Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mike_J on January 08, 2016, 01:31:29 pm
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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
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When I click on the photo and open it up is displays standing up right.
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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
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When I click on the photo and open it up is displays standing up right.
Same here. AND it looks real nice! :icon_biggrin:
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When I click on the photo and open it up is displays standing up right.
Same here. AND it looks real nice! :icon_biggrin:
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
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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
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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. :icon_biggrin:
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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. :icon_biggrin:
Thanks
I didn't want to start something that is known to not work well or cause instability in a build.
Thanks
Mike
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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 (http://el34world.com/Forum/index.php?board=17.0)
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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 (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
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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.
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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?
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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
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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
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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
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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
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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.
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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
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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.
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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
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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...
(http://sluckeyamps.com/sunn/sunn_02.jpg)
(http://sluckeyamps.com/hammond_2/after_3.jpg)
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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
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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
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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
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Here is a picture from the outside back.
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Here is a picture of the front control wiring.
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Here is a picture of the back panel control wiring.
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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
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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.
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Notice V1 is DC
Have you checked that dc voltage? You may want a series resistor to drop the voltage down to about 6vdc.
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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
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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
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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
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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.
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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
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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?
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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
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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.
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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
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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.
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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
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220K 3W metal oxide.
I would set the bias to max neg. voltage BEFORE plugging in the rectifier tube.
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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.
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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
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That bias range will also cover 6L6s if you ever plan to do that.
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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
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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
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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.
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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
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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
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Raw control is as simple as replacing the 10K mid pot with a 100K or 250K pot.
EDIT...For an even more gainy sound, remove the 47K from the board, or make it switchable.
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Finally tested the voltages with tubes in (voltages listed below).
Plate Cathode Grid Screen
V1a 260 2.1
V1b 261 2.0
V2a 435 7.8
V2b 435 7.8
V3a 257 1.3
V3b 259 1.3
V4a ? ?
V4b 439 ?
V5a 228 92 60
V5b 216 92 62
V6 437 15.1mA -49 435
V7 437 18.8mA -49 435
V1, V3 and V5 are significantly higher than the Fender AB763 Deluxe Reverb schematic shows for the respective tubes. Any suggestions would be appreciated. The question marks for V4 are because a voltage could not be determined because the voltages kept varying. The V4b voltage is considerably higher than what the Fender schematic shows. The power tubes were supposed to be balanced but they aren't very balanced. Have a replacement set on order. Biased the tubes to 68% dissipation based on the higher current rating for V7.
Checked the DC voltage on the Heater supply. It is 46VDC using a 22K resistor to ground. Willabe suggested a 100K resistor to ground and looks for a DC voltage on the heaters of between 70 and 80VDC. Can I use 1/2 watt resistors in the voltage divider?
Amp sounds good and is pretty quiet. Voltages need to be fixed though.
Thanks
Mike
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Can I use 1/2 watt resistors in the voltage divider?
Yes. You have 46 volts across a 22K resistor. So, P = E2/R, or 46*46/22000 = .1 watt. I'd feel better using a 1 watter though.
Voltages need to be fixed though.
Nothing wrong with the voltages on V4. If you want steady voltages, disable the trem oscillator with the footswitch or shorting plug.
I don't see voltages for V3a and V3b?
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Can I use 1/2 watt resistors in the voltage divider?
Yes. You have 46 volts across a 22K resistor. So, P = E2/R, or 46*46/22000 = .1 watt. I'd feel better using a 1 watter though.
I don't see voltages for V3a and V3b?
Have more 1/2 watt resistors so will determine which values are needed and order one watt resistors if necessary. Fixed the mistake in reply 51. Somehow left out results for tube three.
Thanks,
Mike
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Double checked the 1K and 4.7K dropping resistors and they test correctly. I have had the Solen fast cap (power cap feeding tubes one and three) for 15 years. Is it possible that the cap is bad and isn't charging? Would that cause higher voltages on tubes one and three?
Thanks,
Mike
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If you want lower preamp voltages then use Deluxe Reverb values.
