Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: NO_H2O on July 18, 2015, 07:54:18 pm
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I picked up a very clean Hammond AO-43 organ amp/reverb unit. After some reading I know the B+ will have to come down. I am hoping that swapping the RT to a 5Y3 will get me in the pall park.
So far I have run all the original tubes across my tube tester to check for shorts and grid leakage. They all test good so I plugged them in, wired up a 10 inch speaker (unmounted flopped on the bench top), dug up a 1/4 in jack to RCA adapter, brought it up slow with my variac and had my frien try it with a Tellicaster. It was clean, clean, clean. No hum, etc. But it was not real loud either.
In the end I would like to have a VOX AC preamp an AC15ish power section. I think tremolo and reverb would be sweet too. If I were able to pick my favorite Tremolo sound ever. It would be just like my Fender Vibro Champ. If I were to pick my favorite reverb ever it would be either from a Fender Princeton or an Ampeg Reverborocket.
I am no expert when it comes to designing tube amp circuits, but I can follow a schematic and layout drawing. I like a Hoffman layout found in an AC 30 build thread on this forum. It is nice and tidy, one normal and one top boost input, 3 12AX7's and 4 EL84's. The schematic is nice, but the layout drawing is flipped. I could deal with the flipped drawing but it would be cool if I could find one that did not require a mirror to read.
I am thinking of using that preamp and plug it into the existing power section of the Hammond with the 5Y3 and see were I am at with that. Then plan out the finished circuit and transfer everything into a new chassis.
Has anyone gone down the AO-43 road before. Are the any bumps in the road I need to know about or derailments I am headed for?
Thanks Dave.
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Several people here have used the AO-43. It's a good amp with excellent iron. However, if you build an EL84 amp you will likely have a lot more B+ than you'd like. My solution was to use 6V6s instead. I built a Plexi 6V6 this year and Toxophilite built two 6V6 AB763s. He used the original chassis but I just used the iron in a new blank chassis. You can find info on all these amps in this same forum. And there is another member about to start a Plexi 6V6 conversion.
Here's a link to my AO-43. And I have another AO-43 for a future project.
http://home.comcast.net/~seluckey/amps/6v6plexi/6v6plexi.htm (http://home.comcast.net/~seluckey/amps/6v6plexi/6v6plexi.htm)
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Sluckey the's the main forum member who guided me through my builds and they turned out great considering my previous experience.
I will add
Any speaker not on a baffle will be really really quiet(phase cancellation)
Moving already soldered components around to a new chassis probably won't be too fun/easy or 100% successful(unless you mean just the transformers)..If you plan to upgrade your build anyway go for broke and build what you want right away
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I was not worried about the volume when I tested it. The fact that it was not mounted and they it was a 16 ohm speaker. I was wanting to see if everything was working and if it had any hum. The super clean sound with no hum or noise made me happy.
I don't think I would have a problem converting to 6V6's. But I really want to hear these old Sylvania Black plates in action. I think I owe it to them to stab in a 5Y3 or 5R4, turn the voltage down to 110 on my variac and see if the B+ is in the ballpark. If so, I will use the Hoffman AC30 preamp section coupled to the Hammonp output section and roll it with a bucking transformer.
If it does not sound good, 6V6's here I come.
I do currently have a sweet sounding Vibro Champ that has a few mods that has some very impressive 6V6 tone. My son has taken it over and the folks he plays with could not believe that much good tone could come from a 5 watt Vibro Camp. But hey, if you are going to mic everyone's amp, that little Champ will never know it is small.
I might be swimming upstream for a bit, but I have to hear these old tubes first.
I know I won't be able to reuse the old board or resisters/capacitors over but they are cheap and I have a pile of them. So what the hell. I have to try it.
You guy are probably right and by the time I get the B+ down enough, the heaters will be at 4 volts. But I got to try it once.
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by all means
Have at 'er and have fun!
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Well after making a list of what I would need for the first stage of conversion, then digging thru a couple boxes of stuff I have hoarded over the years. I have most of the list covered. I will need 5 or 6 things so I think I will run up to Ack Radio and pick up my short list and get started. All I will need is some time.
