New AB763 (Deluxe Reverb) Build

[Mike_J]

I was looking through amps and parts I have around.  Remembered I put strange transformers in my tweed Deluxe build so I went to check them.  The PT and OT are both for a Deluxe Reverb.  Don't like how clean my Deluxe is so I am happy to find some iron for the project.  Will replace the tweed Deluxe with appropriate iron later.


Thinking about a cabinet and chassis for project when I see an extra cabinet I made at the time of the Sluckey inspired Plexi/800 project.  Got a new phone for Christmas and thought I would take a picture to post on the site but something is wrong.  When I look at the picture it shows up correctly but doesn't in this post.  Anyone have any ideas as to how I would repair this.  My experts are still in school so I am all by myself on this one.


Thanks
Mike

[mresistor]

When I click on the photo and open it up is displays standing up right.

[Mike_J]

When I click on the photo and open it up is displays standing up right.

Guess I will have to live with it the way it is.


Thanks
Mike

[Willabe]

When I click on the photo and open it up is displays standing up right.

Same here.  AND it looks real nice!   

[Mike_J]

When I click on the photo and open it up is displays standing up right.

Same here.  AND it looks real nice!   

Thank you for the nice comment. 

The biggest dilemma I have is with the head cabinet.  It measures 29-3/4" wide X 10" deep and 10-3/4" high.  Much more room than is needed for the AB763 – 1 Channel board and power supply.  I am thinking about adding an ODS - HRM channel as I made one with four 6L6GCs and very much liked the tone.  Can anyone suggest another option?


Has anyone tried to install a PPIMV in an AB763 with the 220Ks tied to the intensity pot?  If I add an ODS - HRM channel the 6.3 VAC @ 3A will be stretched. Two 6V6s, seven 12 A_7s and a Fender type light would draw 3.07A if my math is correct.  If a PPIMV would not work well with the vibrato circuit is the vibrato used enough to warrant the tube it uses?  Would you rather have a PPIMV in a Deluxe Reverb or the vibrato channel?


Thanks
Mike

[Mike_J]

Decided to just do the AB763 - 1 Channel using the Deluxe Reverb iron I already have.  Only deviation may be addition of PPIMV and a passive effects loop.  Does anyone have confidence that a PPIMV and passive effects loop would work in a Deluxe Reverb?


Thanks
Mike

[Willabe]

Does anyone have confidence that a PPIMV and passive effects loop would work in a Deluxe Reverb?

Yes, it's been done by guy's here a number of times, or at least on AB763 builds.   

[Mike_J]

Does anyone have confidence that a PPIMV and passive effects loop would work in a Deluxe Reverb?

Yes, it's been done by guy's here a number of times, or at least on AB763 builds.   

Thanks


I didn't want to start something that is known to not work well or cause instability in a build.


Thanks
Mike

[Willabe]

I didn't want to start something that is known to not work well or cause instability in a build.

It still needs to be inserted in at the rights points of the circuit and it needs to be laid out correctly in the chassis.

Can't just jamb it in anywhere.

Look in here for schematics and layout drawings with those 2 additions to an AB763 amp circuit;

http://el34world.com/Forum/index.php?board=17.0

 

[Mike_J]

I didn't want to start something that is known to not work well or cause instability in a build.

It still needs to be inserted in at the rights points of the circuit and it needs to be laid out correctly in the chassis.

Can't just jamb it in anywhere.

Look in here for schematics and layout drawings with those 2 additions to an AB763 amp circuit;

http://el34world.com/Forum/index.php?board=17.0

Would you check the attached layout that shows the way I think the FX loop and PPIMV should be installed?


Thanks
Mike

[sluckey]

That should work. Some things I would have done differently (just personal preference)...

Leave the cap on the board and leave the 1.5K resistors on the sockets. Do away with that shielded cable for the bias/trem wire. Then just connect one end of the shield for the signal cable to the left lugs of the MV pots and the other end of the shield to the turret that connects to the wiper of the INT pot.

[Willabe]

I'd put the PPIMV on the front panel of the amp next to the trem intensity.