Look at the schematic for a Deluxe Reverb AB763. You'll notice that the 1K and 4.7K dropping resistors in the B+ rail are really 10K and 10K. The resistor values you used are for the bigger 6L6 amps. Doug noted the differences in his two channel AB763 BOM but not in his single channel AB763 BOM.
http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-Reverb-AB763-schematic.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-Reverb-AB763-schematic.pdf)
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If you want lower preamp voltages then use Deluxe Reverb values.
Look at the schematic for a Deluxe Reverb AB763. You'll notice that the 1K and 4.7K dropping resistors in the B+ rail are really 10K and 10K. The resistor values you used are for the bigger 6L6 amps. Doug noted the differences in his two channel AB763 BOM but not in his single channel AB763 BOM.
http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-Reverb-AB763-schematic.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-Reverb-AB763-schematic.pdf)
Thanks Sluckey, you solved the mystery again. Checked the voltages on the Fender Super Reverb schematic and they are in line with what I posted above. Couldn't find two three watt 10K metal oxide resistors but had two 9.1Ks. Should be close enough.
Thanks,
Mike
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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
Well..if you are going to rotate the photo 90 degrees right, it would be nice to warn the old folk in the viewing audience, because they see the sample pic and they get up out of the chair and position themselves in anticipation of the enlarged pic displaying 90 degrees left. Did you do this intentionally? :laugh:
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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
Well..if you are going to rotate the photo 90 degrees right, it would be nice to warn the old folk in the viewing audience, because they see the sample pic and they get up out of the chair and position themselves in anticipation of the enlarged pic displaying 90 degrees left. Did you do this intentionally? :laugh:
I have no idea why it looks sideways. Since it corrects itself when you click on it I didn't spend much time trying to figure it out. Could get a neck ache trying to view it though.
Thanks,
Mike
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I have been following your progress, so keep the reports coming!
I have a loaded Hoffman AB763 board, modded to single-channel (he didn't offer them at that point) that I didn't finish as I realized I wanted a few simpler projects under my belt first.
We (it is for my son) had planned to build it out as a Pro Reverb-sized amp (6L6s/ 2-12"s) but I think a Deluxe will suit his needs better, so I have an even greater interest following your thread.
Chassis & cabinet are good to go with mine but the faceplate is still TBD. Your faceplates look great & I'd be interested in the specifics of the process; graphic program, stencil material, ink, etc.
Best, TD
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I have been following your progress, so keep the reports coming!
I have a loaded Hoffman AB763 board, modded to single-channel (he didn't offer them at that point) that I didn't finish as I realized I wanted a few simpler projects under my belt first.
We (it is for my son) had planned to build it out as a Pro Reverb-sized amp (6L6s/ 2-12"s) but I think a Deluxe will suit his needs better, so I have an even greater interest following your thread.
Chassis & cabinet are good to go with mine but the faceplate is still TBD. Your faceplates look great & I'd be interested in the specifics of the process; graphic program, stencil material, ink, etc.
Best, TD
What kind of chassis do you have now? I use Inkscape to layout the faceplate and back plate, send it to my local printer in an email and a few days later it is ready. Costs $12.50 per side. He prints on vinyl and covers the printing with a lamination. Have found it to be quite durable. Has some advantages and disadvantages versus the Fender style nameplates. I like it because when I make changes, which happen all the time, I have only wasted $12.50.
Thanks,
Mike
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What kind of chassis do you have now? I use Inkscape to layout the faceplate and back plate, send it to my local printer in an email and a few days later it is ready. Costs $12.50 per side. He prints on vinyl and covers the printing with a lamination. Have found it to be quite durable. Has some advantages and disadvantages versus the Fender style nameplates. I like it because when I make changes, which happen all the time, I have only wasted $12.50.
Thanks,
Mike
Your method for the faceplates is what I had been thinking of trying. I have/have used Inkscape & considered printing decals (for the base metal to show) as well as the whole faceplate. I misread your post about screen printing the NAME plates.
I am making this one tweed-style using an aluminum chassis I got from Dirty Dawg a few years ago. I had thought to polish the chassis side & use decals but am not adverse to a full plate like you have used.
