Confirming that the Mk2 EL34 version requires an external power supply including bias, HV and DC recommended for heaters. The GB offered PS PCB does all that plus delay HV switching. One PS PCB can serve both channels on a stereo amp.
The EL84 PCB includes the power supplies (but no delay switching) and does not need the GB PCB. Benefits of the delayed switching of B+ is questioned by many and probably fine not to have it on the EL84 BH.
The EL84 PCB includes the power supplies (but no delay switching) and does not need the GB PCB. Benefits of the delayed switching of B+ is questioned by many and probably fine not to have it on the EL84 BH.
As I’m finally getting into my build I was reviewing previous posts and noticed your issue regarding the use of the smps heater supply, mentioned 10 months ago. I don’t think it’s a problem to apply the HV and heater supply simultaneously, as in most vintage amplifiers, but would think it could be a problem to apply HV 20-30 seconds before the heater supply comes on. How have you resolved the issue, or did it prove to to be not a problem? Please share an update on you use and enjoyment of your BH.
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Guys,
Thanks for setting up the Mouser Project for the MKII and PS, that made things really easy.
Placed order today to build using the board set Prasi sent me.
For your info - I am going to use KT77 output tubes with some old Hammond 1650P output trannies I've had on the shelf for years.
Cheers,
Ian
Thanks for setting up the Mouser Project for the MKII and PS, that made things really easy.
Placed order today to build using the board set Prasi sent me.
For your info - I am going to use KT77 output tubes with some old Hammond 1650P output trannies I've had on the shelf for years.
Cheers,
Ian
Mouser Projects
Yes, that does make things easier. Be sure to go through those as they've been tweaked a bit and just need to make sure all the parts are correct.
In particular, I never actually found the correct molex connectors. It was more about the "other end" of the connector and not the ones on the boards. Finding the right part number to put on the end of the wire to connect to the one on the board was what I never found. I actually wound up removing the ones from the BOM on the board and using ones that were a bit different that matches.
That's the one and maybe the only critique of the boards, the connectors for the HV, bias/driver, and the heaters. Mostly just the HV ones, I'm not entirely sure the connector on there is actually specified for over 400v, it seems the ones I purchased listed as good up to only 300v or something.
The connectors from the power tranny are good, it's only the ones from the PSU feeding the channel boards that I had problems with. All pretty minor really. If it were up to me (and I'm a bit old school), I would prefer a bit more space on the boards connection holes and some robust screw terminals.
gabo
PS - I hope nobody takes offense to any of these comments, this has been a very good and rewarding project and I appreciate everything that was done. It's all good, just a tweak I would make if there is ever a MK3 version.
Yes, that does make things easier. Be sure to go through those as they've been tweaked a bit and just need to make sure all the parts are correct.
In particular, I never actually found the correct molex connectors. It was more about the "other end" of the connector and not the ones on the boards. Finding the right part number to put on the end of the wire to connect to the one on the board was what I never found. I actually wound up removing the ones from the BOM on the board and using ones that were a bit different that matches.
That's the one and maybe the only critique of the boards, the connectors for the HV, bias/driver, and the heaters. Mostly just the HV ones, I'm not entirely sure the connector on there is actually specified for over 400v, it seems the ones I purchased listed as good up to only 300v or something.
The connectors from the power tranny are good, it's only the ones from the PSU feeding the channel boards that I had problems with. All pretty minor really. If it were up to me (and I'm a bit old school), I would prefer a bit more space on the boards connection holes and some robust screw terminals.
gabo
PS - I hope nobody takes offense to any of these comments, this has been a very good and rewarding project and I appreciate everything that was done. It's all good, just a tweak I would make if there is ever a MK3 version.
Good to hear and great to have you on this thread again. Please give feedback as you proceed. Good luck.
A special thanks also to gabo - we learned a lot from you build and info sharing. Thanks.
Hello,
while waiting for the pcbs sent by Prasi I was reading all posts from the beginning and I read gingertube in article #607 which advocated resistances r33 and r38 a 270 ohms for the kt88? Are there any modifications to be made for the kt88 or can I follow the original EL34 bom without worry with the resistances 390 ohms?
while waiting for the pcbs sent by Prasi I was reading all posts from the beginning and I read gingertube in article #607 which advocated resistances r33 and r38 a 270 ohms for the kt88? Are there any modifications to be made for the kt88 or can I follow the original EL34 bom without worry with the resistances 390 ohms?
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Need this to be 100% correct in my brain
Hello Francois, I am getting rid of some pcbs that I have an excess of so I need to get this correct:
1. Using 2 x EL34 MK2 pcbs or 2 X EL34 original pcbs, I can use 1 MK2 PS pcb?.
2. Using 2 x EL84 pcbs, I do not need an external PS.
Just want to make sure I sell the correct boards.
Thanks for the help.
MM
Hello Francois, I am getting rid of some pcbs that I have an excess of so I need to get this correct:
1. Using 2 x EL34 MK2 pcbs or 2 X EL34 original pcbs, I can use 1 MK2 PS pcb?.
2. Using 2 x EL84 pcbs, I do not need an external PS.
Just want to make sure I sell the correct boards.
Thanks for the help.
MM
Couple of comments:
1. You can use the PSU PCB with any of the boards to get more capacitance and the delayed HV turn-on relay. But it is only required for the EL34 Mk2 PCBs, since the Mk2 PCBs do not have on-board power and bias supplies, like the original PCBs. One PSU board can supply two channels.
