Here's some pix of work from forum member mscaggs. His builds and pix are super, most of your questions will probably be answered just by looking at his pix. http://p2pamps.com/rmpr (http://p2pamps.com/rmpr)
This is one of those things you have to resolve for your particular project; and the metal you have and the parts you have and how much you want to trick out your project.
There are probably more than 50 things people on this forum have done that are, yes, mods, but fairly minor ones. If you did all 50 of them, that would be hairy.
I don't know if you pretty much wish to build just an ordinary BF DR clone or spend some research time to make some changes. If you *DO* wish to enter the mod mod world of mods, there are lots of cool and useful things available; I will only suggest you do the research BEFORE building it! Eg; finalize the design before execution.
As far as the push-pull pot would the one called "CTS amp pots with SPST pull switch - 1ma" on the pots page work?Yes, that is the one you want.
To be honest, I don't even have an expectation that the amp will sound way better with PTP wiring using the same speaker and transformers.
To be honest, I don't even have an expectation that the amp will sound way better with PTP wiring using the same speaker and transformers.
Well, having completed numerous re-issue BFDR conversions for customers, let me be the first to say that a PTP conversion amp (whether it be to an original Fender layout or to a Hoffman AB763 and I've done several of both) will leave behind all kinds of noise and artifacts that the re-issue amplifier has inherently. I'm not talking hiss or hum but low level parasitic noise I can't describe. You really don't realize this until you A/B a reissue next to a PTP version. I've heard this with the Fender Re-issue BFDR and the re-issue Bassmans next to converted units and it is astounding. If you want just pure guitar tone that's puts a smile on your face without amp noise, ditch the PCP board. I am building an AB763 DR for my studio right now and I've chosen the Hoffman layout to get the sweet sounding bias vary tremolo that Sluckey mentioned above. I've built several Hoffman Vibroverb versions for customers who love them and IMHO they are fine sounding amps that put the re-issue AB763s to shame. Read the reviews on the Reverb King amp at the link below which are both Hoffman AB763s with 6L6s I built years ago. Clean tone no noise is described:
http://www.harmonycentral.com/reviews/brand/corona-ampworks (http://www.harmonycentral.com/reviews/brand/corona-ampworks)
Barry
Here's some pix of work from forum member mscaggs. His builds and pix are super, most of your questions will probably be answered just by looking at his pix. http://p2pamps.com/rmpr (http://p2pamps.com/rmpr)
Are these wire pairs equivalent? Does (fender)red/yellow = (hoffman)black and (fender)red/blue = (hoffman)purple ?That's correct.
Ok, next question: are the transformer coils polarized? For instance on the PT does it matter which of the red wire pair goes where? What about the choke, is it directional? On the OT does the Blue Pin 3 need to go on the + speaker side?No, no, no, and no. The OT blue wire connects directly to pin 3 of a 6V6 socket. That should already be made. The OT brown wire should be connected to pin 3 of the other 6V6. The OT blue and brown wires 'may' need to be swapped later on, so don't trim them to finished length initially.
Does this mean that this wire connects to the circuit board at the "Bias Tap" box on there just like the A, B, C, D points?Correct. If you want to add bias test points they will connect to pin 8 of each 6V6. IOW, you'll have two bias test points. Some people also provide a third black test point for ground. I would use pin jacks, not banana jacks.
on the Hoffman diagram I see two "Board A" boxes and two "A" boxes. Do all four of these get connected together?Yes
So how do you know if these will need to be swapped or which way to wire them? I'd imagine this determines which way the speaker moves for a positive or negative voltage?QuoteOk, next question: are the transformer coils polarized? For instance on the PT does it matter which of the red wire pair goes where? What about the choke, is it directional? On the OT does the Blue Pin 3 need to go on the + speaker side?No, no, no, and no. The OT blue wire connects directly to pin 3 of a 6V6 socket. That should already be made. The OT brown wire should be connected to pin 3 of the other 6V6. The OT blue and brown wires 'may' need to be swapped later on, so don't trim them to finished length initially.
Ok, so those "Bias Tap" boxes have nothing to do with bias testing and they could have just been called box "E"? And if I make some bias test points I'll need to wire them up to pin 8 instead? How many bias test points would there be in total then, 2 or 3? One from each 6V6's pin 8 and then do I also need a ground?QuoteDoes this mean that this wire connects to the circuit board at the "Bias Tap" box on there just like the A, B, C, D points?Correct. If you want to add bias test points they will connect to pin 8 of each 6V6. IOW, you'll have two bias test points. Some people also provide a third black test point for ground. I would use pin jacks, not banana jacks.