Much shorter wire runs to/from, + it will be a tight fit in between the power tubes. Might even be a problem with oscillation putting it by the power tubes? 

[Mike_J]

I'd put the PPIMV on the front panel of the amp next to the trem intensity.

Much shorter wire runs to/from, + it will be a tight fit in between the power tubes. Might even be a problem with oscillation putting it by the power tubes?

It would certainly be easier to use if it was on the front panel.  My reason for putting it on the back panel is solely because I heard it is best to keep grid wires as short as possible.  If the pot is on the front panel then I would need to run the grid wires all the way across the amp.  I don't know if that is a problem or not.  I do know it is best to ask knowledgeable people for their advice before drilling holes in a chassis.  I very much appreciate your input.


I would sure like more input concerning having the pot close to the power tubes.  I did a rebuild on an AC30.  The PPIMV pot was on the back panel between two power tubes, albeit EL84s and not 6V6s, and the amp has no problem with oscillation.  That is my only experience with this though.  I wouldn't think the cable going from the circuit board to the pot would be a problem as it crosses other wires at approximately 90 degree angles.  I might be wrong though.


Thanks
Mike

[tubenit]

I think I have done the PPIMV on the front panel of every amp I've done it on (maybe 6+ amps?) and on the back only once.  Having it on the front has never proved to be an issue & that includes Dumblish inspired reasonably higher gain amps.   

with respect, Tubenit

[Mike_J]

I think I have done the PPIMV on the front panel of every amp I've done it on (maybe 6+ amps?) and on the back only once.  Having it on the front has never proved to be an issue & that includes Dumblish inspired reasonably higher gain amps.   

with respect, Tubenit

Thank you for your comments.  I revised the layout putting the MV pot on the front panel.  Does it seem to make sense the way I have it now?


Thanks
Mike

[Mike_J]

That should work. Some things I would have done differently (just personal preference)...

Leave the cap on the board and leave the 1.5K resistors on the sockets. Do away with that shielded cable for the bias/trem wire. Then just connect one end of the shield for the signal cable to the left lugs of the MV pots and the other end of the shield to the turret that connects to the wiper of the INT pot.

Changed the MV to the front panel based on a suggestion by Willabe that was supported by comments from tubenit.  It reduces the bias/trem wire problem.  I put the 1.5K resistors from sockets 1 to 5 because it just seemed to flow better.


Electronically isn't it the same to run the cap to V-5-2 like I have it shown on the revised layout versus keeping it on the circuit board.  Eliminates having to run a wire to the circuit board.  I would use a terminal strip and run the .001 cap from the terminal strip to the socket and a wire from the power amp in jack to the terminal strip so the cap would be well supported.  If you are sure that the board is superior I would certainly differ to your judgment because you have been right before when I wasn't.


Thanks
Mike

[Willabe]

From the drawing it looks about the same distance. 

As soon as you use shielded cable for the grid wire it doesn't matter if that grid wire is long(er). If you keep the grid wire short then you don't have to use shielded wire.

The power tubes have the highest dcv's, the highest heater current draw, the highest ac signal voltages and the most heat. I would not want to stuff anything else in there. There's already enough going on right there.   

[Mike_J]

From the drawing it looks about the same distance. 

As soon as you use shielded cable for the grid wire it doesn't matter if that grid wire is long(er). If you keep the grid wire short then you don't have to use shielded wire.

The power tubes have the highest dcv's, the highest heater current draw, the highest ac signal voltages and the most heat. I would not want to stuff anything else in there. There's already enough going on right there.   

Thank you again for the suggestion to move the MV to the front panel.  It will make the pot much easier to use and helps with some wiring issues in addition to the power tube issues you mentioned.  I will try initially to not use shielded cable and only added if necessary.


Made the changes to the faceplate and back plate.  Will send them off to the printer and start the circuit board tomorrow.  Need to figure out what parts are on hand and what need to be ordered.  Hope to have that done tomorrow too so the parts can be ordered.


Thanks
Mike

[Willabe]

I will try initially to not use shielded cable and only added if necessary.

There might be enough ac signal on the hot/cold going to the MV and then going to the power tubes to just twist those 2 wires into nice tight pairs for noise cancellation/rejection.

