Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rakkassan34 on May 11, 2014, 03:41:29 pm
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Hi all I think I've bitten off more than I can chew here and need some help. I don't know squat about electronics even though I've been repairing and putting computers together for 15 years. Don't ask because I don't know how I do it either I guess I just have a knack for them. I don't even know what inspired me to build this amp. I was just surfing eBay one day saw a Gomez "el sonido" board for sale and decided I'm going to build a Bassman 6g6-b. I don't know how to play guitar but I love rockabilly music. I have been obsessed with this build and have spent numerous hours reading and researching but none of that can compare to experience so all of you experienced people please take a look at my build as I go and give me some advice. Just to fore warn you I am using a Fender Chorus chassis that had burnt up it ain't gonna look pretty I already know that. I just want to hear that Setzer sound come out of this one day soon I hope.
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I used plexiglass for turret boards and Xbox360 heat sink pegs as turrets since I had a bunch of them laying around from numerous red ring of death fixes. I replaced the copper wire on the rectifier board with some that I ordered from hoffmanamps. The main cap board (what's the proper name?) isn't soldered up yet I was just doing a test fit. My main concern right now is the cap on the presence pot. Every other build I've seen the capacitor is huge compare to this one. Should I replace it?
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... I'm going to build a Bassman 6g6-b. ...
Cool! Good luck with the build!
I don't know if your boards came with a schematic, or if you're referencing one. So here's the Fender 6G6-B Bassman (http://el34world.com/charts/Schematics/files/fender/Fender_BASSMAN_6G6B.pdf) schematic.
Look at your rectifier/bias board (with all the 1N4007 diodes). You're missing a 27kΩ 1w resistor which goes in parallel with the cap on that board (reference the layout; this board is towards the upper-left corner).
On you main filter cap board, you have a green-insulated jumper wire and a pair of 220kΩ resistors connected to the first two 20uF caps. Get rid of those, they're not present in the 6G6-B. I think I know what you were trying to do, but as-is the jumper is shorting high voltage to ground and the 220kΩ's are not in the right places for what you were looking to copy. The main filter board is not shown on the Fender layout (because it was outside the chassis under a metal cover), but the schematic shows these first two 20uF caps connected in parallel. So you will remove the green jumper and replace the 220kΩ resistors with wire.
On that main cap board, you probably also want to connect the - ends of the first two caps to the - ends of the other caps. Or, if you wanted to keep those grounds separate, make sure you install a wire for each set of grounds so you don't have a hard troubleshooting problem by having a missing ground.
On your main fiberboard, I see the 100kΩ plate load resistors for V2, but there are two caps connected to them (with a lead hanging in the air for each?): a silver mica cap to the left in the picture and an orange drop on the right. In the Fender layout, it shows only a single cap (0.002uF or 2000pF) across the 100kΩ which connects to V2 pin 6.
Other than those items, everything looks okay as far as I can see (pics aren't close-up enough to see color codes on resistors to know all values are correct).
... My main concern right now is the cap on the presence pot. Every other build I've seen the capacitor is huge compare to this one. Should I replace it?
Nope.
The schematic and layout says 0.1uF 200v. You cap appears to say 0.1uF, and it really doesn't need a 200v rating. Your cap appears to be metallized polyester, which is a dielectric and construction style which results in more uF's per unit volume. Others might be hung up on using orange drop caps everywhere, and the most commonly-used variety of those is polypropylene film & foil. That dielectric and style of construction makes a cap which is much bigger for the same number of uF's. Often, guys wind up using a 630v cap they have because it's on-hand, even though the presence control circuit will never see more than 50vac under any circumstance. A higher voltage rating also makes the cap bigger for the same number of uF's.
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You probably already know this but if not: get a schematic and or a lay out and mark every wire and component you install and connect as you do it. It will save you a lot of heart ache. Double check and measure where you can every component. Don't assume they are correct.
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Thank you for the reply. I didn't get any layout or schematic I've been referencing some from the internet and other builds.
"Look at your rectifier/bias board (with all the 1N4007 diodes). You're missing a 27kΩ 1w resistor which goes in parallel with the cap on that board (reference the layout; this board is towards the upper-left corner)"
I added a bias pot like I've seen from other builds and they've all removed the 27k resistor from the rectifier board. I'm using 5881 tubes which is why I added the bias pot. Should I put the resistor on the rectifier board?
I haven't soldered the main cap board yet. I'll rearrange some things on it and post again. I used the jumper wire because I have all the caps facing the same way. Most boards I've seen one cap on the end is inverted. I just thought it would look a little cleaner with them all facing the same way.
"On your main fiberboard, I see the 100kΩ plate load resistors for V2, but there are two caps connected to them (with a lead hanging in the air for each?): a silver mica cap to the left in the picture and an orange drop on the right. In the Fender layout, it shows only a single cap (0.002uF or 2000pF) across the 100kΩ which connects to V2 pin 6."
I was in the process of replacing the orange cap with a lower value silver mica. I've heard most remove that cap completely for that Setzer sound but these Gomez boards it lets all the high end of this channel through. I plan on using a switch to select straight thru or capped just to add my own little mod to it
So the presence pot cap is ok?
Thanks again for your help.
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A few more pics
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Thanks for the order.
Hopefully you will need more stuff before you are done with your build. :icon_biggrin:
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I added a bias pot like I've seen from other builds and they've all removed the 27k resistor from the rectifier board. I'm using 5881 tubes which is why I added the bias pot. Should I put the resistor on the rectifier board?
No, if you're adding a bias pot you won't put the resistor on the board. But now that you have the pot, you will need a resistor from the left lug (as seen in your picture; nothing is on this lug) to ground. If you have a 10kΩ pot, a resistor of ~18-22kΩ should be good.
Using that resistor insures you can't turn the bias down to 0v, which would cause your tubes to redplate. Not connecting that lug to ground through a resistor also will prevent the pot from doing anything; bias will always be at maximum negative voltage, keeping your tubes running cool.
So the presence pot cap is ok?
Yes, it's fine.
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Thanks for the order.
Hopefully you will need more stuff before you are done with your build. :icon_biggrin:
If this one turns out ok I'll be needing plenty more parts for my own version of a bassman with a reverb pan. I already told ya all my parts are coming from you from now on. Superfast shipping and it's just nice to see a box packaged by a human and stuffed with newspaper.
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No, if you're adding a bias pot you won't put the resistor on the board. But now that you have the pot, you will need a resistor from the left lug (as seen in your picture; nothing is on this lug) to ground. If you have a 10kΩ pot, a resistor of ~18-22kΩ should be good.
Good catch, thanks again
How about these input jacks. They're mono jacks from the local radio shack. I hope the connections are the same as I'm seeing on layouts I've been looking at. In one of the pics I'm using green/black wire to point to the face. Should I put a plastic washer there to insulate it from the chassis?
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The jacks look fine.
On those Alpha pots, the solder joints to the case (to make a ground connection) look like colder solder joints. If you can push at them with a screwdriver and pop them off, they're cold joints.
First, unless you have a ground buss along the back of the pots, there's probably not much use in soldering to them to establish a ground. Many/most pots don't have reliable conductivity from the shell to the metal bushing that would contact the chassis. Second, Alpha pots in particular have a coating of some kind that inhibits soldering; you need to sand/grind the surface to get a silvery patch that exposes bare metal, then solder to that.
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I'll second the motion on getting shorter lengths of bare wire...either on your 68K's hanging off the input jacks or the various wires connecting to the tube sockets. The rule of thumb is, the insulation should be back from the terminal the outer diameter of the wire; however, in this case, and I'm not trying to set up the impossible challenge for you, I would be trying to get the insulation back from the terminal by about the diameter of the BLACK, internal insulation, not the white outer cloth insulation.