So how do you know if these will need to be swapped or which way to wire them?You won't know for sure until you turn the amp on. We have a 50/50 chance of getting it right. That's why I suggested don't trim to finished length until you positively know they are connected right. This deals with the negative feedback phase. Get it wrong and you will have a positive feedback circuit. An AB763 will usually squeal or howl loudly if the phase is wrong.
One from each 6V6's pin 8 and then do I also need a ground?You don't actually need the ground test jack but some people find it convenient. You could just use a gator clip to connect the black meter lead to chassis. In fact, you don't really 'need' any test jacks. You can use pin 8 of the tube as the test point. Or clip a lead to one of the on-board 1Ω resistors which connect to pin 8. The test jacks are a convenience only. But if you are nervous or have shaky hands, I suggest you install test jacks.
Ok, so those "Bias Tap" boxes have nothing to do with bias testing and they could have just been called box "E"?Correct. There is no significance to the boxes other than to quickly draw your attention to what's written inside the box. Hoffman simply uses the box as an annotation callout. The phrase 'bias tap' is more meaningful than 'E', especially when it refers to several different pages. Hoffman uses 'bias tap' to indicate the AC source for the bias supply. This annotation convention works well. Others use different conventions. Here's my style of annotation. Notice I did use 'E' to represent the bias voltage points. Using different colors helps to quickly show where those points are connected on the schematic and eliminates the need to clutter the schematic with long connecting lines.
QuoteSo how do you know if these will need to be swapped or which way to wire them?You won't know for sure until you turn the amp on. We have a 50/50 chance of getting it right. That's why I suggested don't trim to finished length until you positively know they are connected right. This deals with the negative feedback phase. Get it wrong and you will have a positive feedback circuit. An AB763 will usually squeal or howl loudly if the phase is wrong.QuoteOne from each 6V6's pin 8 and then do I also need a ground?You don't actually need the ground test jack but some people find it convenient. You could just use a gator clip to connect the black meter lead to chassis. In fact, you don't really 'need' any test jacks. You can use pin 8 of the tube as the test point. Or clip a lead to one of the on-board 1Ω resistors which connect to pin 8. The test jacks are a convenience only. But if you are nervous or have shaky hands, I suggest you install test jacks.QuoteOk, so those "Bias Tap" boxes have nothing to do with bias testing and they could have just been called box "E"?Correct. There is no significance to the boxes other than to quickly draw your attention to what's written inside the box. Hoffman simply uses the box as an annotation callout. The phrase 'bias tap' is more meaningful than 'E', especially when it refers to several different pages. Hoffman uses 'bias tap' to indicate the AC source for the bias supply. This annotation convention works well. Others use different conventions. Here's my style of annotation. Notice I did use 'E' to represent the bias voltage points. Using different colors helps to quickly show where those points are connected on the schematic and eliminates the need to clutter the schematic with long connecting lines.
http://sluckeyamps.com/sunn/sunn_sceptre_1971.pdf (http://sluckeyamps.com/sunn/sunn_sceptre_1971.pdf)
The OT blue wire connects directly to pin 3 of a 6V6 socket. That should already be made. The OT brown wire should be connected to pin 3 of the other 6V6. The OT blue and brown wires 'may' need to be swapped later on, so don't trim them to finished length initially.
I guess to use them I'd read a voltage to ground though, instead of current, right? And the two different points are for reading the voltage on each tube? Is that the "plate voltage"?That's correct. But notice that the voltage you read will be across a 1Ω resistor. So, the current through that resistor will equal the voltage across the resistor divided by the value of the resistor. That 1Ω resistor is called a current sense resistor because the voltage across it represents the current through it. Dividing by 1 is easy. IOW, if you measure 25mV across the 1Ω resistor, there will be 25mA flowing through the resistor. This is called the cathode current and is considered the same as the plate current. Plate current is actually slightly higher because some of the cathode current flows into the screen grid.
When I was unsoldering things I noticed a lot of the pins in the tube sockets are very wiggly and loose - that doesn't seem like a good thing to me.The pins on the new sockets will be wiggly too... until you plug the tubes in. :icon_biggrin:
QuoteWhen I was unsoldering things I noticed a lot of the pins in the tube sockets are very wiggly and loose - that doesn't seem like a good thing to me.The pins on the new sockets will be wiggly too... until you plug the tubes in. :icon_biggrin:
It is not a today problem for you. Once you build your amp we can help you with start up procedures that would cover the pin 3 phasing mentioned earlier, biasing your power tubes, going through the schematic in comparison with your amp with a yellow highlighter and a few other things. These are not a problem for today though. All you need to do now is build the circuit board like the layout documents and pictures show and install the wires to the tube sockets exactly the way the layout and pictures indicate. If you do that you will have a successful build.