   

[Mike_J]

Ran into a problem ordering a reverb tank.  Since I am building a Marshall style (tubes up) head cabinet it is best to have a horizontal reverb tank mounted on the sidewall.  The tank I ordered has a 150 ohm input whereas the reverb driver is eight ohms.  Is this reverb tank useable with the driver, is this not a problem or is it a problem and there is a solution to it?  Help!  I am confused again.


Thanks
Mike

[sluckey]

That tank will not work in the AB763 circuit. Input needs to be about 8Ω. Output should be about 2000Ω. Here are a couple alternative ways to mount a tank...

[Mike_J]

Thanks sluckey


Fortunately they hadn't shipped the order yet so I had them include the correct eight ohm tank.  It will have to hang down from the top of the cabinet which will be okay.


Thanks
Mike

[Mike_J]

As mentioned earlier I am adding a PPIMV and a passive FX loop to the AB763 – 1 Channel amp I am building.  I have made some changes which will hopefully improve the layout given inclusion of those items.
 
The first change is to rewire the power string so the vibrato and reverb power cap would be closer to where it is needed in the circuit.  The reason I did this is I read somewhere that it is advantageous to keep a power cap as close as possible to the stage it will be feeding.  This is supposedly true for both the positive and negative ends of the cap according to what I recall reading.  I have shown where I would put each electrolytic cap in relationship to the circuit board.  The first cap is 47uF at 500 volts and the rest of the caps are 22uf at 500 volts.  Does anyone see a problem with this change?
Another change, which is possible because of having a PPIMV on the front panel, is to rearrange the plate resistor and coupling cap coming out of the phase inverter.  It shortens the wires a little bit so hopefully I can keep from using as much shielded cable going into the grids of the power tubes.  Again, does anyone see a problem with this change?

There is one thing missing from the schematic and that is allowance for longer caps on the circuit board. My favorite sounding amp has almost all Xicon polypropylene caps so I am not opposed to using them in my build.  However, I have some of the old 100nF blue molded caps that to the best of my knowledge were polyester.  These caps were used on the original Fender blackfaced amps.  I have had good luck with them in the past and may consider using them for the bass cap in the tone stack and for the two coupling caps in the PI.  I don't have a 22nF blue molded cap so I would probably use an orange drop 6PS because I have used them in the past and like them.   I also have some 22nF yellow mustard caps that I might want to try.  Does anyone have any suggestions concerning where they would use polyesters?   I know there was a recent post on capacitors but I am curious as to opinions specifically concerning the AB763 – 1 channel build.

Thanks
Mike

[Mike_J]

Here is the build from the inside looking straight down. There are no heater wires yet and the feedback wire from the 820 ohm resistor to the 8 ohm output transformer secondary tap (actually 1K adjustable pot) is not connected. Use the feedback wire to test power tube grids phase (which cause the terrible scream). If they are in phase (no terrible screech) then the feedback wire is connected. If the terrible screech appears the grid wires are reversed and then the feedback wire is connected.


Thanks
Mike

[Mike_J]

Here is a picture from the outside back.

[Mike_J]

Here is a picture of the front control wiring.

[Mike_J]

Here is a picture of the back panel control wiring.

[Mike_J]

Installed the heater wires. There was a thread recently that discussed whether it is better to tuck the heater wires in the corner or run them high over the sockets. As you can see this amp has both. Sometimes it makes sense to tuck the wires in the corner and sometimes it is better to fly them overhead. To me the key is the wires should be twisted to the middle of the socket and then go straight down to the heater pins. If it is deemed better to tuck them in the corner then come in to the socket between pins four and five.


Notice V1 is DC and V2-7 is AC. First time in any of my builds for placing DC on the heater supply line, using a Humdinger pot and running DC only to V1. Supposedly not really necessary on an AB763 one-channel build but will hopefully be helpful in my Sluckey inspired Plexi/800 build to get rid of the small hum that is in that amp.


Thanks,
Mike

[Mike_J]

Here is a picture showing how the reverb tank was installed. Was hoping to find a tank that could be installed on the front panel but could not find a tank with that orientation that had the input and output ohm ratings needed.