This may seem difficult, but frankly your solder joints look pretty good in the sense that they are "stingy", you don't have a big honking glob of solder on them. That must mean you are not overheating or overfeeding them. One could say that this will never be a problem, but at some point, it *can* be should you ever need to stick a probe in there to troubleshoot something. Besides, you'll never get better at it unless you have a visual ideal to shoot for.
You don't want the insulation to actually touch the terminal, you want that "golden" distance. In terms of older Fender amps, this was of course never a problem because they used that wire with the "pushback" insulation so if the bare wire was a little bit too much, the insul could be easily shoved closer to the terminal and nobody would ever know.
My advice would be to grab something with a bunch of terminals on it like an extra tube socket or a multi-pin connector and practice trying to get that distance down. You seem to have good control over your soldering, so this would not destroy the socket for later re-use. It's only a matter of knowing how you want the finished product to look and practicing a couple dozen times.
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I'll work on shortening the ends today, thanks all. I also have an idea for grounding the pots that I've seen somewhere. Take a long grounded stripped wire run behind the pots and ground them to that. Good idea or bad? I've read that it's best to have one ground to avoid ground loops but don't ground AC with DC is that right? if so I have no idea what's AC and what's DC in there.
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Thanks for the order.
Hopefully you will need more stuff before you are done with your build. :icon_biggrin:
If this one turns out ok I'll be needing plenty more parts for my own version of a bassman with a reverb pan. I already told ya all my parts are coming from you from now on. Superfast shipping and it's just nice to see a box packaged by a human and stuffed with newspaper.
Thanks, that's awesome!
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"I'll work on shortening the ends today, thanks all. I also have an idea for grounding the pots that I've seen somewhere. Take a long grounded stripped wire run behind the pots and ground them to that. Good idea or bad? "
Yes, it's a good idea but rarely do-or-die. To do this, it's generally necessary to file off or sand off an area on the back of every pot to expose clean metal (it's steel--not copper--we don't ordinarily think of steel being very solder-friendly but it can be if it is freshly filed off and given a little more oomph than a normal solder joint) and to have a soldering iron of perhaps larger size/temp than normal. And get to it soon after you do your filing, whether the pots are already mounted or before they are installed into position. All you need is maybe a 3/8" x 3/8" patch of clean metal. DO NOT use any kind of acid flux if you have soldering trouble!! If you can't get it done with your current iron, forget about it or get a bigger iron/tip.
"I've read that it's best to have one ground to avoid ground loops but don't ground AC with DC is that right? if so I have no idea what's AC and what's DC in there.
It's a little more complicated than that, but not much. Fender amps only partially obeyed "best practices" in this area but they DID make power supply grounds and filament grounds---when the filaments were a CT---close to the power trans, all together on one bolt. But when Fenders used the dual-100 ohm synthetic center tap scheme, that was grounded to the pilot lamp frame. Do a little more reading on "ground loops" and "star grounding". This can get to be a whole religion, but in general, we want NOT to use 15 different points on the chassis for gnd points and intermingle power and signal grounds any old place where we might grab them and particularly in the case of a steel chassis, we don't want ground currents running all over the place.
The other thing I wanted to suggest about your wiring is, I like to try to get the wires to a tube socket to approach the pins perpendicular to the circumference of the socket. Not tangent. This is a style thing, I suppose, but is kind of in the category as the "less exposed wire" reco I made earlier. You can readily see, that if your wires come into the tube socket at the tight angle AND have lots of bare wire exposed at the tube-pin solder joint, this is asking for trouble. This makes your wiring lots easier to look at should you need to, later. It is no more work to do when it's being built...so it's good insurance. Another one of those visual things that you'll easily adapt to once you get the picture.
[/size](http://i172.photobucket.com/albums/w32/ttm4/wires_zpscd1a2f27.png)
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... I've read that it's best to have one ground to avoid ground loops but don't ground AC with DC is that right? if so I have no idea what's AC and what's DC in there.
BLUF (bottom-line up-front): You already have your first two filter caps with separate ground lugs from the rest of the filter caps; solder a long wire per set of grounds (1st two caps, all other caps) to the turrets, feed them inside the chassis, attach a ring terminal, bolt them to the chassis on separate bolts. Put the power transformer center tap on the same bolt as the 1st two filter caps; consider the possibility of having a wire for the grounds for the output tube cathodes going to the same bolt.
Every other ground can be placed where convenient in the chassis.
"I've read ... don't ground AC with DC is that right?"
If the original author for that statement knew electronics, they never would have said it. There's no such thing as separate a.c. and d.c. grounds in the average guitar amp (maybe even the non-average guitar amp). I can give a technically-accurate explanation how a.c. essentially rides on d.c. throughout the amp, but that discussion won't help you get your amp built today.
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I can't thank y'all enough for the advice keep it coming. I didn't get much done on the amp today was busy cleaning up a flooded carpet fun fun. I did shorten up the exposed wiring on all my tubes, upon closer inspection there were a couple that were dangerously close to another pin. I bet once I put a tube in that would've moved that lead just enough to touch another, WHEW that would've put a hamper on things. I also wired up my treble bleed mod switch.
"while Gomez was trying to stay true to the Bass channel's .002uf "treble bleed cap" (sends the highs to ground) per Leo fender's idea for a bass guitar, it
is a horrible thing to have on a guitar amp so that needed to be clipped out. While this is all that is needed on an original 63' Blonde 6G6-B bass channel to open it up nicely for guitar, for some reason on the gomez it lets ALL the high end of this channel through and it needed to be tamed with a 250pf silver mica"
To hear for myself I decided to give me an option to switch between no cap and the 250pf so I threw a switch in and tested the continuity a dozen times to make sure I got it right.
I made up a ground bar for my pots also, I just have tape holding it in there as a mock up. I will file the back of the pots before I solder it to them and I'll ground the resistors to it rather than the pot.
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I just realized I made a mistake with my treble cap switch. I see both of the leads going into the same socket on the board. :BangHead:
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Any residue from that tape isn't going to help you; either with filing OR eventually soldering to the pot-cans. Remove it, I say. You can also scrape the back of the pots (where you intend to solder them) with a razor blade or a little patch of sandpaper under your thumb or even a sharp screwdriver blade. All you are trying to do is to expose some bright, fresh, unoxidized metal so that when you solder, your flux has to do the least work and you're giving yourself the best chance at success. You don't need to make a 200 Amp connection. Personally, I like to heat up the can of the pot with NO ground wire involved, and get a pea-size area of solder adhered to the pot. Then you come back later, reheat the solder "pad" and embed your bus bar into it. The bus bar is generally tinned, which means it will drop right into your bead and you're done. With a big soldering gun/iron, you don't have to worry about this, but a soldering implement big enough to make those pot-pads is arguably too hot for making your 12AX7 tube-pin connections.
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I got a little more done today. That ground bar across the pots was a bigger challenge than I thought. I filed the backside of them, put a small pool of solder on them then pressing the bar against them I heated the solder, pot, and bar. Looked good but a couple of them failed the screwdriver pry test. So I repeated the steps and it's good to go. I also hooked up the pilot light and a bunch of ground wires.
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... the screwdriver pry test. ...
That was the thing that taught me the difference between a good solder joint and a cold joint. A good joint cannot be dislodged by that test.
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Appears that you have created the world-famous "synthetic center tap" comprised of two 100 ohm resistors connected to the 6.3 volt heater wires and junctioned to ground at the pilot lamp ass'y *AND* you have a REAL 6.3 volt center tap: the green-yellow wire coming out of the power transformer. Normally, one grounds the CT *OR*, if not present, creates the synthetic center tap. One or the other, not both. I don't think it will cause any problems should you do both; probably the wired real CT is slightly preferable...but only one of these efforts is needed.