Right, "solder with tubes installed" is standard procedure?Not for me!
When you are soldering pins on a socket you can flow solder into the socket pin if no tube pins are present.If this happens to you I suggest you 'may' be using too much solder and/or using cheap sockets.
I doubt very much that I need the tubes in the sockets today. Much better at flowing solder than I was years ago. The old tubes in the tube sockets are an ounce of prevention for me. Don't know if I haven't had any problem since using the old tubes in the sockets is due to learning to solder better, not using cheap sockets or the old tubes themselves. Only know that I haven't had a socket problem, at least related to solder, since I started using the old tubes. Sure everyone has their own system. Mine stems from a problem I encountered in one of my first builds. Maybe my first build. It was quite a while ago. Haven't had the problem since using the old tubes. Just passing along my experience.Quote from: davegardner0Right, "solder with tubes installed" is standard procedure?Not for me!Quote from: Mike_JWhen you are soldering pins on a socket you can flow solder into the socket pin if no tube pins are present.If this happens to you I suggest you 'may' be using too much solder and/or using cheap sockets.
Solder will stick to octal tube pins. That's how the wires coming through the glass are attached to the socket pins. If you shove enough solder down into an octal socket, you may end up with the tube soldered to the socket. :embarrassed:Haven't ever had that happen but Sluckey probably has a point. Built my first amp about 15 years ago after having built a car and house from scratch. Said I would never ever build another car or house but do like amp building, my wife would say maybe too much. The obvious key is proper soldering technique. When I first started there were no forums to get help from. Had never done any electrical soldering in my life. So a lot of what I do is because I messed something up in the past and tried to learn from the mistake. Still make many mistakes, thankfully most of which Sluckey got me out of.
Right, "solder with tubes installed" is standard procedure?
... Well, having completed numerous re-issue BFDR conversions for customers ...
... All torn down ...
I have always heard that it is best to twist the AC secondary wires tightly together. That would be the yellow, red and green wires coming out of your power transformer. Looks like you may be a little gun shy about the amount of solder you use on the socket pins. Impressed with how little you used. Probably my fault for being so neurotic about getting solder in the pins. I am sure there are others on the forum that are more classically trained in soldering technique than I am but I try to flow enough solder to fill the hole in the pin.
Thanks
Mike
Some wiring tips I have learned over the years. Supposedly it is best to keep grid wires as short as possible. The grid wires carry very small voltages. You want to keep them as far away from the plate (that carry high voltages) or cathode wires as possible. If they cross it should be at a 90 degree angle. There is some square rule that I will probably butcher but it said something like distance squares the reduction in cross-talk between wires. So wires that are twice as far apart have 1/4 of the cross-talk. Three time as far apart have 1/9th the cross-talk and so on. Don't forget that you have three dimensions. Pictures and layout diagrams usually only show two dimensions. Use all three dimensions to your advantage.
With your crimped slip-on connectors, pulling those AC-in and PT feed wires off the fusepost and running them under the fuse would be easy and I would recommend that. And it would good to twist all those AC-line wires; the ones coming in from the power cord and the ones running back to the PT. Just as a point of "propriety" we like to see the black wire hit the fusepost first, the inside lug first. Then the AC line switch. That way, if the fuse blows and the amp is on your bench, there is one and only one item still connected to the AC line. As you have it wired, the AC switch under those conditions remains all the way hot. It's certainly less of a big deal with those insulated push-on crimp connects you are using and it affects utterly nothing but is a "best practice". I would try to get the black-white from the AC line and the black-white feeding the PT all in one 4-wire bundle. Twist or tie wrap. The raw B+ from the rectifier tube can also run in or along that bundle. Just for neatness, and it's also the idea that once you wire those fundamental elements, you should never have to touch them again.+1. Keeping the unfiltered AC or DC (red wire from the rectifier to standby switch) wires together and behind the power tubes will help you make a quieter amp. Would have your black and white OT primary wires tie wrapped together and run them between the power tube and rectifier tube if they are long enough.
I'd also like to see some sort of wire control on the HV and the 5V wires from the PT. A nylon "P" cable clamp is the usual way.
