Charlie,
Yes, that makes sense. As I understand it you were referring to the voltage divider circuit comprised of the 2 resistors from B+ to ground with a tap between the two Rs.
According to what I have read on JB's Glassware's site: No delay is needed to preheat tubes prior to B+ voltage as no signal (shouldn't be any yet) is present to the input. That being said, I'm sure it won't do any harm and I was thinking of doing the same with a 555 timer or Programmable chip. ;-)
It is comforting to have experienced help with this project. Simple for some, not so for me.
Thanks,
Ron
Yes, that makes sense. As I understand it you were referring to the voltage divider circuit comprised of the 2 resistors from B+ to ground with a tap between the two Rs.
According to what I have read on JB's Glassware's site: No delay is needed to preheat tubes prior to B+ voltage as no signal (shouldn't be any yet) is present to the input. That being said, I'm sure it won't do any harm and I was thinking of doing the same with a 555 timer or Programmable chip. ;-)
It is comforting to have experienced help with this project. Simple for some, not so for me.
Thanks,
Ron
Ron,
The simplest way to allow for you to pre-heat your tubes is to use separate on-off switches. However, leaving the heaters on too long without B+ can be bad. If you can source a used or NOS Amperex 10S delay tube, they do look kind of Retro. Also, if you went with an indirectly heated rectifier, then the filaments would get 5-15 seconds of preheat prior to full B+ voltage.
I have spent this morning practising cutting dovetail joints by hand. When I build my new Aikido chassis, I want some stylish dovetail joints, rather than my usual which are made using a router and jig. I have loads of spare lumber and as it is only in the low 90's outside in the shade, it is not too uncomfortable working at my workbench.
While, I would love the re-house my Aikido as quickly as possible, I have until next May before it'll be too hot to work at my workbench, so I am forcing myself to take my time and get things right at each step of the way.
Charlie
The simplest way to allow for you to pre-heat your tubes is to use separate on-off switches. However, leaving the heaters on too long without B+ can be bad. If you can source a used or NOS Amperex 10S delay tube, they do look kind of Retro. Also, if you went with an indirectly heated rectifier, then the filaments would get 5-15 seconds of preheat prior to full B+ voltage.
I have spent this morning practising cutting dovetail joints by hand. When I build my new Aikido chassis, I want some stylish dovetail joints, rather than my usual which are made using a router and jig. I have loads of spare lumber and as it is only in the low 90's outside in the shade, it is not too uncomfortable working at my workbench.
While, I would love the re-house my Aikido as quickly as possible, I have until next May before it'll be too hot to work at my workbench, so I am forcing myself to take my time and get things right at each step of the way.
Charlie
Ron,
Sorry.....I suppose that there are two voltage dividers for my DC heaters. The important one as far as the B+ is involved is the 300K and 100K/0.1uF, the center of which sees 1/4 B+, which in my case is around 78V.
The second voltage divider for regulated DC heaters is that formed by the 47R resistors which are across the output of the regulator.
Charlie
Sorry.....I suppose that there are two voltage dividers for my DC heaters. The important one as far as the B+ is involved is the 300K and 100K/0.1uF, the center of which sees 1/4 B+, which in my case is around 78V.
The second voltage divider for regulated DC heaters is that formed by the 47R resistors which are across the output of the regulator.
Charlie
Buzz in transformer when voltage divider used
HI.
I am running a srpp with 6sn7's and i decided to apply the 47r to the heater pins.
The amp i am using is my test rig/study amp.
I rewired the srpp so that one tube does both channells on the input side and the other tube does the output for both channells.
I realise the heater supply is common for both tubes which means i cant reference one side to 1/4 b+ without affecting the other side which didnt have the heater to cathode difference in the first place. I have at this point adjusted the values of the voltage divider such that the cathode to heater voltage is 44 v for all cathode heater point in the pair od 6sn7's.
I have a 6.3V output from the transf i use the i have a bridge rectifier with rcrcrc to the heaters(both tubes are in parallel supply) I measure the voltage divider volts right back to the bridge rectifier.
It is impratical to wire up seperate heater supplys as there is no room for a seconfd transformer.
The transformer does buzz as well althought the sound doesnt seem to have suffered.
Is there a way to isolate the section of the srpp to not have a voltage divided b* at its heaters when the heaters are in parallel?
Thanks
Nick
HI.
I am running a srpp with 6sn7's and i decided to apply the 47r to the heater pins.
The amp i am using is my test rig/study amp.
I rewired the srpp so that one tube does both channells on the input side and the other tube does the output for both channells.
I realise the heater supply is common for both tubes which means i cant reference one side to 1/4 b+ without affecting the other side which didnt have the heater to cathode difference in the first place. I have at this point adjusted the values of the voltage divider such that the cathode to heater voltage is 44 v for all cathode heater point in the pair od 6sn7's.
I have a 6.3V output from the transf i use the i have a bridge rectifier with rcrcrc to the heaters(both tubes are in parallel supply) I measure the voltage divider volts right back to the bridge rectifier.
It is impratical to wire up seperate heater supplys as there is no room for a seconfd transformer.
The transformer does buzz as well althought the sound doesnt seem to have suffered.
Is there a way to isolate the section of the srpp to not have a voltage divided b* at its heaters when the heaters are in parallel?
Thanks
Nick
Sheldon,
Please could you explain why a little more current flow would be better and larger cap would be better?
I expect that the larger cap improves filtering. Also, if I decrease the resistors to increase current, will I need higher powered resistors? If I used 150K and 50K, I get a current flow of 1.6mA and power requirement of 0.36W and 0.12W per resistor, respectively. In other words, 1W resistors would be fine.
