I am just starting my Baby Huey research so I haven't read the thread in full yet (disclaimer), but I was wondering why a DC/DC converter is being used to power the heaters?
I understand that the DC rectification done by the PSU is not enough, and an aux circuit is required to get the voltage down to the 6.3V DC that the heaters require.
Why the DC/DC buck converter though?
https://www.diymore.cc/products/diy...table-step-down-converter-voltage-buck-module
It seems most are using this DC/DC converter. Seems like a cheap chineese part. This stand alone prebuilt circuit has been fine in Baby Huey builds?
I understand that the DC rectification done by the PSU is not enough, and an aux circuit is required to get the voltage down to the 6.3V DC that the heaters require.
Why the DC/DC buck converter though?
https://www.diymore.cc/products/diy...table-step-down-converter-voltage-buck-module
It seems most are using this DC/DC converter. Seems like a cheap chineese part. This stand alone prebuilt circuit has been fine in Baby Huey builds?
I don’t think you have to use a DC converter. You can power the heaters on AC if you like it probably doesn’t make much difference on the power tubes but might help a little on the input tube to have DC.
I have used those and the equivalent step-up too, to power heaters (not baby-huey though), yes, they are cheap chinese parts, work pretty well, at least for me. You need to ignore the claims about 300W/20A, just divide by two.
No need for DC heaters: elevated AC are fine.
CRC is fine for the B+, especially if you stick to EL34 datasheets with higher Raa and lower UL.
CLC is better: I remember @Francois G suggested a good choke few pages ago (159T and 159S IIRC).
IMHO no need of regulated B+ in a low wattage (so low current) PP amp.
CRC is fine for the B+, especially if you stick to EL34 datasheets with higher Raa and lower UL.
CLC is better: I remember @Francois G suggested a good choke few pages ago (159T and 159S IIRC).
IMHO no need of regulated B+ in a low wattage (so low current) PP amp.
Thanks for the quick replies gents!
I will avoid the DC/DC converter and do elevated AC heaters to start. Let's see how that goes!
I was reading that if one did choose to go the DC heaters route that the bridge rectifier can get a little hot anyways when pulling ~7A through it, so maybe this is an COOL added bonus 😎
Thought I had a choke for this amp in my parts bin. Just looked up the part number and it is for a Fender Twin Reverb, only 90mA bummer 🙁
PS: why does the documentation advise for trim pots on the top (tube side) of the PCB?
I will avoid the DC/DC converter and do elevated AC heaters to start. Let's see how that goes!
I was reading that if one did choose to go the DC heaters route that the bridge rectifier can get a little hot anyways when pulling ~7A through it, so maybe this is an COOL added bonus 😎
Thought I had a choke for this amp in my parts bin. Just looked up the part number and it is for a Fender Twin Reverb, only 90mA bummer 🙁
PS: why does the documentation advise for trim pots on the top (tube side) of the PCB?
I suppose ease of adjustment, but then you have to have access to the measurement points too.
How often is an adjustment required? I have tried to make mine so everything is accessible and it can be flipped over without any contact to the output tubes.
I have not bothered with the DC heating, but currently they are not elevated. I suppose I should look into that.
How often is an adjustment required? I have tried to make mine so everything is accessible and it can be flipped over without any contact to the output tubes.
I have not bothered with the DC heating, but currently they are not elevated. I suppose I should look into that.
To be able to adjust the working point when you change the tubes. Of course you need to measure the needed points.
Just looking for some initial advice.
My Baby Huey project has been on hold for about 24 months but it's time to pick it up again! 🙄
I have two different OPTs. OPtion 1) Toroidy 4k RAA 80w 43% UL or, 2) Toroiday 6k6 Raa 50w 43% UL
I haven't decided what values to use but I have EL34's, KT77's, KT88's and a quad of 6550's in my cupboard.
I've read this tread and it's been suggested that 6k6 Raa is best for KT77. What are the implications of using the 6K6 for the EL34,s KT88's and 6550's. As i understand it, less power but more class A...is that correct?
Thanks
Andrew
My Baby Huey project has been on hold for about 24 months but it's time to pick it up again! 🙄
I have two different OPTs. OPtion 1) Toroidy 4k RAA 80w 43% UL or, 2) Toroiday 6k6 Raa 50w 43% UL
I haven't decided what values to use but I have EL34's, KT77's, KT88's and a quad of 6550's in my cupboard.
I've read this tread and it's been suggested that 6k6 Raa is best for KT77. What are the implications of using the 6K6 for the EL34,s KT88's and 6550's. As i understand it, less power but more class A...is that correct?
Thanks
Andrew
It’s a very versatile circuit, and you can really use what you prefer.