With your crimped slip-on connectors, pulling those AC-in and PT feed wires off the fusepost and running them under the fuse would be easy and I would recommend that. And it would good to twist all those AC-line wires; the ones coming in from the power cord and the ones running back to the PT. Just as a point of "propriety" we like to see the black wire hit the fusepost first, the inside lug first. Then the AC line switch. That way, if the fuse blows and the amp is on your bench, there is one and only one item still connected to the AC line. As you have it wired, the AC switch under those conditions remains all the way hot. It's certainly less of a big deal with those insulated push-on crimp connects you are using and it affects utterly nothing but is a "best practice". I would try to get the black-white from the AC line and the black-white feeding the PT all in one 4-wire bundle. Twist or tie wrap. The raw B+ from the rectifier tube can also run in or along that bundle. Just for neatness, and it's also the idea that once you wire those fundamental elements, you should never have to touch them again.
I'd also like to see some sort of wire control on the HV and the 5V wires from the PT. A nylon "P" cable clamp is the usual way.
Looks like your chassis has been painted? If so, you need to make absolutely certain that you have a good connection between the ground wires and the chassis, especially that green wire from the power cord. Never had a painted chassis before so don't know anything about them. Have some old Fender chassis with quite a bit of rust in them so the paint makes some sense. However, critical that the grounds are sound. May want to use emery cloth to get a clean ground point. Your red and yellow wires are adequately twisted but when you twist the green wires (heaters) I would make them tighter.
Keep taking pictures as you go. Easier to fix these items as you go along.
Guess if I don't see rust on a Fender chassis I think it is painted. Not a bad idea still to use a little emery cloth under the ground connections to make sure you have the best connection possible in my opinion. Don't mind checking your work at all. Others have done so for me.Looks like your chassis has been painted? If so, you need to make absolutely certain that you have a good connection between the ground wires and the chassis, especially that green wire from the power cord. Never had a painted chassis before so don't know anything about them. Have some old Fender chassis with quite a bit of rust in them so the paint makes some sense. However, critical that the grounds are sound. May want to use emery cloth to get a clean ground point. Your red and yellow wires are adequately twisted but when you twist the green wires (heaters) I would make them tighter.
I don't see any evidence of paint on the chassis, it appears to be bare metal. I'll check the continuity to that new ground lug to confirm.Keep taking pictures as you go. Easier to fix these items as you go along.
If you guys don't mind checking my work I'm happy to keep posting photos. Thanks!!!!! :icon_biggrin:
The way you did yours, soldered to the back of the pots, is the way Fender did their grounds historically.I've never seen a Fender amp with a wire buss soldered to the backs of the pots.
If you look at Sluckey's picture on the last post you will notice he did his buss bar a little differently than you did. The way you did yours, soldered to the back of the pots, is the way Fender did their grounds historically. That is how I did mine on my first few builds. Potential problem with it is every pot body is a chassis ground point.
If you notice on Sluckey's picture he has a buss bar that is NOT soldered to the back of the pots. Every ground from the pot connections and the circuit board go to the buss bar. The buss board is terminated at the input jack so there is only one preamp ground connection (in your case two, one for the normal channel input jack and one for the vibrato channel input jack). Don't know that you need to redo your buss bar as Fender did it that way for a long time but information for future builds.
Remember you need to install your grounds from the circuit board to the chassis in the order they appear on the schematic. Don't want your grounds to cross over each other.
I'm curious about this single vs. multiple grounding points issue and also the grounds "crossing over"...what effect does this sort of thing have on the amp if done wrong? For instance what effect does having every pot body be a chassis ground have on the amp? Since the pot body is in contact with the chassis aren't they already grounded? I'd assume there's something subtle here I'm missing.All the fuss over the grounds is to make the amp quieter and more stable. When I mention crossing over it has to do with relationship to the signal chain from input jack to output. When wiring the wires on the back of the turret board you should wire them where Doug shows them on his layout board. They are the dashed lines but you probably already knew that. Usually they are not in a straight line.
What about the crossing over grounds, what do you mean by that? Is that in relation to the signal chain, like the order in which the signal goes through the amp? Or do you mean the wires physically crossing each other on the board?
One other question I forgot to ask earlier, when I get to soldering the wires on the back of the turret board, should I run them in straight lines? Does it matter?
