DIY Audio Projects Forum
http://diyaudioprojects.com/Forum/

Mini Block class-A PP EL84 Amp project
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4055
Page 6 of 12

Author:  gofar99 [ 05 Feb 2015, 20:37 ]
Post subject:  Re: Mini Block class-A PP EL84 Amp project

Hi, Yes the minis are rather sweet sounding. Glad to have another happy diyer. I have started to fiddle with Arduinos and would like to see the sketchs. It maybe should go into the solid state place though. Just let us know where it is.

Good listening
Bruce

Author:  lukemiller3000 [ 11 Feb 2015, 22:53 ]
Post subject:  Re: Mini Block class-A PP EL84 Amp project

Bruce,

The sketch can be found at viewtopic.php?f=10&t=5104

Cheers,
Luke

Author:  John Smith [ 11 Oct 2015, 18:00 ]
Post subject:  Re: Mini Block class-A PP EL84 Amp project heater diagram

Forgive me for a newbie question, I looked at the pinout of the 5751 and your circuit does not show how the heater pins hooked up, other than mentioning 0.1uF capacitor, is there any reference that explains this?

Author:  gofar99 [ 12 Oct 2015, 16:04 ]
Post subject:  Re: Mini Block class-A PP EL84 Amp project

Hi John. Fortunately the tube pin outs for most tubes are loosely standardized. For nine pin tubes it is generally 4 and 5. If there is a centertap it is generally pin 9. This is the situation with the 5751, and all the 12AU7, 12AT7, 12AX7 and all the ECC variations of them. Octal (large 8 pin tubes) vary a bit... common power tubes (6V6, 6L6, KT66, KT77, KT88, 6550 and many others ) use pins 2 and 7 for the heaters. I don't know of any that have centertaps. 8 pin preamp tubes usually use pins 7 and 8. For a good reference I attached a link to an on line tube data base. I lists nearly all tubes you are likely to run into.

http://tubedata.milbert.com/index.html

Good listening
Bruce

Author:  wdecho [ 25 Jul 2016, 11:43 ]
Post subject:  Re: Mini Block class-A PP EL84 Amp project

Another question on the heater circuit. The EL84 heaters work on 6.3V but you have a 12V PS, but the EL84 tubes are wired in series. Does wiring the output tubes in series make it possible to run the output tubes on 12V?

Author:  gofar99 [ 25 Jul 2016, 12:23 ]
Post subject:  Re: Mini Block class-A PP EL84 Amp project

Hi, Yes. When you put them in series each sees approximately 6 volts. There will probably be a slight variation because individual tubes will consume a little more or less current than each other. As long as the tubes are from the same source, company and hopefully same manufacturing batch they will be very closely matched. Tubes from different brands should not be used this way. They may work OK and may not. Not all manufacturers follow the spec closely. If you chose to use a different power arrangement you could use 6 volts on everything. It will not have an effect on the sound though. I use 12 volts as it is easier to get a well filtered 12VDC at a given current than 6 VDC at twice the current. This feature carries over into all the power amps and indeed is used in my commercial designs.

Good listening
Bruce

Author:  wdecho [ 29 Jul 2016, 08:49 ]
Post subject:  Re: Mini Block class-A PP EL84 Amp project

I finished building this amp yesterday and I am impressed with its performance. I build for a hobby and this year I have built a 45 tube, a 300B, and a Decware Zen, among others. This amp will hold it's own against any of them. I have not done any A/B'ing yet but I was mesmerized for a few hours and had to make myself cut it off to go to bed. This was my first push pull tube build. I have built 4 Nelson Pass Firstwatt clones both SE and PP and still have 2 that are in my possession, a F6 and M2 both which are push pull amps. This is my 3rd Oddwatt project and I am very satisfied with everyone of them. I am a cheap diy'er, we are noted for that. I do try and use a very good part but nothing extravagant. My coupling capacitors of choice has been orange drops but they are not available in .33uf from my supplier so I thought I would try some very cheap polyester DME caps from Cornell Dubiliear while I was making my Mouser order until I could order some better ones. I am not going to be in any hurry to change them out. They sound fine to me. I have tried some Russian PIO caps in my SET builds and did not particularly care for them over a decent poly. They may be great in this amp though. I had very good results using the 6P15P-EV tubes in the Decware build and decided to give them a try in this amp. The suppressor grid and cathode pins on the sockets will need to be tied together which is not a big deal. They are not tied internally as the EL84 or the 6P14P tube. This amp sounds fantastic as is with the cheap, but good, caps and these 6P15P-EV tubes. I have intentions of buying some EL84's for comparison at a later date.

This is a great kit for a fantastic sounding amp that will hold it's own against far more expensive retail amplifiers. Bruce has put a kit together with quality parts for builders to buy at a great price without sourcing everything themselves. Building is a hobby for me as much as a challenge than having another amp. I have over a dozen around my house now and I hope to build many more.

Again, hats off to Bruce for designing such a lovely sounding amp.

Author:  wdecho [ 29 Jul 2016, 08:55 ]
Post subject:  Re: Mini Block class-A PP EL84 Amp project

I forgot to mention that I had distortion upon firing it up and figured it was probably the feedback circuit wired wrong. I cut the wires that make the feedback circuit and solved the problem. The amp is behaving itself and sounding great without feedback so I will probably not try and hook it back up. My horns are very efficient so I am using very little power to drive them. I took the feedback from the 8 ohm tap and if I understand Bruce correctly I need to connect the feedback wire to the common or - wire if I want to see how it sounds with feedback.

Author:  gofar99 [ 29 Jul 2016, 09:51 ]
Post subject:  Re: Mini Block class-A PP EL84 Amp project

Hi, Having the phase of the output transformer windings reversed is a common thing. The factory markings indicate how they expect it to be done. I use it to invert the signal so you need to swap the blue and brown wires (if you use the Edcor ones). Alternatively if you don't need the 4 ohm tap you can swap the ground and 8 ohm ones on the output side. The tap between 4 and 8 ohm would logically seem to work, but my experience is that it doesn't do well. But that is back to trannies 101 (remember that the Zin vs Zout are ratios squared of the turns).

I'm glad you like the amp it is one of my favorites. IMO a Poddwatt with the current mods, The CXPP10 trannies and good coupling caps (I like the Audyn True CopperCaps at present) will easily perform with amps with much higher costs and according to the manufacturers superior pedigrees.

Good listening
Bruce

Author:  wdecho [ 29 Jul 2016, 10:40 ]
Post subject:  Re: Mini Block class-A PP EL84 Amp project

[quote="gofar99"]Hi, Having the phase of the output transformer windings reversed is a common thing. The factory markings indicate how they expect it to be done. I use it to invert the signal so you need to swap the blue and brown wires (if you use the Edcor ones).


How about the screen wires, do they need to be swapped as well, white/blue with blue and white/brown with brown?

Page 6 of 12 All times are UTC - 6 hours [ DST ]
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/