[sluckey]

Notice V1 is DC

Have you checked that dc voltage? You may want a series resistor to drop the voltage down to about 6vdc.

[Mike_J]

Here is a picture of the back of the amp and 212 speaker cab the amp will be using. Currently have two Celestion Creamback speakers in a closed back cabinet. The cabinet can be made open backed by remove the center slat from the back panel. Will try combination of Jensen Reissue P12N and C12N open backed. Might need to build a slant backed cab to match.


The speaker cabinet is based on the Bogner 212 oversided cabinet. Looked at Harmony Central years ago and that cab was the highest rated of any at the time so I used it as the pattern. It is 30" wide like the Marshall cabs. Like the look of the Marshall cab so borrowed the Marshall look. Speaker cabinet can be used mono at either 4 or 16 ohms or two amps in stereo at eight ohms each.


You may notice the head cab has vents in the top, a metal grill in the back and allowed about 1/4" around the chassis to draw cooler air into the cab.


Thanks,
Mike

[Mike_J]

Notice V1 is DC

Have you checked that dc voltage? You may want a series resistor to drop the voltage down to about 6vdc.

Thanks Sluckey. No, I haven't checked the voltage yet. Can I check it without tubes in the sockets to get the reading? Hoping to get to that either today or tomorrow.


Thanks,
Mike

[Mike_J]

Here is the amp from the front. Placed nameplates on the amp heads and speaker cabs because all that black and white needed some chrome to balance it. Screen printed the nameplates which was an experience. Need to use an epoxy ink not the tee shirt ink. Can only make about five nameplates before the screen gets all gunked up and has to be replaced. Not fun but have to order about 250 pieces to get a reasonable price if a business makes them.


Thanks,
Mike

[sluckey]

Can I check it without tubes in the sockets to get the reading?

Yes. It will be about 8 to 9 volts. If that's correct, plug V1 in and see if the voltage drops to a reasonable amount.

[Mike_J]

Can I check it without tubes in the sockets to get the reading?

Yes. It will be about 8 to 9 volts. If that's correct, plug V1 in and see if the voltage drops to a reasonable amount.

Pin 9 had 2.93VDC and Pins 4/5 had -2.93VDC on them. Plugged in a 12AX7 and saw no light. Any suggestions?


Thanks,
Mike

[sluckey]

Put one meter lead on pin 9 of the tube. Put the other meter lead on pin 4/5 of the tube. What have you without the tube and then with the tube?

[Mike_J]

Put one meter lead on pin 9 of the tube. Put the other meter lead on pin 4/5 of the tube. What have you without the tube and then with the tube?

Without the tube = 8.32VDC
With the tube = 6.71VDC


You were right about the 8 to 9 volts without the tube. Since the voltage dropped must be lighting something wouldn't you think? Does it matter whether the positive side goes to pins 4/5 or pin 9?


Thanks
Mike

[sluckey]

Does it matter whether the positive side goes to pins 4/5 or pin 9?

Not to me. With 6.7v across the filament you should be able to see it glowing.

[Mike_J]

Does it matter whether the positive side goes to pins 4/5 or pin 9?

Not to me. With 6.7v across the filament you should be able to see it glowing.

Changed preamp tube and could see the heater glowing. Other tube was a new production Mullard. Guess it is hard to see those tubes glow.


Thanks,
Mike

[PRR]

Yes, some 12A_7 it can be very hard to see the hot cathode.

If you kill B+, but the tube warms-up in an hour, it's glowing.

This got very annoying once. Metal 6SJ7. Sometimes it worked, sometimes not. Can't see through steel. Didn't have my X-ray vision. Didn't have even a basic tube-checker. Heater read low-Ohms in my hand. Finally said "argh!" and mail-ordered a new tube. Now it worked all the time. Old one probably had a heater crack, good cold, bad hot.

[Mike_J]

Getting ready to put the GZ34 rectifier tube in the amp and start it up, check voltages, set the bias pot to the highest negative voltage, etc. Noticed that there is no bleeder resistor across the B+ cap. What value and voltage bleeder resistor would you use across a single 47uF at 500 volt cap? This build will use a pair of 6V6GCs.