I'm curious about this single vs. multiple grounding points issueThe idea is to keep power amp grounds away from preamp grounds. Power amp grounds are high current and usually kinda noisy because of less B+ filtering. Preamp grounds are low current and quiet because of much higher B+ filtering. Power amps deal with large signals, preamps deal with much smaller signals that are more susceptible to noise pickup. If you allow high current from the power tubes to flow through the same ground wire as a preamp tube, it's likely that the sensitive preamp will be affected in a noisy manner. Best to keep those grounds separated. There are plenty of successful grounding schemes out there. Many are just variations of what I just tried to explain. Amp grounding is a book of it's own. But, if you are going to use a Hoffman board, just use his grounding scheme as well. His grounding scheme is the same high quality as his boards.
what effect does having every pot body be a chassis ground have on the amp? Since the pot body is in contact with the chassis aren't they already grounded? I'd assume there's something subtle here I'm missing.Yes, they are already grounded. It ain't about making sure the body of the pot is well grounded. It's about providing a convenient ground buss for some components (including the pot element), switches, and shielded cables, etc. Soldering the buss to the back of the pots is a personal preference. It looks neat and works well. But look at your ground buss. Looks neat but that big wire is stiff. What you gonna do if you ever need to change a pot? I bet you'll do some cussin' and start thinking of a different way to do it. That's the main reason I float my buss above the pots. A lesser reason is you need to sand the finish off the back of the pot to get a good solder connection. So, remind me again, why are you doing this? Is it just so the body of the pot will be grounded? :wink:
when I get to soldering the wires on the back of the turret board...They don't have to be run in straight lines but when I can, I do. I won't run a wire across a turret though. The important thing is that the wire has a reliable connection and won't fall out later when you solder something else in the turret. So, don't just poke the wire into the turret and expect it to stay there. Mike told you one good way to do it. And you can always just run the jumpers above board. I prefer that if it doesn't look too busy. Here's how I do my under board wires. Reliable and a lot less work...
Fender Super Reverb (1971) and a blackface Twin Reverb I owned had the wire soldered across the back of the pots. Both purchased in the Houston area. Suppose it is possible they were serviced by a tech that liked to run a buss wire to each pot. Admit my sample would be much smaller than yours so will differ to your experience. What did they use then? That brass plate?Quote from: Mike_JThe way you did yours, soldered to the back of the pots, is the way Fender did their grounds historically.I've never seen a Fender amp with a wire buss soldered to the backs of the pots.
I bought the better quality switches, I'm hoping to put them in this weekend. I think I can orient the contacts downward in the chassis and keep all of the power wires including the unfiltered B+ in the bottom corner of the chassis. I don't think I want to physically move the switches or fuse so hopefully this will keep things orderly and our of the way...The Visio layout I posted above is for a Marshall style tubes up amp. In that case the contacts for the on/off and standby switches are towards the bottom of the chassis. Your chassis is tubes down. In your case the contacts should face up when you are looking in the chassis. This won''t be a problem. That will keep them even farther from the power amp tube socket. Just keep the wires flush to the back of the chassis and you should be okay.
I don't think it's a big deal to run power by your 6V6 / 6L6 tubes. That's how (eg; where the holes for the parts are) the amp was made! It's a bit "ehhh, I dunno", but we assume the AC is twisted wires; the output tubes are swinging big volts, hundreds of time bigger than any imagined field emanating from the AC wires, and those tubes are in push-pull anyway which is inherently hum-canceling.The wire going to the standby switch is unfiltered DC not twisted AC. Since he is rebuilding this amp there is no reason not to try to isolate that wire from interfering with the grid wires going to the power tubes to the extent possible. Obviously Fender constructed the amp with the standby switch sitting right on top of one of the power amp tubes. In my opinion this was much more to cut manufacturing cost versus best practices.
Too many cooks opining. It *IS* a big deal to run AC next to preamp tubes, in fact, it's potentially a big deal to run ANYTHING past preamp tubes. Or tone/vol controls.
The wire going to the standby switch is unfiltered DCNot true. It is filtered by two parallel 16µF caps in the original. Ripple voltage will be under 10V. It will be fine around the power tubes.
Obviously Fender constructed the amp with the standby switch sitting right on top of one of the power amp tubes. In my opinion this was much more to cut manufacturing cost versus best practices.How does that cut costs? Same parts count, same number of holes in the chassis, same amount of labor to mount and wire the switch.
I am confused. Looking at the Hoffman schematic and layout the standby switch is fed from pin 8 of the rectifier tube. It then feeds the first filter cap. Is this how you say it is filtered? Got the "dirty" wire idea from a post by PRR. He suggested I keep the wire away from the PI/driver. (Reply #8, Where to place the humdinger pot? thread) He said why run a sewer that way if you aren't forced to. Made good sense to me then as it does now. He still needs room for his heater wires above the sockets. Awfully crowded as it is now. Cleaning up that wiring solves the sewer issue and makes more room for heater wires. Just makes sense to me. Will differ if you still think I am off base. Looked awfully tight around that power tube socket to me.QuoteThe wire going to the standby switch is unfiltered DCNot true. It is filtered by two parallel 16µF caps in the original. Ripple voltage will be under 10V. It will be fine around the power tubes.QuoteObviously Fender constructed the amp with the standby switch sitting right on top of one of the power amp tubes. In my opinion this was much more to cut manufacturing cost versus best practices.How does that cut costs? Same parts count, same number of holes in the chassis, same amount of labor to mount and wire the switch.