Thanks, TD
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What kind of chassis do you have now? I use Inkscape to layout the faceplate and back plate, send it to my local printer in an email and a few days later it is ready. Costs $12.50 per side. He prints on vinyl and covers the printing with a lamination. Have found it to be quite durable. Has some advantages and disadvantages versus the Fender style nameplates. I like it because when I make changes, which happen all the time, I have only wasted $12.50.
Thanks,
Mike
Your method for the faceplates is what I had been thinking of trying. I have/have used Inkscape & considered printing decals (for the base metal to show) as well as the whole faceplate. I misread your post about screen printing the NAME plates.
I am making this one tweed-style using an aluminum chassis I got from Dirty Dawg a few years ago. I had thought to polish the chassis side & use decals but am not adverse to a full plate like you have used.
Thanks, TD
I have used decals. The decals look nice when installed. However, to make them somewhat permanent you must spray them with a clear top coat (best to use three or four coats). The spray was too toxic to use inside so I sprayed it outside. Problem is a lot of dust is attracted to the finish while it is drying. When you have a mirror finished chassis the dust particles become very obvious. If you have a dust free paint booth you could probably get good results.
The advantage of using the vinyl with the laminated cover is the printer controls the process and the end result is always very acceptable. Screen printing is a process that takes practice to perfect. Would be hard to get all materials necessary to do the screen printing for less than $100.00. While silk screening I used transparencies to make the screens. They are 8-1/2" X 11" so I am not sure how you would create a screen to do the whole chassis all at one time. Lining up two screens would be very difficult but maybe possible. Silk screening using proper inks would give the best result for your chassis given proper application.
Haven't checked to see if clear vinyl is available for use with Inkscape. If it is then you would be far better off using laminated clear vinyl in my opinion versus either decals or screen printing. That doesn't mean ink screening wouldn't be preferred, it just isn't cost effective for a one-off project.
Thanks,
Mike
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Installed the 9.1K resistors and tested the amp with humbuckers. Turned it up to max volume and she honked like a goose. Used a Strat with volume on six with the higher preamp plate voltages before installing the 9.1K resistors. Sounded great. Wish I had tried the humbuckers at max volume with the higher plate voltages.
One of the changes I made to the circuit was changing the .001 cap feeding the PI to .01. I know I should change this back and see what happens to the honk and if it doesn't go away change the Solen cap that feeds the preamp, that I keep mentioning, for a new cap. Any other suggestions would be greatly appreciated.
Thanks,
Mike
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If proper value, that Solen cap ain't causing you any grief. Many people change the .1µF coupling caps between the PI and PA to .047s or even .022s. And they also change the 25µF cathode bypass caps in the signal chain to 5µF or smaller. Makes a big difference in the sound. Speaker choice makes a huge difference in sound.
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If proper value, that Solen cap ain't causing you any grief. Many people change the .1µF coupling caps between the PI and PA to .047s or even .022s. And they also change the 25µF cathode bypass caps in the signal chain to 5µF or smaller. Makes a big difference in the sound. Speaker choice makes a huge difference in sound.
Thanks Sluckey,
Not sure we are talking about the same cap. The one I am mentioning is the .001 cap that feeds the grid (V5a) of the the PI tube. Read a post by Groundhog Ken from about ten years ago if I recall. He mentioned that increasing that cap can cause an amp to honk. He suggested the schematic value of .001 or a value as low as 500pF. My guess is the humbuckers are letting in a hotter signal to the PI which is more than it can handle but I defer to your judgment concerning this matter. Groundhog Ken mentioned this mod was something Gerald Weber was suggesting. I got the .01 from another site. Wonder myself if this isn't something good for a switch. Determine a single coil value and a humbucker value and put them on a switch. I have the cap coming off the power amp jack in the passive FX circuitry. Could place the switch right next to it.
I was wondering about the speakers but these speakers are Celestion Creamback 12M65s. The reviews for the speakers say they are not honky. These speakers in this amp could win the prize for honkiness. The cabinet is closed back. It is filled with acoustic foam (trying to make it sound like a 412 with 212 weight). The speakers have an hour or two of time on them. One thing some reviews said was time makes them better. Have a Dumble clone oval backed cabinet with Celestion Heritage 1265s and another with EV12Ls in it. Will try those cabinets and see what happens.
