Thanks nightanole for the explanation. I understand it clearly now. I didn't know the screw posts are internally connected on PCB to AC GND.
In the same picture of Pete's amp a thin white cable is running from red speaker terminals to "NFB" on PCB per each channel(all the way to the front near driver tubes). But the "GND" terminal right next to it..is not connected to anything. What does it mean?
Also how to use NFB or how to not use it. And within each scenario, what changes do I need to make with respect to speaker binding posts grounding?
I know these are incredibly stupid questions but I'm new at this and hopelessly clueless.
In the same picture of Pete's amp a thin white cable is running from red speaker terminals to "NFB" on PCB per each channel(all the way to the front near driver tubes). But the "GND" terminal right next to it..is not connected to anything. What does it mean?
Also how to use NFB or how to not use it. And within each scenario, what changes do I need to make with respect to speaker binding posts grounding?
I know these are incredibly stupid questions but I'm new at this and hopelessly clueless.
If you want global feedback, you connect as shown. If you dont want global feedback, then you jumper global feedback to ground and disconnect the little white wire from both global feedback and ground. You can even make a switch like alot of people do to turn global feedback on and off.
Its your choice if you want to use global feedback or not. The amp already has 10% local feedback going so you can run it fine with no global feedback. It kinda depends on the music and the speakers. In some cases gnfb can remove some dynamic range, in other cases it can really tighten up the sloppy bass. In petes measurements it lowered distortion by half, but also required 2x the volume input. It only cost a few bucks to install a dual pole switch for turning it on and off.
speaker binding post grounding does not change. Here is a summary;
gobal feedback= wire from fb to positive binding post.
no global feedback= wire from fb to ground next to it.
Its your choice if you want to use global feedback or not. The amp already has 10% local feedback going so you can run it fine with no global feedback. It kinda depends on the music and the speakers. In some cases gnfb can remove some dynamic range, in other cases it can really tighten up the sloppy bass. In petes measurements it lowered distortion by half, but also required 2x the volume input. It only cost a few bucks to install a dual pole switch for turning it on and off.
speaker binding post grounding does not change. Here is a summary;
gobal feedback= wire from fb to positive binding post.
no global feedback= wire from fb to ground next to it.
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Im having a moment...
Does this look right for the bias if i am not using a center tap transformer? The whole negative voltage thing is throwing me off.
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Does this look right for the bias if i am not using a center tap transformer? The whole negative voltage thing is throwing me off.
An externally hosted image should be here but it was not working when we last tested it.
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Does some one have the layout for the booster circuit for the b+? A couple of people figured out how to keep the red board at 300v and then add a booster power supply at the OT's to get above 450v.
Im doing the wood work this weekend so i need an idea of how the booster works/wired so i can fit it in the chassis.
Im doing the wood work this weekend so i need an idea of how the booster works/wired so i can fit it in the chassis.
Post #637 on page 64. If you are going to run the 6HJ5 make sure you configure the resistors R8, R9, R10, R11 like shown in post #346 on page 35. I believe these resistors are also supposed to be changed to a lower value than 1K. I believe George was running 510K.
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Thanks, im not sure about George's values since he was using stock 1k, but at 1/4 watt instead of 1/2 watt. I think now hes trying 2 watt 500ohm. he is also shooting for 125watt. Im going for 600v with 6.6k primaries, which would be around 60-75 watt.
Right now im just shooting for stock, with 6hj5's, with 3k primaries, with stock 300v power. Ill work my way up from there once i get the base version going. I have swapped around r8 etc.
Man i feel dumb, i still cant figure out where the boost goes. "connect to plate connection on output transformer", um there is 2 taps for plate on the transformer, one for each tube.
Right now im just shooting for stock, with 6hj5's, with 3k primaries, with stock 300v power. Ill work my way up from there once i get the base version going. I have swapped around r8 etc.
Man i feel dumb, i still cant figure out where the boost goes. "connect to plate connection on output transformer", um there is 2 taps for plate on the transformer, one for each tube.
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When using the 6HJ5 outputs, what is the bias current setting when using 600V on the plates and 5K OPTs?
I believe also read that the rectifier diodes should be rated for 3A. Is that correct?
Thanks.
I believe also read that the rectifier diodes should be rated for 3A. Is that correct?
Thanks.
Yes, there are 2 connections on the OPTs for the tube plates. There is also the 3rd connection on the OPT for plate B+ supply.
