@stocktrader200
There is a coupling capacitor between the 2 stages. If the driver dies, the DC gets blocked by the coupling capacitor.
There is a coupling capacitor between the 2 stages. If the driver dies, the DC gets blocked by the coupling capacitor.
And that is why . . . A Complete and Accurate Schematic is worth 1000 words, and needs 3 less Postings.
@6A3sUMMER a complete and accurate schematic has already been posted at the beginning of the thread by the OP.
My comment clearly specified that "These are the mods to the biasing circuitry'.
Reading the whole thread before posting, instead of quickly jumping to incorrect conclusions, needs 4 less postings. 😘
My comment clearly specified that "These are the mods to the biasing circuitry'.
Reading the whole thread before posting, instead of quickly jumping to incorrect conclusions, needs 4 less postings. 😘
Post # 38 does Not show any coupling capacitor.
Just my observation.
Just my observation.
Childish comment 6A3sUMMER.....post #1 is the schematic under discussion; post #38 merely an extraction.
daanve,
Post # 40, not mine . . .
"Interesting drive , if the driver tube dies the outputs go into meltdown"
So, I concluded that the driver plate was DC coupled to the output tube grid, which is the most common way that a dead driver could kill the outputs.
I am sorry for my incorrect interpretation of Post # 40.
Post # 40, not mine . . .
"Interesting drive , if the driver tube dies the outputs go into meltdown"
So, I concluded that the driver plate was DC coupled to the output tube grid, which is the most common way that a dead driver could kill the outputs.
I am sorry for my incorrect interpretation of Post # 40.
I recently moved to Allentown PA and when unpacking I noticed I have 10 pcbs for this amp. Its just the audio portion. But if anyone wants one email me and we'll make it happen. 300B/D3a, Zero feedback. Personally the best sounding SET amp I have heard. FWIW. I will include a schematic and moderate tech support if required.
Jeff
Jeff
Attachments
@jwags81818 Did you end up using 4.7uF Duelund CAST coupling caps in your amplifier? I am gonna be using 2.2uF Duelunds in mine and they are HUGE.
Agreed, with 0.47u there would be too much low end rolloff. I ran some simulations on my side and decided to use 2.2u as a trade-off between bass extension and capacitors size/cost.
I also decided to go full film caps for the power supply. I am planning to use a mix of Wima DC-link and Obbligato PSU caps.
I also decided to go full film caps for the power supply. I am planning to use a mix of Wima DC-link and Obbligato PSU caps.
Make sure you use a good DC filament supply for the 300Bs. My amp is dead silent at full volume with 106db spl speakers. You can tell its turned on if you put your head in the speaker but thats what it takes to hear that its turned on. My D3as are using AC heat with no problem at all. Another suggestion is if you have never tried a transformer volume control you are missing out. It was like pulling 2 bed sheets off my speakers when I hooked that up. I am using Intact audio autoformers. I'll never build anything with a resistive volume control again. They rob you of a significant amount of detail in my opinion. Also I bought a pair of the LinLai western electric clone tubes and am very happy with them. For 1/3 the price and I can't tell the difference between them and a new issue pair of western electrics. Make sure you have a good heatsink or a large wattage resistor for the bias. I burned several up before I got a heatsink of sufficient size. Bypass caps on the cathode bias too. I am using 100v in this position after burning up some 65v caps. they should have lasted but they didn't.
@jwags81818
For the 300B I am using Rod Coleman's filament supply which, according to many, performs really well.
I also made other variations compared to the original circuit:
I am bulding the circuit in sub-blocks so I will be able to replace any of the sub-block at any time and try for a different circuit.
At some point I'd be curious to try the high frequency AC filament supply, but it's something that I am leaving for the future
Thank you for the suggestion about the LinLai WE clones, at $699/couple the price seems very reasonable if they perform as good as the original WE!!
Which 106db/W loudspeakers are you using? .. as my next project I was thinking about building some speakers using lil-audio drivers.. or maybe have them built by someone else, because I am not very good at cutting and gluing wood ..
For the 300B I am using Rod Coleman's filament supply which, according to many, performs really well.
