I've been all over the Internet looking for a good answer to lowering the voltage down after The rectifier tube. I have a 5U4GB rectifier tube in A 6l6 GC PP amplifier. 525 on The Plates , 400 on The screen and - 26 Bias. This is with the Rectifier tube in and the output tubes out. Also I have a 100 ohm 1 watt resistor going to the second can getting extremely hot. I'm guessing that it is the one lowering the pre Amp section down to 400 At the second can. My Filter Cans are 500 volts 50/50 and 32/32. A little bit more filtering than the amplifier had in it originally. 40 and 20 were in it originally. I'm going to The 50/50 first. Line is At 123 AC. My plan was to put a 10 watt 100 ohm cement resistor after the rectifier tube and before the first filter can. Also to put one in the place of the one getting hot for the pre Amp power on the second Filter can if the first resistor doesn't cool it down to a reasonable amount of heat. I would think that It should be able to stay cool especially with the two 6l6 tubes out. I also put a 1 ohm resistor on the cathodes so I can read the ma of the tubes..I wasn't sure where to put the two 5k Bias pots At. Or if I really need them or not. I have switched over the chassis with this thing and I don't have any type of wiring diagram for it. It came out of a 1960 Whirlizer Organ and without knowing what organ it came out of the wiring diagram is impossible to find. The amplifier number is pretty much useless in finding it. Whirlizer 501273 is the amplifier number for what it's worth. I've been reading about using chokes also but I don't know if I should go that way without knowing anything about the specifications. Seems much easier to use resistors first to get it under control. It seems like 100 ohms in 10 watts resistance is pretty standard for lowering down the voltage. I've Used 120 ohms Cement resistors At 5 watts before in small tube line amplifiers to get the running voltage down after the rectifier tubes. It seems to work pretty good in them. But A small line amp and this 6l6 GC seem like they are world's apart. I'm also A little concerned with the low amount of bias voltage -26 being supplied. Any help appreciated.
It is unreasonable to look at this with the output tubes not inserted. These draw most of the load current and that would pull down the high voltage appreciably. Running the amp and the cans without the output tubes considerably increrases high voltage and risks overload down the line.
Jan
Jan
^ What he said... and I in the other thread. Resistors get hot to the touch even dissipating half of their rating.
Okay I will try it with the tubes installed and see what happens. But I don't see how it will Cool down that resistor that's getting super hot.
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I am really curious about your thought process - you complain that the resistors feeding your 500V rated cans with 550V get hot, yet you persist.
EVERY book about tube basics warns about not running it without the output tubes installed because of the hazard caused by too high B+, yet you actively seek to destroy your amp.
You don't take 1 minute to put 8 ohms across the OT output yet you seem happy to let your amp die slowly?
What am I missing?? Is this diyaudio 2.0?
Jan
EVERY book about tube basics warns about not running it without the output tubes installed because of the hazard caused by too high B+, yet you actively seek to destroy your amp.
You don't take 1 minute to put 8 ohms across the OT output yet you seem happy to let your amp die slowly?
What am I missing?? Is this diyaudio 2.0?
Jan
You can pull the driver tube when checking the output conditions. This type of teching takes some experience to do in the right order. If you suspect an issue with the ''hot '' resistor then you need to do resistance checks from that point to see if there is too much load from a bad driver bypass cap or some other problem when voltage is applied. Pull the driver tube. It's not needed for output checks. What type of tube is the driver? It looks to be a combined driver/phase splitter, yes? Or is it just a phase splitter?
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To address the ''hot'' resistor issue, you'll need to confirm the value of it, then as voltage is applied to it, check the voltage drop it creates across it, and use Ohm's law to calculate the wattage it is dissipating. Then you can be assured if it's getting loaded too high by a downstream problem or whether the voltage drop is normal and the wattage rating of the resistor is too low for the application.
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Even if the circuit is conservatively designed, the resistor could still be quite hot.
Look at the data sheet for proper use.
Look at the data sheet for proper use.
For an unloaded CRC B+, that goes to 525VDC or more, and the 2nd cap is rated at 500V . . . Ouch!
The 2nd capacitor that is rated at 500V (500V for a New cap, on a Good day), and is getting 525V or more, just might be very hot,
leaking lots of current, and making the R of CRC very hot too with all that leakage current.
Run the amplifier this way for a couple of days, and see if the 2nd capacitor explodes!
The 2nd capacitor that is rated at 500V (500V for a New cap, on a Good day), and is getting 525V or more, just might be very hot,
leaking lots of current, and making the R of CRC very hot too with all that leakage current.
Run the amplifier this way for a couple of days, and see if the 2nd capacitor explodes!
Here's my series dropper resistor circuit when I changed my KT88SE to KT66SE, with a lot of help here at DiyAudio.
