Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: USAampsRus on May 17, 2018, 01:30:11 pm
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Hello everyone here from PA,
I'm on a mission. I have a dear friend that's been fighting cancer. Non Hodegkins Lymphoma. His amp was put into the wrong hands for repair. long story short, its a 2011 Fender Hot Rod Deville.
The Chassis,All the Transformers, speakers & Cabinet are in great shape. all the tubes are new. I Would love to build him an all handwired amp while he has to go in for a Steam Cell Transplant. And as a Surprise Birthday gift.
I have done work on amps like Mods and some repair work.
If i could get help on what to do here to make this work with what i have here.
60 watts is a little loud so im up for any Suggestions.
Any Help will be Greatly Appreciated.
i Really could use a little Distraction at this time.
Thanks
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Welcome... sorry to hear of your friend's illness, but this is a great thing to do for him!
Get familiar with vacuum tube safety. This page is a good start: http://www.ax84.com/safety.html
Those tubes/transformers are suited to 60W output. Same power as a Deville would be easiest and surest for a beginner to make a working, reliable amp. You could use 6V6s, maybe cathode bias to reduce voltage. I'm not sure I'd recommend worrying about that unless you really need to decrease power.
The guy who hosts this forum sells boards to hold/lay out your circuit.
Eyelet: http://hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&thispage=EyeletBoard.htm
Turret: hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&thispage=TurretBoard.htm
The AB763 is a vintage Fender design used with many tubes and power levels, but they're similar in principal.
You could do a single-channel (no reverb) AB763 build for simplicity, but maybe buy a dual-channel board. You'll need more space and connections due to power supply differences to accommodate the Deville's different power transformer.
Hopefully somebody will chime in about a HRD conversion and what circuits fit in the chassis, or match its transformers best.
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Thank you 92Volts,
Thanks for the kind words.
Im All about Safety
I do Make Sure I Discharge The caps and check for anything holding voltage. Im gonna print out the safety link you sent.
If I could use the transformers i have that would help keep the cost down :)
I was looking at AB763-2 channel|Black Epoxy|Lugs Installed looks like it might fit But maybe the Single Channel might make life easier.
Im hoping i can order everything soon.
thanks again!
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Not clear -- do you want to build anew into the existing chassis?
Is the birthday impending? An amp tech's nightmare is to work under a looming hard deadline. This is a big job.
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Yes I would like to build new in the existing chassis .
I'm looking to get as much information on exactly what parts I need to make this happen .
Thanks in advance for all your help.
I am so ready to start working on this amp. I've taken off of work for a couple months
To care for him.
So I figured I would do this project while I'm home.
Thanks
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http://el34world.com/charts/Schematics/files/Fender/Fender_hotrod_deluxe.pdf
That's the schematic and layout diagram. I agree, this is a huge project. Unless there's something distinctive about the Deville circuit, I'd seriously think about making an amp with lower parts count in that chassis, but that's just me. Regardless, sending positive thoughts for you and your friend!
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I've stripped out a Hot Rod Deluxe and build a new tone board and new cap board. The hardest part was using the existing standoffs, marking the new board and drilling. Once done your off and populating the new board to the circuit you have chosen. You can use clear plastic to mark and make a drill guide if needed. I would not worry about including reverb, a reverb pedal can always be used.
Mark
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Here's the correct schematic...
http://el34world.com/charts/Schematics/files/Fender/Fender_hotrod_deville.pdf
Study it. You'll need to use the same power supply circuit for B+ and bias. Everything else can be replaced by your favorite circuit that only uses three little tubes (or less). You could make a killer AB763 Lite...single channel with/without tremolo and no reverb.
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Pots, sw's, tube sockets & jacks can be chassis mounted. The holes are already there. You'll need to add screw or rivet holes for tube sockets,
The problems with relays are space & the possibility of induced noise, which boils down to a space or shielding issue.
Components on handwired terminal strips, eyelet or turret boards will take up much more space than on the existing PC boards. You need to account for that in advance.
What I would do: make cardboard cutouts of the existing PC boards. Figure how to layout rows of terminal strips, eyelets or turrets to accommodate the circuits of the amp you choose to build. Maybe use a layout program. That's a time-eating learning curve if your not already facile with that.