I also made other variations compared to the original circuit:
- DC Filament + LED bias circuit for the D3a
- Fixed biased through an external negative supply (whose value can be set with a trimmer) for the 300B
- Monolith Magnetics custom OPTs based on the SX-11 nanocrystal core (I have high expectations on these)
- Replaced all the electrolytics with high low ESR DC-Link caps
- 2.2 uF Duelund CAST Cu-Sn coupling capacitor (I love Duelunds)
I am bulding the circuit in sub-blocks so I will be able to replace any of the sub-block at any time and try for a different circuit.
At some point I'd be curious to try the high frequency AC filament supply, but it's something that I am leaving for the future
Thank you for the suggestion about the LinLai WE clones, at $699/couple the price seems very reasonable if they perform as good as the original WE!!
Which 106db/W loudspeakers are you using? .. as my next project I was thinking about building some speakers using lil-audio drivers.. or maybe have them built by someone else, because I am not very good at cutting and gluing wood ..
You can get the Lin Lai tubes for $540 if you join their vip club https://premiumvacuumtubes.com/product/tubevip-membership/
At least thats what it cost me when I bought mine. Also they sent me the premium tubes for the price of the standard ones. They test them and sell the top 5% or so for a little more. I think its 5% been awhile. But the membership was like $30 and it extends the warranty too. I had a pair of new issue WEs here and AB tested them and I couldn't tell them apart. For what thats worth. I am not saying I have a golden ear or anything but for the price it was certainly worth it. Assuming they last 5 years. And my speakers are Klipsch La Scalas. I redid the cross over on them to flatten out the response but they are very sensitive speakers. A guy brought his Ele kit 300B amp over and it buzzed pretty badly on my speakers where as mine is silent. His amp sounded ok playing but between songs you could certainly tell it was on. So you don't have any cathode bias then on the 300Bs right?
Also if you haven't ever listened to Klipsch Cornwalls or Fortes you should before planning a speaker build. I know Klipsch polarizes some people but I love them.
At least thats what it cost me when I bought mine. Also they sent me the premium tubes for the price of the standard ones. They test them and sell the top 5% or so for a little more. I think its 5% been awhile. But the membership was like $30 and it extends the warranty too. I had a pair of new issue WEs here and AB tested them and I couldn't tell them apart. For what thats worth. I am not saying I have a golden ear or anything but for the price it was certainly worth it. Assuming they last 5 years. And my speakers are Klipsch La Scalas. I redid the cross over on them to flatten out the response but they are very sensitive speakers. A guy brought his Ele kit 300B amp over and it buzzed pretty badly on my speakers where as mine is silent. His amp sounded ok playing but between songs you could certainly tell it was on. So you don't have any cathode bias then on the 300Bs right?
Also if you haven't ever listened to Klipsch Cornwalls or Fortes you should before planning a speaker build. I know Klipsch polarizes some people but I love them.
Or: audition and choose (build) speaker first before deciding about the amplifier, especially in case of Single Ended.
I'd say that is a simulation of your best sounding 300B amp:
Ideal transformers
Ideal CCS.
Ideal power supply.
🙂
Ideal transformers
Ideal CCS.
Ideal power supply.
🙂
That Elekit shouldn't make any noise at all. He might have a grounding issue or a bad filament regulator. I've heard one that was professionally assembled and tuned up, and it was dead silent.
In regards to speakers with my 300B amp. Impedance appears to matter more than spl does in regards to being able to drive them satisfactorily. I have yet to try a pair of 4 ohm speakers that my amp could drive well. But I have tried speakers with 90spl that it drove just fine. Not as loud as it does with higher spls but there wasn't any clipping or dynamic compression that I could tell. Your output transformers will have 4 ohm taps so I don't know if that will help. I know it is supposed to but I haven't had any experience with multi tap output traffos. I just know that 4 ohm speakers are a no-go with my amp. So if you are going to build your own I'd stay north of 8 ohms even with multi-tap outputs.
grovergardner said:
"That Elekit shouldn't make any noise at all. He might have a grounding issue or a bad filament regulator. I've heard one that was professionally assembled and tuned up, and it was dead silent."I have heard several amps that were dead silent with 90spl speakers that weren't with my 106spl speakers. The owner said it was silent on his system at home. Thats all I can go by. I have no other experience with that amp. Highly sensitive speakers can bring out noise that otherwise went unnoticed. Not that there needed to be something wrong with the amp. It's just the nature of sensitive speakers. They are less forgiving of such things.