What might be my final 5f6a Bassman question.

[Mike_J]

I have attached a section of Doug's layout showing the spaces on his board for the entry for the bias cap and a connection to the 100 ohm balancing resistors for the heater supply. I saw a picture of the inside of an original '59 Bassman chassis and it had the green heater wires tightly coming out of the PT twisted together with the bias wire loosely wrapped around the twisted heater wires. They then traveled towards the lamp holder and the bias wire was dropped off at the silicon rectifier and the heater wires went to the lamp holder. There were four holes in the lamp holder, two for each wire. One of the holes on each side got used for the incoming heater wires from the PT. The other hole in the lamp holder was for a twisted pair of wires going to the heater connections on pins two and seven of the V5 tube socket (the heater connections for the power tubes the amp used.) The then were daisy chained all the say to V1. That is the normal way.


The picture below shows how I would like to wire my heater supply. I would tightly wrap the heater wires with the bias wire loosely wrapped around it going under the board and come up where the pink dots are on the picture. From there I would branch off from the heater supply in two directions. One to the lamp holder and the other to pins two and seven of V5. The reason for this question is the old to the lamp holder and to V5 puts everything in series. The way I propose it I don't know what you would call it. Just want some confirmation based on experience that my method won't  create a voltage problem to either the lamp or the heaters. My proposed method would be much cleaner and it would allow the DC wire going from pin 8 of the rectifier tube to the standby switch to be lifted above the AC wires. Don't know how important that is but it seems like it might be a good idea to me. Also I am pretty sure I can make it look better as well.

[HotBluePlates]

... The picture below shows how I would like to wire my heater supply. I would tightly wrap the heater wires ... going under the board and come up where the pink dots are ...

You will make your build very much easier if you don't insist on routing wires under the board.  Neat Appearance needs Short Wires, but Short Wires makes for Harder Assembly.

If it's too much trouble, move the 100Ω resistors off the board to somewhere else along the heater circuit.  I've mounted them at the Input tube before.  Nothing says they have to be at the pilot light end of the heater circuit.

[sluckey]

I would connect the PT wires DIRECTLY to the closest 6L6 socket. Then run itty-bitty 24AWG neatly to the board and on to the lamp.

[Mike_J]

... The picture below shows how I would like to wire my heater supply. I would tightly wrap the heater wires ... going under the board and come up where the pink dots are ...

You will make your build very much easier if you don't insist on routing wires under the board.  Neat Appearance needs Short Wires, but Short Wires makes for Harder Assembly.

Definitely harder reassembly. Haven't counted yet but there must be at least ten wires I will need to remember to push through holes in the board. Tried to leave a lot of wire length to install the wires but I need to make sure to wire everything properly because this board is not coming out again with out a lot of pain getting it back in no matter how I treat the heater wires. They would be just one more thing to deal with if the board needs to come out. Would have to wire some 20awg wire to the end of the wires to get them back in but as long as the holes are large enough it shouldn't be a problem. It will just be a huge pain if I have to deal with reassembling the whole amp. Any wire will go in if the hole is large enough.


My largest concern continues to be will I get 6.3VAC going in both directions if I send the heater wires from the PT to the center of the tubes and lamp. Not a question I shouldn't have learned in more than 20 years of building amps but I don't remember doing anything like this in the past and like we both said before this is not something we want to do twice. Of course I spend half my time deciding I need something, walking in the room where what I needed is and wondering why I am the room. Happens all day long. Usually figure it out in a few seconds but age does take its toll but I refuse to give up.


Take this amp for example. I want a growler not an amp that purrs. Amp before was in between and sounded like my Bassman LTD reissue amp not the amp I saw in a video. The video amp sounded just like an amp I built that I didn't check the bias on before I started playing it. Was so impressed with the sound that I didn't realize the power tubes were smoking. Well they may have cut off the video before that original Bassman started smoking but it sure was a growler.


Thanks
Mike

[Mike_J]

I would connect the PT wires DIRECTLY to the closest 6L6 socket. Then run itty-bitty 24AWG neatly to the board and on to the lamp.

