One of the nice things about CCS loading is you don't worry much about the B+. Of the 3 quantities: IB, grid bias voltage, and anode voltage, any 2 define the 3rd. As long as the B+ rail is "tall" enough to operate the CCS and put the anode where it has to be, all will be well.
The red LED defines the grid bias voltage and the CCS defines IB. Therefore, the anode will automatically be at the right potential.
Decouple the small signal circuitry's B+ from the O/P tubes. The CCS substantially improves the PSRR of the 6GK5. So, undesirable interaction between voltage amplifier and LTP is highly unlikely.
I thought that could be the case. Now where did I put that flippin' 12AT7...
That's a good idea. You guys will have to keep me clear on which version you're talking about. I'm (obviously) already confused.
But I've already learned quite a bit. I'll ask some more questions before uploading the next schematic. I'm still fuzzy on a couple points...Todd
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My first question has to do with the current regulator. Where does this want to be? On the 12AT7 tail (where I have it currently), or only used on the 6GK5 version? And it wants to be referenced by a red LED (as the BJT CCS currently is in that spot?).
Second question is about the power supply: The 2nd coil (the one with the full wave rectifier providing -80V), is that a separate transformer, or another coil on the Edcor core? If it's the latter, then in the schematic symbol the core lines would be common, correct?
..Todd
Second question is about the power supply: The 2nd coil (the one with the full wave rectifier providing -80V), is that a separate transformer, or another coil on the Edcor core? If it's the latter, then in the schematic symbol the core lines would be common, correct?
..Todd
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The bias winding is another winding on the Edcor core.
The 10M45S does not need the red led, IIRC it's on the plate of the 6GK5 and a red LED is on the cathode to ground (the red LED is used to bias the cathode up). The 10M45S is somewhat equivalent to the BJT CCS, two different ways of doing a CCS. There is a thread around here somewhere discussing the differences.
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I have been thinking about this since we lowered the KT88 B+ to 465V. Now the KT88 B+ (465V) and the 12AT7 B+ (460V) are only separated by a 220 ohm R (and a 220uf C).
Is this enough additional filtering for the phase splitter? The PSUD ripple looked good........
Hi!
Great work!
Could the cascoded CCS as on El Cheapo be the better one for a few more $ as Eli picked it for it's better performance? Of the two choices from K&K Audio the more expensive one of looks to be much the same. SY's Red light district has a similar Cascoded CCS also. Maybe it wouldn't make much difference on this application, and with the added complication.
This is a voltage doubler PS like on El Cheapo right?
Randy
Great work!
Could the cascoded CCS as on El Cheapo be the better one for a few more $ as Eli picked it for it's better performance? Of the two choices from K&K Audio the more expensive one of looks to be much the same. SY's Red light district has a similar Cascoded CCS also. Maybe it wouldn't make much difference on this application, and with the added complication.
This is a voltage doubler PS like on El Cheapo right?
Randy
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Some specific questions for the updated schematic of the original EF86 version amp...
..Todd
- For the 12AT7 tail CCS, which method is wanted? The original BJT/red LED or the current regulator?
- How are the heaters wired? (I'm new to this). Which V winding, any rectification, filtering, etc?
- I'd like to finish drawing the power supply. What is the preferred method of fusing and switching it?
- The OPT input impedance? I've seen mention of the Hammond 5K unit, and the Edcor 3K3 unit. Which impedance is optimal?
..Todd
Some specific questions for the updated schematic of the original EF86 version amp...
Anything else need updating, fixing (other than what has already been mentioned?) I need specific instructions. Including napkin drawings and aerial photos if you've got them.
- For the 12AT7 tail CCS, which method is wanted? The original BJT/red LED or the current regulator?
- How are the heaters wired? (I'm new to this). Which V winding, any rectification, filtering, etc?
- I'd like to finish drawing the power supply. What is the preferred method of fusing and switching it?
- The OPT input impedance? I've seen mention of the Hammond 5K unit, and the Edcor 3K3 unit. Which impedance is optimal?
..Todd
BJT/LED....10M45S...I'll leave this to the experts.....I think they'll both work, but there are some finer points.
Heaters are AC wired right off of the heater taps on the edcor. check out Duncan's tube data for the correct pin outs for the heaters.
TDSL Tube data [KT88] (heater is pins 2 & 7)
TDSL Tube data [EF86] (heater is pins 4 & 5)
TDSL Tube data [6GK5] (heater is pins 3 & 4)
TDSL Tube data [12AT7] (heater is pins 4&5 tied together and pin 9)
Note: The 12AT7 can be wired for either 12.6V (series connection) or for 6.3V connection (parallel connection)
Also Note (before anyone starts drilling any holes): The 6GK5 is a 7 pin tube.
Switch and fuse on the mains side of the edcor, either single pole on the hot side for both, or double pole on both hot and neutral for switch and fuse.
OPT impedance.....good question...4K or 5K....
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Dynaco MkIII (KT88 PP/UL 480v B+) used 4300 ohm OPT for their amp, which means there may be another option for OPT...
A431S Dyna Clone Output Transformer 4300 Ohm 60W/120W
..Todd
A431S Dyna Clone Output Transformer 4300 Ohm 60W/120W
..Todd
Yes, I would say that the two resistors 100 ohm and 2K2 in the EF86 need reversing, otherwise the 100R does not make much sense. If so then the 2K2 would probably need bypassing, otherwise two resistors again do not make sense.