(http://i172.photobucket.com/albums/w32/ttm4/63ct_zps288cd629.png)
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Appears that you have created the world-famous "synthetic center tap" comprised of two 100 ohm resistors connected to the 6.3 volt heater wires and junctioned to ground at the pilot lamp ass'y *AND* you have a REAL 6.3 volt center tap: the green-yellow wire coming out of the power transformer. Normally, one grounds the CT *OR*, if not present, creates the synthetic center tap. One or the other, not both. I don't think it will cause any problems should you do both; probably the wired real CT is slightly preferable...but only one of these efforts is needed.
I do have a center tap. Should I remove the resistors on the pilot light? Or is not grounding the pilot light not necessary?
(http://i172.photobucket.com/albums/w32/ttm4/63ct_zps288cd629.png)
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I do have a center tap. Should I remove the resistors on the pilot light?
That's what I would do. Then just connect the green/yellow stripe wire to chassis.
I only use the two 100Ω resistors when the PT has no center tap. However, there is a safety argument for using 100Ω 1/2W resistors instead of a real wired centertap. It's not unheard of for the output tube pin 3 (plate) to short to pin 2 (filament). This can happen while playing loud with no speaker connected, ie, OT secondary is open circuit. A high voltage will be reflected back to the OT primary and to the tube plate. This high voltage will often arc to the nearest ground which would be pin 2 (since the filament is referenced to ground via a center tap or the 100Ω resistors). That arc will likely require a socket replacement, but it can be even more damaging. If you are using the real wire center tap (remember the filament winding is big wire and has almost zero ohms resistance to dc voltage) there is a strong chance that the tiny wire for the OT primary winding AND/OR the tiny wire of the PT high voltage winding will burn open, making the transformer(s) useless. But, if you are using 100Ω 1/2W resistors instead of a real wire center tap, the small resistors will act as a fuse and burn open. Once that happens, there is no longer a path to ground for the arced socket. So, the 10 cent resistor saved the $$$ transformers in this scenario.
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Excellent point by Sluckey. Although it may seem "unnatural" to use the synthetic center tap (made with the 2 resistors) versus the "real" CT, I have never found there to be any performance difference between the two schemas. One or other other is almost always necessary or serious hum will result. I was curious if anyone else had any contrary or confirming experience. I've never used the synthetic mode when a real CT was present, but he makes a good point about the piece of "insurance" the synthetic mode offers.
"Or is not grounding the pilot light not necessary?"
It's not about grounding the pilot ass'y---it is done to lower hum. Most tube amps will hum badly without one or the other heater-center-tap schemes.
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... there is a safety argument for using 100Ω 1/2W resistors instead of a real wired centertap. It's not unheard of for the output tube pin 3 (plate) to short to pin 2 (filament). ...
The only time I've had a tube fail was an internal pin 2 to pin 3 short. On a blackplate RCA 6L6GC. I think the amp used a heater center-tap, and it popped the fuse (because I use the correct fuse, every time). Had I been a knucklehead and used a too-big fuse, I'd have been buying a new PT.
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BLUF (bottom-line up-front): You already have your first two filter caps with separate ground lugs from the rest of the filter caps; solder a long wire per set of grounds (1st two caps, all other caps) to the turrets, feed them inside the chassis, attach a ring terminal, bolt them to the chassis on separate bolts. Put the power transformer center tap on the same bolt as the 1st two filter caps; consider the possibility of having a wire for the grounds for the output tube cathodes going to the same bolt.
Every other ground can be placed where convenient in the chassis.
Ok so Put a ring ring terminal on each of the 1st two caps and bolt them to where I have my power transformer grounded. I have my center tap, power transformer grounded to where my pot ground bar is bolted to the chassis. Then bolt the output tube grounds to this spot also. Sound ok?
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I love working on this amp head. I find it almost therapeutic, it puts me in such a calm focused state. Every morning I start off double checking my work from the day before. I was checking resistor values and connections yesterday and found out that I can't read as quite a few resistors had wrong values :cussing: for example my main tubes call for 470k 1W resistors my meter (I double checked with a diff meter also) says they are 47k. I don't get it the color codes look right but the meters don't lie. A couple of my pot resistors were wrong also. I'm still second guessing myself on the resistor on my rectifier board now. Any ideas on what it should be on this setup? I've got a bias pot and using 5881 power tubes the rest are 12ax7-c5's.
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I slept in and missed my morning workout so y'all please forgive me for not putting this all in one post. Here's the work I completed yesterday.
Today I hope to find out where the black and red wire coming from the main board go, I think the standby switch, I don't know but I'll figure it out.
The colorful wires from the output transformer go to the main cap board don't they?
One that has me confused is the brown wire going to the bass pot, original schematics show it connecting to the treble pot casing then to the bass pot. Is this grounded to the treble pot before it goes to the bass pot? My treble pot has 4 connections at the top not 3. I've looked at other builds with the same treble pot and it looks like they connected the brown to the far left tab on the treble pot and a wire from there to the far right tab on the bass pot. Is that the way to go?
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example my main tubes call for 470k 1W resistors my meter (I double checked with a diff meter also) says they are 47k. I don't get it the color codes look right but the meters don't lie.
I'm assuming that what you call your main tubes are the 5881 output tubes? If so, you still don't have it right. Those resistors should be 470Ω. That's yellow, violet, brown.
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Yes main tubes 5871's the correct name power tubes?
You're right again about them needing to be 470ohms I think I out 470k ones in there. All I know is I gotta change em out and I don't have any on hand. Hoffmanamps here comes another order
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Ok, I am sitting at the computer waiting :icon_biggrin:
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I got busy at work today and didn't get time to put an order in. I gotta make sure resistors is all I need. I didn't have time to take progress pics today either. I'm down to wiring the output transformer, the choke, and the main cap board. I've been scratching my head for a couple days trying to figure out how to wire them all in especially the choke. Anyone know where those two black wires from the choke go?
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On you main filter cap board, you have a green-insulated jumper wire and a pair of 220kΩ resistors connected to the first two 20uF caps. Get rid of those, they're not present in the 6G6-B. I think I know what you were trying to do, but as-is the jumper is shorting high voltage to ground and the 220kΩ's are not in the right places for what you were looking to copy. The main filter board is not shown on the Fender layout (because it was outside the chassis under a metal cover), but the schematic shows these first two 20uF caps connected in parallel. So you will remove the green jumper and replace the 220kΩ resistors with wire.
On that main cap board, you probably also want to connect the - ends of the first two caps to the - ends of the other caps. Or, if you wanted to keep those grounds separate, make sure you install a wire for each set of grounds so you don't have a hard troubleshooting problem by having a missing ground.
Is this layout minus the 220K resistors on the first two caps correct?
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The original used two 20µF/600V caps in parallel. The only 20µF/600V caps that I'm familiar with today are Sprague Atoms. They're $22 each and are probably too big to fit under the doghouse.
I recommend that you use your original plexiglass board but replace the two caps on the left with 100µF/350V caps. Much cheaper and Doug has them. See pic...
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Steve is right.
Click this link and print it out. It is what I believe an accurate layout of the filter cap board (very first pic). You can see a pic of the mounted filter cap board on page 6 of the post.
Dub's build is super nice.
Match your resistors and layout to the printout and orient the wires accordingly.
http://www.mosriteforum.com/forum/viewtopic.php?f=30&t=5096 (http://www.mosriteforum.com/forum/viewtopic.php?f=30&t=5096)
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How's this
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That's fine ***IF*** your unloaded B+ will be less than 500VDC.
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I took a few days off from working on the amp. My wife got rear ended by a minivan doing 60mph. Thank God my wife was in a minivan also and only suffered minor injuries. I gotta give it to Chrysler, I was able to drive it home, the other minivan that his us (Toyota) is a complete loss but no injuries in there either. I know crumple zones had a lot to do with the other van's damage and safety of the driver. I'm just glad no one was seriously injured.
Now back to the amp!