That may be a good solution. Will have to ponder it. That would give me three sets of wires at the V5 socket though. The very thick wires coming from the transformer, the 20awg to the rest of the tubes and then the 24awg wires to the board and on to the lamp. Not sure there is enough room inside the center of the tube socket for all that wire. However, it is essentially the same thing electrically as what I was thinking except that the wires would branch out at the power tube socket instead of on the board.


Thanks
Mike

[HotBluePlates]

... will I get 6.3VAC going in both directions if I send the heater wires from the PT to ...

It's not plumbing that needs to slope so many inches per foot.  If you stick a hand in a live chassis, the volts will find a way to flow uphill & bite you!

The 6.3v flows from one one heater wire to the other heater wire, through the heaters & pilot light.  In the amp you're building, all those heaters are in parallel.

So you could run the wires from PT to the input tube, back over to the pilot light, down to the phase inverter, over to the furthest 6L6, back to the middle-12AX7, etc.  The tubes & pilot light won't know the difference, but you sure will when you try to work around the rat's nest to swap a capacitor.

[glass54]

+1 with Sluckey and HotBluePlates
That's exactly what I did as I don't like lengthy Heater wiring.
Remember V=IR and I like to achieve 6.3Vrms at my Output tube Heater terminals 
Also try to avoid excessive AC wiring floating about in the chassis.
Kind regards
Mirek

[Mike_J]

+1 with Sluckey and HotBluePlates
That's exactly what I did as I don't like lengthy Heater wiring.
Remember V=IR and I like to achieve 6.3Vrms at my Output tube Heater terminals 
Also try to avoid excessive AC wiring floating about in the chassis.
Kind regards
Mirek

Those are some healthy sized heater wires you are using. I am starting to lean towards the old Fender method of running the PT heater wires  to the lamp and then across to the power tube heater pins. Nothing new there. Will probably insert the 100 ohm resistors at the lamp tying into a two lug terminal strip that isolates the ground which I will send to the solder lug attached to the PT bolt. Gets rid of a possible ground problem. Probably will use the two columns on the board that were going to be used for the 100 ohm resistors to install circuitry that will allow for elevation of the heater supply and maybe the addition of a humdinger pot. Can cut those off the end of the board if they prove to be unnecessary.

[glass54]

You're right Mike (healthy wire sizes) 
But I had some short lengths of the Black and Green in my "wire box"
Note I resorted to a more conventional size on the rest of 12a-7.
I also had an compact LED Bezel so I generated an alternative power supply for that.
Kind regards
Mirek

[Mike_J]

Thank you for the replies but I had a humdinger of an idea which I will share with you below for you assessment of its ability to do its job. Have an F&T 47uF @ 500VDC cap that would be perfect for the job but it is a little too large. I am thinking the ideal situation would be to install the humdinger pot between the power tube and rectifier tube sockets with hopefully a small enough cap to fit underneath the pot. Would connect the cap to the wiper of the humdinger pot and the negative end to the ground lug on the power transformer bolt.


Have included a picture of the place I would like to put the ecap between the power tube and rectifier tube sockets. I can cut out some of the G10 in the corner to make room for it if the cap is small enough.

[Mike_J]

The other choice is to use the turrets that are already there for the anchor points for the ecap. Have to connect the wiper and positive end of the ecap to the junction of the resistors anyway. Could run the positive end of the ecap to the turret on the end that is already there and the negative end of the cap to turret next to it. Use that double sided foam tape to help hold the ecap in place. Would need to connect the positive end turret mechanically to the junction of the two resistors, straight shot. Run the negative side to the other side of the 22K/2W resistor and it would be a neat job. Would have a short run from the PT to the humdinger pot and to the power tubes. Would need to buy some 24awg stranded to run the wires to the lamp. Right now I have 20awg stranded but will use 18awg for the power tubes if I can fit all that wire in the humdinger holes. Think I could run the 24awg to the lamp flush to the chassis most of the way. Would cross the bias supply wire at a 90 degree angle on the way to the lamp but I don't see that as any big deal.