Looking at the back of a Deluxe Reverb, I'd say the standby switch position is logical and efficient.
There is a sizable labor saving in being able to snap on wires and ribbon strips instead of soldering.Now you're talking about construction techniques. Sure there's a big savings in the whole PCB technology. But I responded to your comment about the physical location of the switch.
We're talking about a Fender Deluxe Reverb so I referenced the Fender schematic. Filter caps are connected directly to the rectifier tube. But it really doesn't matter if the caps are on the other side of the standby switch. When the switch is in standby mode, the amp is dead, so who cares about unfiltered B+. When in operate mode the filter caps are connected to the rectifier through the switch contacts.Thanks Sluckey, you are probably right. A lot of ways to build an amp successfully.
IMO you're making a lot to do about nothing.QuoteThere is a sizable labor saving in being able to snap on wires and ribbon strips instead of soldering.Now you're talking about construction techniques. Sure there's a big savings in the whole PCB technology. But I responded to your comment about the physical location of the switch.
He said why run a sewer that way if you aren't forced to. Made good sense to me then as it does now.And it makes good sense now. But, in that analogy, the power tubes are PART OF THE SEWER.
Quotewhen I get to soldering the wires on the back of the turret board...They don't have to be run in straight lines but when I can, I do. I won't run a wire across a turret though. The important thing is that the wire has a reliable connection and won't fall out later when you solder something else in the turret. So, don't just poke the wire into the turret and expect it to stay there. Mike told you one good way to do it. And you can always just run the jumpers above board. I prefer that if it doesn't look too busy. Here's how I do my under board wires. Reliable and a lot less work...
(http://sluckeyamps.com/VAC15/underboard_jumper.jpg)
Very nice pics. Sharp, clear, and big.
Yes, [you absolutely must] ground the cathodes of the 6V6 (pin 8) unless you are going to install a bias-testpoint between those cathodes & ground by lifting them atop 1-ohm resistors.
Correct. Such a wire would short out that 1 ohm resistor.
Remember (or know) that a 1 ohm resistor is essentially nothing but a wire. If you have a multimeter and touch the leads together on OHMS, you'll probably get something like .2 or .4 ohms...if your meter goes that low. That's with big fat wire in the test leads, whereas in your amp, you're using probably 20 or 22 AWG = fairly thin wire = higher resistance. A 6V6 doesn't have the slightest idea what a 1 ohm resistor is. Doesn't know it's there.
Today I installed the filter capacitors, using the by-the-pots method. I want to keep the external bias pot from the PCB amp layout, so I had to get creative with the position of the first two caps that go to "A". ...
Today I installed the filter capacitors, using the by-the-pots method. I want to keep the external bias pot from the PCB amp layout, so I had to get creative with the position of the first two caps that go to "A". ...
To me, those two "A" node caps look scary off the board.
I'd want to see some kind of sleeving over the positive leads, or some good method of securing them which ensures the positive leads could never short to the chassis, the bias pot or a nearby bolt...
Do you think that's sufficient?
Do you think that's sufficient?
No. :w2:
Hey could you elaborate some? What's the preferred filter cap mounting method?
You could measure the diameter of those caps and get a few of those nylon "P" clamps (most often used for bundles of cable) ....Doug sells them though I don't know if he sells them with sufficient diameter...the 6th pix down on the Hoffman catalog page:"Tube Amp Fuses, Power Cords, Fuse Holders"
Then drill a 6-32 or 8-32 clearance hole near the edge of the parts board. Place the clamp around the caps, then install the clamp "upside down" (flat side up, circular side down) with a machine screw through the parts bd and the cable clamp. Looks like you'd need this in 3 places. Definitely reco a star washer lock nut or kep nut in the picture AND a flat washer in contact with the cable clamp....I *think* you can get these at an Ace Hdwe though they are expensive there.....but those would make an excellent mechanical mounting method for them caps.
Ok I see what you're saying now. What if i do want to drill a hole in the chassis though? I ask because I may have an alternative mounting solution with parts on hand but id need an 8-32 thru hole in the chassis.You just have to be careful and watch what you're doing. Almost every scratch build amp I do requires some drilling after a lot of wiring has been done. Same with all the conversion projects I've done.