Then cut out permanent garolite boards; add the terminal strips, eyelets or turrets; and populate.
You can add tube reverb; or keep it SS to save space.
Caveat: the more complex you make the amp, the more likely it is to have vexing and hard to trace issues; and the less likely it is to be noise free. Relatively speaking, I think few of these conversions have been done. IOW, this might be considered a research & development project, which is inconsistent with the goal of a pleasant & timely birthday gift. It just might not work right the first try. That's nobody's fault, but something to keep in mind.
EDIT: This gives me the idea to build a Blues Jr. into it (preamp section). Doug already has a board & layout for that. If issues arise it will be easier to get help.
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The problems with relays are space & the possibility of induced noise, which boils down to a space or shielding issue.
True. Also, the Deville's brown wires (medium voltage) are convenient for bias. As sluckey suggests, the section producing -55v for "C-" could be directly reused. Not so convenient for running relays... the +/-16V regulator is less elegant and I'm not sure how much current it can supply.
Without relays, you may not want remotely-switched channels. Running audio to a pedal and back is asking for noise. But you can switch reverb and vibrato with pedals, exactly as it's done in the AB763 circuit. So you can certainly add features including remote (pedal) control to the amp without worrying about relays.
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I don't think the OP is interested in any relays. So far all he has mentioned is Hoffman's AB763.
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Guys Thanks so much for the replies,
I think not using a relay is a good call. wanna make this Noise free and as simple as possible.
And i think what was mentioned about making an amp with lower parts count in that chassis is a great call.
The idea to build a Blues Jr. into it (preamp section) sounds like a good idea.
He has a reverb pedal and never used the one that the deville had because it hasn't worked in years.
So i can use the existing transformers that the deville came with? or do you think i should scratch that idea?
im gonna start taking the guts out today carefully and take measurements of the Chassis.
Thanks so much everyone for the help.
And at the end of this project if this Doesn't work out at least it was a Distraction for me.
Anthony
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Sorry for the incorrect schem, and also I totally missed the AB763 comment you made. Yeah, something like that would be way easier, or like Sluckey says a Lite version.
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This guy converts them to a 5E5A I'm sure you could do a Deville too.. and the build looks nice and tidy and easy to do.. he makes a new faceplate too..
check out his process pages
http://www.tjadamowicz.com/amps/convert.html (http://www.tjadamowicz.com/amps/convert.html)
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I highly recommend you do some research before you start ripping the amp apart. Study the schematic. Study the schematic of the amp you think you may want to build. If you can't read and understand a schematic you will be severely handicapped. Not saying you can't still do it, but saying it will be considerably more difficult. You will likely need to adapt the FWB power supply to the amp you decide to build. You can use the same transformers and choke if you build a 2x6L6 amp. Most everything other than the transformers and chassis will need to be replaced. That means jacks, pots, tube sockets, circuit boards, etc.
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Ditto to sluckey
mresistor: great reference (I'm also looking at a gut job to my HRD). Really shows the space / layout aspects.
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Wow thanks guys.
I'm back home. Been at the docs with him all morning.
I haven't done anything with the amp yet been crazy busy.
I'm reading the posts here and seeing some good knowledge and info here.
Again I'm very grateful to have you guys help me out here And letting me know What I'm up against.
I don't necessarily have to keep the factory chassis if you guys recommend something else that will fit in the cabinet. I am definitely down for some suggestions. I do know I wanna use a turret board. I used to do some wiring on ambulances about 20 years ago along with welding and cabinetry.
I can read schematics but not at advanced levels. I've been looking over the schematics that you guys had sent my way and I have done a great deal of research on the web and YouTube videos. Came across this video and it really got my interest!
I would like to use the same transformers and choke and go with the 6L6 Build.
I'll keep checking back.
Thanks again
Anthony
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mresistor
That link you sent definitely something I'm interested in also.
http://www.tjadamowicz.com/amps/convert.html
Awesome work guys! Getting so excited I can't wait to get my hands on this and start working.
Anthony
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I've stripped out a Hot Rod Deluxe and build a new tone board and new cap board. The hardest part was using the existing standoffs, marking the new board and drilling. Once done your off and populating the new board to the circuit you have chosen. You can use clear plastic to mark and make a drill guide if needed. I would not worry about including reverb, a reverb pedal can always be used.