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I am sure you thought I fell off the face of the earth. I had to put the AO-43 aside as life life happens. I have recovered and pulled that project out again. I thought I would just gut it and start over. After 2 or 3 plans I ran across the Hoffman AC30 layout and started down that path. Only I will do it as a 15 watt. More to follow.
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This is an AO-43 i built i think in 2005. It was a great sounding amp. I just had to relocate the choke and add another PS cap next to the existing one. Plus strip that tiny board down and mount all the parts. It worked out. Very small board for sure.
http://www.triodeamplification.com/18Watt.html (http://www.triodeamplification.com/18Watt.html)
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That plexi a nice set up. Maybe I should have gone that way.
I started with the idea of using a clean (new) chassie and mod the layout. But it turned into a gut and start over job. I am shooting for a small 1-12 combo in the end. It will be a bit tight and busy inside but I think I can get it all in there if I take my time and keep it neet.
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Bought a box when The plan was to mod the AO-43 and just have a clean box to start with. But then I found the Hoffman AC30 no trem layout. I stuck with the narrow build idea to keep the size of the combo small. We will see if that was a good idea or not.
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I modified an off the shelf board and used a section of the original Hammond board for the filter caps.
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Filter cap board.
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Main board and ground buss/control pots in.
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The "NO LICK" power section is in.
Fell free to point out anything I have screwed up. No thin skin here.
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I've built 3 amps in a narrow 3 x 4 x 17 Hammond chassis. Is that the same as yours? They are a challenge to build in but it's doable. I had to really plan in layers for my TDR. They are not fun to work on later. Keep in mind how you will replace filter caps, etc. down the road.
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I think it is the same chassis. And yes, it is a bit of a stacking/layering build. I will give enough slack to be able to pull the filter cap board up and replace the caps. the main board will have to be un-soldered to remove it. I will have to take my time and keep it neat.
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Another trip to Ack Radio for the rest of my components and I finished and mounted the main board to the chassis. And mounted the output transformer and choke.
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Damn. It will be tight down it there. I think I will leave the heater wiring until last and keep the twisted pairs up toward the opening of the chassis and everything else down toward the closed face.
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Definitely a tight chassis to work in. No two ways about it, especially with mounting vol/tone controls which the original did not have.
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That hook up wire is not the easiest type to work with in tight spaces. :w2:
The cloth push back hook up wire that Doug sells is much easier to work with. It bends easy, stays in place well.
And no striping the insulation. You just cut it to length, push the cloth braid back, solder the wire in place, push the braid back, done. :icon_biggrin:
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Willabe, your are correct about this wire. I may have to order some of the good wire from Doug to do the twisted pairs for the heaters. I went as far as I could today. I stopped short at the heater wiring. Here are some pix so let me have it.
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More pix.
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Your build looks excellent, to me. I didn't quite notice at first you have the tubes mounted on the long narrow side of the chassis, like a tweed amp. Sharp. I think you're doing fine.
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Thanks. We will find out when I start to bring the power up on it. It is my first full build. I have done some mods and a couple repairs and recaps but this is ground up amp.
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Well I am not sure how "neat and tidy" it is but the heater wires are in. This wire is tricky on a single run. But a twisted pair is down right bulky. I was trying to keep it away from al the other stuff but that was tough. I wanted to finish up but came real close to ordering some new wire.
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I caught a mistake as I was double checking. I joined the heater wires to th grounded end of the simulated center tap resisters. :BangHead: But it was a quick fix.
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I caught a mistake as I was double checking. I joined the heater wires to th grounded end of the simulated center tap resisters. :BangHead: But it was a quick fix.
Good catch! :icon_biggrin:
And it all looks real good! :icon_biggrin:
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I guess the next step is to stuff a rectifier tube in and bring the power up slowly and watch the amperage and see if I can get to full power without finding any more mistakes. Then take voltage readings on all the tube socket pins and report back here to the amp builders guild.
My variac is down at a friends place but he does have an 8 ohm cabinet to plug into while I power it up.