35ma for bias at 600v according to george with 3.3k 25ma with 300v.
diode sub is 625-UF5408-E3/73 1000 Volt 3.0A 75ns
And still on confused mode, the OT has 2 plates and a center b+. Normally this is red board 300v to b+, and the other 2 are connected directly to the plates of the output tubes. So where does the other 300 volts go? Do i disconnect the red board 300v b+ from the ot and connect the other 300v power supply?
Next question would be do we still have to Change 220k ohm schade feedback resistors(R29, 30, 31, 47) to 2-3 two watt resistors in series to handle the voltage spikes, and do we have to get rid of the 820pf capacitors C7, 9, 10, 15 or replace them with some 2kv monsters or soemthing?
diode sub is 625-UF5408-E3/73 1000 Volt 3.0A 75ns
And still on confused mode, the OT has 2 plates and a center b+. Normally this is red board 300v to b+, and the other 2 are connected directly to the plates of the output tubes. So where does the other 300 volts go? Do i disconnect the red board 300v b+ from the ot and connect the other 300v power supply?
Next question would be do we still have to Change 220k ohm schade feedback resistors(R29, 30, 31, 47) to 2-3 two watt resistors in series to handle the voltage spikes, and do we have to get rid of the 820pf capacitors C7, 9, 10, 15 or replace them with some 2kv monsters or soemthing?
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Thanks for the bias and diode info. That is correct. The boost voltage goes directly to the OPT plate B+ supply connection. There will be no connection to the RED on the red board in that case.
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Concerning the 220K feedback resistors, the part number on the parts list is a 2W device. I'm going with that and hopefully they don't explode. I also am using the 1000V 820pf caps. I guess I see if they also blow up. Hopefully not. I have not had much luck finding a 2KV device yet.
The problem is the resistors and caps are going to see 2x b+, in the boosted version thats 1.2kv. I know what the caps are rated at 1000v, but the resistors are rated at 500v.
I have some extra 594-S103M69Z5UP63K7R .01uf 2kv disc caps...
Then again this is from me filtering the thread, and those 2 items might not be of concern if we are doing the b+ boost and not raising the whole board to 450v+.
I have some extra 594-S103M69Z5UP63K7R .01uf 2kv disc caps...
Then again this is from me filtering the thread, and those 2 items might not be of concern if we are doing the b+ boost and not raising the whole board to 450v+.
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Mouser lists a non-stocked 820pF mica cap at 1.5kV. They do stock a Murata 820pF 2kV ceramic cap, but I'm not sure if they are the appropriate type for this application. Any ideas on that?
Got no idea, George said leave them out in his Jan post when he was decribing the 300v red with external boost. Then months later he says you can do bone stock other then changing grid stopper positions because 6hj5s grids are not in the stock place.
On the other hand the stock bom is 5982-19-500V820 which is a 500v part, and almost 3 bucks each. Kinda sucks that i think i just wasted 12 bucks...
The closest i cann't find anything in the 1.5kv range that doesnt cost $7-14 each. Im not sure if i should just take them out, but im not spending 60 bucks on some non audio path caps.
On the other hand the stock bom is 5982-19-500V820 which is a 500v part, and almost 3 bucks each. Kinda sucks that i think i just wasted 12 bucks...
The closest i cann't find anything in the 1.5kv range that doesnt cost $7-14 each. Im not sure if i should just take them out, but im not spending 60 bucks on some non audio path caps.
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That's funny. I thought I went by the BOM, but I guess I must have upgraded the voltage and not made a note. These are the ones I bought but they are also pricey. 598-CDV16FF821JO3F
The 2kV murata ceramic discs are only 22 cents, but not sure about the application.
Sorry for being rather scarce lately. Life has become rather complicated lately and I haven't had the time to listen to my red board amp much less work on it.
I simply soldered 4 diodes to an electrolytic cap and connected it to the power transformer. Look at the picture in post #685. The cap on the left is wired in parallel with C6 on the PC board. The cap on the right has 4 diodes connected in a bridge soldered right to it. Its negative terminal is connected to the positive terminal of the cap in parallel with C6. Its positive terminal is connected to the red wires of both OPT's. I want to try an Antek toroid for the booster transformer since I don't have room for two 10 pounders on my chassis, but I haven't had the time to do it.
Yes the diagram in post #637 is correct, except for the name of the connection. What Nic calls the "plate connection" should be called the OPT B+ connection. On my OPT's (and many others) it is the red wire.