Mark
Awesome thank you! Still learning how to navigate the forms. I appreciate your input!
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Well i'm getting ready to tear down this amp.
no turning back now!
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Take pictures!
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Definitely take LOTS of clear detailed pictures before taking anything apart, at every significant stage of the new build (layout board, heater wiring etc.....), and when you have the finished build. This may prove to be a tremendous help IF you need some trouble shooting.
Since you are somewhat new at amp building, I would suggest consider going cathode biased instead of fixed bias. When you change tubes you won't need to rebias. Maybe 250R -330R 10watt resistor with 60uf to 100uf 50v cathode cap. Just my 2 cents worth. You'd have a little less wattage then fixed biased which might be preferred if playing mostly at home?
With respect, Tubenit
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The other thing I'd recommend is posting your working schematic on this thread so we can help you when needed. And preferably your layout.
Sluckey has a website with incredibly well done schematics you can consider using. And we have an entire Library of editable SCH schematics & layouts that you can use IF you download the free ExpressSCH program that allows editing and drawing.
BEFORE you tear stuff apart & before you order parts I'd recommend posting your schematic here and ask for feedback to make sure your on a "do-able" and realistic project.
I've seen too many new builders get stuck and then post word descriptors (often inaccurately) when asking for help instead of posting a schematic for us to visually look at.
With respect, Tubenit
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Take pictures!
I have definitely taken pictures before and after.But I'm having a problem uploading them to the site and I feel like such an idiot. Keep saying your file size is too large and I have decreased the file size but for some reason it's not excepting it.
Anthony
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Not sure how far into this you are or if you have decided what to build. If you have not decided on a circuit take a look at sluckey's AB763 lite. Add a master volume control. It is pretty straight forward build and and a heck of an amp. Steve may have some sound clips.
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Not sure how far into this you are or if you have decided what to build. If you have not decided on a circuit take a look at sluckey's AB763 lite. Add a master volume control. It is pretty straight forward build and and a heck of an amp. Steve may have some sound clips.
So far I have just been researching on what build to go with . I have carefully disassembled the amp.
I'm definitely interested in sluckey's AB763 Lite. Sounds like the way to go.
Thanks again for the input.
Anthony.
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There isn't a need to load pics for us. Hang on to them for yourself. Just post pics IF you run into a glitch.
Sluckey's schematics and layouts are easily among the best! So those guides would already be proven circuits & the work is done for you. :thumbsup:
With respect, Tubenit
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There isn't a need to load pics for us. Hang on to them for yourself. Just post pics IF you run into a glitch.
Sluckey's schematics and layouts are easily among the best! So those guides would already be proven circuits & the work is done for you. :thumbsup:
With respect, Tubenit
where do i go to find Sluckey website & schematics that you mentioned? Definitely interested!
Thx
Anthony
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http://sluckeyamps.com/misc/AB763_Deluxe_Lite.pdf (http://sluckeyamps.com/misc/AB763_Deluxe_Lite.pdf)
OR
http://sluckeyamps.com/6v6plexi/6v6plexi.pdf
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http://sluckeyamps.com/misc/AB763_Deluxe_Lite.pdf
So Awesome thank you. .
Can I use the existing transformers from the hot Rod Deville and -6L6 tubes?
Sorry for so may questions ..
Thanks
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I would use your chassis, tubes and transformers.
Study Sluckey's schematic and layout paying attention to the preamp and LTPI (phase invertor) and power amp.
On your original Fender schematic study the power transformer, fixed bias and B+ power rail.
The idea is to follow Sluckey's layout (preamp, LTPI & POWER AMP) while using the Fender's trannies, B+ rail and fixed bias.
Make a schematic (try Window's PAINT) using a "cut & paste" to draw up your new schematic and then post it here for feedback.
Once you post it, we can help with guesstimated values for dropping resistors on the B+ rail. The idea is to keep your 6L6 voltages original to fender schematic on the plates and screens BUT have voltages similar to Sluckeys amp on the LTPI and preamp.