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Do you have a light bulb limiter? If not there very simple to build, link below. Use it for 1st power ups.
http://sluckeyamps.com/misc/Amp_Scrapbook.pdf (http://sluckeyamps.com/misc/Amp_Scrapbook.pdf)
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I have thought I need to build one.
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I think you did a very good job with your heater wires in that confined space.
You've come in from the top and kept the signal wires and board down low and about as far away as you could.
Hopefully you will have very good results! :icon_biggrin:
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+1
I think you've done a damn fine job working in the tight space of that chassis. :bravo1: Good luck on the power up!
(And yes, I fell victim to buying that exact same wire before... Never again!!)
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It looks very very nice... great work... :icon_biggrin:
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Thanks guys. it will be a couple days before I get a limiter built and get with my friend and get to my variable power supply.
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Everything I've seen looks top notch. I bet it fires up just fine on the first try.
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You don't need the variac for 1st power up when using the lamp limiter. Just make sure you use a small wattage (60w to 100w) light bulb.
There have been a few guys who posted here that they were using a 200w and a 300w bulb and that's too large for even a 100w amp to give enough protection for a short.
The smaller the wattage of the bulb the more protection it will give.
I and others here have a variac but don't use it for 1st power ups, we use the lamp limiter alone with a small wattage bulb.
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Thanks. I will build one and fire it up and start recording my voltage at each pin.
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> build one ... recording my voltage
Don't take voltages while on a lamp-limiter. Fire it up, watch lamp, wait for smoke, and quick check you have "some" light in heaters and "some" voltage at B+. You might even play a bit, but don't fret that it sounds lame or unhappy.
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Built the current limiter.
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Looks real nice. :icon_biggrin:
If you can test it on a known working tube amp so you get a feel for the brightness/dim look of the bulb at 1st turn on, how it looks with a working amp with no shorts.
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Will do. Thanks for all the help.
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Thanks. I will build one and fire it up and start recording my voltage at each pin.
To avoid frustrations later on I've gotten into the habit of testing connections for continuity or voltages - without any tubes in place for SS recto or only with the recto tube in place. This is without the limiter. You can test your heater wiring down the entire string, power tube plate & screen points, and B+ down the string - all unloaded of course. This can catch all voltage mis-wiring and get confirmation for proper voltages at all respective pins. It's not just for mis-wiring as you may also catch cold solder joints. I had this happen once on a preamp tube heater pin. It was found pretty fast after getting no sound upon 1st fire up. I take pride in getting things right the first time but this little diddy caught me by surprise, made me frustrated a bit at first, and caused me to laugh at myself for not practicing what I preach & know to do. Murphy's Law always finds a way to raise his ugly head.
Anyway, you can still have other mis-wiring issues but at least the basics and or fatal things are out of the way upon 1st fire-up and you can be reasonably sure you will not have any big issues BUT - it's highly recommended to still use the lamp limiter for your first fire up with all tubes in place.
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Thanks. That was my plan for the first power up. I my have a chance to do that today. I will post results when I get it powered up.
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I ran down to my buddy's place to borrow a pair of spare Russian EL84's and pick up my variac power supply. I remember now why I hate moving the damn thing. I opened it up to see about mounting a household outlet to plug into instead of using a pigtail with a ground jumper. Now I know why it weighs a ton. And it has a lamp limiter built in. You just can't see it when it is closed up. It has some huge transformers in it. Way more power supply than I need but they were throwing it out at work years back so I loaded in the car.
And I think I will stick with the pigtail.
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Power up with only a 5Y3 and an 8 ohm cabinet plugged in. No noise and no smoke and the limiter lamp behaved well.
Voltage check was as follows.
