If you are referring to the cap at the plate of the output tube, it sees the 300 volt B+ AND the AC signal voltage. THis can easilly go to twice the B+ voltage under normal conditions. When the big dumb blonde one plugs his guitar preamp into a HiFi amp like the big red board and cranks it to 11 the spikes can go to 1KV. Mere 500 volt caps will EXPLODE. I just left them out of my red board, since my B+ goes to 650 volts.
Compactron for the elves
Still working on #2 amp. The breadboarding revealed the 10lb transformer has hum with the 6lb6 tubes, not the 6jm6's. Heater current seams to be the issue. I have a couple 4 amp 6.3 volt transformers on order to sneak in to help out. With the output tubes close together, I'l use the 6JM6's for 40w/channel. The mod to the board for the next amp has increased the spacing, but the PCB artwork still just fits in a 8.5x11" sheet of paper for the toner transfer method. The idea is to increase the spacing and use 1650P iron for 60 watts a channel with the 6lb6 tubes, probably need the extra heater transformers if I use the 10lb'r.
I find the aluminum sheeting to be very gummy to work with, is there a special alloy to look for that is a little more brittle, that will machine without forming the large burrs that need to be trimmed??? I still need to open up the trimmer holes a little and file some of the openings. The wood work will be a copy of the last one but with a smaller amp meter. The 2" meter just cleared the PCB, so this time I'l use a 1.75" meter. I found a pic of a McIntosh MC5000 500watt amp with 8 sweep tubes grouped next to each other with fan cooling.
This is proof that time travel is possible and engineers from the past have come to steal our innovative designs for their benefit.
Still working on #2 amp. The breadboarding revealed the 10lb transformer has hum with the 6lb6 tubes, not the 6jm6's. Heater current seams to be the issue. I have a couple 4 amp 6.3 volt transformers on order to sneak in to help out. With the output tubes close together, I'l use the 6JM6's for 40w/channel. The mod to the board for the next amp has increased the spacing, but the PCB artwork still just fits in a 8.5x11" sheet of paper for the toner transfer method. The idea is to increase the spacing and use 1650P iron for 60 watts a channel with the 6lb6 tubes, probably need the extra heater transformers if I use the 10lb'r.
I find the aluminum sheeting to be very gummy to work with, is there a special alloy to look for that is a little more brittle, that will machine without forming the large burrs that need to be trimmed??? I still need to open up the trimmer holes a little and file some of the openings. The wood work will be a copy of the last one but with a smaller amp meter. The 2" meter just cleared the PCB, so this time I'l use a 1.75" meter. I found a pic of a McIntosh MC5000 500watt amp with 8 sweep tubes grouped next to each other with fan cooling.
This is proof that time travel is possible and engineers from the past have come to steal our innovative designs for their benefit.
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I currently have my red board running with 6JH5's which eat as much heater current as 6LB6's. I am using 2 10 pounders. One is running the board by itself using only the green wires for heater power. It does not hum or get warm. Raw B+ is about 300 volts. The second transformer is wired to produce a second 300 volt supply which is wired in series with the first to provide 600 volts for the plates of the output tubes. Only the red wires are used. I get 75 WPC with the OPT's wired for 6.6K ohms and 125 WPC with them wired for 3.3K.
Transformer buzz is usually caused by the current drawn in short pulses when feeding rectifiers with a cap input filter. Heater windings draw a steady constant current and shouldn't cause buzz, but may be enough to push your particular transformer over the edge.
Transformer buzz is usually caused by the current drawn in short pulses when feeding rectifiers with a cap input filter. Heater windings draw a steady constant current and shouldn't cause buzz, but may be enough to push your particular transformer over the edge.
I tried to use the orange 6.3 volt windings for the input stage, but that just make it worse ( after thought;did not do the resister center bias to ground trick), I'm using the yellow 6.3 with the blue 55 volt winding to boost the neg bais voltage, had a problem pinching off the current in the 6LB6's to 40ma. With the 6JM6's the 10lbr is just warm after several hrs of fun, with the 6LB6 biased at 50ma, its hot, fails the 5 sec hand test. With the bias backed off to 40ma, it still will get too hot in time for the hand test.