NOTE: The 6L6 plates & screens on the DeVille have higher voltage then on Sluckey's "Lite"
power tube plates.
You can get help on bias circuit from forum (IF it needs tweaking) ..... OR go cathode biased (which is what I would personally do simply because its a preference for me).
Hope that helps. With respect Tubenit
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My Deluxe Lite is based on a Deluxe Reverb. R32 needs to be changed to a 1K@3W and R33 needs to be changed to 4.7K@3W. R15 will need to be 100Ω half watt if you plan to use 2Ω or 4Ω speakers.
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thanks so much for the info,
i am going to print out Sluckey's schematic and layout .
Time to start Studying.
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Such good advice and help from forum members, very inspiring to read. You guys Rock!
Mark
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If your friend likes the Marshall sound you may consider my Plexi 6V6 (using 6L6s). It's a simple amp that would easily fit that chassis. You may even be able to run EL34s if the PT can handle an extra 1.2 amps of filament current.
http://sluckeyamps.com/6v6plexi/6v6plexi.pdf
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If your friend likes the Marshall sound you may consider my Plexi 6V6 (using 6L6s). It's a simple amp that would easily fit that chassis. You may even be able to run EL34s if the PT can handle an extra 1.2 amps of filament current.
http://sluckeyamps.com/6v6plexi/6v6plexi.pdf
Funny that you mentioned that. As of matter of fact he does..
I was looking at that that build. I’m thinking that’s probably the way to go .
I’ve been reviewing the info that’s been provided and doing a lot of research learning how to the schematics.
You guys have been extremely helpful and can’t thank you enough.
I think I found the parts list for that bill build I’m not 100% certain .
Anthony
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Here is an idea to consider. Having said that, follow Sluckey's advice on this and NOT mine. Steve is far more knowledgeable then I am.
This is how I would consider approaching the conversion. Note the things that are different from original schematics. Please look over this carefully. I think you can still use Sluckey's layout with this idea.
On Sluckey's Plexi
1) changed to cathode biased instead of fixed biased
2) changed grid resistors from 1.5k to 5.6k (for 6L6 grids)
On original Fender DeVille schematic
1) did NOT use fixed biased circuit because of using cathode biased instead of fixed biased
2) Suggested different dropping resistor between node B & node C (changed it from 6.8k original to 33k/3w)
The reason for this was to get node C from 413 v on LTPI plates closer to 270v on LTPI plates (I think it will end up in the 300+ range)
3) Instead of original 10k resistor on DeVille, maybe try a 22k/2w? This is to try to get node D from original 364v to closer to 232v
4) Adding a node E with a dropping resistor of 10k/2w between node D and node E. Trying to get node E headed towards 217v range
I would be shooting for something like:
Node A = 471v like on Deville Node B = 468v like on Deville Node C = 300+? Node D= as close as reasonable to 232v
Node E = as close as reasonable to 217v
Hopefully, Sluckey will weigh in on this. Again, follow his lead on dropping resistors and everything else. You certainly do NOT have to have a cathode biased amp. I think it might make the conversion an easier project to do so, but maybe not?
With respect, Tubenit
EDIT:[/color] I've added an ExpressSCH editable schematic & the same schematic in GIF format. In the schematic I just added, I changed two more things which are simply a personal preference and not necessarily "better". I don't care for the 47p "snubbing cap" as I think it muffles the tone, so I changed to a 220p "enhance cap" across the 82k LTPI entrance resistor. The other thing was simply to add a passive effects loop for reverb or delay pedals.
I also have an editable ExpressSCH layout for this schematic that uses paralleled turrets or eyelets. NOT an improvement on Sluckey's great layout, just different.
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Awesome thank you!
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Be sure to wait for Sluckey's advice on this. Especially before ordering parts. Again, he is far more knowledgeable then I am on this. He may have different thoughts on the B+ dropping resistors ........... or he may advise you to use fixed instead of cathode bias. Follow his lead on it.
Just be sure to note the changes on his layout IF you work with this schematic. Not many of them to make and (if I am correct?) then you can easily use his layout & layout board .
With respect, Tubenit
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Will do!
Thx
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Here is an idea to consider. Having said that, follow Sluckey's advice on this and NOT mine. Steve is far more knowledgeable then I am.
