Deluxe Reverb

I am building my “dream amp”, a Blackface Deluxe Reverb (AB763 circuitry). I have always loved these amps, great clean tone, love the features and just the right size and output power for me.

Anyways I am going to try and make this one very close to the originals. That means carbon comp resistors, Sprague filter caps caps, Orange Drop caps, cloth wire etc… In the end the circuitry will change a bit though with some mods and tweaking and making up for some of Fender’s “mistakes”. Well it should sound killer, I don’t really care if it doesn’t sound the same as an original. It will however look almost identical to the original Deluxe Reverbs.

I am buying the chassis, faceplate(s) and eyelet board from Weber Speakers. All other parts will be sourced out.

Here is the schematic I am working from, nice and clear… https://taweber.powweb.com/store/6a20_schem.jpg

Some features…
- Two channels (standard controls but bright switch is added on each channel)
- Push pull intensity pot on vibe channel to turn vibrato on and off
- RCD 1/2W carbon comp resistors
- Orange Drop caps
- Sprague cathode bypass caps (and all other electrolytic caps)
- Alpha/CTS pots
- Switch-craft Jacks
- Ceramic tube sockets
- AUX power socket
- Amp can use a GZ34 recto or a solid state cap can (requires slight mod [5V filament tap])

Mods/Ideas…
- Universal presence control for both channels
- Improved taper on reverb pot (logarithmic)
- Reverb works on both channels
- Pentode/Triode Switch (allows the amp to run at 10ishW.)

Potential mods…
- Beefing up the normal channel. I want a super clean vibe channel with the normal channel having a bit more grit and being a bit fatter.
- Coupling caps, experiment with values and di-electrics. To make the amp a bit warmer and fuller, in particular on the normal channel.
- Cathode bias the pair of 6V6 pentode output tubes
- Mid pot (probably will just tweak then set with fixed resistor)
- DC filaments

The chassis, eyelet and more arrived from Weber. Work has now started and the turret board is about half done. Pretty much all hardware has been mounted in the chassis. This thing is starting to look like an amp!

Tubes have arrived which now brings all the supplies/parts together for me to finish this amp and get me playing it. I also got Weber Speakers to build me a custom AlNiCo speaker and cabinet, they arrived as well! More progress made on the eyelet board.

Heaters (filaments) have been wired and the eyelet to tube socket connections have been started.

First note worthy issues have come up. The wiring is complete and the first startup/voltage check has taken place. The rectified/filtered voltage (also known as the B+) is quite low though.

First issue I had was when I first started the amp up I got this terrible smell. I also saw a bit of smoke, I could not tell exactly where the smoke was coming from though. Naturally I start inspecting the entire inside of the chassis where most components are. After searching and not finding all burnt resistors, bubbled caps or blackened joints or wires I gave up. The next day I tried checking voltages again, terrible smell returns. I then decide to flip the chassis over to check the tubes. Then I see it! The choke was smoking a wee bit and had condensation all over it. In my cool workshop the choke was getting so hot it was causing water to form. I removed the choke and performed some times on it with my multi meter. I determined the choke was internally failing causing it to short out to ground. Hmmm....one issue solved! New choke on order.

Second issue was a low B+. With a solid state rectifier and no load installed the B+ was only 358V DC. A Deluxe Reverb should have a B+ of approximately 420V DC - 460V DC when under load using a tube rectifier. Clearly there was an issue at hand.

After weeks of searching the chassis, checking connections, going over layout/schematic I finally sound the problem. The power transformer had two high voltage "taps". One was for 540V AC and one for 680V DC. On all layouts and the people I had talked to I was told to use the 540V AC tap. Well turns out there was a mistake in my layout and/or the people were wrong. For a Deluxe Reverb I definitely had to use the 680V AC tap. With the taps now switched I had a healthy B+ of 498V DC with no tubes installed and using a GZ34 tube rectifier!

As of right now the amp is working. Notice how I said working not sounding great and playing like a charm?

I killed one power transformer in getting the amp running. I was doing some work re going the input jacks and when I soldered the wire from the jacks to V1's grid I accidentally pushed one of the filament wires to the cathode beside it (pins 8 and 9). Of course I did not realize this at the time so there was some smoke after that start up. Yeah fun, a $80 transformer down the drain.

After spending some time finding that cathode/filament short I ordered a new transformer. Now the amp is "fine". Like said the amp works but there is some bad background noise. I haven't had much time to go through it and "chop stick" it and try different grounding methods so that is next. The other issue is reverb isn't working, on the bright side though the tremolo is!

So up next is...reducing noise, going over ground scheme, fix reverb then tweaking the amp for optimum sound.

I haven't updated this in a while. I haven't worked on my Deluxe Reverb in a long time though. It pretty much sat on my bench almost untouched for a few months. I got a bunch of time to work on it in the last month though. Made some major progress, so close to it being totally complete and done now!