I recommend that you use your original plexiglass board but replace the two caps on the left with 100µF/350V caps. Much cheaper and Doug has them. See pic...[/quote]
Sluckey, Would the 100uf/350V caps give a better tone? I'm hesitant to replace what I already have only because I already have them and I'm soooo close to finishing that waiting another few days for an order would... well actually it would make me slow down, take my time, and focus more.
Oh the resistors on the first two capacitors. Should I use those or not? I've seen 3 diff setups, 1 without the resistors, another had them running from + to - on each cap. I'm confused.
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My output transformer has red, brown, blue out of one side and the other side has yellow 4ohm, purple 8ohm, green 16ohm, black
I just wanted to confirm where all these go
Red to +430v on main board
Brown to pin #3 of power tube (5881) 1
Blue to pin #3 of power tube (5881) 2
From the other side of the OT
Black to ext speaker
Yellow to speaker
What would I do with the purple and green? make more speaker outputs?
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I had a few more connections I'm just unsure of. The wires from the main cap board mounted under the chassis and wanted to verify the Brown, black, red, blue from the OT. I've attached what I think should happen. Damn I wish I'd have known to highlight a layout wire by wire as I connected it before I started. It's not as overwhelming as it was when I started because a lot of it is making sense. Has anyone got a 6g6-b layout for Jschem ?
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Would the 100uf/350V caps give a better tone? ...Oh the resistors on the first two capacitors. Should I use those or not?
The series caps will not give better tone. But they will give you a 700V rating. You only need the resistors if you use series caps.
Brown to pin #3 of power tube (5881) 1
Blue to pin #3 of power tube (5881) 2
DON'T TRIM THESE WIRES TO LENGTH JUST YET! You may need to swap them when you power up.
What would I do with the purple and green? make more speaker outputs?
You could do that, one jack for each wire. Or you could use Doug's rotary speaker impedance selector switch. Or you could just tape the ends of the unused wires.
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wanted to verify the Brown, black, red, blue from the OT. I've attached what I think should happen.
The black wire you highlighted on the layout drawing IS NOT FROM THE OT. Only the RED, BROWN, and BLUE wires coming thru that chassis hole are from the OT. Both of the black wires coming thru that same hole are the choke wires. Look down near the SPKR jacks and you will see the BLK and YEL wires coming from the OT and connecting directly to the speaker jacks.
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Appreciate the help Sluckey, I caught another mistake today; got the blue and second yellow wire from the cap board mistaken. It's coming along slower than I wanted but I'm enjoying every minute of it especially with the help from y'all on this forum.
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Well I should be done today. All I have left is to wire and install two input jacks for the norm channel. I had a hell of a time yesterday wiring the input jacks for the Bass channel because I bought input jacks from radioshack and the pin out on them is different than a switchcraft. I kept confusing myself and still second guessing myself so keep your fingers crossed. I used a light dimmer switch to build a way of slowly powering up the amp. I don't know if it's necessary just something I read somewhere to be safe. I'm going to surf some first start up tips and biasing instructions in a min. If any of y'all have any please let me know.
Hold on to your butt!! I'm gonna fire up this thing today!!! I'm sooooo excited and more nervous.
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give this a read http://www.paulrubyamps.com/info.html (http://www.paulrubyamps.com/info.html)
Also google "Lightbulb limiter" for first power up.
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Light bulb limiter from Sluckey's web site.
http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf (http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf)
Brad :icon_biggrin:
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It's done!!! Now I'm second guessing myself. I checked all connections more than a few times. Running over everything with a continuity tester I noticed that I have continuity all over my output jacks; from lead to lead to tip to chassis, just everywhere. The lead on the right doesn't have anything connected to it either, should this be grounded, should they have a plastic spacer so the body don't ground out on the chassis?
I soooo want to plug it up but scared to do so.
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I have continuity all over my output jacks; from lead to lead to tip to chassis, just everywhere.
Don't worry about that. That's normal. You're reading thru the secondary winding of the OT and that's just a long piece of big wire wrapped in a coil. It's very low resistance.
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I noticed that I have continuity all over my output jacks; from lead to lead to tip to chassis, just everywhere.
And it should. The hot wire solder to the jack tip runs through the output transformer secondary and becomes the speaker jack ground wire. The secondary resistance is small enough that you will read continuity.
I think you're fine on that one.
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Thanks guys, I was really concerned about those output jacks. I still haven't plugged it in and to resist the temptation I left it at work which I won't be at till tuesday. That'll give me enough time to study and decipher first startup procedures and checks. I really don't want to disconnect my transformers and all that but I also don't want to just plug it up and hope the fuze will blow before anything else if something's wrong.
Biasing is another unknown art to me. I've downloaded a chart to write my voltages and other readings down on but again I just want sooo bad to plug it up turn it on and turn the bias until it sounds good but I know that's the wrong answer so I really need these few days to calm down and study.
wish me luck!
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lightbulb limiter is your friend.
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I built a lightbulb limiter but the first startup instructions I've found are telling me to unsolder my transformers first then check voltages here n there, then start wiring in one transformer at a time to check again and again. It just keeps going on and on looking like it'd take all day to safely start it up.
Anyone ever just say heck with it and fire it up using a light bulb limiter and skipping all that other stuff? does anyone actually do all that other stuff?
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Remember you must have the output of a tube amp connected to a speaker when ever it is turned on.
The Paul Ruby startup guide is the safest way to do it but it is best if you were following it during construction. For what it is worth: I usually pull all of the tubes, plug the amp into the light bulb limiter and turn it on. The bulb should only glow after the initial charge of the power supply caps if it is on at all. If all is well I then start installing one tube at a time and checking. If all seems good with all of the tubes installed I unplug the amp and disconnect the light bulb limiter. Then I pull the power tubes, plug the amp back into the mains, turn it on and check the bias voltage at pin 5. Even without the power tubes installed the bias voltage will be very close to what it is going to be. (I am assuming this is a fixed bias amp). Adjust the bias to maximum negative voltage. In stall the power tubes and complete biasing the amp. This is a pretty good article on how to bias: www.duncanamps.com/technical/lvbias.html (http://www.duncanamps.com/technical/lvbias.html)
When you are through biasing the amp, plug in guitar, turn volume up, hit a cord and scream "It Works" like bloody hell when the cord comes blaring out of the speaker. Best feeling in the world every time I do it and I have built a bunch of amps.
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Anyone ever just say heck with it and fire it up using a light bulb limiter and skipping all that other stuff?
Yes we all do.
Brad :icon_biggrin:
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The Paul Ruby startup guide is the safest way to do it but it is best if you were following it during construction.
Amen!
One of the few things I got right on my first build was just that, I installed the PT, checked voltages (thru limiter), then each successive step in the power supply did the same thing.
Still didn't keep me from mis-wiring the last filter cap and sending most of the audio signal to ground, though. :laugh:
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I know y'all said not to worry about the output jacks but I'm still scratching my head as to why the tip and chassis have continuity, the sleeve and chassis have continuity, and the sleeve and tip have continuity. Transformer causing all that?
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I know y'all said not to worry about the output jacks
We also told you why. Read replies 50 and 51 again.
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Y'all have been a great help. I didn't expect it to work perfectly upon first power up due to my lack of experience but I got nothing but a buzz that was hard to hear and that was it. No power light, nothing. I plugged it up again same thing as soft almost in audible buzz then a small whisp of smoke. I'm gonna dig into it today n troubleshoot it starting from the power cord n make my way through it.
Thanks again all
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I've got the power transformer out now. One of the green leads going to the pilot light has a bare spot on it, no burnt look but more like it melted and grounded out on the transformer.
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I think I've found the problem. I have a center tap which I grounded but I also grounded both leads of the pilot light, no resistors just two wires straight to ground. With a center tap grounded I don't ground the pilot light do I?