This is how I would consider approaching the conversion. Note the things that are different from original schematics. Please look over this carefully. I think you can still use Sluckey's layout with this idea.
On Sluckey's Plexi
1) changed to cathode biased instead of fixed biased
2) changed grid resistors from 1.5k to 5.6k (for 6L6 grids)
On original Fender DeVille schematic
1) did NOT use fixed biased circuit because of using cathode biased instead of fixed biased
2) Suggested different dropping resistor between node B & node C (changed it from 6.8k original to 33k/3w)
The reason for this was to get node C from 413 v on LTPI plates closer to 270v on LTPI plates (I think it will end up in the 300+ range)
3) Instead of original 10k resistor on DeVille, maybe try a 22k/2w? This is to try to get node D from original 364v to closer to 232v
4) Adding a node E with a dropping resistor of 10k/2w between node D and node E. Trying to get node E headed towards 217v range
I would be shooting for something like:
Node A = 471v like on Deville Node B = 468v like on Deville Node C = 300+? Node D= as close as reasonable to 232v
Node E = as close as reasonable to 217v
Hopefully, Sluckey will weigh in on this. Again, follow his lead on dropping resistors and everything else. You certainly do NOT have to have a cathode biased amp. I think it might make the conversion an easier project to do so, but maybe not?
With respect, Tubenit
EDIT:[/color] I've added an ExpressSCH editable schematic & the same schematic in GIF format. In the schematic I just added, I changed two more things which are simply a personal preference and not necessarily "better". I don't care for the 47p "snubbing cap" as I think it muffles the tone, so I changed to a 220p "enhance cap" across the 82k LTPI entrance resistor. The other thing was simply to add a passive effects loop for reverb or delay pedals.
I also have an editable ExpressSCH layout for this schematic that uses paralleled turrets or eyelets. NOT an improvement on Sluckey's great layout, just different.
WOW,Thx so much. The passive Effects loop is a great suggestion. will this have a buffer also?
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Passive effects loop does NOT have a buffer per say ..................
However, since it follows the master volume which follows the tone stack which follows the cathode follower ................. I think you will find it useful still.
I've run Carbon Copy delay, Boss digital delay, Moen Pretty Dolly delay and Digitech Reverb thru passive delays and found they worked just fine for me.
Since it just involves two jacks, it's only a $10 mod and easy to do.
with respect, Tubenit
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I want you to keep in mind that Sluckey's Plexi 6V6 is a proven design. Mark Huss's Plexi 6V6 is a proven design. Hoffman's Plexi 6V6 & Plexi 50w are proven designs.
However, none of those designs are reusing a Fender DeVille power trannie, output trannie and/or bias circuit. So what I did for you was to try and marry what is proven in those proven designs to the Fender DeVille PT, OT and B+ rail.
My schematic is NOT a proven design. I have not built it. I posted it for you to look at and for others to make comments, corrections and edits around. In other words, I posted it as a focal point of discussion and maybe a catalyst to help you get some direction and traction on the build.
It's how I would approach it and it reflects some personal preferences that are not necessarily better but simply different then how others would approach it. IF I built this, I am quite confident that I could trouble shoot it if it didn't work right ......... OR mod it to sound more like I want IF it didn't to begin with. You may not have that same skill set? And IF that is the case, then try to use proven designs or ask for help from the guys that really know ALOT about these builds and designs.
I hope you will post whatever questions, concerns you have it and seek input from guys on the forum who know more then I do.
with respect, Tubenit
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Lots of good advice here. I would definitely stick with 6L6 tubes as you already have suitable power and output transformers. I would opt for either a 6L6 Plexi or a 5f6A Bassman. Doug has the boards for either in his store. The B+ is a little on the high side for my tastes. But it's nothing that a 200 ohm or so sag resistor wouldn't cure.
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I would opt for either a 6L6 Plexi or a 5f6A Bassman. Doug has the boards for either in his store.
Either of those would be good options, IMO.
With respect, Tubenit
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Something I am NOT understanding about the original power transformer for the Blues DeVille (Fender part # 041752)
I don't recognize the type of solid state rectification being used? On the specs for the replacement trannie for the Blues DeVille, it lists FWB which I would have thought is a full wave bridge rectifier? However, I don't see that the PT has a center tap that is grounded?