The Schade resistors are going to see lots of voltage. In theory they should be rated for 1.2 KV. It might be a good idea to use two 110K resistors in series. My board still has the stock part number resistors in it, but I can change them if they fry.
Ditch the 820 pF capacitors. I guess that I wasn't clear on these. Pete added them to compensate the board for OPT ringing. At best the value would need to be changed to work with the OPT that you use. A builder of a similar amp in another thread has shown that the 600 volt silver mica caps explode at voltage levels lower than used here.
I put 1K 1/4 watt resistors in my first board and they fried. 1/2 watt parts might work, but I have blown 1/2 parts in an SSE board when the amp hits clipping a lot, so I tend to use 1 or 2 watt parts. I also tend toward lower values for screen resistors based on my experiments on other amps. It has been stated that the 6HJ5 will produce lower distortion with a lower value resistor. I have two working boards. One uses 100 ohm 2 watt resistors and the other uses 510 ohm 1 watt reisitors. I don't see a difference.
I carefully tweaked my latest board with a distortion analyzer. I want the lowest current that doesn't cause the distortion to increase at low power levels (less than 1 watt). My cheap OPT's seem to favor a slight imbalance since they are not interleaved or symmetrically wound. I wound up with 30 mA in one tube and 32 in the other. Both channels liked this current. If you lack distortion measuring equipment just set the current to 32 mA or so. 32 mA at 600 volts results in an idle dissipation of just over 18 watts per tube. I don't want to run them hotter if it isn't needed. If you are running 300 volts of B+ you can run 50 mA or more, but I found no audible benefit to running over 35 mA.
When I had the board connected up to my big power supply I saw the current meter bouncing over 1 amp when the power was turned up all the way. This should not be a problem with music since the average current will be lower, but 3 amp diodes are cheap, so I used them.
I simply soldered 4 diodes to an electrolytic cap and connected it to the power transformer. Look at the picture in post #685. The cap on the left is wired in parallel with C6 on the PC board. The cap on the right has 4 diodes connected in a bridge soldered right to it. Its negative terminal is connected to the positive terminal of the cap in parallel with C6. Its positive terminal is connected to the red wires of both OPT's. I want to try an Antek toroid for the booster transformer since I don't have room for two 10 pounders on my chassis, but I haven't had the time to do it.
Yes the diagram in post #637 is correct, except for the name of the connection. What Nic calls the "plate connection" should be called the OPT B+ connection. On my OPT's (and many others) it is the red wire.
The Schade resistors are going to see lots of voltage. In theory they should be rated for 1.2 KV. It might be a good idea to use two 110K resistors in series. My board still has the stock part number resistors in it, but I can change them if they fry.
Ditch the 820 pF capacitors. I guess that I wasn't clear on these. Pete added them to compensate the board for OPT ringing. At best the value would need to be changed to work with the OPT that you use. A builder of a similar amp in another thread has shown that the 600 volt silver mica caps explode at voltage levels lower than used here.
I put 1K 1/4 watt resistors in my first board and they fried. 1/2 watt parts might work, but I have blown 1/2 parts in an SSE board when the amp hits clipping a lot, so I tend to use 1 or 2 watt parts. I also tend toward lower values for screen resistors based on my experiments on other amps. It has been stated that the 6HJ5 will produce lower distortion with a lower value resistor. I have two working boards. One uses 100 ohm 2 watt resistors and the other uses 510 ohm 1 watt reisitors. I don't see a difference.
I carefully tweaked my latest board with a distortion analyzer. I want the lowest current that doesn't cause the distortion to increase at low power levels (less than 1 watt). My cheap OPT's seem to favor a slight imbalance since they are not interleaved or symmetrically wound. I wound up with 30 mA in one tube and 32 in the other. Both channels liked this current. If you lack distortion measuring equipment just set the current to 32 mA or so. 32 mA at 600 volts results in an idle dissipation of just over 18 watts per tube. I don't want to run them hotter if it isn't needed. If you are running 300 volts of B+ you can run 50 mA or more, but I found no audible benefit to running over 35 mA.
When I had the board connected up to my big power supply I saw the current meter bouncing over 1 amp when the power was turned up all the way. This should not be a problem with music since the average current will be lower, but 3 amp diodes are cheap, so I used them.
Russ, where do you get the voltage rating for the resistors. The spec sheet and Mouser both show 750 volts. Eeither way that's what's in my board and they haven't fried yet.