I've a few quick questions on the Baby Huey:
I like the idea of the Toroidy TSTA 0250/001 PT, but the 275 winding is probably a bit high. I'm thinking it might be just as easy to get a custom PT with, say, 225V@0.4A, 50V@0.1A and 18V@>2A windings for a PCL86 design, or lower heater winding for ECL86.
- For an EL84 stereo build, what is the recommended PT HV winding? Reading through this and the original thread there seems to be some variation for the target B+ value.
- Would there be any problem 'porting' the improvements (source follower, fixed bias etc) on the latest EL84 board backwards on to the ECL86/PCL86 design?
- What is the input sensitivity? e.g., for 1W output, full output before clipping etc?
I like the idea of the Toroidy TSTA 0250/001 PT, but the 275 winding is probably a bit high. I'm thinking it might be just as easy to get a custom PT with, say, 225V@0.4A, 50V@0.1A and 18V@>2A windings for a PCL86 design, or lower heater winding for ECL86.
Another couple of questions from me and potentially an answer or two.
I see the Toroidy PT linked above would be fine, but voltages would be a bit high. And the EDCOR PT used in Pete Millett’s DCPP could be used too I reckon, which is lucky as I have one spare.
I’ve also started drawing a PCB for the ECL86 version with MOSFET followers etc. I’ll be making some changes to make it a bit more modular - taking PS circuitry and moving it to a separate board. Will probably copy a lot of the PS from the DCPP - so ripple filter / zener follower for the HT - and add in some recommendations from Merlin’s power supply chapter.
New questions:
- Where are people grounding their OT secondary? The obvious place would be the Feedback screw connector to GND. But I don’t see that in photos posted.
- Secondly, if no GNFB is being used is it OK to leave R2 & R4 populated?
I see the Toroidy PT linked above would be fine, but voltages would be a bit high. And the EDCOR PT used in Pete Millett’s DCPP could be used too I reckon, which is lucky as I have one spare.
I’ve also started drawing a PCB for the ECL86 version with MOSFET followers etc. I’ll be making some changes to make it a bit more modular - taking PS circuitry and moving it to a separate board. Will probably copy a lot of the PS from the DCPP - so ripple filter / zener follower for the HT - and add in some recommendations from Merlin’s power supply chapter.
New questions:
- Where are people grounding their OT secondary? The obvious place would be the Feedback screw connector to GND. But I don’t see that in photos posted.
- Secondly, if no GNFB is being used is it OK to leave R2 & R4 populated?
@tristanc,
For the EL84 Baby Huey 275 V AC will be too much (385 V DC), I recommended 230 V AC max, this is quite convenient because you can find easily isolation transformer 115 x 2 primary / 115 x 2 secondary (320 V DC)...
On my EL84 Baby Huey I have used a 250 V AC transformer (350 V DC) without any problem with SOVTEK tubes, if JJ and other indicate 300 V max for the EL84, the Russian military version EL84M is working up to 500 V : EL84
I don't think it is a good idea to make a PCB with MOSFET for the ECL86 because this tube is (unfortunately) no more produced and when NOS are available they are very expensive... If you really want to make an ECL86 or a PCL86 amplifier you can use the PCB that I have already given on the forum
I have never used the NFB on the Baby Huey amplifiers and they are very stable without it, even when I tested the EL34 BH in pentode mode it was not necessary, that's why you didn't see it on the photos
Marc
For the EL84 Baby Huey 275 V AC will be too much (385 V DC), I recommended 230 V AC max, this is quite convenient because you can find easily isolation transformer 115 x 2 primary / 115 x 2 secondary (320 V DC)...