Thanks,
Mike
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Not sure we are talking about the same cap. The one I am mentioning is the .001 cap that feeds the grid (V5a) of the the PI tube.
I'm aware you changed that coupling cap. I would have left it alone. You also mentioned the Solen again in that same paragraph.
My Solen comment was in response to your "change the Solen cap that feeds the preamp, that I keep mentioning, for a new cap" comment. It ain't a problem and probably never will be.
Fender never used any Celestion speakers in the '60s. If you want a blackface sound, get a bright sounding speaker.
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Not sure we are talking about the same cap. The one I am mentioning is the .001 cap that feeds the grid (V5a) of the the PI tube.
I'm aware you changed that coupling cap. I would have left it alone. You also mentioned the Solen again in that same paragraph.
My Solen comment was in response to your "change the Solen cap that feeds the preamp, that I keep mentioning, for a new cap" comment. It ain't a problem and probably never will be.
Fender never used any Celestion speakers in the '60s. If you want a blackface sound, get a bright sounding speaker.
Good to know we are in agreement as to which cap we are talking about. I guess it is a coupling cap since it couples the V3b plate to the V5a grid. Two identical caps in series which if my memory is correct halves them. There is already a .1uF cap near V3b and the .001uF cap is in series. So the combination must be less than .1uF. If the .1uF is changed to a .02uF and the .001uF cap is in series with it what impact does it have on capacitance versus a .1uF/.001uF combination. Pretty sure a .1uF/.01uF combination causes serious honkiness in the case of my amp.
Okay I will leave the Solen cap alone. I bought a Jensen C12N to go with a Jensen P12N I already had. That is another combination I can try. Will take the Creambacks out and run the Jensen's in the oversized cabinet, take the middle slat out and make it open backed.
You have given me much great advice, most of which I have followed. Wish I hadn't added active effects and an overdrive channel to my Sluckey inspired Plexi/800 build, which you advised against. Just too much, although it doesn't sound too bad. Easy to switch the cap back to .001. Live and learn.
Thanks,
Mike
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Total capacitance for series caps will ALWAYS be LESS than the smallest cap.
Look at this easy to understand page...
http://www.coilgun.info/theorycapacitors/capacitors2.htm (http://www.coilgun.info/theorycapacitors/capacitors2.htm)
The input impedance to the PI is so high that you probably wont hear a difference between a .001, .01, .02, or even a 500pF. Those other caps I mentioned are popular tried and trusted mods that you will hear a definite difference. All will reduce the flubby bass of an AB763 that some people don't like. This may be your honky sound?
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Total capacitance for series caps will ALWAYS be LESS than the smallest cap.
Look at this easy to understand page...
http://www.coilgun.info/theorycapacitors/capacitors2.htm (http://www.coilgun.info/theorycapacitors/capacitors2.htm)
The input impedance to the PI is so high that you probably wont hear a difference between a .001, .01, .02, or even a 500pF. Those other caps I mentioned are popular tried and trusted mods that you will hear a definite difference. All will reduce the flubby bass of an AB763 that some people don't like. This may be your honky sound?
Calculated the capacitance of a .001 cap in series with a .1 and a .001 in series with a .02 as 990 and 952pF, respectively. Thought, certainly this can't be what Sluckey was talking about when he said changing the caps between the PI and PA from .1 to .02. Then a light bulb went off. I bet he meant PA to mean power amp and not preamp. He wasn't talking about changing the cap in series with the .001 from .1 to .02. He was talking about the coupling caps tied to the V5 plates being changed to impact the bass issue.
Sorry. The confusion was mine. Got focused too narrowly on the .001 cap issue and had trouble seeing past it. Will change the .01 cap back to a .001 tomorrow and go from there. Will keep you informed.
Thanks,
Mike
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As Sluckey mentioned the RAW is simple. The stock Deluxe and any 2 tone Fenders limit to usability of the amps to a great degree creating the scooped mid tone. I do love a Fender so I am not dissing it at all.