Node A 440 vdc
Node B 440 vdc
Node C 438 vdc
Node D 438 vdc
Node E 438 vdc
V1
Pin 1 430 vdc
Pin 2 0
Pin 3 0
Pin 4 7.3 vac
Pin 5 7.3 vac
Pin 6 430 vdc
Pin 7 0
Pin 8 0
Pin 9 7.3 vac
V2
Pin 1 435 vdc
Pin 2 0
Pin 3 0
Pin 4 7.3 vac
Pin 5 7.3 vac
Pin 6 435 vdc
Pin 7 435 vdc
Pin 8 0
Pin 9 7.3 vac
V3 PI
Pin 1 432 vdc
Pin 2 0
Pin 3 0
Pin 4 7.3 vac
Pin 5 7.3 vac
Pin 6 432 vdc
Pin 7 0
Pin 8 0
Pin 9 7.3 vac
V4 output
Pin 1 0
Pin 2 0
Pin 3 0
Pin 4 7.3 vac
Pin 5 7.3 vac
Pin 6 0
Pin 7 440 vdc
Pin 8 0
Pin 9 440 vdc
V5 output
Pin 1 0
Pin 2 0
Pin 3 0
Pin 4 7.3 vac
Pin 5 7.3 vac
Pin 6 0
Pin 7 440 vdc
Pin 8 0
Pin 9 440 vdc
Voltages seem high to me. Anyone catch something I missed. Ok I must admit. The first power up was a dud. Everything was a 0. No limiter lamp surge, on voltage no jewel lamp. It helps if you put in a jewel lamp bulb and a fuse before you star. :BangHead:
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All voltages will be high with no tubes plugged in. Now put all tubes in and power up on the lamp limiter again. If lamp limiter does not glow brightly then plug amp straight into the wall.
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Ok. All tubes in. Powered up with the limiter and bulb went back to a dim glow. No smoke no funky noises. Plugged it in the wall and powered it up. Warmed it up a bit. No smoke only a faint tube amp hum. I don't have an ave here so I passed a 500 MHz tone thru it and it makes noise thru both channels.
Voltages as follows.
V1 12AX7
Pin 1 1.3 vdc
Pin 2 0
Pin 3 143 vdc
Pin 4 6.8 vac
Pin 5 6.8 vac
Pin 7 143 vdc
Pin 8 1.3 vdc
Pin 9 6.8 vac
V2 12AX7
Pin 1 183 vdc
Pin 2 0
Pin 3 1.3 vdc
Pin 4 6.8 vac
Pin 5 6.8 vac
Pin 6 297 vdc
Pin 7 183 vdc
Pin 8 183 vdc
Pin 9 6.8 vac
V3 PI 12AX7
Pin 1 235 vdc
Pin 2 45.5 vdc
Pin3 67.9 vdc
Pin 4 6.8 vac
Pin 5 6.8 vac
Pin 6 238 vdc
Pin 7 46 vdc
Pin 8 67.5 vdc
Pin 9 6.8 vac
V4 EL84
Pin 1 0
Pin 2 12 vdc
Pin 3 16.6 vdc
Pin 4 6.8 vac
Pin 5 6.8 vac
Pin 6 26.8 vdc
Pin 7 323 vdc
Pin 8 21.5 vdc
Pin 9 341 vdc
V5 EL84
Pin 1 0
Pin 2 0
Pin 3 15.5
Pin 4 6.8 vac
Pin 5 6.8 vac
Pin 6 2 vdc
Pin 7 347 vdc
Pin 8 2 vdc
Pin 9 346 vdc
Not sure why small voltages are on pins 2, 6 and 8 of V 5 and not V 6.
Looking over the numbers, what do you think. I need to haul it down to my buddy's place and run it thru the 8 ohm greenbacks and see what it sounds like. I need the check the place disapation first to see if it is in the ballpark.
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Tell me about your EL84 tubes. Are they old tubes that may have come with that AO-43 amp? Or new, modern tubes?
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They are older tubes pulled from a modern H and K combo. I used some Russian /China tubes to power it up and once I am sure about it, I will put the original black tubes back in it. Didn't want to risk them.
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There is a bit of non standardization with EL84 tubes. They don't all have the same pin out. For instance, I have some that have pins 1 and 2 tied together inside the tube. Can't use those on Doug's AC30 layout. Maybe your Russian/Chinese tubes have some peculiarities that might account for voltages on pins that don't even have anything connected? Put some good tube in and recheck voltages. Oh, and recheck V1 voltages too. I think you dropped a stitch when you were typing them.