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"I think I've found the problem. I have a center tap which I grounded but I also grounded both leads of the pilot light, no resistors just two wires straight to ground. "
What happened to the two resistors you showed from either side of the pilot lamp to ground? In the picture 8 or so posts back that shows your transformer and the two yellow circles. That isn't direct---it's through resistors. Are you now saying you've grounded EVERY WIRE of the 6.3 winding? The center tap AND either side??
Yes, we would call that a complete short. Use either method, not both. But both won't hurt anything.
"With a center tap grounded I don't ground the pilot light do I?"
[/color]What do you mean "ground the pilot light"? The frame, the metal body of the pilot light? No, not needed, it is screwed to the chassis and thereby grounded. And now I guess I have to ask you, when you say "I have a center tap which I grounded but I also grounded both leads of the pilot light, no resistors just two wires straight to ground." [/size][/font]
[/size][/size]Are you saying that the center tap which you grounded is green-yellow-----or red-yellow? [/font][/color][/size]
My friend, you are not making this any easier. Do not shun certainty. Embrace it.[/color]
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I removed the resistors and just ran ground wire shorting it out. I just found out the green yellow wire from the transformer got hot too I guess cause it pulled away from the transformer. I'm going to try n solder it back on but I got a feeling that transformer ain't gonna work anymore
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STOP! you're killing me (but you, worse)
When you say "I removed the resistors and just ran ground wire shorting it out. "
[/size]Shorted WHAT out? You have no business using unreferenced pronouns! Nobody can know what you mean by that sentence! Shorted WHAT? The CT? The 6.3 winding? The frame of the pilot lamp? Both sides of the pilot lamp? Both sides of the pilot lamp with the green wires attached?
[/size]You've now apparently desoldered the CT (the green-yellow wire) of the green----green-yellow---green winding with the heat caused by shorting out ALL THREE WIRES of the 6.3 winding to ground. We will leave what your intention was in doing that for some other time. Or maybe not.
[/size]You have one chance to save this power transformer. And that is to reconstruct the synthetic center tap using the two resistors. But before you do that, just connect the two green wires (you don't have the green yellow any more) to the pilot lamp assy and see if you light up the bulb. If you can light up the bulb, leave the amp on for a while and see if the transformer survived.
[/size]
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eleventeen you've given me hope, hope that I can still use this transformer. I had a synthetic center tap but replaced the resistors with wire, why I don't know, not one person here said to replace the resistors with wire they recommended that I remove the synthetic tap since my transformer had a center tap. I had the green/yellow and the red/yellow from the power transformer grounded and both leads on the pilot light grounded. Tomorrow instead of taking the transformer apart and trying to solder that green/yellow back on I'll put the synthetic tap back in, disregard the green/yellow wire and connect the two green ones to the pilot light. I should ground the red/yellow CT wire from the transformer right? I've also disconnected the power wires going to the rectifier board too, can I put power to the transformer with those not connected to anything?
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eleventeen you've given me hope, hope that I can still use this transformer. I had a synthetic center tap but replaced the resistors with wire, why I don't know, not one person here said to replace the resistors with wire they recommended that I remove the synthetic tap since my transformer had a center tap. <<Exactly!! "Remove" = snip-snip. Or in this case snip-snip-snip. Period, done, end.
I had the green/yellow and the red/yellow from the power transformer grounded <<<Correct, but green/yellow does not exist any more. It's gone. Forget it.
.....and both leads on the pilot light grounded. <<<Why?? How can it get the volts to light it up if both sides connect to the same thing, eg; ground, your left index finger, or a Chevy out on the street??
.....Tomorrow instead of taking the transformer apart and trying to solder that green/yellow back on [I very seriously doubt you'll be able to do this successfully] I'll put the synthetic tap back in, <<NO!!! Not yet! Just see if you can light up the pilot lamp and have it cook for an hour without the tranny emitting smoke and stink or getting overly hot. If you can not, then you need a new tranny and >>IT<< will likely have a center tap. So, no synthetic CT needed.
.....disregard the green/yellow wire and connect the two green ones to the pilot light. I should ground the red/yellow CT wire from the transformer right? <<Ummm, this is how you can drive me and anyone who is trying to help you thoroughly batty. In all your prior posts and in the third sentence of the post right above this one, this red-yellow wire is ALREADY connected to ground! Why is it now a question?
You
can
not
work
this
way.
You cannot start to build a brick wall and once you get midway through the third course, you start chipping away at the bottom course.
....I've also disconnected the power wires going to the rectifier board too, can I put power to the transformer with those not connected to anything? <<Yes. Put some tape or some insulated tubing over the wire ends so you don't zorch yourself.
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Success!!! I hooked the power transformer up as per eleventeen's advice and it's working fine. I measured output voltages again all within range. I left it on for an hour and no smoke, heat or anything unusual. I'm soooo happy. I'm also no longer in a hurry to complete this thing. I'm taking my time and triple checking all I do from here on out
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Does anyone know what the letter "A" on the layout represent? I circled them on the attachment.
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Does anyone know what the letter "A" on the layout represent? I circled them on the attachment.
There should be a wire connecting those "A"s together. If you don't connect those points then you will not have any sound from the BASS channel.
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Just learned the same lesson about the 6.3volt CT stuff. Hooked up some DC heaters, added the 100 ohm resistor artificial center-tap, and forgot to disconnect the CT wire coming from the power transformer. Flipped power, Funky blue smoke and I fried a bridge recto. Then my father informed me that I can't have the CT connected...DOH! Lesson learned. :BangHead:
There is something about seeing that power light shine for the first time. Awesome right?
Sometimes on a first power up I will flip the power on....test voltages....let the light shine and walk away for a while, just to come down from the excitement....then I remember I have another switch to flip...the Stand-by! The light bulb limiter dimming down...then coming back up. I'm sick...I know.
Peace
Aaron
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Thank you Sluckey. I just noticed those today. I haven't powered on my amp yet cause I'm triple checking things as I said I would. I have the same sickness staring at the pilot light when I was checking my power supply. I can't wait to hear it but I'm real nervous.
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[/size]"[/color][/size][/font][/size]Flipped power, Funky blue smoke and I fried a bridge recto. "
May all your cooked parts be so cheap!
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IT'S ALIVE!!! And it sounds beautiful! Clear as a bell not one bit of hum! I'm soooo happy thanks to y'all for helping me have this moment. I must admit I can't find any 1 ohm resistors to set the bias and I've been checking over things for 3 days now n it was driving me crazy not hearing it so I said to myself just turn bias pot all the way down n try it which I did and luckily it sang to life. I connected the two "A's" on the board but no bass at all. I'll have to check that again. Normal sounds crystal clear and can get loud as hell.
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Do you have a light bulb current limiter to protect the amp and you if there's a dead short?
Build looks great for your first one cheers!
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IT'S ALIVE!!! And it sounds beautiful! Clear as a bell not one bit of hum! I'm soooo happy thanks to y'all for helping me have this moment.
:blob8: :bravo1:
I must admit I can't find any 1 ohm resistors to set the bias
Our host Doug sells them in his on line store, here's a link;
http://hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=Resistors&ORDER_ID=632450164 (http://hoffmanamps.com/MyStore/perlshop.cgi?action=template&thispage=Resistors&ORDER_ID=632450164)
Brad :icon_biggrin:
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Light bulb lids limiter was used upon first power up but not while playing guitar. I know our host sells the resistors, I just got impatient.
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Congrats!! :bravo1:
I would bet you're now officially hooked!
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Yes I am hooked! I got the Bass channel working and Done more testing today tried to get it to break up which we did. Plugged into high gain it breaks up about mid volume. Plugged into low gain it can stand a little more volume. lower volumes it is sooo clean and clear it gives me goose bumps. I'm thinking that too much voltage is the problem. I'm getting 470V into the board and the tubes not the 420V on the schematic. How can I lower it? Diff resistor on rectifier board? diff resistors on main cap board?