[Mike_J]

Another idea. Couldn't I purchase a radial lead electrolytic capacitor and connect it on the board? Aren't they smaller than axial capacitors generally? Need a 47uF @ 500VDC ecap. Need to do some research here.

[sluckey]

Another idea. Couldn't I purchase a radial lead electrolytic capacitor and connect it on the board? Aren't they smaller than axial capacitors generally? Need a 47uF @ 500VDC ecap. Need to do some research here.

You don't need a 500V cap. 100V rating will be plenty.

[Mike_J]

Another idea. Couldn't I purchase a radial lead electrolytic capacitor and connect it on the board? Aren't they smaller than axial capacitors generally? Need a 47uF @ 500VDC ecap. Need to do some research here.

You don't need a 500V cap. 100V rating will be plenty.

Does the 195K/2W resistor knock down the voltage from the standby switch that much? This is great information sluckey. Thank you.

[sluckey]

Not by itself, but when combined with the 22K it forms a voltage divider. Do the math.

[Mike_J]

Not by itself, but when combined with the 22K it forms a voltage divider. Do the math.

Regretfully, I don't know the math. I am a retired certified public accountant. The formula you are using was unfortunately not on any of the tests I took in school and for reasons unknown to me I haven't learned it since. Help with the formula would be greatly appreciated. I could probably take it from there.


Kemet has a 47uF @ 100VDC 105C 10K hour radial cap for $.47. Anyone hate Kemet radials for any reason? Also, I am at 47uF right now. Can I increase the uF rating and can you see any reason for doing so? Is this cap limited by the first cap rule for the rectifier tube which is a GZ34 in this case. I believe the maximum for that tube is 50uF.

[sluckey]

The formula is Ohm's Law, E = IR

Why not spend some money with Doug?

[Mike_J]

The formula is Ohm's Law, E = IR

Why not spend some money with Doug?

Thank you for the formula. I have heard of ohms law. The only time I ever used it was when someone was trying to sell me a generator for my home. It would purportedly power the entire house in the event we lost power during a hurricane. Using ohms law it was obvious it wouldn't even provide the amperage necessary to start the A/C compressor during the surge at start up let alone anything else. My wife chased him away because she could see I was about to beat him to a bloody pulp. You have to be very careful here in south Florida. Some very crooked contractors out there.


As for Doug. I very much appreciate his store. Got my last order from him last week. Of course I forgot many things I wish I had ordered. Will be making another order soon. In the case of a 47uF radial lead capacitor, Doug for common sense reasons doesn't carry them. If I want to buy them then I need to go where they are. Additionally, you yourself told me a number of years ago I needed a five watt 250r pot for my humdinger. For common sense reasons Doug does not supply five watt 250r pots. Have to go where the parts are. Used to get a lot of my parts from CE. Have noticed Doug is very competitive with them and often beats their price. Made an order for F&T 22uF @ 500VDC ecaps and other parts from Doug about a month ago. Doug's prices on F&T ecaps were lower than CEs which is supposedly a wholesale business. We are very fortunate to have Doug's store and his forum. I will try to purchase as much as I can from him but he for very common sense reasons can not stock every part you might want for a build. Especially when going off plan like I very often do. I can't help it. You are the one that was trying to get me to stick three pairs of wires in a tube socket that only has two holes per pin. Had to find an alternative that would meet the requirements and I think the humdinger pot would be a better place to install three pairs of wires and it never hurts to have one and have your AC riding on top of DC at least from my experience. Plus I have a spot on my board for the circuitry.


If the 47uF @ 100VDC is the way to go the radial ecap I mentioned is about 3/8" wide by 1/2" high. The leads are about 3/16" apart whereas Doug's spacing is closer to 5/16". Haven't decided if I should put the turrets any closer together but that is no problem because I bought turrets and the tools needed to install them in a board from Doug.