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The EL84's should have been a pair of EH's. So much for that. I got the Hammond 6BQ5's (I think they are Sylvia) out and plugged them in and remeasure V1, V4 and V5. Heater voltage remained the same.
V1 12AX7
Pin 1 142 vdc
Pin 2 0
Pin 3 1.3 vdc
Pin 6 143 vdc
Pin 7 0
Pin 8 1.3 vdc
V4 6BQ5
Pin 1 0
Pin 2 0
Pin 3 12.7 vdc
Pin 6 0
Pin 7 352 vdc
Pin 8 0
Pin 9 356 vdc
V5 6BQ5
Pin 1 0
Pin 2 0
Pin 3 12.7 vdc
Pin 6 0
Pin 7 351 vdc
Pin 8 0
Pin 9 357 vdc
And it is bit quieter.
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Those voltages look like they should make a joyful noise.
Take a look at this short thread about EL84/6BQ5...
http://el34world.com/Forum/index.php?topic=18789.msg192602#msg192602 (http://el34world.com/Forum/index.php?topic=18789.msg192602#msg192602)
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So no "standard" for the EL84's. That is good info when selecting replacement tubes. I was thinking that 350 vdc was a bit high for plate voltage on a 6BQ5 and was thinking of building a bucking transformer and mounting it in the cabinet when I put it together. I can't wait to hear this thing, but I will have to wait a bit.
Thanks for your help. When I get this one done. I think I might take a stab at a Re-Vibe to go with it :icon_biggrin:
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The safe way to treat an EL84/6BQ5 is to not use any of the "extra" pins for tie points. They may not really be free. If this were my amp I'd move that grid stopper resistor off pin 1.
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When you say remove the grid stop resisters from pin 1. I take that as just remove them all together. True?
Also. It looks like I will have to go back in it to increase the cathode resister a good bit to get the plate disapation down. I increased the resister value in the Hoffman AC30 layout from 50 ohm 10 watt to 120 ohm 10 watt because this amp is a 2 output tube 15 watt. I doubled the value and added 20 ohms for today's household voltage.
As I calculate it. With a plate voltage of 352 vdc, and measured cathode resistance of 119.3, and a voltage drop across that of 12.68 vdc. The plate disapation for each output tube is 18.7 watts. I don't think that will make the tubes very happy. I bought a few 10 watt resisters ranging from 100 to 150 ohms to dial it in and started with a middle of the range 120 ohm. I think it will take something more along the lines of 200 to find the happy spot.
Would you agree? Or am I an idiot? Or should I use a bucking transformer and knock everything down to 115 at the plug and start calculating again?
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We knew that AO-43 PT would be too hot. But you're on the right track to tame it a bit. I would use one of those 150Ω 10W resistors to knock the B+ down. Put it between the rectifier and the first filter cap. Then mess with the cathode resistor.
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I had the same thought just now as I have an unused pair of turrets at that end of the board. I will ad the 150 ohm 10 watt there. Run thru it and then to filter cap A and see what I get.
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We knew that AO-43 PT would be too hot. But you're on the right track to tame it a bit. I would use one of those 150Ω 10W resistors to knock the B+ down. Put it between the rectifier and the first filter cap. Then mess with the cathode resistor.
Hmm, using a 5Y3 I get 322Vdc at the first node. Maybe no_water is using the 5U4 that comes with these?
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Nope. I used a 5Y3 in the hopes it would knock the voltage down enough.
So the 10 watt 150 ohm is now in line between the rectifier and the first filter cap using the prev empty turrets on the end of the board. I tried to be as neat as possible so it did not look like the after thought that it is.
I had to desolder some things to give myself some room to work, them solder them back in place.
I will now do the power up as if it were the first time again and post the results.
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Ok. It is happier, but I don't think it is in its happy place just yet. Heater values are unchanged.