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I'm getting 470V into the board and the tubes not the 420V on the schematic. How can I lower it?
See the red wire that connects between the rectifier board and the main board? Replace that wire with a 500Ω/10W resistor. Recheck your voltages. Increase the value of that resistor if you want to lower the voltage even more. Decrease the value of that resistor if it decreases the voltage more than you want.
Biasing the amp hotter will cause the voltages to decrease. Maybe even enough to satisfy you.
Using a PT that will give you lower voltages to begin with is a better but more expensive way to drop the voltage.
But... if you are using 6L6s, 470V is not unreasonable on Fender amps.
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Your voltages are a tad high....but instead of entering into an exercise of reducing them.......if you have a 12AX7 as your first preamp tube, try a 12AY7 or a 5751 for the first tube. Those have rather lower gain than a 12AX7 that could solve your problem, it's 100x easier just to use a lower gain 1st preamp tube than to get into circuit mods. This will affect both channels.
It would probably be nice to chop 40 or 50 volts out your B+ as a matter of having your tubes last longer and the thing running a little cooler, but as much abuse as we have handed you during your build, maybe it's better that you enjoy the amp for a while as it is.
The easiest way to reduce those volts is to install a power zener diode or two in series with the B+, and there have been a couple of threads quite recently about doing this. This is easy in some ways but not necessarily so for a newb; these diodes will require a heatsink which need not be fancy but it has to be there.
Should you make that reduction you *may* want to change your V1 back to a 12AX7...or not.
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but as much abuse as we have handed you during your build, maybe it's better that you enjoy the amp for a while as it is.
I deserve the abuse cause a guy with no experience or knowledge in electronics shouldn't be building an amp like this heck I don't even know how to play a guitar. I don't know why I even attempted this, I should've started with a simple 1tube amp or something. I can say it was well worth it though. This thing sounds so clear and good at lower levels. I asked a buddy to bring a couple of his guitars in to give me his opinion and stress the amp out. When he plugged his Gretsch in and gave it a strum he looked at me and said I just sold it (which I have no intentions of doing cause it's now my fav toy to tinker with). He beat on it with his Gretsch and Fender for over an hour and kept wanting to play but I didn't want to take the chance of burning something up with the high voltages. Once I get the bugs worked out I'll post some sound clips.
Keep the abuse coming I am grateful to y'all for taking your time out to give me a hand.
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In the "reduce the 470 volts to 420 volts" department, Sluckey's way is easier (and cheaper) than what I suggested. Just leave a bit of room around that resistor -- it will get warm. Not hot, just warm.
By the way, you opined that you probably should have started w/a one-tube something, eg; a Champ. Tell you what, reading this forum, I have seen plenty of folks who have had problems with Champs, many more than I would have thought. People who have been building stuff for years and years forget what it's like for newbs. I'm sure my early stuff was hit & miss. Electronics has a funny way of letting you know whether you done it right or you done it wrong.
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RE: lowering voltage.
But... if you are using 6L6s, 470V is not unreasonable on Fender amps.
This option should be the most appealing!!
later Bassman amps used a very similar circuit and bumped voltages to at least 450 or 460v.
You started another thread and mentioned 'bad breakup' at high volumes. Are you still having that trouble?
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It's still breaking up and when I say breaking up I'm not talking a little distortion. It sounds like the speaker is getting punished to the point of exploding, loud crunching sounds from cutting in and out, like it's getting wayyyy to much power in from the guitar. I haven't tried any fixes yet. I've been putting all other stuff aside to build this amp and I decided to take this weekend and catch up. Just finished putting new struts on the stang and I have a pile of vintage electronics I bought at a flea market to go through and maybe I'll have the parts I need to try n fix this one.
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I note that your 6G6 design uses a 12AX7 as the phase inverter---thus I assume you don't have any 12AT7. Most (more recent) Fenders use a 12AT7 in that spot, thus I was going to reco placing that 12AT7 in your V1 position to reduce the gain from the first preamp stage. I'd again urge you to try that, even better, go get a 12AY7 or 5751 tube for V1.
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I'll order a 12AY7 and try that. Wish me luck
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It's still breaking up and when I say breaking up I'm not talking a little distortion. It sounds like the speaker is getting punished to the point of exploding, loud crunching sounds from cutting in and out, like it's getting wayyyy to much power in from the guitar.
If you built a 6G6 without extra gain stages (which I think is the case), then something is wrong. You might be able to "fix" it by lowering overall gain (like replace all 12ax7s with lower gain tubes), but that won't fix the problem.. you'll just lower the total possible gain below the threshold of 'broken'... ("the steering wheel shakes violently at highway speeds"... "staying off the highway fixed it!")
One thing to clarify: at this high volume knob setting, is this noise (exploding, loud crunching..) present regardless of instrument play? or is the amp quiet until the instrument is played?
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It's still breaking up and when I say breaking up I'm not talking a little distortion. It sounds like the speaker is getting punished to the point of exploding, loud crunching sounds from cutting in and out, like it's getting wayyyy to much power in from the guitar.
What is the speaker? Is it rated to handle 100w?
100w for a pair of 6L6's sounds excessive. But assume the pair of 6L6's can output 50w RMS of clean sine wave. The peaks of the sine waves touch 100w, but are offset by all the time the wave is not at its peak. Now imagine the sine wave is distorted so severely as to produce a square-wave.
The square wave has a non-changing positive peak, which then drops to a non-changing negative peak. If this square wave's peaks are the same amplitude as the sine wave's peaks, RMS power is now 100w (instead of the 50w for the sine wave).
So to be certain the speaker won't be damaged by distorted output, the total speaker load should be rated for double the clean RMS sine output power.
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One thing to clarify: at this high volume knob setting, is this noise (exploding, loud crunching..) present regardless of instrument play? or is the amp quiet until the instrument is played?
[/quote]
It's quiet as a mouse without a guitar plugged in. Plug in a guitar it's still quiet until you start playing. With the volume at say 3 and under it sounds great, no distortion, hum, buzz, anything, just clean clear notes. Turn the volume up and it's cutting out/breaking up I don't know how to describe it. I found out with the guitar plugged into the low input jack you can turn the volume up a little more than you can when it's plugged into the high input jack. That's what has me thinking it's getting too much input from the guitar and the higher volts are causing it. Remember I haven't biased it yet also. I'm just taking a break to catch up on things for a few days. Once I bias it I'll post some sound clips.
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It's still breaking up and when I say breaking up I'm not talking a little distortion. It sounds like the speaker is getting punished to the point of exploding, loud crunching sounds from cutting in and out, like it's getting wayyyy to much power in from the guitar.
What is the speaker? Is it rated to handle 100w?
100w for a pair of 6L6's sounds excessive. But assume the pair of 6L6's can output 50w RMS of clean sine wave. The peaks of the sine waves touch 100w, but are offset by all the time the wave is not at its peak. Now imagine the sine wave is distorted so severely as to produce a square-wave.
The square wave has a non-changing positive peak, which then drops to a non-changing negative peak. If this square wave's peaks are the same amplitude as the sine wave's peaks, RMS power is now 100w (instead of the 50w for the sine wave).
So to be certain the speaker won't be damaged by distorted output, the total speaker load should be rated for double the clean RMS sine output power.
I'm using 5881's not 6L6's but I still shouldn't be having this issue. I tried a single peavy 4ohm speaker cabinet and a 4 speaker cabinet both with the same effect. I'm only using the 4ohm output on the output transformer currently and I have the speakers plugged into the speaker out jack. not the output speaker jack. I don't know if there's any difference between output jacks or not.
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Finally got around to putting 1 ohm resistors in to bias the amp. I am taking measurements from pin8 where the resistor is attached and ground. Turned all control knobs all the way down. Turned bias pot until I got 35mv is that correct?