Can someone explain to me what is actually going on with the rectification, please?
With respect, Tubenit
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It's a bridge rectifier. You have an error in your schematic.
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It's a bridge rectifier. You have an error in your schematic
Ah OK, finally caught the error and corrected it. I will say I am NOT familiar with this type of bridge rectifier & I'm not recognizing it to be like any of the solid state rectifiers that Doug illustrates in his Library of Information.
And I don't see a separate ground for negative end of the rectifier ? It appears it's using one of the high voltage wires as a ground?
With respect, Tubenit
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In your schematic, you just made a drawing error: there's no connection from the neg. end of your diodes to the filter cap grounds.
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The original is hard to see.
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And honestly, that's a confusing way to draw it. I got spoiled reading Doug's schematic.
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Thanks John! Finally saw it and corrected the SCH schematic in the earlier post.
I still am NOT familiar with a bridge rectifier looking like that before that I can remember?
With respect, Tubenit
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You're welcome. I got stymied by the way a voltage doubler was drawn on a Heathkit schematic. After following it closely and wiring everything just like it said, and having it work, I'm still befuddled by the drawing!
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You guys Rock!
With much Respect
Anthony
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So is this a half wave voltage doubler? :w2: :dontknow:
And NOT a bridge rectifier?
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It's a bridge rectifier. You have an error in your schematic
Ah OK, finally caught the error and corrected it. I will say I am NOT familiar with this type of bridge rectifier & I'm not recognizing it to be like any of the solid state rectifiers that Doug illustrates in his Library of Information.
And I don't see a separate ground for negative end of the rectifier ? It appears it's using one of the high voltage wires as a ground?
With respect, Tubenit
The Fender schematic is drawn in a confusing manner. It took me a while this afternoon examining it to figure out what they were doing.
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I felt the same thing very confusing it was giving me a headache. :help:
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So is this a half wave voltage doubler? :w2: :dontknow:
And NOT a bridge rectifier?
Plain Jane bridge rectifier. Just drawn in a confusing manner by our friends at Fender. Probably some kind of schematic drawing software.
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> So is this a half wave voltage doubler? :w2: :dontknow: And NOT a bridge rectifier?
It is a plain old common Full Wave Bridge.
You can draw it with diodes slanty. -OR- you can draw it with diodes horizontal. Hoffman drew in an all-purpose graphics program with arbitrary orientation. The common circuit drawing software does not do slanty, so we use that tangled-up layout. But they are exactly the same.
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Some may like to stack the diodes vertically... :wink:
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Gentleman, thanks for your help with this! I will confess some embarrassment in not being able to see that for myself. :BangHead:
With respect, Tubenit
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USAampsRUS,
Looking at the "back" of your DeVille combo/chassis with back off ................. your input jack is on the right in your "tweed" style chassis.
Sluckey's Plexi 6V6 layout will work for you. And he has all the documentation you need to make your own layout board. I saw Doug's board material with a hacksaw and it's very easy & quick to do it that way and it makes very little dust.
It's easy to make your own turret board using Doug's layout board material and staking tools. http://el34world.com/Forum/index.php?topic=9800.0
Presuming that you have enough room in your chassis & have measured space and compared it with size of Doug's layout boards .........
Hoffman's 5F6A Bassman will work. Hoffman's Plexi 50w will work. Both have input jack on the right looking at back of combo. Hoffman's sells boards for these and has a Bill of Materials, schematic, etc ....... These are in his Library of Information & his boards are in his online store.
http://el34world.com/schematics.htm#Hoffman_Plexi_50_
You would change the input jacks to a single one if you're using Sluckey's Plexi 6V6 schematic. While there is no need to change the Bassman or Plexi 50w to cathode biased, you could still do that using one of Hoffman's boards IF you wanted to?
With respect, Tubenit
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Good Morning,
That sounds like the way to go. Ill order both Boards to have on hand. 5F6A & Plexi 50w. :icon_biggrin:
Can't Hurt.
Life by the Drop.!
I can see Clearly Now.
Doyle Bramhall
Im Gonna Start the Parts List here in the next hour.