V1 12Ax7
Pin 1 130.5 vdc
Pin 2 0
Pin 3 1.24 vdc
Pin 6 131.5 vdc
Pin 7 0
Pin 8 1.25 vdc
V2 12AX7
Pin 1 177.5 vdc
Pin 2 0
Pin 3 1.24 vdc
Pin 6 286.2 vdc
Pin 7 177.1 vdc
Pin 8 176.9 vdc
V3 PI 12AX7
Pin 1 225.7 vdc
Pin 2 43.8 vdc
Pin 3 65.4 vdc
Pin 6 227.5 vdc
Pin 7 44.1 vdc
Pin 8 65.4 vdc
V4 6BQ5
Pin 1 0
Pin 2 0
Pin 3 11.4 vdc
Pin 6 0
Pin 7 322 vdc
Pin 8 0
Pin 9 325.7 vdc
V5 6BQ5
Pin 1 0
Pin 2 0
Pin 3 11.4 vdc
Pin 6 0
Pin 7 320 vdc
Pin 8 0
Pin 9 325.7
Cathode resister 119.3 ohms
Voltage drop across it. 11.20
Plate voltage 322 vdc
Plate current 46.9 mA
Plate disapation 15.1 watts.
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I got my son to move the behemoth variable power supply down to the work area. I plugged the amp into it and dialed up the wall voltage of yesteryear, 110 and ran the numbers again. I won't post them all but here are the results. The heaters are now 6.25 vac. Plate voltage is 294 vdc. Plate current is 42.3 mA. Voltage drop across the 119.3 ohm cathode resister is 10.1 vdc. And plate disapation is 12.4 watts. That is damn near happyville USA. And the amp is dead quiet until I put a 500Hz tone thru it.
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I think you are about there. 150Ω cathode resistor may just do it for you. Oh, if you build a bucking transformer for this amp, consider building it in a small box that can be used with any of your amps.
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I see you used a transformer from Radio Shack. Be that we have no more RS stores does Doug sell one for use as a bucking transformer? I think I would build one and mount it in the amps cabinet permanently as it will always need one.
Would a Hammond 186D12 be what I need?
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That will work. I'd rather have this one...
https://www.tubesandmore.com/products/transformer-hammond-filament-126-vct-4 (https://www.tubesandmore.com/products/transformer-hammond-filament-126-vct-4)
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What if I up the B+ resister to 300 or so 10 watt and move the 150 to the cathode resister spot? It would make for a cleaner combo build. I think a 10 watt would have the duty life. What say you?
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Sure. Just play around with it. Just do some math to make sure you don't exceed the power rating of the B+ dropping resistor. Measure the voltage dropped across the resistor. Square the voltage and divide by the resistance (P = V2/R). Then double that actual power for a safety margin and get the next available wattage resistor. For example, say you measure 40v across a 250Ω resistor. Then, P = 402/250 = 1600/250 = 6.4 watts. Double that to 12.8W and use the next larger available power rating, probably 20 watts.
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sluckey you answered as I was figuring things out but ball parked it about the same:
But if you want to test things out then think about to get the same power out when dropping more voltage then it requires more current to operate. The Hammond PT has plenty of reserve capacity. Next going by your unloaded voltage of appx 360 and with your increase in voltage drop guessing a round number to be 300v = 60v dropped across the 300r/10w resistor? And since it will be running a higher current - going by the data sheet info @ max signal current at 300V = 46mA (x2) + screens 11mA (x2) + 12ax7's 3mA (x3) = 123mA total (potentially). 60v * .123A = 7.38w x2 for safety = 14.76w 300r resistor wanted.
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True. I will hit the calculator.
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I ordered the bucking transformer Sluckey recommended along with a box and strain reliefs to mount everything in. I will mount it inside the combo cabinet.
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I found a 300 and a 350 ohm 20 watt resister a mouser. Swapped the 150 ohm 10 watt B+ resister to a 300 ohm 20 watt. Moved the 150 ohm 10 watt to the cathode bias spot in place of the 120. Parts for the bucking transformer came today's as well but I have not started that yet.
Plate voltage is now 309. Plate current is now 38 ish Ma. And plate disapation is 11.8 watts. And no bucking transformer yet.