Years ago when I began really trying to get a true Bakersfield tone (Think Red Simpson) I was playing a twin in clubs where I could use one. All I had to do is turn up the mids all the way, bring the treble to around 4 or so and no bass at all. When the stage volume decreased and I began using a Deluxe and a Princeton I could no longer get the tone.
At a show I met Pete Anderson who has a great tone to me and he was using a 65 Blackface Deluxe and I asked him. Well low and behold in the EXT speaker slot sat a 100K mid pot. He was running it almost wide open and very little treble and no bass.
Since, I have been able to get quite a variety of tones with a Deluxe. Platefire just went through doing some of the mods to a deluxe build.
Here is a list of mods on a Deluxe I love.
Adjustable NFB
Cathode bypass switching on V1 if we are speaking of a 1 channel amp. I use a 3 position rotary with stock, a 10uf and 2.2uf
Raw pot for mids
Plate voltage close to 360 loaded for lower headroom and quicker breakup.
I prefer a 8K to 10K OT
The AB763 Circuit of course
A tone stack bypass with a .022 cap.
I normally only use a Blue Molded cap at the first coupler, the rest I use something a little less articulate. Anything from a Sozo to original Philips mustard.
Also I prefer cathode bias as to me I seem to get more bloom.
I know you are building closer to stock, but all of these things will enhance the amps flexibility. I can get a Tweed tone, the BlackFace tone and with the NFB off and the first cap the 2.2uf playing a Humbucker guitar really will make the amp nasty, but easily will switch back to the stock tone.
My preference is Big Bottle amps, but I do love the Deluxe because the the LTPI and the distortion. Very hard to beat unless you are wanting a real clean amp.
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Ed, thank you so much for the mods you listed. Have some questions if you don't mind answering them.
Adjustable NFB – I placed a 2K pot in series with the 820R resistor. Do you think this is adequate? Sounds like you have an option for no NFB. If so, would you just remove the 820R resistor?
Cathode bypass switching on V1 if we are speaking of a 1 channel amp. I use a 3 position rotary with stock, a 10uf and 2.2uf – Are you referring to the a or b side of the 12AX7? Where do you place the switch? Is there a very noticeable difference between the 22uF and 10uF settings? The reason I am asking is if not then a DPDT switch could be used.
Raw pot for mids – put a 10K pot in the middle position but will up it to 100K. I am guessing an audio pot would be preferred compared to a linear, correct? That way it would be easier to keep it close to stock if that is what I wanted to do. (Somewhere around four on an audio pot and less than one on a linear) Sluckey mentioned either removing the 47K from the board or putting it on a switch. Have you ever tried that mod?
Plate voltage close to 360 loaded for lower headroom and quicker breakup – Thankfully the PT has 330 volt and 300 volt HT taps. I am guessing the 300 volt taps would produce in the neighborhood of 380 to 390 volts loaded when using a GZ34. Do you use a different rectifier tube to achieve that voltage or do you have a transformer with lower secondary voltages?
I prefer a 8K to 10K OT – I took the PT and OT for this build out of my Tweed Deluxe build. I made the mistake of putting higher power Deluxe Reverb iron in my TD build. Wasn't happy with the sound, didn't sound like a Tweed Deluxe so I had to build this amp so the iron would be used appropriately. Need to purchase iron for the 5E3 now. TD uses an 8K OT. Magnetic Components has the 40-18090 with 4, 8 and 16 ohm taps. Could try that in this amp and if I don't like it put it in the TD.
A tone stack bypass with a .022 cap – Would you explain how you accomplish that?
I normally only use a Blue Molded cap at the first coupler, the rest I use something a little less articulate. Anything from a Sozo to original Philips mustard - Have .1 @ 200V as well as .01 and .1 Philips mustards. Have some .02s and .047s mustards in some of the builds that could be borrowed. Easy enough to buy the Sozo's, either yellow or blue, if there isn't a significant difference between the Sozo's and mustards. Have a .02 Sozo blue cap. I haven't been able to get my hands on a Blue Molded .02 cap I guess what I am not sure of is what type caps would you use in the tone stack, the .02 coupling cap on V1b, the V3b .1 coupling cap and the .1 coupling caps on the V5 plates? Don't you think the Xicon PP caps would be okay for the reverb and vibrato sections? Are you talking about the caps in the tone stack when you say the first coupler or do you mean the .02 cap on V1b?