Thanks everyone for all the help on this Project!
And if for some reason this does Not Work out for me ........at least i tried.
Thanks Again,
Anthony
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Gentleman, thanks for your help with this! I will confess some embarrassment in not being able to see that for myself. :BangHead:
With respect, Tubenit
There's no need for embarrassment. The original (Fender) schematic was drawn very poorly IMO and the connection dots were not very clear.
Nice job on the schematic of your ideas for the OP. :thumbsup:
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Good Morning,
That sounds like the way to go. Ill order both Boards to have on hand. 5F6A & Plexi 50w. :icon_biggrin:
Can't Hurt.
Life by the Drop.!
I can see Clearly Now.
Doyle Bramhall
Im Gonna Start the Parts List here in the next hour.
Thanks everyone for all the help on this Project!
And if for some reason this does Not Work out for me ........at least i tried.
Thanks Again,
Anthony
Hi Anthony,
There's no need to buy two boards. They are very similar circuits. IF it were me, I would buy Doug's Plexi board and modify the circuit (component values) to land somewhere between 5F6A Bassman and 1987 Marshall. That part is easy. The areas that need work IMO are in the power supply and bias supply.
The HR Deville schematic shows 485 volts B+ supply to the output transformer center tap. IMO this is getting outside of the sweet spot for 6L6 tubes. I would add a dropping (sag) resistor (200 ohm, 15 watt) immediately following the bridge rectifier to get the B+ at idle down to around 460 volts. At maximum signal this would drop the B+ an additional 25 volts or so, simulating the sag effects of a tube rectifier. Additionally, I would tweak the dropping resistor values in the B+ rail to provide 385 volt DC supply to the PI and 325 volt DC supply to the preamps as reflected in the 5F6A schematic.
The cathode follower in both Marshall and Bassman circuits have DC voltage of about 180 volts. This is almost double the 100 volt DC cathode to heater rating for the 12AX7 tube. The peak AC plus DC rating is plus or minus 200 volts. I would look towards adding a DC voltage divider in the power supply to reference the heaters 90 volts above ground. This would allow the 12AX7 cathode follower triode and other 12AX7 triode sections to operate within the cathode to heater voltage ratings. The 90 volt reference is within the 200 volt heater to cathode rating for the 6L6 tube as well.
I would rebuild the negative bias supply on a new board and revise the circuit so that the negative voltage supply is not dependent upon the wiper connection. I would swap the 100K resistor and 25K potentiometer locations and reference the wiper of the 25K pot to ground. This way, if the wiper connection fails, the bias voltage goes to a more negative (colder) operating point.
Good luck with your project. It looks like a lot of fun.
Regards,
John
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Well thank you
John.
I still have a lot to learn and i'm enjoying the feedback here.
Anthony
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Here is an idea to consider. Having said that, follow Sluckey's advice on this and NOT mine. Steve is far more knowledgeable then I am.
This is how I would consider approaching the conversion. Note the things that are different from original schematics. Please look over this carefully. I think you can still use Sluckey's layout with this idea.
On Sluckey's Plexi
1) changed to cathode biased instead of fixed biased
2) changed grid resistors from 1.5k to 5.6k (for 6L6 grids)
On original Fender DeVille schematic
1) did NOT use fixed biased circuit because of using cathode biased instead of fixed biased
2) Suggested different dropping resistor between node B & node C (changed it from 6.8k original to 33k/3w)
The reason for this was to get node C from 413 v on LTPI plates closer to 270v on LTPI plates (I think it will end up in the 300+ range)
3) Instead of original 10k resistor on DeVille, maybe try a 22k/2w? This is to try to get node D from original 364v to closer to 232v
4) Adding a node E with a dropping resistor of 10k/2w between node D and node E. Trying to get node E headed towards 217v range
I would be shooting for something like:
Node A = 471v like on Deville Node B = 468v like on Deville Node C = 300+? Node D= as close as reasonable to 232v
Node E = as close as reasonable to 217v
Hopefully, Sluckey will weigh in on this. Again, follow his lead on dropping resistors and everything else. You certainly do NOT have to have a cathode biased amp. I think it might make the conversion an easier project to do so, but maybe not?