What say you guys?
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I found a 300 and a 350 ohm 20 watt resister a mouser. Swapped the 150 ohm 10 watt B+ resister to a 300 ohm 20 watt. Moved the 150 ohm 10 watt to the cathode bias spot in place of the 120. Parts for the bucking transformer came today's as well but I have not started that yet.
Plate voltage is now 309. Plate current is now 38 ish Ma. And plate disapation is 11.8 watts. And no bucking transformer yet.
What say you guys?
Those are all good numbers - right there. You don't need no stinking bucking transformer now :icon_biggrin:
How warm does the 20watter get? Just slightly?
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It stays cool at idle. I will have to give it a workout to know for sure.
I am still going to build the bucking transformer as a stand alone tool. Just so I have one.
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I took the amp down to my buddy's place for a tone test today. Put it thru an 8 ohm 4x12 cabinet full of greenbacks. Ran a Tele-Sonic, Sheraton and standard Telecaster thru it. Had to sort out one preamp tube that was not up to the task and sadly had to put a Russian 12AX7 in its place. But the result was fantastic. The normal channel was very Vox like and the top boost channel no dought a top boost Vox tone. Even with greenbacks it had all the chime you could ever want. I could drive the top end past the sweet chime spot if I wanted to and dial it right back. Lows and mids were right there. Great response and definition. My hat is off to Hoffman Amps and anyone that had a hand in the design. And thanks to Sluckey and all the fine folks on this forum for your help.
Now I have to hit the wood shop and build a cabinet. Then pick out tolex and grill cloth, or do a wood finish. Even more tasking, select a 12 inch speaker to pair up with it. I was leaning toward the Weber Blue Dog Alnico. But I don't think this amp will have any shortage of chime after hearing it with greenbacks.
Once I have it put together I will have to record a few tracks and link them here.
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Also. The 300 ohm 20 watt did not heat up too bad. The amp was driven fairly hard for an hour solid.
So my short list for sealers is the Weber Blue Dog, Weber Silver Bell, Weber Grey Wolf, Scumback Scumnico. I have the Blue Pup in a Champ and like it. I have built a single 12 with a smooth cone WGS and a 4x12 with Eminance (can't remember the model). I have never owned a Scumback.
Anyone have recommendations?
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I really like the Celestion blue with a Vox AC-15. The Celestion gold is supposed to sound similar but at a higher power rating. Ed Chambley knows this stuff pretty well. I trust his ears.
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I really like the Celestion blue with a Vox AC-15. The Celestion gold is supposed to sound similar but at a higher power rating. Ed Chambley knows this stuff pretty well. I trust his ears.
The Gold needs to be pushed, use the Blue if considering this speaker? I love Scumbacks and have the Scumnico & PVC alnico & ceramic both (& others too). For Webers, the blue dog in a low watt 15w or no more than 30w as they get darker with higher wattage and the 12A125A & 12A150A are maybe better? The Silver alnico is dark, not chimey. WGS also is good & a great bargain. Check out the "speakers section" for further info & feedback.
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15 watt 8 ohm Celestion Blue (made in UK) on the way. Now to clean out my wood shop and start on a cabinet.
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When you say remove the grid stop resisters from pin 1. I take that as just remove them all together. True?
I think Sluckey meant that if you use a different type tube someday in the future that has an internal connection at pin 1, the tube may become very angry with you (or the reisistor on pin 1 LOL). If you dissconnect that side of the resistor and attach it to an insulated lug on the chassis or somwhere besides pin one and leave the other side of the resistor where it is
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All grid resistors function best when attached directly to the tube socket. In lieu of another point available for that free floating other end you can solder a wire directly to it, and helps to make a mechanical connection by crimping or twisting the two together before soldering. Then protect if possible with a little heat shrink tubing and you're set.
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My Celestion Blue made it here. It is made in the UK and date coded Aprill 30 1991. I mounted it in a 1x12 open back cab and had my son give the combo a test drive. It is the perfect speaker for this amp. It still needs some brake in. I don't think the prev. owner gave it much playing time at all.