I have some of these zip tie basesThat's perfect.
http://www.thorlabs.com/thorproduct.cfm?partnumber=CMS010 (http://www.thorlabs.com/thorproduct.cfm?partnumber=CMS010)
Which will hold a zip tie, and the hole would be directly under the caps. I'm thinking that will be super secure and the hole goes in an easily accessible location. Not that I don't like the P clip idea, id just rather use parts on hand.
I have some 1 Meg 1/4W 5% carbon film resistors on hand, can I safely substitute one of those in? And if so, where's the best place in the circiti? I noticed the Hoffman kit came with 1/2W 1% metal film resistors throughout, is that overkill or is the 1/2W power dissipation needed?1/4W can be used in some places. My first choice would be the 1M on the input jacks, but you already have those installed. Second choice would be R59 or R60 in the tremolo oscillator circuit.
but it looks like I received an extra 0.047 µF capacitor and I'm short a 1 MOhm resistor.Just a crazy thought... Make sure you don't have a 1M on board in a position where a .047µF should be. :icon_biggrin:
Quotebut it looks like I received an extra 0.047 µF capacitor and I'm short a 1 MOhm resistor.Just a crazy thought... Make sure you don't have a 1M on board in a position where a .047µF should be. :icon_biggrin:
... I can't stand the attachment size limit on here. All the pictures I take are super high quality and come out to like 4 MB each...
... I can't stand the attachment size limit on here. All the pictures I take are super high quality and come out to like 4 MB each...
There are a number of picture-hosting sites. You could also upload your pictures there (of any size you prefer) and simply post a link here...
Then when you power up with the tubes in you want to see the correct voltages at each PS node.
You can then double check your preamp plates, which should now read their correct voltage referenced to ground.
Then I adjust the fixed bias voltage to the desired level.
I think the footswitch jack is not wired correctly. You have the black wire from the reverb tranny connected to a hot terminal. That black wire needs to go to a ground lug on the reverb send jack. Then put a wire from the tremolo circuit to the FS jack terminal that you just removed the reverb tranny black wire from.
Then when you power up with the tubes in you want to see the correct voltages at each PS node.
You can then double check your preamp plates, which should now read their correct voltage referenced to ground.
Then I adjust the fixed bias voltage to the desired level.
Thanks for the info. By "PS node" you mean the "A", "B", "C", "D" points on the schematic? Also what would be the correct voltages on those and also on the preamp plates?
You need 1 of these, a light bulb limiter for 1st turn on, just in case there's a short.
http://sluckeyamps.com/misc/Amp_Scrapbook.pdf (http://sluckeyamps.com/misc/Amp_Scrapbook.pdf)
If you pull up the Deluxe Reverb schematic in Doug's schematic library the voltages are shown for each tube.Then when you power up with the tubes in you want to see the correct voltages at each PS node.
You can then double check your preamp plates, which should now read their correct voltage referenced to ground.
Then I adjust the fixed bias voltage to the desired level.
Thanks for the info. By "PS node" you mean the "A", "B", "C", "D" points on the schematic? Also what would be the correct voltages on those and also on the preamp plates?
Anybody have this info on the expected voltages? Can I look them up somewhere or calculate them?
Reverb hum seems to be a common problem in the Fender reverb circuits these days. Unplug the RCA cables that connect to the reverb tank. Still got hum with the reverb pot turned up? If so, the problem is in the reverb recovery circuit (V4). Try several different tubes. If no help, look at the grounding for the recovery stage and the RCA connectors. Some have had good luck with isolating the return jack from chassis and grounding it to the same place that V4 cathode resistors are grounded on the board. There should be a 220K resistor mounted directly on the reverb return jack. Since you used the same mounting as the original DRRI jacks, we can't see that resistor. Is it there?
Did you fix the footswitch problem? I ask because the reverb transformer secondary (black wire) was not grounded.
Nothing critically important, but I noticed on your input jack you used a red wire for the Gnd connection to the board.
I like to use red wire on wires carrying power, and black or green wires for Gnd wires.
This helps me easily identify the powered and grounded wires. :icon_biggrin:
I got some "topic reply notification" emails this morning but don't see any replies since Paul's from the other day???I made a reply this morning and as soon as I posted I realized I had made the same reply earlier. So I deleted my new post but apparently even though the post had only been live for a couple minutes, that was long enough to trigger the email notification.
So what do you guys think about a ground being off in one of the transformers (maybe the PT center ground tap)? Is that something that could cause this hum? And if so, could I open up the PT and fix it or is it dead?If the PT center tap was broken you would have no B+ and the amp would be completely silent. Do you have the heater wires connected to the board in order to use the 100Ω artificial center tap?