KT77 are very linear and nice sounding, EL34 are my favourite, for KT88 and 6550 IMHO a bit more voltage on B+ will make them shine.
I built a variation of the BH with EL34 at 460V and 6k6 Raa with 20% UL (following old Mullard guidelines), higher plate loads for the phase splitter and higher currents for the powerdrive.
If you want a Class A push-pull, go towards big bottles and flatter loads (6550 fits better than KT88: being thinner you have more space between tubes, so better heat dissipation) and you’ll get less distortion. Just be aware you’ll need to calculate power drive supply.
Be aware that you’ll always be in SET damping factor territory (less than 4 generally), so take care of it when considering the speakers (flatter impedance curves work better).
KT77 are very linear and nice sounding, EL34 are my favourite, for KT88 and 6550 IMHO a bit more voltage on B+ will make them shine.
I built a variation of the BH with EL34 at 460V and 6k6 Raa with 20% UL (following old Mullard guidelines), higher plate loads for the phase splitter and higher currents for the powerdrive.
If you want a Class A push-pull, go towards big bottles and flatter loads (6550 fits better than KT88: being thinner you have more space between tubes, so better heat dissipation) and you’ll get less distortion. Just be aware you’ll need to calculate power drive supply.
Be aware that you’ll always be in SET damping factor territory (less than 4 generally), so take care of it when considering the speakers (flatter impedance curves work better).
It is fine for all of these tubes
If you have a minimum of test set you can check the class A simply look in at the cathode resistors of the power tubes with scope ( it easy with fixed bias)
Use the 43% of UL
I this way you can also get a good DF
But the power tubes must me well selected
Hello Andrew:
I do not think there is a "best" for any tube.
I do think that there is a series of compromises or a balance that need to be addressed depending on the desired outcome the designer hopes to achieve.
As you have these two sets of output transformer. You could go through the exercise of creating the load lines and calculating the likely outcomes from the various tubes you have to choose from. The process is not that cumbersome with all the simulation tools available on line. There is a certain comfort when going through the process.
I particularly like the published work from Patrick Turner @ Turner Audio. He goes through the mathematics in a logical fashion that I can understand. Gaming with the online simulators is also a good way to understand how hte relationships work.
I hope this helps in your quest for the right combination of power tube and output transformer.
I do not think there is a "best" for any tube.
I do think that there is a series of compromises or a balance that need to be addressed depending on the desired outcome the designer hopes to achieve.
As you have these two sets of output transformer. You could go through the exercise of creating the load lines and calculating the likely outcomes from the various tubes you have to choose from. The process is not that cumbersome with all the simulation tools available on line. There is a certain comfort when going through the process.
I particularly like the published work from Patrick Turner @ Turner Audio. He goes through the mathematics in a logical fashion that I can understand. Gaming with the online simulators is also a good way to understand how hte relationships work.
I hope this helps in your quest for the right combination of power tube and output transformer.
6k6 Raa (compared to 4k) gives "more class A", higher damping, lower distortion, lower power, higher shunt feedback.
Given a certain B+, fixing a percentage of maximum plate dissipation, KT88 and 6550 (compared to EL34) will give "more class A" and higher damping.
You also need to consider that KT88 and 6550 will need more swing on g1 to give full power, so at a certain point you could be short in gain on the phase splitter, especially with high shunt feedback.
What I generally do is deciding a B+ and loadline based on the output tubes, then set the phase splitter at around 0,6-1 mA per triode (it depends on the needed swing and powerdrive mosfet input capacitance) and set the load in order to have around 2V on triodes' cathodes and 1/2 B+ on triode's plates. If gain is short you can reduce the value of the balancing trimmer on the cathodes (it will reduce local current feedback and increase gain).
I've built both the EL84 and EL34, tested other tubes as well and in all cases I preferred the 20% UL with more shunt feedback, rather than the opposite.
Simulators help you save time, then there's need of refinement by ear and measurements.
I saw the question but I didnt see an actual experience. Did anybody try Antek output transformer for this project? Antek output transformers pricing is significantly better than Hammond or Toroidy but how Antek compares with those?
As a guideline, circuits like this one, that take feedback from the primary, are not obliged to use very good irons, because they drive the output transformers with a lower impedance, so "make them perform better". Same transformers in other project will perform worse. Then of course the overall project can be better or not.
I guess, I could give it a try to those Antek output transformers, it will take me a while to get the project tested, I will report back when i have tried it.
does someone know how to make more output power ?
I use 6v6GT tubes, and I do need to use 80% of my volume control to listen at home.
I think my amplifier can sound louder. OR maybe I need to check something?
I use 6v6GT tubes, and I do need to use 80% of my volume control to listen at home.
I think my amplifier can sound louder. OR maybe I need to check something?