I got started on the cabinet and got the 4 sides glued up.
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Made some more sawdust and some forward progress. 2 more back panels and cleats left to fit and it will be time to dress it in tolex and grill cloth.
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One more for today.
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Back panels fitted. Tolex and grill cloth will have to wait a week or so.
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I got the baffle and panels covered today. Main cabinet left for another day. The damn piping is very stiff. It will be super tight going together. Might have to lube it up and drive it together. Or ditch the piping.
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I really like the Celestion blue with a Vox AC-15. The Celestion gold is supposed to sound similar but at a higher power rating. Ed Chambley knows this stuff pretty well. I trust his ears.
I've got the gold on my current AC30, and it sounds incredible. Love it. I can't wait to hear it on my AC30/4 I'm starting now.
~Phil
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I got busy in the shop today and started wrapping the cabinet. I did get the baffle and front upper panel in with the piping on. Had to use a bit of dish soap to help it slide in place. It was a tight fit. It did take some tension out of my grill cloth but I am not going to pull it back apart. Still have to modify a couple corners for the upper back corners.
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Looks great!!! :icon_biggrin:
Where did you get the tolex?
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Found it at Mojotone. They had some at my local fibric store but they were sold out and would not get more until October.
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Has anyone used a hair dryer or heat gum to snug up grill cloth?
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Found it at Mojotone. They had some at my local fabric store but they were sold out and would not get more until October.
I thought it looked like Mojo stuff. :icon_biggrin:
The stuff at your local fabric store is it the same or a little different? Gator is my favorite but I like the kind with what they call the 'medallion' included in the skin pattern. The 'medallion' is a roundish plate on the back of the neck just behind the head that has like 4 to 7(?) raised bumps.
Faux gator/crock patterns are different, some are copies of the belly skin, some are the back and sides and some are the back and sides with the 'medallion'. I like those the best as they have more variation of pattern texture and shape.
Mesa has some amps with the 'medallion' gator skin that look great to me from pics on line but you have to see them in person to be sure.
I have at least 50 different samples that I requested from different fabric store and tolex dealers and they all are terrible looking and/or to soft to use on an amp. :BangHead: :cussing: (I have well over 300(?) possible samples for amp coverings and over 100 grill cloth samples.)
I can't find the good stuff anywhere.
Has anyone used a hair dryer or heat gum to snug up grill cloth?
Yes. I used 1 on my old BF SR and it worked great, also used it on a few new builds.
Others here have also used a heat gun to tighten up grill cloth.
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This is the pattern I like best. :icon_biggrin:
So as not to hijack this thread, I started a thread here;
http://el34world.com/Forum/index.php?topic=20822.msg220137#msg220137 (http://el34world.com/Forum/index.php?topic=20822.msg220137#msg220137)
The medallion is under the left side of the handle, by the right chassis strap and on the top of the left side center in the 2nd/bottom pic.
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The gator on that Mesa looks nice. The ostrich in my local fibric store was very close to the mojo stuff. They had black and brown. They also had a lighter lizard that I almost went with. But the backing had too much contrast and I did not want to risk it.
I am going to pull the speaker back out and try the hair dryer trick to snug the grill cloth back up.
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I like the look of faux ostrich very much. Mesa has a very nice tan faux ostrich. I have been able to find several good looking and tough faux ostrich patterns. They do cost more then the common tolex colors/patterns like from Mojo, but tweed costs more then tolex too. And you have to add a little more to have it lacquered. So.......
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I like that ostrich a lot too.
I used my daughters hair dryer and fanned my grill cloth with the speaker out for quite sometime with little results. So I pulled up the big boy pants and got out my variable Millwaukee heat gun and dialed it down. I was very carefull and found the sweet spot. The grill cloth is nice and tight now.i got all the corners installed. I had to modify to upper back corners due to the way I did the cutout for the controls.
Guess I will color this one done. I have really enjoyed this project. Thanks to everyone for all your help.
Now the question is. What will I pick up for my next up cycle amp build. Hummmm I wonder.