I like the idea of beefing up the power supply in a ebay dyna 70. I have several tube amps, but my hopped up dyna gets all the play time.One thing I know is bass takes a lot of power. With the right mods a st70 can put out as much as 60 watts per channel simutanious. If you decide on a dyna mod, I have some info. Also it cool to watch the lights flicker when you turn it on!
pengboon said:Ok triode wired EL34 PP sounds like a good start. Can you guys point out some good, safe and relatively easy schematics for me to start looking at?
thanks.
Take a long look at "El Cheapo". Think in terms of building its "big brother".
Dhaen's PP 7591 thread shows a tube rectified, choke I/P filter, B+ PSU you could use. The 7591 project also shares a negative rail between bias for the "finals" and the constant current sink (CCS) in the tail of the splitter. I suggest you do the same thing.
Triode Electronics part # 22848ULT is a 35 USD O/P trafo intended for use in Fender Bandmaster and Vibrolux guitar amplifiers. Like the smaller TF-110-48-UL trafo used in "El Cheapo", the 22848ULT will work for HIFI at reduced max. power. Perhaps a local winder can replicate the Fender original too.
Eli Duttman said:
My recommendation for PP triode wired EL34s with loop NFB stands. That gives you enough power for transients, decent voice coil control, and a relatively easy build. Run the EL34s with 400 or so V. on the plate and an idle current of 40 mA. EL34 screen grids are tough, so tie them to the plates with 100 Ohm resistors of the "flavor" you like best.
The PP tube amp WILL be between the SS and the SET.
I looked at a few schematics, and I like this one for simplicity.
http://audiotropic.netfirms.com/Projects/ampEL34.html
Since I have a preamp, I can start with the 6SN7? Will this work well for me?
This looks very doable as well: http://www.vacuumstate.com/schematics/pp-1c_s.gif And I read there is a revision of it..?
thanks again for helping this noob...
pengboon said:
I looked at a few schematics, and I like this one for simplicity.
http://audiotropic.netfirms.com/Projects/ampEL34.html
Since I have a preamp, I can start with the 6SN7? Will this work well for me?
This looks very doable as well: http://www.vacuumstate.com/schematics/pp-1c_s.gif And I read there is a revision of it..?
thanks again for helping this noob...
Pengboon,
IMO, the Infinity speakers LIMIT your options. You need an amp with a substantial damping factor.
The VSE (Allen Wright) circuit does not use loop NFB. Therefore, it is probably inadequate in the damping factor dept. BTW, the VSE design uses a differential cascode and a CCS. That's not very simple.
The AudioTropic (Poindexter) circuit is 3 stages, while the "El Cheapo" topology is 2 stages. Also, good 6SN7s are costly. NICE 12AT7s are available at relatively reasonable cost. 25 USD can get you a Mullard made 'T7. NOS 6SN7s carry hefty price tags.
Nonsense. Sovtek 6SN7's are quite reasonable and also quite nice. I just completed a project using the Sovtek's and had no problems with them at all. These showed no tendency to be microphonic (a big problem with US NOS 6SN7's) were solidly constructed, and even included grid cooling "wings" that the US NOS 6SN7's don't have. "NOS" isn't always the magic word, and you don't have to go broke buying over priced small signal VTs.
Eli Duttman said:
Eli, thanks for your advice once again.
I understand that about my speakers. And much as I would like to, at this point of time, I can't do anything about them. My eventual goal will be DIY with full range drivers.
But that's a different story in the future. Right now I will have to make the best of what I have. I can and am willing to "invest" a little more on good quality parts to prepare for the eventual goal. God a couple more questions:
1) can the CCS be implemented by a LM317? Reason being only one IC, and consequently one heatsink. Will this work?
2) Can I use a pot for the feedback (as Claus Byrith has done in his Lundahl paper)? To provide for some adjustability.
3) Can I combine phase spliiter and power stage like what www.diyparadise.com/simpleel84.html has done, thereby effective having only one stage since I already have a 6h30 line stage, which I suspect has quite a high gain, or is it still insufficient (I hope that it will reduce the sentivity this way)? If possible, then I can save on a B2+ and a B- and their associated components too! I could also use a CCS tied to ground to bias the EL34s. Or is one of the purpose of the 12AT7 to "shape the sound"?
