the reverb driver plate should not cross the cathode/grid leads, very noisy. I wrapped it around the tube socket and the noise floor was lowered dramatically. Sloppy edits, but you get the point.

Needs is a strong word. A good idea perhaps, but not necessary. The originals didn't bother to connect the extra bass pot lug.

Some amps will be perfectly fine with plate, grid, and cathode crossing the tube but some will hum, some will oscillate. Running the plate or cathode around the side is probably the safest bet, but running them across the top could be quieter in some instances. I have personally experienced all of those possibilities. No idea why it is different from amp to amp.

[Bob-I]

Well, without the bass pot connection the bass control was ineffective. Yes, “need” is a strong word. As for the reverb plate. My build was humming like crazy until I moved it, now it’s very quiet, so I’d say that’s important.

[maxkracht]

Well, without the bass pot connection the bass control was ineffective. Yes, “need” is a strong word.

Perhaps we are talking about different things, or I am looking at an already updated layout from the OP, but you only need two lugs connected to the bass pot. It is wired as a variable resistor. Check out the original fender layout.

My build was humming like crazy until I moved it, now it’s very quiet, so I’d say that’s important.

Yes, this was important for your build. I was saying that on someone else's amp it can be different.

You made helpful suggestions, but they were not necessarily mistakes in the original layout.

[Bob-I]

Ok, I’ll agree with that. I felt they were needed, but maybe not everyone does.

Either way, this is a great approach to a classic design. I don’t have use for the normal channel or the tremolo, so it suits my needs perfectly.

[telentubes]

Thank you for these edits , corrections, and suggestions. I never did quiet this amp down to where I like it so maybe now I can! Tone wise, I love the amp. Just too much background noise. I use it every day.

[telentubes]

I wrapped the reverb driver plate around the tube socket as recommended and it made a noticeable difference in lowering the background noise. I have a couple of Rocket Reverbs that I will try that lead dress on.
Adding the the bass pot jumper didn't seem to do anything so I removed it.

[maxkracht]

The bass pot jumper can be useful in case of a pot failure. This way, if the wiper becomes disconnected from dirt or other pot failure, the pot still acts like a fixed resistor and you get full bass. Connecting the two lugs does nothing in normal operation. It is wired as a variable resistor, not a voltage divider.

[pjd3]

Interesting to follow this thread. And certainly informative.

Well Telentubes, you have indeed been a bad influence on me and consequently, I've made the moves to update my Blackvibe 6L6 to a sort of Pro Reverb with reverb, no tremolo.

It wont be too bad - all the transformers, chassis, switches, AC, fuse, switches, jacks and most of the pots are already there. Just need to build up an AB763 board very similar to what you are using on your project, and should be good to go.

Thanks for sharing your project and may it always move towards a more desirable amp! Good thread with good input here, I'm grateful.

Best,

Phil D (PJD3)

[stratomaster]

Made a bunch of changes and the amp is working now. The grounding was changed per Martin Manning's DR suggestions. V3 wiring was flipped around a bit. The first dropping resistor went from 10K to 12K lowering the voltage for B+C and B+D. The 47K resistor that sends some signal to ground before the 220K mixing resistor was reduced to 33K. Most changes were to reduce the gain going into the PI which tamed the hum and hiss and made the amp feel better under the fingers. I may or may not change the Stand By configuration. I like the amp and am going to use it for a while and tweak if needed. But happy at this point. Now I need to build a cab! I'm liking the Eminence Cannabis Rex 12" speaker the best so far.

Are your cathode resistors on the first and second triode 1k instead of 1.5k?

Reducing the 47k to 33k is masking but not addressing the noise problem. You can go stage by stage grounding the grids to identify the noisy stage or bypassing the plates with a large-ish 630v cap on gator clips.

Finally, the lack of bias could have damaged the output tubes, so the common mode cancellation would be off, but that noise wouldn't respond to gain reduction like the 33k resistor.