I tried in the power supply to do without the inducter, just a resister, in the first amp but had low level hum. the inducter made the standard pie filter and quiet as a church mouse a duh moment but I was going for a $imple de$ign. This one has the inductor for the pie filter, starts off quiet but the low level hum starts after she's warmed up and is at full bias. For prototyping the board, this is the same transformer that I used for the first amp so it is a direct comparisom. I tried to increase the first filter cap, 47u with an aditional 560u no difference. I'm trying to solve the issue before the next PCB with increased output tube spacing for the 6LB6's in case I need to mod the PCB as part of the solution. Another thought was to go to DC bias on the inputs and just run the outputs on AC, I'l play after the iron arrives.
It could still be as simple and going to shielded input wires instead of twisted pairs, might be picking up radiated noise from the power supply when she gets under a full load and starts to grunt. With the 6JM6's this board and 10lb'r are fine as is, quiet as a church mouse...... until you turn it up!
ps: question.... what B+ is necessary to get the "blue plasma glow" the honest way...
I tried in the power supply to do without the inducter, just a resister, in the first amp but had low level hum. the inducter made the standard pie filter and quiet as a church mouse a duh moment but I was going for a $imple de$ign. This one has the inductor for the pie filter, starts off quiet but the low level hum starts after she's warmed up and is at full bias. For prototyping the board, this is the same transformer that I used for the first amp so it is a direct comparisom. I tried to increase the first filter cap, 47u with an aditional 560u no difference. I'm trying to solve the issue before the next PCB with increased output tube spacing for the 6LB6's in case I need to mod the PCB as part of the solution. Another thought was to go to DC bias on the inputs and just run the outputs on AC, I'l play after the iron arrives.
It could still be as simple and going to shielded input wires instead of twisted pairs, might be picking up radiated noise from the power supply when she gets under a full load and starts to grunt. With the 6JM6's this board and 10lb'r are fine as is, quiet as a church mouse...... until you turn it up!
ps: question.... what B+ is necessary to get the "blue plasma glow" the honest way...
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Just started the wood work and did a dry fit. I didn't like to do wood working when its too cold out, might make a mistake and take 2 hands to order 5 beers.
Iron closer together that I like. I have room under the output iron for 6.3 volt 4amp for the heaters when I go with the 6LB6's in the next amp. One will light a set of outputs and input tube at 6.4 volts AC.
I don't need them for the 6JM6's or 6GV5's that I'l use for this amp. Plan to use the nixie tube trick to display which tube the amp meter is monitoring, using a 1.75" dia meter for more clearance to the PCB.
Iron closer together that I like. I have room under the output iron for 6.3 volt 4amp for the heaters when I go with the 6LB6's in the next amp. One will light a set of outputs and input tube at 6.4 volts AC.
I don't need them for the 6JM6's or 6GV5's that I'l use for this amp. Plan to use the nixie tube trick to display which tube the amp meter is monitoring, using a 1.75" dia meter for more clearance to the PCB.
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True Compact Compactron Completed
Back from China, and days are still nights an nights are still days. Finished the wood work, 8 coats of tung oil and I gave up. Polished the top plate and started to put her together. Advantage of not being able to sleep at night...
The 10lb'r can handle the 6JM6/6GV5's without a problem but the heater current for the 6LR6/6LB6's causes a little low level hum. ( hooked up as 300v B+) Hammond 166N6 are 4-Amp heater transformers that are quite small and can be added if necessary. Also to get the -V bias for the larger tubes, I had to tie an extra 6.3 winding (orange) into the bias to get ~-70 volts to pinch them off to around 40ma. One of the 6LR6 wanted a little more..
All I need are the 6GV5's for the audio level for the room and speakers... I also tried the 6AC10 for the front end and they are also a good replacement for the 6U10. The Hammond output iron was a step up from the original Compactron Amp that was the stocking stuffer that used the 25watt 8k-8, more detail at a higher power level, expecially more authority on the bottom end. The 2 pics are almost the same, but I rotated the meter select switch for a different tube, as seen in the nixe tube....
For those of you that want the pure bliss of triode power and don't want to do your own amp from paper design and up, consider Pete's big red board, it would be a lot easier that doing what I did..... and you will love the clarity and sound stage.!!!
Other upgrades would be voltage doubler for a 580V B+, use the 6LB6/6LR6 output tubes and larger output iron.... just food for thought, hummmm......