I do know that whenever I touch the plate and screen grid to take voltage readings (which are at 465v) I can hear my test lead touch through the speakers. Same thing when I take Voltage measurements inside the chassis I get that tapping/popping sound through the speakers. All knobs are turned all the way down when I'm doing this. Is that normal?
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"I do know that whenever I touch the plate and screen grid ...." Yeah, a little pop is normal.
With no signal applied to the amp, 35 mv, implying 35 ma plate current per tube is IMO a touch on the highish side, but that is my opinion, as one who wants a cleaner sound and not that concerned with maximum wattage output. Let me be clear, it is within spec. You have 465 volts * .035 which is 16.27 watts at idle. Max rating is in the low 20's, so this implies that full-blast is a mere 25-40% over idle when we know it is a lot more. Plus, you have 5881's which are usually considered a tad downrated from 6L6GC, you have highish plate voltage, and you are driving a 4 ohm load. All 3 of those things in that last sentence work to stress those output tubes. So considering that, I would crank the bias colder.
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I'm getting 36 out of one 30 out of the other.
I did just discover what I think caused the breaking up. I have a ceramic disc cap on my treble pot that is micro phonic, I am going to find a cover for it or wrap it with something. I don't think replacing it with a new ceramic disc one will fix it
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"ceramic disc cap "
Doubt it. They are often noisy when tapped, if that (tapping it) is what's causing the noise that's bothering you. Snip one leg and see if the breakup persists. Where that cap is, is right in front of gain stages, it's not surprising to find it "microphonic" if that's what you want to call it. Those tend to be surprisingly reliable, but go ahead and change it if you think it's evil. You *should not be able* to change its in-circuit performance by covering or wrapping it.
If it were me, I'd be dialing back the bias to "25" which in your case might be something like 22/28. See how you like how the amp plays.
I'm lazy. I tend to try work the controls (which can be put back exactly where I found them, at zero cost) before I warm up the soldering iron.
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I haven't plugged a guitar into it yet. I still have the 1 ohm resistors in there that I used to bias it. I don't know if it's ok to plug a guitar in while those are still in
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Those get left in as a permanent item, for any time you wish to measure bias. A vacuum tube amp circuit doesn't have the slightest idea what a 1 ohm resistor is, it doesn't know or care that it is there.
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Well it seems to work fine now. No more noise but I'm going to have my bud bring his gretsch and humbuckers tomorrow and put it through hell.
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I'll give it a try tomorrow. Previously it was the opposite. It broke up sooner the hotter I made the bias eve though it lowered voltage across the tubes.
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It is getting better and better. It only breaks up now when he hits the top string hard and the volume is at least half way up. It sounds like someone kicking a door one time really hard. I tried the 12AT7 tube in V1 with the same result. Other than that this thing is very very clear, has a great tone and surprisingly loud.
Further testing revealed the 12AT7 tube have the amp a better tone
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You could become even happier with a 12AY7 or a 5751 in there. Sometimes, even often I would say, using those really, really tames an amp nicely.
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Would you reccomend replacing all 4 of the pre amp tubes or just V1?
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This depends upon how you use the amp and I should have clarified this. When I used the term "V1" I was meaning more in the generic sense of the word as in "the first preamp tube" = meaning the first tube your guitar signal hits. Fender amps of this era DO NOT use a labeling of tubes such as "V1" or "V2" ---there simply is no such nomenclature on the schematics. So, in the absence of such labeling, we amp dudes often refer to "the first preamp tube" as "V1" even if there really is no such thing in this case. But we seem to know what is being talked about. (Now you can send in and get your magic decoder ring!) Most other manufacturers DO apply such a label to the tubes...which is completely arbitrary. One mfr could label the GZ34 as V1, another might label the first little tube V1 and it would not matter.
If you want to lower your gain which will have the effect of A: giving you more rotation before breakup on the volume control (meaning, you will be able to turn that control up to say 8 instead of 5 before the amp starts to break up--but this does not affect watts at the output) and B: kind of smoothing out the response of the amp, then swapping a 12AY7 or 5751 for the stock 12AX7 in "the first preamp tube the signal hits" is a very painless and obviously reversible way to achieve this.
On a 6Gx or AAxxx (meaning white or brown or black separate-head-style, not Tweed) Bassman, the "first" channel is labeled "BASS INSTRUMENT" and if you are plugged in there, the first tube your signal hits is the rightmost (as viewed from the rear) little tube, the tube most distant from the power tubes.
Should you use the amp for guitar and you plug into the "NORMAL" channel then "the first preamp tube your guitar signal hits" would be >>"V3"<< the THIRD physical tube, starting your counting at the right.
So if you NEVER play through the BASS channel, there is no need for or benefit to changing the first tube....you'll never hear it. If you only play through the NORMAL channel and wish to do this change, swap out >>V3<<. The third-from-the-right tube. For the normal channel, that is "the first preamp tube".
You should probably NOT change out V2 = post tone stack control gain recovery nor V4 (phase inverter) But you can, if you want to. The 12AU7, 12AY7, 12AT7, 12AZ7, and 12AX7 tubes all have the same basing diagram and current consumption and voltage capability and swapping them out in any fashion you can imagine will definitely not hurt anything. If you believe your amp sounds better with a 12AU7 phase inverter, by all means, swap it out. The 12AU7 is about the lowest-gain member of this family....who knows, maybe if this "overload" problem you mention on big fat notes is an issue, there's a case to be made for making that change on V4. You can't hurt anything by doing so. You either like or don't like the result, leave it or swap it back.
Many people like using a 12AU7 as the reverb driver in Fender reverb amps. More (actually less) power to 'em. On Fender reverb amps, I have found you really can't turn the reverb knob past about 3-1/2 anyway without going full mud. Answer: Swap in a lower gain 12AU7 tube for the 12AT7. Easy, obvious solution. Also on Fender reverb amps, most people never, ever use the normal channel. Ever. Such people who wished to try the 12AY7 trick on the reverb channel would swap out THE SECOND little tube.
If you consider that any of those four tubes could be changed to 4 or 5 different types (12AZ7 is rather uncommon) and of those types, 6-10 different brands (if you think Sylvanias sound different than RCAs and different from JJ's and different from Telefunkens) there are hundreds and hundreds of different possibilities. There are lots of adherents to this type of thing and lots of web pages devoted to this particular religion.
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That would explain why it took me forever to find V1 :laugh: This amp was built focusing on chasing that Setzer tone mainly focusing on the normal channel being used with hollow body guitars. With that said guess where I put the 12At7... Yep right where the Bass channel input goes. I had two diff people play on it yesterday and they both told me the whole amp sounds great but the Bass input sounds better. On a side note not mentioned before in any of my posts I did clip the treble bleed cap as suggested by numerous internet posts to get a better tone out of a guitar since I don't plan on this being used for a bass guitar. With no treble bleed cap in, no guitar plugged in, volume turned all the way up, all other controls turned all the way down, I turned the bass all the way up and don't have the slightest hum, buzz, or any type of noise at all through the speakers. This was the same for both channels. Now for the treble test, all other controls turned all the way down, volume up, each treble control had a buzz, very quiet and two different tones. I also noticed that the treble on each channel affects the other. I've since put a treble bleed cap in but went with a 250pf silver mica. I think that helped with the breaking up I was having issues with earlier. The treble pots still buzz nothing's changed there and they both affect each other still. Yesterday I got the best tone out of the normal side with its treble on about 2 and the bass side treble on about 5.