4) I am able to buy Hammond (http://www.hammondmfg.com/claspg.htm), James (http://www.octave-electronics.com/Parts/james.shtml) and Tamura brands of transformers, and I am willing to spend more to get a good OPT. Which specs should I be looking at? I tried to find out the ideal anode to anode resistance for triode strapped EL34 PP for lowest distortion, but had no luck there...
thanks again, you (and the rest on the board) have been very helpful and patient in helping me learn... sorry for so many questions too..
pengboon said:
1. I would consdier this ckt
http://www.diyaudio.com/forums/attachment.php?s=&postid=779085&stamp=1133366034
it is from another thread.
http://www.diyaudio.com/forums/showthread.php?s=&postid=811408#post811408
2. Since you are in Singapore locate Poly Electronics. Guy called Steven Tay. He makes nice OPTs for about S$300/pr. Should be nicer than Hammond. For about twice that price he can roll you C core versions like Lundhal.
3. BTW what preamp are you using? Also there is some global feedback so you can eliminate any tubes in the ckt you state.
pengboon said:
This is a preamp, no...?
Nope just part of the power amp. add EL34 to make power amp. i also suspect that KT88 or 6550 could be added. Wayne (the designer) should be consulted though.
http://www.diyaudio.com/forums/attachment.php?s=&postid=811638&stamp=1136905599
this is the ckt with EL34 added.
Eli Duttman said:
Eli Duttman said:
My recommendation for PP triode wired EL34s with loop NFB stands. That gives you enough power for transients, decent voice coil control, and a relatively easy build. Run the EL34s with 400 or so V. on the plate and an idle current of 40 mA. EL34 screen grids are tough, so tie them to the plates with 100 Ohm resistors of the "flavor" you like best.
The PP tube amp WILL be between the SS and the SET.
Eli,
I like your Idea of a 2-stage amp. But got a few more questions I hope you or anyone from here could help me answer...
I did some measurements. I have about 0.35V at input of preamp, 3.5V at almost max vol after 6h30p preamp. I read that I need about 24V for full output of the EL34, is this correct?
Are there any good suitable alternatives to 12AT7/ECC81 in my situation? Can anyone share their experiences using different tubes as phase-splitters/input drivers for the EL34?
When you mention fixed bias above, do you mean for the phase splitter?
Where does grid 3 of the EL34 go to? Some circuits connect it to cathode, some to anode through a resistance, a little confused over that at the moment...
I am also looking at Steve Bench's circuit, and it looks like there is some feedback into the EL34 grid? What's the difference between taking feedback from primary and speaker side of the OPT?
thx for helping... !
Eli Duttman said:
Hi,
I have changed my speakers to Coral Beta 8 (single driver full ranger) in a bass reflex box, and my preamp to a 12B4 one on the 12B4 thread. Currently using a EL84 PP based on Gabevee's Magnavox circuit running in UL. I found the UL to be more punchy. Had to reduce the plate voltage to 300V as my old philips miniwatts glowed at the 330V I used to run the JJs. What do you think of this setup? How can I improve it without running up the costs?
Just for discussion, what power amp would you recommend for this setup?
pengboon said:
No I dont think you can feed the feedback in from C1.
Better still ask Wayne (see 1st link) and follow the links below
http://www.diyaudio.com/forums/showthread.php?s=&threadid=69042&perpage=10&highlight=&pagenumber=5
http://www.diyaudio.com/forums/showthread.php?s=&threadid=72536&perpage=10&highlight=&pagenumber=17
i'd recommend the one i'm about to build:
http://www.dc-daylight.ltd.uk/Valve...ltra-linear-Hafler&Keroes/UL-H&K-Nov1951.html
schematic at the bottom
however, you want to replace C2 and C3 with .47uF instead of .2, and C4 and C5 with .047uF instead of .2, it stabilizes the filter networks. if you want to use an 8-ohm tap only, change R4 to 8.48k or as close to that as possible, and C7 to 170pF. personally i use an overrated 60w edcor output, 8 ohms output. it should sound very nice at around 20 watts, but it can hit 25 or so for transients i hear
http://www.dc-daylight.ltd.uk/Valve...ltra-linear-Hafler&Keroes/UL-H&K-Nov1951.html
schematic at the bottom
however, you want to replace C2 and C3 with .47uF instead of .2, and C4 and C5 with .047uF instead of .2, it stabilizes the filter networks. if you want to use an 8-ohm tap only, change R4 to 8.48k or as close to that as possible, and C7 to 170pF. personally i use an overrated 60w edcor output, 8 ohms output. it should sound very nice at around 20 watts, but it can hit 25 or so for transients i hear
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