I appreciate your help sluckey. It like Doug, his store and his forum are invaluable to my ability to still build amps. Without all of that, a hobby that makes me happy probably wouldn't be available to me.


Thanks
Mike

[Mike_J]

Not by itself, but when combined with the 22K it forms a voltage divider. Do the math.

Sorry, I still don't get it. If we start out with 432VDC, which I believe is in the ballpark and we apply a 195K resistor to it we get an amperage of .022A and wattage of .96, if my calculations are correct. If we add both resistors together in series we get 217K of resistance with the same 432VDC or .02A and wattage of .86. Which doesn't tell me a thing because we are pulling voltage from the junction of the two resistors and what I am interest in is voltage at the juncture of the two resistors. Think I remember using a pot to dial in one of the resistor values to arrive at 75VDC but there was very little scientific in it. Pretty sure I started with a 22K resistor as the second one and grabbed a 250K pot and turned it until I arrived at 75VDC at the juncture of the two resistors. Meant the first resistor needed to be 195K. Think I found a resistor I had that was close to that value and went with it. Didn't understand how it worked but made it work and it did. Please help, I am confused.

[Mike_J]

Just thought of a solution to my pot backorder problem. Have to find the amp with the humdinger pot in it. Turn it on and make sure there is no hum. If there is turn the humdinger pot until the hum goes away. Then carefully disconnect the wires and measure from the wiper to each side of the pot. Get precision resistors to replace the pot. Problem solved.

[Mike_J]

For that matter why do I need a humdinger pot? Can't I just use it to find the setting that reduces the hum the most? Then measure the resistance from each end of the pot to the wiper? Buy precision resistors to equal the resistance on each side? If it is 125r/125r then I could use 100r/100r precision resistors I already have I would think? Can't remember why it was important to use the humdinger pot. May have had to do with how the PT was made related to heater wiring?

[ckilgore]

I am with sluckey.  The hum produced by the heater wires is in direct proportion to the current they are carrying. Wire directly to the highest current draw that has the least gain to minimize hum.  That would be the output tubes.  From there I split to the pilot lamp one direction while the other path goes to the PI on down the line ending up with the least current in the wires feeding the most sensitive stage, the input tube.

[Mike_J]

I am with sluckey.  The hum produced by the heater wires is in direct proportion to the current they are carrying. Wire directly to the highest current draw that has the least gain to minimize hum.  That would be the output tubes.  From there I split to the pilot lamp one direction while the other path goes to the PI on down the line ending up with the least current in the wires feeding the most sensitive stage, the input tube.

Don't disagree with a word you said. It is also in direct proportion to how close the voltage is on each leg of the heater wires and a plethora of other factors such as wiring technique.


Thanks
Mike

[sluckey]

Just use the 100Ω resistors on Hoffman's board and quit trying to improve Doug's work. Ain't gonna happen.

[sluckey]

Not by itself, but when combined with the 22K it forms a voltage divider. Do the math.

Sorry, I still don't get it. If we start out with 432VDC, which I believe is in the ballpark and we apply a 195K resistor to it we get an amperage of .022A and wattage of .96, if my calculations are correct. If we add both resistors together in series we get 217K of resistance with the same 432VDC or .02A and wattage of .86. Which doesn't tell me a thing because we are pulling voltage from the junction of the two resistors and what I am interest in is voltage at the juncture of the two resistors. Think I remember using a pot to dial in one of the resistor values to arrive at 75VDC but there was very little scientific in it. Pretty sure I started with a 22K resistor as the second one and grabbed a 250K pot and turned it until I arrived at 75VDC at the juncture of the two resistors. Meant the first resistor needed to be 195K. Think I found a resistor I had that was close to that value and went with it. Didn't understand how it worked but made it work and it did. Please help, I am confused.

Your math procedure is boogered up. If you apply 432V to the circuit you posted you will have 43.8V on the wiper of the pot.

