I'll say again, you can use a 1:1 EI core gapped transformer which then feeds the toroidal transformer.
So, for example, a Hammond 157G with 30H, 40ma and 595 Ohms in a parafeed with a 3200k to 8 Ohm ungapped OPT with 6L6G tubes triode connected. Doable and worth doing or not? Or should I just return the OPTs and move on. I have all the parts.
Doable - yes, worth doing - not unless you want to buy more parts and spend more money... Just return the OPT's and get the air-gapped SE OPT's.
I also have a four Hammond 157L with 14H 75ma and 429 Ohms, that I could put in series to add up to 28H per side at 75ma. Another option is to use the157Gs with a lower dissipation tube such as Type 46 or 45. I know almost nothing about parafeed, but I am willing to try it out. Any advice would be appreciated.
Hi Tizman
I say go for it.You've got all the parts, now built it.
Parts Express have 157g listed at $29.I say buy another pair and stack a pair in series for 60H,much better!
Increase current thru the 6l6gc for improved performance.
Hammond is Canada based so I'm sure you'll find it cheaper!
PS bread board your efforts before committing to a chassis.....you will have a gas building this.
I say go for it.You've got all the parts, now built it.
Parts Express have 157g listed at $29.I say buy another pair and stack a pair in series for 60H,much better!
Increase current thru the 6l6gc for improved performance.
Hammond is Canada based so I'm sure you'll find it cheaper!
PS bread board your efforts before committing to a chassis.....you will have a gas building this.
We've posted within seconds of each other😀.
Read J Broskie Tubecad Blog0308 for parafeed amplifier design.
Read J Broskie Tubecad Blog0308 for parafeed amplifier design.
Is it ok to put different chokes in series such as one 157G and one 157L per side? The resistance and Henrys add up, but what does that do for the current capability?
Just my two cent here. I am also a beginner but I like to learn and happen that as first project (budget limitation) as I had in house industrial component I build an SE with EL34 using normal toroid transformer (no air gap).I used a Para feed connection with a chock 20 mA and a capacitor of 3.3uF.I have limited test equipment but using my pc with a software I could see a bandwidth (-3db) from 30Hz to 22KHz.I also manage to see a perfect sinusoidal at 1000hz.that is all I can tests probably an accurate measurement would show many flow that I cant detect however the amp sound damn good considering the chip component and the my limited assembling capability.
Later I both from the very same Polish seller two toroid transformer for EL34SE.As the seller specified they are air gapped I remove the para feed assembly and I install them on the same amp same as they were EI transformer. They work very well the sinusoid at 1000Hz is very clean and compared with previous set up they have a more extended low band .The sound is more full and balanced than the previous set up. So as said I have limited technical experience but I do appreciate the good sound and just happen I have just been trough the same path like the first poster and i did not had the problem he had and just thought was right to report my experience. Good music all -)
Later I both from the very same Polish seller two toroid transformer for EL34SE.As the seller specified they are air gapped I remove the para feed assembly and I install them on the same amp same as they were EI transformer. They work very well the sinusoid at 1000Hz is very clean and compared with previous set up they have a more extended low band .The sound is more full and balanced than the previous set up. So as said I have limited technical experience but I do appreciate the good sound and just happen I have just been trough the same path like the first poster and i did not had the problem he had and just thought was right to report my experience. Good music all -)
Is a 20mA choke enough for the EL34? What is the current rating of the Polish OPT? I suspect it is higher than 20mA...
1. Both DC chokes and SE output transformers follow the same rules:
For a given unsaturated inductance at a given standing current (output tube quiescent current), a given peak current, and a given low frequency, and a given DC B+ drop:
the volume of the core laminations, the number of turns, and the wire size will all be the same for both the choke and the SE output transformer.
If you want to use your toroid transformers, you will find that the One Electron Plate Chokes cost less than the One Electron 3K SE output transformer.
But by the time you purchase a Parafeed coupling cap, and a choke that is good enough,
it will be less expensive to use an SE output transformer (depending on the model). But you already have the toroid transformer.
Both SE and Parafeed are known to work well if implemented properly.
2. A CCS for a 6L6 parafeed will require a very high B+ voltage, probably 600 to 700V.
A choke with a good DCR will require about 1/2 of the B+ voltage in order to have the same output power in an otherwise identical circuit.
Ditto for an EL34, 300B, etc.
For a given unsaturated inductance at a given standing current (output tube quiescent current), a given peak current, and a given low frequency, and a given DC B+ drop:
the volume of the core laminations, the number of turns, and the wire size will all be the same for both the choke and the SE output transformer.
If you want to use your toroid transformers, you will find that the One Electron Plate Chokes cost less than the One Electron 3K SE output transformer.
But by the time you purchase a Parafeed coupling cap, and a choke that is good enough,
it will be less expensive to use an SE output transformer (depending on the model). But you already have the toroid transformer.
Both SE and Parafeed are known to work well if implemented properly.
2. A CCS for a 6L6 parafeed will require a very high B+ voltage, probably 600 to 700V.
A choke with a good DCR will require about 1/2 of the B+ voltage in order to have the same output power in an otherwise identical circuit.
Ditto for an EL34, 300B, etc.
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Is it ok to put different chokes in series such as one 157G and one 157L per side? The resistance and Henrys add up, but what does that do for the current capability?
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Nothing, the current capability stays the same, what are the operating conditions for the 6L6G? Can your chokes even handle the bias current?
I actually have 4 157L chokes. That would give me 28 Henry, 75mA and 858 Ohms if I used two per side. If I use one per side, it's 14 Henry and 429 Ohms with the same 75mA. Is one 157L workable? From my calculations it appears to create a lower -3DB point that is too high, but I'm not sure if I've calculated correctly.
I don't think 40mA is enough to work with. 75mA should be more than enough for EL34 and any of the 6L6 variants. I have a number of power transformers, so I can provide whatever B+ is appropriate.
I don't think 40mA is enough to work with. 75mA should be more than enough for EL34 and any of the 6L6 variants. I have a number of power transformers, so I can provide whatever B+ is appropriate.
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