Also I prefer cathode bias as to me I seem to get more bloom - think I will stick with PP for this amp. Have cathode bias on the Tweed Deluxe.
Thanks
Mike
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Sluckey mentioned either removing the 47K from the board or putting it on a switch. Have you ever tried that mod?
This is specific to the Hoffman AB763. A real AB763 does not have a 47K in that position. However, that 47K is meant to simulate the 50K INT pot in a real AB763. A popular mod is to switch that INT pot out for a gain boost.
All you gotta do is just lift one end of that resistor. The gain increase is obvious. If you don't like it, put it back.
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Just received another matched set of power tubes. Put them in and set the grid voltage to -35VDC. Cathode voltage across a one ohm resistor measured 27.9mV with a plate voltage of 423VDC. Calculated dissipation is 98%. Sluckey has mentioned more than once that the grid voltage should be set at -35 volts so I am quite certain he has a good reason for it.
Reset the bias so the lower tube had 20mV on it. Other tube measured 20.7mV, 3.4% difference, so this matched set is really a matched set, at least so far. Plate voltage measured 434VDC. Voltage on grid pin is -39.7VDC. Dissipation is 72.3%. Didn't want to burn tubes in at 98% dissipation without posting these results first for any comment.
Thanks
Mike
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Cathode voltage across a one ohm resistor measured 27.9mV with a plate voltage of 423VDC. Calculated dissipation is 98%.
Something is wrong with your dissipation calculations. Those numbers yield 11.8 watts, which is 84.3% of 14 watts (max plate dissipation for 6V6).
Sluckey has mentioned more than once that the grid voltage should be set at -35 volts so I am quite certain he has a good reason for it.
That's not what I said. This is what I said... "Bias should end up at about -35VDC if you are running 6V6s." Big difference. -35vdc will get you in the ballpark.
...bias so the lower tube had 20mV on it. ...Plate voltage measured 434VDC. ...Dissipation is 72.3%.
Something wrong again. Those numbers yield 8.68 watts, which is 62%.
Looks like you are using 12 watts for PaMax. Why?
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Looks like you are using 12 watts for PaMax. Why?
Mass confusion. No idea how I got 12 watts maximum dissipation for a 6V6 but the corrected number of 14 watts does shine light on your about -35 volt statements. Makes a whole lot more sense to me now.
Thanks
Mike
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Also I prefer cathode bias as to me I seem to get more bloom - think I will stick with PP for this amp. Have cathode bias on the Tweed Deluxe.
Thanks
Mike
NFB, in all my builds it is only a switching pot. Or a switch and a pot. More important on big bottle marshall amps or similar to get the crunch.
A cranked Deluxe Blackface gets loose on the bass end as I find with 6V6 tubes running high voltages and distorting.
I would do a drawing on the switch on the cap switching for v1, but I am writing on a tablet. In the back of the amp I put a 3 position switch and connect the cathode to the center and from each switching position I put a cap and resistor combination from each switch point to ground which will bias the tube differently. Position 1 is stock, position 2 I will use a 10uf and a 820 resistor and finally the 2.2uf and even lower the resistor value some.
Fargen calls this a Decade switch. The 2.2uf to 4.7 uf will remove a lot of the looseness in the bass. You can do it with as many or as few as you prefer.
I get the transformer I want from Edcor. While I mention this a lot of guys do not heavily consider a PT, but a friend who has a shop here in town, Jeff Bakos has shown me the differences a PT can make and it is a lot. Depending on the attack you want, you can consider using a PT that will help provide it. I am not using much in the way of rectifier tubes on new builds, but having one and changing to achieve different voltages is cool.