QuoteI got some "topic reply notification" emails this morning but don't see any replies since Paul's from the other day???I made a reply this morning and as soon as I posted I realized I had made the same reply earlier. So I deleted my new post but apparently even though the post had only been live for a couple minutes, that was long enough to trigger the email notification.QuoteSo what do you guys think about a ground being off in one of the transformers (maybe the PT center ground tap)? Is that something that could cause this hum? And if so, could I open up the PT and fix it or is it dead?If the PT center tap was broken you would have no B+ and the amp would be completely silent. Do you have the heater wires connected to the board in order to use the 100Ω artificial center tap?
What all is humming? Everything? Normal channel only? VIB channel only? VIB channel only when reverb is turned up? Divide and conquer...
Remove all tubes except power tubes, rectifier, and PI (12AT7). Does it hum? If so, the problem is in the power amp or power supply. If not, the power amp is clean. Now plug in the normal channel tube only (probably V1). Does it hum? If so, problem is in V1 circuit. If not, normal channel preamp is OK. Next, plug in VIB preamp tube V2. Does it hum? If so, problem is in V2 circuit. Next, plug in reverb recovery tube V4. Does it hum? If so, problem is in V4 circuit. Half of V4 is the reverb recovery amp and the other half is the wet/dry mixer amp.
Does the above help you narrow it down a bit?
One question, will channel 2 work with V2 and V6 only? Don't I also need V4 for the vibrato channel to work at all?V4 must also be in the circuit for the VIB channel to work. But I'm not interested in hearing a guitar thru the amp. You already said the amp works fine. I'm just trying to find out where the hum is coming from. In the troubleshooting flowchart above, you do need to plug in V4 BEFORE you plug in V2.
QuoteOne question, will channel 2 work with V2 and V6 only? Don't I also need V4 for the vibrato channel to work at all?V4 must also be in the circuit for the VIB channel to work. But I'm not interested in hearing a guitar thru the amp. You already said the amp works fine. I'm just trying to find out where the hum is coming from. In the troubleshooting flowchart above, you do need to plug in V4 BEFORE you plug in V2.
Have you seen if you can start the odd noise by tapping on a/the tubes? Maybe a smallish screwdriver handle.
Sometimes a tube can go microphonic but does so in a "resonant" way where the speaker-driven vibration of the cabinet induces the microphonic and then that gets amplified in a sort of feedback loop. Clue: Did this ever happen when the chassis was outside the cabinet?
Back when the amp still had the PCBs (and it had the EXACT same issue)Sounds like you may have to consider the parts that are still original as the culprit.
QuoteBack when the amp still had the PCBs (and it had the EXACT same issue)Sounds like you may have to consider the parts that are still original as the culprit.
I noticed that one of the wires on the low voltage coil goes straight through the rectifier tube so if there were actually in that wire it wouldn't necessarily be rectified, right?I don't understand what you are saying. Please explain.
Has anyone successfully dissected a power transformer to look for shorts or would I not be able to get it back together?There is no bell cover on the bottom of your PT so you can already see everything you need to see.
QuoteI noticed that one of the wires on the low voltage coil goes straight through the rectifier tube so if there were actually in that wire it wouldn't necessarily be rectified, right?I don't understand what you are saying. Please explain.
QuoteHas anyone successfully dissected a power transformer to look for shorts or would I not be able to get it back together?There is no bell cover on the bottom of your PT so you can already see everything you need to see.
Are you using the same tubes since you rebuilt? Same sockets?
Pardon my interjection - but that sounds like a high voltage arc. If it were my amp I would hook the chassis up on the bench circuit side up and fire it up at night and turn off the lights to check for arcing. If no visible arcing anywhere I would be inclined to think the power transformer has something going on internally.
Additionally as Sluckey has stated if it did this before then it would be logical to think that one of the original parts is causing it, and the PT is one of them.
Mercury Magnetics has a 'drop-in' replacement PT for the Deluxe Reverb Reissue, part number FDR-PRI. I have one in my amp. Kinda pricey. Here's a link...
http://www.tedweber.com/fdr-pri (http://www.tedweber.com/fdr-pri)
http://www.mercurymagnetics.com/pages/catalog/manufacturers/MM_fenderA-D.htm#Deluxe_ (http://www.mercurymagnetics.com/pages/catalog/manufacturers/MM_fenderA-D.htm#Deluxe_)
The trem footswitch is working properly. Hoffman's circuit uses an older style trem circuit that operates quite differently from a full blooded AB763 amp. You may notice that the trem works on the normal channel also.