Everyone's very happy with the amp including me but I still want to play around with different tubes. I have to control myself from getting inside the amp and changing more components out or else I'll never finish this thing. I'm going on a week vacation and then going to finish the cabinet up and get hot on another amp. I'm thinking another bassman build like this one with a reverb pan. :icon_biggrin:
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https://soundcloud.com/tags/my%20amp%20breaking%20up
I hope I figured this out
Here's a clip of a guy that walked into the shop asked about what I was working on. Dan lent him his Gretsch to try it out. After 30 min of playing the guy (Roger) looked up at me and asked if I plan on building any more. He loved it. Unfortunately I'm not confident enough in my building skills to sell one yet. I really never planned on selling any of them I build. I just got hooked on building them and this is my first one as you all know.
https://soundcloud.com/eric-easley-3/roger-playing-my-amp
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"Now for the treble test, all other controls turned all the way down, volume up, each treble control had a buzz, very quiet and two different tones. I also noticed that the treble on each channel affects the other. I've since put a treble bleed cap in but went with a 250pf silver mica. I think that helped with the breaking up I was having issues with earlier. The treble pots still buzz nothing's changed there and they both affect each other still. Yesterday I got the best tone out of the normal side with its treble on about 2 and the bass side treble on about 5. "
I have little experience with "white covered" "early-early" 60's Fenders eg; 6G6....versus "blackface and black-tolexed" Fenders say 1963 and later. That said, the tone stacks look "sort of similar" at first glance but they are not. They are quite a bit different. So I could be way off base and I'd wait to see if any other forum members have any different ideas. I notice the early preamp stages have 220K plate resistors versus the 100K plate Rs typical of blackface models. Then, both preamps (Bass and Normal) feed a common point with 470K resistors versus 220K on later models.
Generically, these higher resistances are more susceptible to noise and of course they are early in the gain chain......so you hear it. It's also quite possible that these amps are inherently more noisy than later ones.
I *do* know that on a blackface Fender, if all the tone controls are turned all the way down, the amp will put out almost nothing.
I am curious about your observation that the treble control affect each other, and buzz. If it were me trying to fix those complaints, I think I would:
1: Replace all the preamp plate resistors with metal films. All of them. Somewhat of a pain in the butt, but for 6 * 30 cents....you could potentially solve a lingering problem. Note that in the case of the first BASS channel preamp tube, the second triode of that channel is a cathode follower and the cathode sits on top of a 100K resistor. THAT is the one I would replace with a MF in the search-and-destroy noise hunt.
1a: It might also make sense to replace the 470K resistors with MFs, AND to consider reducing their values to 220K or 330K.
2: Place 20 ufd/450 volt electrolytic caps on the preamp node, "out in the amplifier"---close to the tubes that those nodes feed---on node B and node C versus in the centralized e-cap section, eg; the "doghouse". These, you can temporarily tack in keeping the leads long and see if they help. If they don't, pull them out and you will use them in your next build, so no big deal. I happen to like radial (eg; PC-mount, cheaper) caps for this application rather than axial (leads at each end-more traditional and more expensive) form factor.
[size=78%](http://i172.photobucket.com/albums/w32/ttm4/6G6_B_zps1b1eb878.png) [/size]
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Your advice has been a tremondous help so far eleventeen. When I get off vacation I'll give your new suggestions a try. Did you listen to the first sound clip? That's the breaking up I was talking about. That sound clip is after I did the fixes. It's only doing it now with treble all the way up and volume about 6
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I also noticed that the treble on each channel affects the other.
Surely something is wired incorrectly.
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Another short soundclip
http://youtu.be/NExvgVKorng (http://youtu.be/NExvgVKorng)
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Another short clip of my buddy Dan playing on my amp
http://youtu.be/77SNo-lFDLY (http://youtu.be/77SNo-lFDLY)
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Ok back from vacation and recorded the buzzing I'm getting. I haven't replaced anything since my last post or tried any fixes yet. My vacation set me back a week. Let me know what y'all think is causing this. The buzz on the normal side is barely noticeable and gets quieter as you turn the treble up. The buzz on the bass side is louder and gets louder as the treble gets turned up. With the bias pot all the way down the buzz is almost gone.
https://soundcloud.com/eric-easley-4/img-2536
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Are you under (or...on the same circuit as) a fluorescent lamp, or do you have a dimmer on the lights in your shop or wherever you're working?
I ask this because some of the noise you are getting is "harsh" type noise, some is hum. Some of that "harsh" sounds like dimmer noise. To me.
Before going nuts trying to banish hum from an amp, external sources should be eliminated. Obviously, nothing you do inside the amp can kill noise originating from outside the amp. Some dimmers, some fluorescent lights really spew lots of noise. Newer fluorescents often having switching ballasts instead of older transformer ballasts. Under the "right" conditions, those can really spray out a lot of noise.
I usually play through a POD. The power supply for the POD will induce a fair amount of hum in the (hopped up) Princeton Reverb I play through half the time if it's placed on top of the amp. In back of the amp, no problem. The Peavey Valveking I use the other half of the time has ONE particular spot where if the POD supply is there it makes an unbelievable cacophony of noise. Like you'd never believe. Move it a foot away, gone.
Amps pulled out of the chassis and lacking the metal shield that's usually present in the underside of the surface where the handle is can be very susceptible to externally induced hum and noise of all kinds.
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Actually I have the amp plugged into the store where I work at and it's all fluorescent lighting crappy ones at that. They flicker and buzz constantly. I don't know if a surge protector power strip would have any effect on it but it was plugged into one of those also. I'll bring it home one day and plug it in to see if I get any noise. I have a good feeling that you're right about the lighting though. Those things make so much noise that it drives me nuts when it's quiet in there and all you can hear are those things buzzing away.
Thank you, you saved my sanity because I was about to go on that never ending buzz elimination hunt. Now I need to get the dag gum cabinet built so this thing can be enjoyed.
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I once had a guy's amp for repair, and he complained of hum. I plugged it in at my place (with nothing in the input jack), and got no hum. Plugged in my guitar, no hum.
I took the amp back over to the guy's place, where he plugged in his fiddle with a pickup in the bridge. Crazy hum. We figured out the hum wasn't the amp, or even his house wiring (I brought an outlet checker to be sure), but a lack of a "string ground" on his fiddle comparable to the string ground on a guitar. We ran a bare copper wire from his output jack's ground over to his chin-rest, and as soon as the fiddle was in playing position, the hum was neutralized.
You'll find cases where the problem with the amp isn't in the amp.
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Now that I have it build I'm trying to learn what all the components are called, what they do and what would changing the value of them do. I've been scouring the net for a simple board layout for the bassman 6g6-b with the names of the capacitors and resistors on it ie. plate resistor, input capacitor etc. Anyone seen anything like that around the net?
Last weekend I cleaned the treble pots just for shtz and giggles and the hiss from the normal channel went away, the bass channel same thing but I'm thinking y'all are right about the lighting doing that. Yesterday the pot on the normal channel started hissing again and now it's operating backwards, I turn it up the treble lessens I turn it down I get more treble. I'm still scratching my head on that one. How can it be working great one weekend and with no changes now working backwards. I'm questioning my treble pot and presence pot wiring now. It's still a joy to work on and everyone that comes to the shop says it sounds great, thanks to you all of course. Without y'alls help I'm pretty sure I'd still be fighting with insurance company over fire damage :laugh:
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... it's operating backwards, I turn it up the treble lessens I turn it down I get more treble. ...
You have a 250kΩ Treble pot, with a 1MΩ resistor and a 0.01uF cap from the "ground lug" of the pot to ground. This is very important!
Normally, the parts to ground aren't there on most Treble controls you're probably used to using. What this means is there is some critical point on the Treble control's rotation above which it boosts treble, but below which it rolls off treble.
So I think your Treble control is working properly, but just exhibits different behavior than you're accustomed to having. All the more reason to fiddle the knob while listening instead of setting the control to a certain number setting you typically use! :icon_biggrin: (it can be hard getting some players out of that habit)
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You're exactly right. The treble is working good, just not what I'm used to. Man this thing sounds great.