[Mike_J]

Apparently I discussed a lot of these things when I constructed my last AB763 amp. Also read up on why there is a need to use a humdinger pot. Appears it is because the voltages coming out of each leg of the two green heater wires is not the same. A manufactures defect so to speak. At one time and I am sure I still do I had an AC wire with alligator clips on the black and white wires. Could use it to test transformers. I should probably giving thought to measuring each heater wire on the PT in this amp. If the voltages are the same then two precision 100 ohm resistors would work perfectly and there would be no need for a humdinger pot at least while using this PT. As far as having the AC riding on DC, it was discussed in detail during the AB763 build.


Excellent comments were provided by Willabe. Among them were change the 22K resistor to a 100K to save a few mA from bleeding off to ground which it doesn't look like I did since the layout and schematic documents I have related to the power section all reflect the 22K resistor. Then solve for the other resistor to get the desired voltage which Willabe and other people seem to think is around 75VDC. He also suggested not taking the voltage from the standby switch because it is dirty which I apparently did because I have a schematic that reflects that change to before the PI circuitry. This also solved the concern I brought up today about putting too much uF on the GZ34 rectifier tube because the voltage was drawn after the choke and the filter cap feeding the screen resistors. After that filter cap and before the screen resistors would seem to be a logical place to take the voltage from. I have a lot of unused room on the board in that area so the circuitry could be inserted there. Whether I ever connect it is another matter but at least it will be there if I decide it is needed. Another thing he mentioned is I didn't need a 450VDC filter cap as sluckey mentioned today. He mentioned he used 180VDC because they were accessible to him although a 100VDC cap was sufficient same as sluckey.


PRR mentioned that it was a good idea to ground the HT CT to he ground side of the which I am confident I did. However for this amp I did not run a separate ground wire for the B+. The B+, screen and PI ecap grounds where run together to one place on the board on a single wire.


Attached the schematic for the way I wired the DC to the heaters on the AB763 build in case anyone might be interested.

[Mike_J]

Not by itself, but when combined with the 22K it forms a voltage divider. Do the math.

Your math procedure is boogered up. If you apply 432V to the circuit you posted you will have 43.8V on the wiper of the pot.

Since I know the answer now it will help. Will also allow me to replace the 22K with a 100K as Willabe suggested and will be able to figure out what the other resistor will be without having to use a potentiometer. Must not have been shooting for 75VDC. Amazed at how much I forgot in the past five years.


Thanks
Mike

[Mike_J]

Just use the 100Ω resistors on Hoffman's board and quit trying to improve Doug's work. Ain't gonna happen.

I have already built an okay '59 Bassman. If I can't make it the way I want it then it can go to the dump as far as I am concerned. Plus my nutty efforts sell more parts so it benefits Doug's store. I am not interested in creating an okay amp.

[Mike_J]

Answer for R1 given R2=100K Vin=432VDC and Vout is 75VDC is 476K if I learned anything today.

[Mike_J]

Wanted to do a little forensics on why sluckey got 43.8VDC as voltage out. One of the reasons for the problem is I used 432VDC at the standby switch which would be accurate if I was using a Bassman transformer and a 5ar4/GZ34 rectifier tube. My memory being what it is I did not recall that the design I gave for elevating the heater supply to DC voltage was instead for the AB763 build. The transformer for the AB763 had high taps of 300-0-300 and 330-0-330 versus the Bassman's 325-0-325, all AC. The Bassman uses a GZ34 that drops around 10VDC while the AB763 used in its final configuration a 5U4-GB which drops around 50VDC. Additionally, after consultation with others on the forum five years ago it was decided that a better entry point for the elevation circuitry would be after the voltage went through a choke and 1K dropping resistor.


For purposes of not making a career out of this exercise I am going to say I had 250VDC at Vin, R1 and R2 are still 195K and 22K, respectively. Using my newfound ability to figure out what the Vout is in the AB763 DC supply to the wiper of the humdinger pot. Calculated it as 25.3VDC certainly not a number I was shooting for.