On my EL84 Baby Huey I have used a 250 V AC transformer (350 V DC) without any problem with SOVTEK tubes, if JJ and other indicate 300 V max for the EL84, the Russian military version EL84M is working up to 500 V : EL84
I don't think it is a good idea to make a PCB with MOSFET for the ECL86 because this tube is (unfortunately) no more produced and when NOS are available they are very expensive... If you really want to make an ECL86 or a PCL86 amplifier you can use the PCB that I have already given on the forum
I have never used the NFB on the Baby Huey amplifiers and they are very stable without it, even when I tested the EL34 BH in pentode mode it was not necessary, that's why you didn't see it on the photos
Marc
Attachments
Thanks Marc,
I take your point on the ECL86, but I'm happy to take a risk here. Comparing the cost for 4 JJ EL84s and 2 ECC83s with 4 ECL86s on a well known auction site gives marginal difference, if any. And PCL86s are even cheaper, but would make the heaters interesting. Choice choices.
On the PT - yeah, it will be high. My DCPP with 280-0-280 @200mA sec gives 365V pre-filtering and 340V B+, but I think Pete was pushing the capabilities... So not too much extra to drop to get 300V if the current load is ~120mA. I'm keen to use my existing iron if possible. If not, I'll get a Toroidy one custom wound to make my heaters easier.
For your OT secondaries, where have you grounded them? Just to the chassis or back to the PCB? I guess the return should be to the main filter cap of the channel.
I've got myself confused - on the DCPP if GNFB isn't used, the schematic shows two connections from the OT secondary both linked to GND:
T
I take your point on the ECL86, but I'm happy to take a risk here. Comparing the cost for 4 JJ EL84s and 2 ECC83s with 4 ECL86s on a well known auction site gives marginal difference, if any. And PCL86s are even cheaper, but would make the heaters interesting. Choice choices.
On the PT - yeah, it will be high. My DCPP with 280-0-280 @200mA sec gives 365V pre-filtering and 340V B+, but I think Pete was pushing the capabilities... So not too much extra to drop to get 300V if the current load is ~120mA. I'm keen to use my existing iron if possible. If not, I'll get a Toroidy one custom wound to make my heaters easier.
For your OT secondaries, where have you grounded them? Just to the chassis or back to the PCB? I guess the return should be to the main filter cap of the channel.
I've got myself confused - on the DCPP if GNFB isn't used, the schematic shows two connections from the OT secondary both linked to GND:
T
But you're probably right. It would be easier with EL84s and ECC83s. This is a build which is likely to take me all of 2019 so no doubt it'll be down to what I can come across easily - iron vs valves etc.I don't think it is a good idea to make a PCB with MOSFET for the ECL86 because this tube is (unfortunately) no more produced and when NOS are available they are very expensive... If you really want to make an ECL86 or a PCL86 amplifier you can use the PCB that I have already given on the forum
Hello,
Here is the new more compact (less than 10 cm) version
If there is no fault I will publish the Gerber files
A bientôt,
Marc
Hi Marc
Amazing work on this compact mk3 version. Many changes and all good one.
A few of us are looking forward for you to publish the Gerbers files of this mk3 version can we count on you to proceed when you get a chance 😀. It would be great.
Thanks in advance and happy holidays to you all !
BR
Eric
How did the EL34 BH project work out? Are you listening to music yet? I am interested in using the 290FEX as well and wondered if you had any additional comments, or issues noted.
I'm not clear if you are using one 290FEX per board (channel), or one transformer for a two board stereo amp?
Thanks!
Hello,
Here it is, after that of Marc I finally finished my Baby amp.
I did not have the courage to redo implementation of LEDs, 4-input selectors and VUs, but I am happy with the final result.
Settings in progress, the sound is already excellent.
Happy holidays to you all.
Here it is, after that of Marc I finally finished my Baby amp.
I did not have the courage to redo implementation of LEDs, 4-input selectors and VUs, but I am happy with the final result.
Settings in progress, the sound is already excellent.
Happy holidays to you all.
Attachments
SRPP preamplifier MK3
Hi Eric,
I didn't publish the Gerber files because I didn't received a lot of inquiries and I have sent them directly to those who contacted me by PM
To make it simpler I put the Gerber files with this message, however while I was working on version MK2 of this preamp, I found that I didn't biased the heater voltage to about +50 to +75 V to limit the voltage between heater and cathode Normally this voltage in limited to 100 V on most tubes ! I should say that I didn't had any problem with this voltage on my prototype, with 295 V power supply I had just 90 V on the top cathode, but it will be safer to take it in account
I would like also to remind you that I didn't build and test the version MK3, but it is just a more compact version with less than 10 cm to make it available at lower price (5 $ for 10 pieces) from PCBWay, however you have to check it and there is always the risk of layout error
Good luck and publish pictures please...