2. If you want to use 6550/KT88 or other higher bias power tube you should use the EL34 Mk2 PCBs and one PSU board (or two if you want to do dual mono power which nice, of coarse.)
3. You will have to build and add a simple 6.3 Vdc supply, or use a DC/DC converter. The BH PCBs (both original and Mk2) are recommended to be used with DC heater supplies, which are NOT on any of these boards. The PSU pcb has a 15Vdc. supply (working from 12.6 Vac input) that is intended to feed a DC/DC converter to supply the 6.3V heaters. (It might be simpler to build the 6.3 Vdc supply directly [same traces on the PSU pcb could be used] and not bother with the 12.6 Vac -> 15Vdc -> Dc/DC converter -> 6.3Vdc heaters approach Marc had intended when using the specified Toroidy power transformer)
So, my responses to your questions are:
1. Yes. However, if you use the PSU with the original amplifier PCBs you can delete the bias supply parts on the the amplifier PCBs.
2. Yes, except for a supply for 6.3 vdc as in 3. above.
Hope this helps.
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Well, you didn't REALLY read all the posts from the beginning or you would have your answer! There are many posts about the BOM for the MK2 version, which is different from the original. There are even posts with links to the BOM on mouser. AND there are many discussions about various resistor values and the use of KT88s.
So please, instead of SAYING you read "all the posts from the beginning," go actually read some of them.
Everyone here enjoys helping, but you also need to help yourself.
Thanks, gabo
Great mentality if it is the spirit of mutual aid! If I have read correctly from the beginning, but I am French and with the interpreter, it is not easy to understand everything that is marked... After you don’t want to answer me down buffis made your project all alone, I don’t think his spirit of sharing!
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I built several amps of Mr Nelson Pass and the people in the forum are much nicer than here and do not hesitate to help people! On the EL34 there is no construction guide , this must be found among the 700 post following in the forum! There is no bom regarding the KT88 so it is not easy to find out when are beginner in the tubes. Too bad that Marc is no longer there because he is one of the only ones who had the area to take the trouble to answer kindly to the person
I agree that it can be difficult to find specific information in looking through pages of posts. Let us work together to make this thread a nice place to visit and exchange information. I had hoped Marc, gingertube, or someone more knowledgeable than I would reply, but here is my view.
In post #607 gingertube talked about optimizing drive at high frequencies he concluded:
“In view of these possibly dodgy calcs I would be using 270 Ohms for R33 and R38 for CCS current of 2.4mA. That will get you to 100V pk-pk at up to about 70kHz.”
I know this had not been tested yet, but when I build my KT88 version I will use 270 Ohms. (Note that Q7 and Q9 would need some small heatsinks) 390 Ohms had been build and works well with KT88, but gingertube was talking about small optimizations that I’m willing to try. This is not necessary for EL34 and other tubes that require lower drive voltage swings, and have lower input capacitances.
In conclusion, if you build a KT88 Baby Huey (as I believe you do), you may decide for yourself between the already tried 390 Ohms, or the “possibly better, but likely inaudible” 270 Ohms for R33 and R38, in which case use small heatsinks on Q7&9. If someone else reads this and build for some smaller output tube then stay with the BOM value of 390 Ohms.
Hope this helps. Best wishes.
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OK thank you François for having answered me it is now clearer for me! Too bad there is no detailed building guide as on the Pass section , I think that during construction I will take quite a few pictures for the new ones who will build this amp after me . I’m very good at transistor amps but tubes are new to me.
Cordialy
Steven
Francois,
You may have answered my question by your question. I would like to build 1 set with a 6CA7 or similar tube and the other would have possibly a KT88 or similar tube. So based on your original suggestions I would use one original set of pcbs for the 6CA7 version & for the KT88 version I will use the MK2 set of pcbs and either 1 or 2 MK2 PS depending on dual mono or not. Thanks for the guidance.
MM
You may have answered my question by your question. I would like to build 1 set with a 6CA7 or similar tube and the other would have possibly a KT88 or similar tube. So based on your original suggestions I would use one original set of pcbs for the 6CA7 version & for the KT88 version I will use the MK2 set of pcbs and either 1 or 2 MK2 PS depending on dual mono or not. Thanks for the guidance.
MM
If I were building with the original boards, I would NOT use the MK2 PSU boards, and WOULD use the PSU that is included on those boards. That was the way those boards were designed and the BOM that was put together for that version corresponds to that.
If you wanted to use the MK2 PSU board with the original boards, it would require understanding what components to leave off the original boards and how to connect from the MK2 PSU to the boards. Which is all fairly easy to do, but if it were me I would keep it simple and just build it as it was designed.
Likewise, with the MK2 boards, I would use the MK2 PSU boards as that's the way that version was designed.
As for parts, I would use the parts supplied in the BOM. For the original version, I would use that BOM, for the MK2 version I would use the MK2 BOM.
The only thing about the MK2 version is R16, which is 47K (and that's correct) in the BOM, but the silk screening on the boards say 15K. All the rest of the silk screening is correct. So the boards are easy, just populate them with the values listed on the silk screening, except for R16 and you should be good.
Using 6CA7 or KT88 or EL34 or others is ok, just adjust your bias correctly.
gabo