Thanks,
Mike

[sluckey]

220K 3W metal oxide.

I would set the bias to max neg. voltage BEFORE plugging in the rectifier tube.

[Ed_Chambley]

Looks very well built.  You have elevated heaters via a humdinger and DC on V1.  I would think if you do have any noise at all it will not be the heater string.  Let us know if it quiet.  I really like amps, especially smaller amps to be so quiet you don't know they are on til you turn up the volume.


Good job, and I agree with your choice of cab construction.  You never know, I know a lot of guys running Celestion speakers in a Deluxe.  I have one with a greenback in it with a raw to crank the mids and adjustable NFB and it will play very nice and also get very nasty.  Roll off the treble completely and get a very convincing Gibbons tone with my Les Paul.

[Mike_J]

220K 3W metal oxide.

I would set the bias to max neg. voltage BEFORE plugging in the rectifier tube.

Bias range goes from -25 to -64VDC which should be good. Set to -64VDC. Need to install the bleeder resistor and then will load tubes. Will follow-up after start-up.


Thanks,
Mike

[sluckey]

That bias range will also cover 6L6s if you ever plan to do that.

[Mike_J]

Didn't have a 220K - 3 watt metal oxide resistor for the bleeder resistor. Only had a 200K, so I used it. Connected the rectifier tube and charged the power caps up slowly with the Variac. Mainly necessary because the Solen Fast Cap, feeding the preamp, is 15 years old. Hoping it still has life because I have two more that I would like to use in this build along with a 47uF which would have to be purchased.


Checked the plate voltages with the rectifier tube only and arrived at the following results:


  V1a = 468VDC
  V1b = 468VDC
  V2a = 475VDC
  V2b = 475VDC
  V3a = 468VDC
  V3b = 468VDC
  V4a = 469VDC
  V4b = 469VDC
  V5a = 469VDC
  V5b = 469VDC
  V6 = 476VDC
  V7 = 476VDC


Will install the rest of the tubes and post results.


Thanks,
Mike

[Mike_J]

Haven't recorded any voltages but have been playing it quite a bit. Like it. Should the vibrato work without a footswitch? This one does.


Thanks,
Mike

[sluckey]

A real AB763 must have a footswitch (or shorting plug in the trem FS jack) for the tremolo to operate. If you built Hoffman's AB763 then the trem circuit is from a 6G16 Vibroverb and does not require a footswitch.

Bias should end up at about -35VDC if you are running 6V6s.

[Mike_J]

A real AB763 must have a footswitch (or shorting plug in the trem FS jack) for the tremolo to operate. If you built Hoffman's AB763 then the trem circuit is from a 6G16 Vibroverb and does not require a footswitch.

Bias should end up at about -35VDC if you are running 6V6s.

Thanks for all your help Sluckey. Ordered some EMI AC power cord recepticles which will be installed when received. Also will place a diode between preamp power and output power as well as two diodes and two one amp fuses between the HT lines from the PT and the rectifier tube. Would these fuses take the place of the fuse Marshall places on the other side of the rectifier? One of the reasons the fuses make sense to me is the fuse holders will make solid connectors for the diodes.


Thanks,
Mike

[Mike_J]

Looks very well built.  You have elevated heaters via a humdinger and DC on V1.  I would think if you do have any noise at all it will not be the heater string.  Let us know if it quiet.  I really like amps, especially smaller amps to be so quiet you don't know they are on til you turn up the volume.


Good job, and I agree with your choice of cab construction.  You never know, I know a lot of guys running Celestion speakers in a Deluxe.  I have one with a greenback in it with a raw to crank the mids and adjustable NFB and it will play very nice and also get very nasty.  Roll off the treble completely and get a very convincing Gibbons tone with my Les Paul.

Thanks Ed, the amp is very quiet. The Celestions are new and definitely need to be run for a few hours. Will be doing that this week. Have a 1K pot to adjust the NFB a little. Wouldn't mind learning about the raw control. Would like to get the Gibbons tone.


Thanks,
Mike