With respect, Tubenit
EDIT:[/color] I've added an ExpressSCH editable schematic & the same schematic in GIF format. In the schematic I just added, I changed two more things which are simply a personal preference and not necessarily "better". I don't care for the 47p "snubbing cap" as I think it muffles the tone, so I changed to a 220p "enhance cap" across the 82k LTPI entrance resistor. The other thing was simply to add a passive effects loop for reverb or delay pedals.
I also have an editable ExpressSCH layout for this schematic that uses paralleled turrets or eyelets. NOT an improvement on Sluckey's great layout, just different.
can i use a 22k/3w instead of the 22k/2w i dont see any?
thx
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Yes.
However, last night I found this old Hoffman Plexi 50w schematic that had voltages on it. I don't remember what the original source was that I copied this from? You will need to check that this schematic matches the Plexi 50w schematic in Doug's Library of Information? Print them both off and circle the differences on one of the sheets to note what might not be the same.
Looking at Plexi 50w volts on the power tube plates, you have 476v. Your DeVille was 472v. Close enough, IMO!
Note that there are voltages listed on the attached schematic that will help you determine if your build has voltages that are within normal limits of what the Plexi 50w should have.
So, in light of that, I think you can copy the resistor values on the B+ rail of the Hoffman Plexi 50w.
AND if you are going fixed biased (instead of cathode biased) then I think you can use the fixed biased system of the Plexi 50w which connects to the HV (high voltage) wiring instead of using a dedicated bias wiring circuit that was originally on the DeVille?
Hopefully, some others will edit/correct this thinking or affirm it.
With respect, Tubenit
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tubenit
Good Job on the find for Hoffman Plexi 50w schematic.
so you think this this is close enough?476v. And the DeVille being 472v?
Thanks Agin
Anthony
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you think this this is close enough?476v. And the DeVille being 472v?
Close enough, IMO!
So, if you use Hoffman's Plexi 50w layout, schematic, bill of materials, etc....... you should have a proven build that sounds great. Take your time. Post questions as you have them. Study the pictures on his build projects. Study his grounding scheme. Doug has given you a ton of excellent information so you can be successful with this.
http://el34world.com/Hoffman/files/CommonHookups.pdf
http://el34world.com/charts/grounds.htm
I've edited Hoffman's Plexi 50w to show the hook up with the Deville transformers * see schematic and CHECK for ERRORS
with respect, Tubenit
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You can't use Doug's bias supply connected to the HT winding of that Deville power transformer.Just use the dedicated bias winding with one lead connected to ground and the other lead connected to R36. R36 will need to be decreased considerably. I'd try 1K initially. Maybe make a note on the schematic calling it the bias range resistor.
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Sluckey, Thanks for the help on this project!
Is this correct the way it is drawn now using the Deville dedicated bias supply? I am understanding this to mean one of the brown wires (either CP16 or CP18 but not both) goes to the bias supply circuit and that the brown/yellow wire goes to ground (CP17)?
http://el34world.com/charts/Schematics/files/Fender/Fender_blues_deville.pdf
And if he is using the original 6L6 power tubes, would this bias circuit work ? (understanding the bias range resistor may need to be changed?)
With respect, Tubenit
EDIT: Corrected schematic bias wiring per Sluckey's follow post.
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You're looking at the wrong schematic Jeff. This is a HOT ROD Deville, not a BLUES Deville. They are different.
Here's the correct schematic...
http://el34world.com/charts/Schematics/files/Fender/Fender_hotrod_deville.pdf
Connect one brown to ground and connect the other brown to the bias circuit. The bias circuit will work ***IF*** there is approx. 40 to 50 VAC between the brown wires. If the voltage is considerably less you'll need to use a simple voltage doubler rectifier. Or, consider using EL34s only since they require less bias voltage than a 6L6.
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Thanks for your help, Steve! Always grateful for your stellar input on the forum. You bring so much good to this amp building community. :thumbsup:
With respect, Tubenit
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Thank you so much everyone going out of your way with this project.
Can't thank you enough!!
I'm going over all the info that's been provided in the last few days.
Been Busy with My friend at the Docs.
Now i have time Again to get back on track here with the project.
Anthony