Right now the amp works and functions fine, no problems at all. Spent most of my time working on redoing the grounding scheme and then tone tweaking.

Took a long time redoing the grounding scheme. Brand new ground buss implemented. Then had to isolate the input and output jacks. I then learned about a nasty ground loop in the reverb section. So then I had to isolate the RCA jacks. They are now gold isolated RCA jacks. Hardly any hum in the amp now, very quiet. Also increased the B+ filter to just under 60mF. That's as much as the GZ34 can handle. This quiets the hum down though and makes the bass more solid and tight.

The amp is sounding very good now. Have added a dwell pot to the front control panel, the dwell controls how long the reverb stays around. Also did a little cap change to slow down the tremolo a bit, makes the trem much more useful. Also experimented with the tonestack. Found a very interesting RC combination for the mid pot. I made this into a FAT mod. With the fat mod engaged the sound is fat, tight and round. The fat mod can be turned on and off with a footswitch.

Amp still needs another 50 hours of playing for the speaker and cap's di-electric's to be fully broken in but I am liking the tone. It can be very clean and sparkly, or very fat or very dirty and bluesy sounding. Sounds like a classic Blackface amp but with more variety and versatility in tone.

Still need to experiment with swapping tubes and variations in biasing. Also want to work a bit more on quieting down the floor noise and tone tweaking. So close to calling it done though. Very happy with it for now.

I mentioned in an earlier post that I originally had a bad reverb tank. A transducer coil broke but I very carefully fixed it. Regardless it was defective so I got a new free one sent to me. I am using an Accutronic tank by the way.

This time I decide to mount it right. When I originally mounted it, it was a hack job. I just added some springs to the bottom of the tank and tried bolting it down. It was lopsided and suffered from mechanical vibration.

So this time I added a piece of shielded thick cardboard to the bottom the tank, then lightly taped the two together. Then put the tank in a heavy duty leather bag. The bag can help prevent mechanical vibration and also keeps the tank safe so it doesn't get damaged. The tank was then bolted down in the cab.

Did some testing when deciding where to mound the tank. High impedence side (output) of the tank needs to stay away from the PT and choke as they can leak flux. The low impedence side is not so sensitive so it went on the side closer to the PT. Anyways with my added shielding, bag and careful placement the reverb is now even a bit quieter background noise wise.

Ok finally calling this amp complete! Almost a year in the making, well worth it though.

Spent the last few weeks completing the final stage of the build, tone tweaking. Spent a lot of time doing critical listening, then tweaking to get the tone I wanted.

One of the first change I made was replace the output tubes screen resistors. I originally used 1K 5W, not the original Fender value. I heard when I started though that this would increase tube life and reliability. Not knowing much about screen resistors I went with 1K. Anyways I installed this neat 400R 6.5W Dale mil-spec resistor. Much closer to the 470R Fender stock value. Screen resistors don't have a huge effect on tone. Did find the tone softened up and smoothed out a bit after the change. This helped tame the highs and smooth the overall tone out.

Next I found the amp a bit sterile and kind of stiff. Not very much and not in a bad way but still it was an issue. I think a lot of this lifeless in Black Face amps comes from the huge amount of NFB used (negative feed back). NFB decreases gain, increases headroom and tightens up the amp. In excess it can make an amp sound lifeless and dull though. A simple change in the feedback path was made. 820R was changed to 22K. Much less signal being fed back now. There was a slight increase in output. The harmonic content was enriched and I find the amp more dynamic. Just seems richer.

Finally I wanted to fill out the vibe channel a bit more. It needed more "substance" when breaking up. Up the mid range, a simple resistor change from 6K8 to 12K. This helped increase space between notes and make everything sound fuller. Normal channel is full and smooth sounding because of previously installed "Fat Mod".

Also did a few minor things. Changed the Normal changes first tube from a reissue Mullard to a Tung Sol. The Tung Sol seems more lively, more musical and a lot clearer. Also decreased the bright cap on the Vibe channel. Still think it might be a little too bright with the switch on. O well, I can always change that latter.

Last thing... I discovered how dynamic and sensitive this amp is. Is really responds to your touch/pick attack. You can control how much distortion you get just by playing light or really digging in. Also the amp responds great to volume and tone changes on your guitar. Roll back the volume a bit to get a nice clean tone, roll it up for a great distorted tone. Also rolling back the tone control slightly to cut highs is really useful. The cutting of highs works best when the amp is breaking up/distorted. Really smoothes out the distortion and makes it nice and creamy and lush. I'd rather have an amp with excess highs than not enough. Easier to cut frequencies than it is to boost them. Even still the amp has just the right amount of high frequency content for me.

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