Back from China, and days are still nights an nights are still days. Finished the wood work, 8 coats of tung oil and I gave up. Polished the top plate and started to put her together. Advantage of not being able to sleep at night...
The 10lb'r can handle the 6JM6/6GV5's without a problem but the heater current for the 6LR6/6LB6's causes a little low level hum. ( hooked up as 300v B+) Hammond 166N6 are 4-Amp heater transformers that are quite small and can be added if necessary. Also to get the -V bias for the larger tubes, I had to tie an extra 6.3 winding (orange) into the bias to get ~-70 volts to pinch them off to around 40ma. One of the 6LR6 wanted a little more..
All I need are the 6GV5's for the audio level for the room and speakers... I also tried the 6AC10 for the front end and they are also a good replacement for the 6U10. The Hammond output iron was a step up from the original Compactron Amp that was the stocking stuffer that used the 25watt 8k-8, more detail at a higher power level, expecially more authority on the bottom end. The 2 pics are almost the same, but I rotated the meter select switch for a different tube, as seen in the nixe tube....
For those of you that want the pure bliss of triode power and don't want to do your own amp from paper design and up, consider Pete's big red board, it would be a lot easier that doing what I did..... and you will love the clarity and sound stage.!!!
Other upgrades would be voltage doubler for a 580V B+, use the 6LB6/6LR6 output tubes and larger output iron.... just food for thought, hummmm......
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Compactron Amp#3
I was side tracked by a Tube- Mosfet hybrid headphone amp. Amazing little amp can drive an efficient pair of speakers, headphones sound great.... I'l post the next set of pics when I get the wood work started.
Still working on the last of the Compactron amps. First was a 25watt/channel, the second was 40 watts/ channel, the last is targeted for 60 watts/channel. The chassis will be like the last two with a slow B+ startup thanks to a compactron damper diode in series with the B+ to the PCB. I tried it out on the KEG-EAR 6550 amp, and it works as expected. Also it has a CCS on the LTP, yes it did make a difference over a resistor. I'm using a 120V rms toroid to boost the 10lb'rs output to 460V and stuck an additional 60 turns of 21 gage wire on it to create the 6.2 volt 2 Amp supply needed for the damper diode heater. The thought is to be able to delay turning it on until the rest of the amp warms up, 6 volts is easier to switch than 460 volts..... I tried the toroid B+ boost on the KEG-EAR amp and it likes the 460V B+, toroid stays cool so does the 10lb'r.
The quality control inspector was caught napping, I guess it was to be expected. He will join me in the listening room when I play Dire Straights or Steely Dan.. Go figure..
I was side tracked by a Tube- Mosfet hybrid headphone amp. Amazing little amp can drive an efficient pair of speakers, headphones sound great.... I'l post the next set of pics when I get the wood work started.
Still working on the last of the Compactron amps. First was a 25watt/channel, the second was 40 watts/ channel, the last is targeted for 60 watts/channel. The chassis will be like the last two with a slow B+ startup thanks to a compactron damper diode in series with the B+ to the PCB. I tried it out on the KEG-EAR 6550 amp, and it works as expected. Also it has a CCS on the LTP, yes it did make a difference over a resistor. I'm using a 120V rms toroid to boost the 10lb'rs output to 460V and stuck an additional 60 turns of 21 gage wire on it to create the 6.2 volt 2 Amp supply needed for the damper diode heater. The thought is to be able to delay turning it on until the rest of the amp warms up, 6 volts is easier to switch than 460 volts..... I tried the toroid B+ boost on the KEG-EAR amp and it likes the 460V B+, toroid stays cool so does the 10lb'r.
The quality control inspector was caught napping, I guess it was to be expected. He will join me in the listening room when I play Dire Straights or Steely Dan.. Go figure..
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Its whats inside that counts. Started on the guts, packaging has always been a challenge to make it look good. I hate to cut the transformer wires short in case I want to use them for another project. This Amp being the last of the sweep tube series, I'l try to over come that fear and package for aesthetics while trying to be practical. I added a 6.3 to 110 transformer to boost the neg bias, the 60 volt tap was lacking when running 460V B+ on the sweep tubes, it was fine at 300V B+. I run the tubes at 45ma, so the 200ma choke is just adequate, there is enough room to add another one if I want to go over 50ma/tube.
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