BUT why is is better to have a little more current flow?
Charlie
Please could you explain why a little more current flow would be better and larger cap would be better?
I expect that the larger cap improves filtering. Also, if I decrease the resistors to increase current, will I need higher powered resistors? If I used 150K and 50K, I get a current flow of 1.6mA and power requirement of 0.36W and 0.12W per resistor, respectively. In other words, 1W resistors would be fine.
BUT why is is better to have a little more current flow?
Charlie
Generally, you want your common references to have low AC and DC impedance. If the impedance becomes very high relative to possible current flow, the reference will move around, sometimes causing noise. The leakage current between heater and cathode might be enough to be a problem in this regard. Might not be too, but why not cover your bets? It costs little.
As for the cap, you want it large enough to get the filter corner well out of the audio range. For your 300k/100k, the impedance is about 75k. Those two are also in parallel with the resistance between cathode and heater, and any path in your regulator to common. In this case, the 0.1 may be ok, but no reason not to be generous here. Again, there is no downside in cost or sound.
I've used the resistor divider method with good results, and I've used MJ's Thingy. The Thingy was for a phono stage, but it may be overkill for your preamp.
Sheldon
As for the cap, you want it large enough to get the filter corner well out of the audio range. For your 300k/100k, the impedance is about 75k. Those two are also in parallel with the resistance between cathode and heater, and any path in your regulator to common. In this case, the 0.1 may be ok, but no reason not to be generous here. Again, there is no downside in cost or sound.
I've used the resistor divider method with good results, and I've used MJ's Thingy. The Thingy was for a phono stage, but it may be overkill for your preamp.
Sheldon
cbutterworth said:
OK, now your just trying to confuse me!
Seriously though, after thinking about this for many days and nights while drifting off to sleep, I think I am getting this.
Is the reason John Broskie did not design the heater wiring into the Circuit Board because;
1) Each valve uses a different voltage?
2) Potential noise from the heater wiring on the same board as the B+ / music?
I understand how they both are voltage dividers, so far so good. But mentioned was the R at Cathode to ground??? I'm lost here
Sheldon, wouldn't having a current flow continuiously through a choke also help stablize DC waveform?Sheldon said:
Rather than making a seperate reference voltage divider at each valve, could just ONE be made and used in a serial connection?
Is it done at each valve to reduce potential noise from heater wires?
Thanks,
Ron ................my Brain hurts............
Ron,
Sorry to confuse. Actually the purpose of the two 47R across the output of the regulator, is I think to make a "center-tap" which lies equidistant with regard to voltage between the +ve and -ve outputs of the regulator. In essence this is a voltage divider. At least this is my interpretation of things.
As for the important voltage divider, the 300K/100K and 0.1uF cap is what is recommended by Broskie. However, Sheldon (and presumably others) recommend slightly different ie. lower valued resistors. Both dividers will yield 1/4 B+, but the latter will allow a little more current-flow, which may be beneficial. Also an increase in the cap seems to be better.
I expect that Broskie did not design a heater wiring system into the board (although he did some of the work on the PCB), exactly for the reason you suggest - customization ability. Some people find that AC heaters work perfectly well in their applications, other people design and build their own regulators, or simply rectify heater AC. Some tubes also use 12V heaters, while other use 6.3V. Broskie's board allows the builder to decide what to use.
Anyway, resistors and caps for the voltage divider are cheap, so it is certainly worth experimenting with some different values. When I get chance, I will try 150K and 50K to give 1/4 B+ and add a larger cap. In fact I have a spare 0.1uF cap that I may parallel with the already installed 0.1uF cap.
However, if you read my newest posting, it seems that part of my hum problem comes from a ground loop and the first thing I need to do is to check the isolation of my jacks from the chassis in both preamp and main amp.
Charlie
Sorry to confuse. Actually the purpose of the two 47R across the output of the regulator, is I think to make a "center-tap" which lies equidistant with regard to voltage between the +ve and -ve outputs of the regulator. In essence this is a voltage divider. At least this is my interpretation of things.
As for the important voltage divider, the 300K/100K and 0.1uF cap is what is recommended by Broskie. However, Sheldon (and presumably others) recommend slightly different ie. lower valued resistors. Both dividers will yield 1/4 B+, but the latter will allow a little more current-flow, which may be beneficial. Also an increase in the cap seems to be better.
I expect that Broskie did not design a heater wiring system into the board (although he did some of the work on the PCB), exactly for the reason you suggest - customization ability. Some people find that AC heaters work perfectly well in their applications, other people design and build their own regulators, or simply rectify heater AC. Some tubes also use 12V heaters, while other use 6.3V. Broskie's board allows the builder to decide what to use.
Anyway, resistors and caps for the voltage divider are cheap, so it is certainly worth experimenting with some different values. When I get chance, I will try 150K and 50K to give 1/4 B+ and add a larger cap. In fact I have a spare 0.1uF cap that I may parallel with the already installed 0.1uF cap.
However, if you read my newest posting, it seems that part of my hum problem comes from a ground loop and the first thing I need to do is to check the isolation of my jacks from the chassis in both preamp and main amp.
Charlie
cbutterworth said:
I'm going to take back some of what I suggested. The more I think about it, the more I think that your original resistor divider values are probably fine. I've done some in that range and they work fine. But I would try a bigger cap. Forget adding a second 0.1uf cap. Parallel in at least 10uf (more won't hurt). Try it with clip leads. If that helps fine. If it does nothing, leave the original alone and look elsewhere for the problem.
Sheldon
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