I also harvest a lot from old Hammond Tone Cabinets. You can get them cheap and the JR 20 has a really nice one and if you watch craigslist or simply stop in by older churches and ask if they have any old organ stuff around. Most still do. I got a Stromberg Carlson PA last Saturday from a church in exchange for a $20 donation. I am careful not to collect too much junk tho. I have been there too many times. No more, if I do not use it in 6 months it goes on Ebay or to a friend.
The 8 to 10K OT's are simply from the 6V6 Data sheet and I prefer lower voltages so these OT's are a better match plus the Hammond Tone Cabinets have some really nice OT's and chokes.
Bypassing the tonestack is just like picking off the signal after the plate of V1. The cap value is simply to shave some of the Bass as I do this to get the amp distorting. You can use switching here as well. Then just insert at the PI. Having a RAW will almost do the same. All you are doing is adding more resistance to the tone stack so less of the signal is attenuated.
Speaking on caps, Blue Molded .02, first coupler vibrato channel. Not the .047 in the normal channel. I am not impressed with the Sozo Blue for this place. A vintage yellow like the Jupiter or the Blue Caps Angela instruments started selling. Big sounding like the old blue molded. Not sure, but that musicap may be good here too. Anywhere the signal is, I use a nice cap. Xicon caps work well too. Have no problem with the chicklets. They are not cheap caps and I really do not now why others dont use the a lot. I built a Super Reverb for a friend and used them all the way and the amp sounds great.
And finally cathode bias does not change the amp from being Push Pull and you can keep fixed and make the cathode bias switchable. I have done it many times. Since the lower volumes that are needed, it is just an easy way to get to the goods that the 6V6 tubes have. I also prefer NOS TungSol 6V6GT's distortion, the JJ's are not as smooth but do have a lower end focus. The new TungSol I would only use in a cathode bias amp. They distort n the brittle side in a stock deluxe granted you are not going to be having as much stress on them.
I hope that answered your questions sufficiently. The tonestack bypass or raw with lowering the coupling caps at v1 will let you get very close to 6V6 Plexi especially if you do the tonestack bypass and select the best cap, but you will not have the Plexi clean which is my favorite part of the Plexi tone.
Have fun with it.
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> No idea how I got 12 watts maximum dissipation for a 6V6
That IS the correct goal if you are selling $19.95 radios. Build-and-ship, cheapest parts, no testing. This leaves considerable safety margin for their sloppy tubes, your cheap resistors, and utility company wobbly wall voltage.
If you are going to carefully consider your parts and voltage, 14W is the "Design Max" number you may shoot for. That still leaves margin for tube variation.
If you are going to actually measure every unit you build, you can probably cheat-up some more. Heck, we know the Champ 600 runs a new-made (tho perhaps tight-spec) "6V6" at something like 17 Watts.
However you should also wonder what you gain by toasting the bottles.
And (generally) if you shouldn't be using a large tube for a large job. True in this case it "would not be a DeLuxe anymore".
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Got back to working on the amp today. Installed four fuse holders; one for the heater supply (3A - Slo), one for the 5V rectifier tube (3.15V - Slo) and two for the HT secondary wires from the PT (1A - Slo), one for each wire. Installed UF5408 diodes between the fuses on the HT wires and pins four and six of the rectifier tube. Also received and installed a 3A AC module that has chokes for both the hot and neutral AC wires. The purpose of the module is to reduce electromagnetic interference. Picture is attached.
Waiting on parts for the bypass cathode/resistor jig. When I receive them will install switch or switches as mentioned by Ed above. Have installed a 100K audio pot in the middle position as mentioned by Sluckey and Ed.
Changed the cap feeding the PI entry grid from the .01 to the correct value of .001. Amp still sounds good, can't tell a difference, until it is cranked. Humbuckers sounded honky, tested with a Strat and I would say it is more blatty than honky with the Strat. Changed speakers in the cabinet from Celestion Creamback G12M65s to Jensen reissue P12N / C12N combination and converted the cabinet to open-back. Still blatty. Pretty sure now Sluckey"s comment about bass is correct. Hopefully a change of bypass caps and resistors will tame it. If not will lower a coupling cap value or two and see what happens.
Thanks
Mike