The clippet from my schematic shows the impact of the resistor. Although indicated as 5w min, I only had a 100w metal encased resistor, so mounted thst to the chassis. No chance of getting hot like that. The current should read 150mA, not 115mA.
Everything with my amp is over rated/engineered. My unloaded B+ is around 530v so all caps are rated at 600v and 630v in the PS.
The clippet from my schematic shows the impact of the resistor. Although indicated as 5w min, I only had a 100w metal encased resistor, so mounted thst to the chassis. No chance of getting hot like that. The current should read 150mA, not 115mA.
Everything with my amp is over rated/engineered. My unloaded B+ is around 530v so all caps are rated at 600v and 630v in the PS.
Attachments
If you can keep your finger only a few seconds on the resistor, it's 50deg C. That's not hot in power resistor land.
Jan
Jan
This is a silly test as the voltage will be at least 50v higher then under load.
As it is a tube rectifier no need to worry about unloaded voltage as the rectifier and outputs heat together at about the same rate.
If you used solid state then yes there would be an early voltage problem
Is there a schematic somewhere?? Get rid of that1 watter and put at I east a 10 watt in there. Then start trou b leshoting if still has problems. -26 sounds low to me for bias. Is that the total bias supply.
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-26V bias would be about right for 6L6 PP with Vp=330V in class A. Compare the Quad II.
and do you mean Wurlitzer?
and do you mean Wurlitzer?
I just got back to working on it and I put the output tubes in as was suggested and I only had a 4 ohm speaker for testing available but it seems to be working now. I moved the screen wires to the second part of the first can from the second can and that got it away from the 100 ohm resistor that was getting really hot and it still gets pretty hot but not as bad. I think that I hooked it up wrong and that is for the pre amp power section and not for the screen grid. Any way I Now have 414 and 411 plates and 371/375 on the screen grid's - 26 and - 26 Bias. And I put two 1 amp resistors on the cathodes to ground to check the ma's, It's reading 81 and 86 ma's on the cathodes. The Plates are not going red and they both look okay. The amplifier is pretty quiet at idle and I hear it click through the speakers when I touch the negative bias pins. Also I Now have 153 negative voltage right out or after of the diode. I was wondering if the negative bias voltage is enough ? And I was thinking about changing the old diode to a modern silicon one and adding two 5 K Bias pots. I'm not sure what is okay Bias with 6l6 GC tubes, I know that they can be pushed a little bit higher than the spec's and still be okay. I'm using A pair of matched JJ tubes from the tube store for the set up. Later on after I get it done I might buy some better vintage tubes for it. I'll see how good I can get it to sound with the JJ tubes first. I'm still waiting on parts for the Preamp section so I have to wait on that for now but I can hook up the splitter, Is 287 a good voltage for running the pre amp section? I have that right now on the first part of the second can. Thanks for All of the help.
Gary,
There is a missing part to your bias/grid circuit. In the drawing you posted in the other thread, there is a missing resistor that must go to ground somewhere between the diode and the 6L6 grids. It may be there, you just didn't draw it in. But there must be some ''grid leak'' resistance to ground for the grids to function. It may be directly connected to the grid and go to ground. With that in place you can adjust the other resistors in the circuit to give more negative bias voltage if needed.
There is a missing part to your bias/grid circuit. In the drawing you posted in the other thread, there is a missing resistor that must go to ground somewhere between the diode and the 6L6 grids. It may be there, you just didn't draw it in. But there must be some ''grid leak'' resistance to ground for the grids to function. It may be directly connected to the grid and go to ground. With that in place you can adjust the other resistors in the circuit to give more negative bias voltage if needed.
Okay there are a few more resistors on the negative Bias A 5 watt cement resistor 447 ohm right after the diode to the 50@150 E cap , and A 47K 1 watt to the 26@150 E cap. Both Backwards The E caps ground to chassis.. There are two resistors from ground in parallel a 2.2k and a 480 ohm 1/2 Watts. They connect to two more resistors one is 15k to the backwards E cap 50@50 to ground and the other 3.3k to the same place in parallel and A blue wire is There also going to the negative bias resistor's two 82k first and then two 10k to pins 5 on the 6l6 tubes. The double parallel resistors Are kind of strange to me ? I don't think that I have seen that done before on A negative Bias they come from chassis ground. And there is another E can 25@6 volts with positive to ground between the two sets of parallel resistors coming from ground. I think that is it other than that I was thinking about putting two bias pots 5k each and changing the two last 10K to 5 K to keep it the same as it was. But I don't know how I should raise the negative bias up or where to do it At ? My smallest E cap is 50 volts so I'm pretty sure that it is safe to go negative 50 or something near it . The 1 watt 15K resistor is where it drops from negative 150 volts down to negative 26 volts before going into the 50@50 E cap.
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I'm thinking about changing the 15K to 12k to raise increase the negative Bias from negative - 26 to negative -50 and adding two 5 K pot's for my Bias adjustments.