Happy new year to you and all others Audio friends
Marc
Hi Eric,
I didn't publish the Gerber files because I didn't received a lot of inquiries and I have sent them directly to those who contacted me by PM
To make it simpler I put the Gerber files with this message, however while I was working on version MK2 of this preamp, I found that I didn't biased the heater voltage to about +50 to +75 V to limit the voltage between heater and cathode
Normally this voltage in limited to 100 V on most tubes ! I should say that I didn't had any problem with this voltage on my prototype, with 295 V power supply I had just 90 V on the top cathode, but it will be safer to take it in account I would like also to remind you that I didn't build and test the version MK3, but it is just a more compact version with less than 10 cm to make it available at lower price (5 $ for 10 pieces) from PCBWay, however you have to check it and there is always the risk of layout error
Good luck and publish pictures please...
Happy new year to you and all others Audio friends
Marc
Attachments
Hi Philippe,
Very nice EL34 Baby Huey with the TOROIDY Transformer, much more beautiful than mine with the Hammond that I had in stock and that I have used
I am now impatient to build the QUAD KT120 Mono Blocks with the TOROIDY CFB transformer that I have already bought
I put again the picture that you take of mine for easy comparison on the same page...
Happy New Year 2019 with new exciting projects
Marc
Very nice EL34 Baby Huey with the TOROIDY Transformer, much more beautiful than mine with the Hammond that I had in stock and that I have used
I am now impatient to build the QUAD KT120 Mono Blocks with the TOROIDY CFB transformer that I have already bought
I put again the picture that you take of mine for easy comparison on the same page...
Happy New Year 2019 with new exciting projects
Marc
Attachments
Hi Francois,
Apologies for the late response, I have been on holiday in a place with no connectivity. The 290FEX (240V in my region) worked well, with the higher value options from the BOM. I also experimented a bit with using the 6.3VAC for the heaters and it worked perfectly, went back to dc, because I had those supplies in the case anyway. But, it’s a viable option.
I found that I didn't biased the heater voltage to about +50 to +75 V to limit the voltage between heater and cathode
Marc
Hi Marc or Prasi
Not biasing the heater will be problematic after a while (from what I read) and will damage your tubes. Would it be a pain to add the 2 required resistors and connect thei junction to one side of the heaters ?
Resistors could be as exemple 220k, 2W and 75k, 1W going to gnd.
Please confirm if you can so I can give it a go w pcbway. If you can’t I will hardwire it.
Maybe SV1 could be removed and that empty space replaced by the 2 resistors
Thanks
Eric
Hi Eric,
No need to modify the PCB, these resistors can be added to the power supply !
The jumper is useful if you want to use 6N1P tubes !
I am planning to make a sub miniature tube version fot the 6N16B ( 6N16B-V double triode tube - OTHER tubes - Tubes-Store.com ) when I will have some time
Rgds
Marc
No need to modify the PCB, these resistors can be added to the power supply !
The jumper is useful if you want to use 6N1P tubes !
I am planning to make a sub miniature tube version fot the 6N16B ( 6N16B-V double triode tube - OTHER tubes - Tubes-Store.com ) when I will have some time
Rgds
Marc
Thanks and no need for apologies - hope Santa brought you nice goodies and plenty of joy to your “place of no connectivity”.
Glad to know the 290 XXX works well for you EL34 BH. Are you using one 290 per stereo side? I was mainly concerned about the bias supply and wondered if the 290 sources sufficient current. Do you perhaps know what the current requirement is on the bias supply per PCB?
Btw., I’m an expatriot living in the U.S, grew up op a farm near Warmbath, Transvaal, as they were called back then.