A person might ask how could that have happened? Let me start with what is known. First I started out using the 330-0-330 voltage taps with a GZ34. Would bet the farm I was shooting for Vout of 50K and used the pot method discussed in an earlier post to get there. Had originally planned on using the voltage from the standby switch which I seem to recall was 454VDC. Was later talked out of it because it was dirty power and moved it to where it is now which as I said I would estimate at about 250VDC. However, knowing very little about electronics at the time I did not even think about recalculating Vout. Thus the low voltages slucky posted which used Bassman transformer numbers for Vin. It ended up being even worse than sluckey thought it was.


You have no idea how happy I am. Didn't know a lot five years ago and still don't now. Haven't lost much at all.


When I get back into the AB763 build I will change R2 to 100K, get an accurate number for Vin and calculate the number for R1 that will give me 75K at Vout. Then change R1 and R2 to what they should be.


For those of you that were as confused as I was until sluckey forced me to get unconfused I will share the formulas I learned.


Vin is what it is. The voltage you are tapping off the power rail.
R2 should be 100K according to Willabe who I trust. Always gave me good information.
R1 needs to be calculated.
Vout should be 75VDC according to a lot of people. Others say 40 to 50VDC is good. Pick your number.


Formulas you need to know:
  i = Vin/R1+R2
  Vout = i X R2


Now all you need to do is solve for R1 given all of the other knowns. Nothing to it. If I messed something up please let me know but I don't think so.


Thanks
Mike

[Mike_J]

Just use the 100Ω resistors on Hoffman's board and quit trying to improve Doug's work. Ain't gonna happen.

Would you please look at my math on reply 29. Don't want to mislead anyone. Also, not sure how you figured out what voltage I would need for the ecap. Also, not sure how to calculate how much voltage one resistor, say a plate load resistor would drop. Any help with those formulas would be greatly appreciated. I always look at things as we need to leave information to generations that follow us. One things my experiences have taught me maybe more than anything is we aren't going to be here forever and whatever knowledge we have needs to be imparted to them. This country could become third world real quick otherwise. So many great American companies have already left for more regulatory and tax friendly locals. If a lot of the younger people don't learn from the older people they and the country are doomed. I am sure my grandfather said the same thing but it was true then as it is now.


Thanks
Mike

[Mike_J]

Thought I would show you my solution to the heater wire 100 ohm resistor issue. Sluckey had a good idea when he suggested going to the power tube sockets and branching out from there as supported by many others. See that I needed a place to put three pairs of wires and my tube sockets only have room for two smallish wires. I use 18awg wire on my power tube sockets. Always have and always will for no other reason than long ago I read somewhere that is how it should be done, 18awg to the tube sockets and 20awg everywhere else.


Needed to come up with an alternative way of making the connection between the three sets of wires. Settled on using a three lug, zero common vertical terminal strip. Nipped one side of the lugs off because they weren't needed and could only be trouble, enlarged the hole for attaching the terminal strip and attached it to the same PT bolt the grounds from the board and OT jack are attached to. Found some 100 ohm .1 precision resistors that matched the same and attached them to the terminal strip as well. Then used my grinder with the diamond blade to nip the last two columns of turrets off the board. The board was too long anyway. Couldn't see the ground tabs connected to the PT bolt it was so long. With the terminal strip attached this way the grounded side of the 100 ohm resistors is only about an inch long. Picture of this is shown below.


Problem I have is sluckey suggested 24awg wires to the lamp and the smallest I have is 20awg which you will see in the picture below. The 20awg will certainly be do the job and I am not in the mood for shopping for Teflon coated 24awg wire right now. However, could use ideas for the best method of isolating the wires going to the lamp and making them look neat.


Use a lot of the white things with the holes in them as you can see, augmented at times with the white cable ties. All the heater wires running from socket to socket are held in place by them as you may notice in another picture below.

[Mike_J]

See by looking at one of the pictures the set of wires going to V5 (power tube socket nearest to the rectifier tube socket) is too long and needs to be shorter or it might interfere with the filtered screen supply or the OT wires to pin three. Easy fix now.


That's better.