I have also not looked at previous circuits; as this stands I presume that the 240V 'supply' to the EF86 is for both channels? Even so (I have not constructed/measured) I would guess that the 2K2 is a bit high to leave approximately 100V on the EF86 anode for proper working of the phase splitter. My value in past circuits were 1K to smaller - but perhaps I should not guess; might have time in the morning to quickly hook this up. Also no desire to interfere with the design of others; there are many possible component value combinations here.
Boywonder,
In what cathode circuit do you want that red LED you previously mentioned? [EF86 is self-biased as is the (future) 12AT7 ...]
Johan: I was regurgitating Eli's post above (post #125). The 6GK5 gets biased by a red LED.
You can use 60 W. "iron" in a 60 W. amp, with certain restrictions. GNFB generates a LF error correction signal. So, either you eschew GNFB or you limit bass extension. A trafo whose core is saturating sounds very bad. Name your poison.
There is more than 1 way to approach the primary impedance issue. I'm viewing things from a voltage swing and step down ratio perspective. P = V2/R. Therefore, "22" V. of drive into 8 Ω are needed to produce 60 W. The impedance ratio of a trafo varies with the square of the turns ratio. The turns ratio for a 4300 Ω primary into an 8 Ω secondary is 23:1. That works out to a (sic) 506 VRMS primary side swing, at full power. Yes, inductive effects allow the B+ rail voltage to be exceeded, but you get the idea.
BTW, the best of the Dyna trafos is the Z565, which is used with "12" W. tubes.
Name your poison.There is more than 1 way to approach the primary impedance issue. I'm viewing things from a voltage swing and step down ratio perspective. P = V2/R. Therefore, "22" V. of drive into 8 Ω are needed to produce 60 W. The impedance ratio of a trafo varies with the square of the turns ratio. The turns ratio for a 4300 Ω primary into an 8 Ω secondary is 23:1. That works out to a (sic) 506 VRMS primary side swing, at full power. Yes, inductive effects allow the B+ rail voltage to be exceeded, but you get the idea.
BTW, the best of the Dyna trafos is the Z565, which is used with "12" W. tubes.
Some specific questions for the updated schematic of the original EF86 version amp...
Anything else need updating, fixing (other than what has already been mentioned?) I need specific instructions. Including napkin drawings and aerial photos if you've got them.
- For the 12AT7 tail CCS, which method is wanted? The original BJT/red LED or the current regulator?
- How are the heaters wired? (I'm new to this). Which V winding, any rectification, filtering, etc?
- I'd like to finish drawing the power supply. What is the preferred method of fusing and switching it?
- The OPT input impedance? I've seen mention of the Hammond 5K unit, and the Edcor 3K3 unit. Which impedance is optimal?
..Todd
OPT input impedance:
There has been some conflicting comments on this. Eli, like the 3.3, and John posted test results indicating that 5K might be the best compromise of Dist. Vs Power. Coin toss? Spilt the middle?
BTW,
I have received a quote from Electraprint for the OPT's, and that route will be about double the cost of Edcors.
As for the splitter CCS, I don't know? I'm hoping an expert will chime in with a "It should, and must be this" Statement.
Taj, where you able to gather the PS BOM list from the previous PS posts by wonderboy?
I'm thinking about the BOM for the main circuit at this time. Would like to start with the resistors, but someone would need to suggest wattage ratings, and types. For the lower wattage resistors, I'm think Dale Vishay metal film, I need suggestions for the higher wattage units such as those in the PS, and plate loads. Ceramic? wirewound? Perhaps this exercize would make another nice little lesson for newbies on how to choose proper componets...
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I'm thinking about the BOM for the main circuit at this time. Would like to start with the resistors, but someone would need to suggest wattage ratings, and types. For the lower wattage resistors, I'm think Dale Vishay metal film, I need suggestions for the higher wattage units such as those in the PS, and plate loads. Ceramic? wirewound? Perhaps this exercize would make another nice little lesson for newbies on how to choose proper componets...
I've been in Audio (as a recording engineer) and building amplifiers long enough to want to go my own way with components. I suggest that unless there is a specific technical reason (not just someone's preference) then we should just specify the parts by value/rating and let everyone decide amongst themselves which type and brand of unobtainium they prefer. Citing some examples that suit those spec's are certainly worthwhile.
The NTC inrush limiting thermistor and the current regulator are good examples of parts that can be spec'd to specific models.
I think that is also the approach needed for output transformers. The BoM just needs to describe the technical requirements; 100 watts, 3.3K input impedance, 40% UL taps, etc. and maybe a couple examples of products that will work. A "builders thread" can go into opinions of which makes/models to spend your money on.
..Todd
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Possibly. But usually there's not much choice based on the value and rating. If a low inductance resistor is preferred in a certain location (for example), that can be spec'd. And I usually do spec the capacitor type, just to make shopping easier for newbies. Again, those are just example products that can be chosen by the builder. If someone wants to try and locate a 100pF electrolytic, or a 330uF polystyrene cap, have at it! The amp will still work fine assuming the value and ratings are followed.
When creating a BoM for printed circuit boards, then you MUST at least specify lead spacing. But we're not going there methinks.
Having said all that, I'm new to this wacky high voltage tube world. So there's probably some things I can't anticipate that someone will surely teach me about.
..Todd
When creating a BoM for printed circuit boards, then you MUST at least specify lead spacing. But we're not going there methinks.
Having said all that, I'm new to this wacky high voltage tube world. So there's probably some things I can't anticipate that someone will surely teach me about.
..Todd
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