Blackface Deluxe non-reverb servicing

[Ronno25]

I have this blackface deluxe non-reverb that has not been touched whatsoever so far as I can tell. I don't know if it works, as I haven't tried to turn it on. Original tubes, original transformers, original speaker. The only oddities are a 2A fuse and a missing output transformer mounting screw.

I believe it's an AA763. As it's missing the output tube grid stoppers.

Transformers date to 1963. Chassis is ink stamped 1963 but the imprinted serial number is 1964. The tube chart is torn and missing the date code. The inside of the cabinet is not painted, which I have read is a remnant of the brown era.

I'd like to service this amp into reliable playing condition so I can use it. That being said, I'd like to respect the originality of the amp and not replace parts that don't need to be replaced.

I understand I have to:

Install 3-prong grounded plug. Is there an optimal way to do this with an amp of this vintage? Can someone recommend a strain relief and power cable that will fit in the existing hole?

Replace all electrolytic/filter caps. The schematic shows 3 16uf caps but I'm seeing 4 16uf caps in my amp.

Replace resistors and diode in bias circuit.

What else should I do?

Also what's the best way to clean the corrosive metallic dust off the chassis?

Do I also need to replace the power rail dropping resistors even if they measure good?

 

[Burning Fingers]

Replace all electrolytic/filter caps. The schematic shows 3 16uf caps but I'm seeing 4 16uf caps in my amp.

AA763 schematic shows 4 X 16uf caps

 

[Jon Snell]

The AA763 is the Showman, 4 x 6l6 output.
You have only 2 x 6l6 making it possibly an AB763. **763 means manufacture start date July 1963

I would replace the filter capacitors and remove the death cap whilst fitting a three core mains cable.
If components read good, no point in replacing them, you won't improve anything.
Give the potentiometers a clean with contact lubricant and check for tarnish on the input jack sockets. Clean as required.
You could wash the chassis with IPA to remove any damaging deposits but possibly this could take some of the age effect away and may reduce the value.

 

[Ronno25]

AA763 schematic shows 4 X 16uf caps

Good point! My mistake.

 

[Ronno25]

All of the resistors in the amp read well within spec. My reading on the NFB resistor is about half what it should be. I suspect it can't get a proper reading with it directly connect to the OPT.

I have a feeling this amp was not played very much in it's lifetime.

 

[Paul G.]

The AA763 is the Showman, 4 x 6l6 output.
You have only 2 x 6l6 making it possibly an AB763. **763 means manufacture start date July 1963

Not exactly. Each model has its own number scheme, which refers to the date circuit was drawn, and revision. So, while there is an AA763 Showman, there is also an AA763 Deluxe. They are related, but not the same.

 

[slider313]

The AA763 is the Showman, 4 x 6l6 output.
You have only 2 x 6l6 making it possibly an AB763. **763 means manufacture start date July 1963

AA763 is the date the schematics were drawn. That date is common to schematics for the: non reverb Deluxe, Vibrolux and Pro, Tremolux, Bandmaster, Showman, Deluxe Reverb, Super Reverb and Vibroverb.

 

[Paul G.]

3-prong plug. Bypass the ground switch completely. Connect hot (black in US) directly to center lug on fuse, connect side lug on fuse to power switch, other side of power switch to transformer primary. Neutral directly to other primary lead. I solder the ground lead to the chassis, but that's not easy, so most solder to a lug attached to a transformer bolt.

All electrolytic, including cathode bypass caps. Increase the bias cap voltage rating to 100V, any capacitance between 50 and 100 uf.

Test the diode, I don't automatically change them, but there's no harm if you do -- modern diodes are superior to the old ones. Check the bias resistor, I don't change them if they're in spec.

Clean pots and jacks and you should be done.

 

[schmee]

I have a 64 Deluxe non reverb and it's my main gigging amp now. I love the tone in these non reverb amps. Thicker, less bright.

I usually use a IEC power cable from AES/CE Distribution to convert to 3 wire.

https://www.tubesandmore.com/products/cord-power-18-awg-3-conductor-black-bare-end

I have used these because they are about the right diameter for the existing strain relief and available long.

Replace the 16UF filter caps.
Check the pots under power for dead spots.
Clean the input jack and speaker output jacks contact surfaces with a Q tip and alcohol.

It would be very unusual for the resistors to be close to spec in my experience. They are often +15% or more, especially the 100k plate resistors. I usually just leave them though as long as there is no hissing or popping.

Dont mess with the chassis.
wiring change:

:

 

[Jon Snell]

Not exactly. Each model has its own number scheme, which refers to the date circuit was drawn, and revision. So, while there is an AA763 Showman, there is also an AA763 Deluxe. They are related, but not the same.

Maybe to add the actual model number would be a good idea .....

 

[Ten Over]

This one is an AA763. It has 100k plate resistors on the PI and a 56k cathode resistor on the tremolo.

 

[Ronno25]

@schmee @Paul G.

You guys have slightly different wiring schemes for the 3 prong plug. Does this boil down to preference or could you argue there is a "right" way to do it.

Paul G., what is the reasoning for keeping the ground switch out of circuit?

 

[Ronno25]

What are these resistors I've circled? They don't seem to be leading anywhere and they aren't on the schematic so far as I can tell.

 

[schmee]

@schmee @Paul G.

You guys have slightly different wiring schemes for the 3 prong plug. Does this boil down to preference or could you argue there is a "right" way to do it.

Paul G., what is the reasoning for keeping the ground switch out of circuit?

The ground switch can be used as a solder point or just bypassed, makes no difference really.

I learned years ago that white or black belongs in a certain location. Previously i didn't think it mattered, I kept getting a slight buzz on the lips from microphones/PA's when white/black were swapped. Once corrected, that stopped.

 

[schmee]

What are these resistors I've circled? They don't seem to be leading anywhere and they aren't on the schematic so far as I can tell. View attachment 1024531

Those old orange caps should be replaced with 25uf/25v or 25uf/50v. Each of those is a dual cap.

 

[Paul G.]

@schmee @Paul G.

You guys have slightly different wiring schemes for the 3 prong plug. Does this boil down to preference or could you argue there is a "right" way to do it.

Paul G., what is the reasoning for keeping the ground switch out of circuit?

Some people use the ground switch as solder lugs, I don't. With a 3-prong, polarized, grounded wire, it is unnecessary.

What are these resistors I've circled? They don't seem to be leading anywhere and they aren't on the schematic so far as I can tell. View attachment 1024531

No clue. Never seen that before. They would be a good place to discharge your filter caps, though, with the 100K resistor suppressing sparks. Someone actually added those eyelets!

 

[schmee]

delete

 

[Ten Over]

What are these resistors I've circled? They don't seem to be leading anywhere and they aren't on the schematic so far as I can tell. View attachment 1024531

Don't see that every day. Don't see series treble capacitors every day, either.

Are those extra resistors 220k? How did you determine that they aren't leading anywhere?

 

[schmee]

delete

 

[Ronno25]

Are those extra resistors 220k? How did you determine that they aren't leading anywhere?

They are 220k. I checked again and they are connected to the point between the series treble caps you mentioned.

***Edit***** This drawing is incorrect. See post #27