I don't think so - just because the issue seems to be with the 317 ccs. When I touch the metal tab of the 317 the hiss goes away.
There's not much stuff out there on this, but I did find a case where someone commented "I'll bet the 317 is oscillating". Not sure how to cure that exactly, I might sub in another 317HV to see if that cures it.
Fran
There's not much stuff out there on this, but I did find a case where someone commented "I'll bet the 317 is oscillating". Not sure how to cure that exactly, I might sub in another 317HV to see if that cures it.
Fran
Are you running 2 LED's per input 6SN7 or just one per tube? I am only running one per tube.
Does the hiss follow either the input or driver tube? I would assume you swapped tubes already but just asking...
You had me thinking about an earlier post about the EL34 heaters...I looked at the Tubelab SimpleSE for reference and while he ignores the heater winding CT the heaters for the power and input tubes are all referenced to B+/4. I believe that i have accomplished the same thing via the CT...
Does the hiss follow either the input or driver tube? I would assume you swapped tubes already but just asking...
You had me thinking about an earlier post about the EL34 heaters...I looked at the Tubelab SimpleSE for reference and while he ignores the heater winding CT the heaters for the power and input tubes are all referenced to B+/4. I believe that i have accomplished the same thing via the CT...
sounds
like a hf oszillation problem
heaters to ground (best to elevate 30-40V)?
gridstoppers everywhere?
and the lm317 tends to oszillate if uesed as cs around 1mhz in some cases, i would prefer a simple battery biases irf830 cs
like a hf oszillation problem
heaters to ground (best to elevate 30-40V)?
gridstoppers everywhere?
and the lm317 tends to oszillate if uesed as cs around 1mhz in some cases, i would prefer a simple battery biases irf830 cs
OK, I figured out the hiss..... the 317s were hot as hell so some extra heatsinking sorted out the hiss. They must get noisy the higher the load on them - do don't ignore that!!
I have a little buzz to sort out, and I want to tidy up my grounds a bit, but I'm planning on hooking it up soon to hear how she sounds. Looking forward to that!
I went for 2 LEDs on the cathode giving me a voltage drop of 3.6V, but it may be that its too much current. I might well have to go back to 1. Referencing the centre tap to 1/4B+ is hardly any harm - and the spec does say a heater to cathode of 100V, so it might be better to send it to 1/4B+ rather than ground. And given that the heaters are AC, then it might be better to use a balance pot to cancel hum.
Fran
I have a little buzz to sort out, and I want to tidy up my grounds a bit, but I'm planning on hooking it up soon to hear how she sounds. Looking forward to that!
I went for 2 LEDs on the cathode giving me a voltage drop of 3.6V, but it may be that its too much current. I might well have to go back to 1. Referencing the centre tap to 1/4B+ is hardly any harm - and the spec does say a heater to cathode of 100V, so it might be better to send it to 1/4B+ rather than ground. And given that the heaters are AC, then it might be better to use a balance pot to cancel hum.
Fran
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And she lives!!!
Got her all fixed up tonight, rearranged the grounding to star and all is well. The amp is quiet as a mouse and all voltages are within a few volts of expected (<10% out anyway). I used the "standard" feedback - I'll try the second scheme at some point.
My PSU is a little different to Broskie's. I have a full bridge made from those nice fairchild stealth diodes, into 470uF-52r-100uF-15h-100uF with a 0.68uF bypass at the end of that chain. I also added 33uF//.33uF bypass as decoupling at the PS feed into the phase splitter. I'm using a twisted pear LCDPS for the 6SN7 heaters and AC heaters for the EL34s. The CT of the heater is tied to star ground, 6SN7 heaters elevated to 1/4 B+. LM317ccs on the EL34 cathode running at 83mA.
ckgpkg: the cathodes of the EL34s are sitting ~40V off ground, which gives a heater to cathode diff of ~35V. If you elevate these heaters to 1/4 B+ (~110V) they are now up at 70V off the cathode so still well within the 100V rating.
I kept the 2 red leds on the input cathode.
Fran
Got her all fixed up tonight, rearranged the grounding to star and all is well. The amp is quiet as a mouse and all voltages are within a few volts of expected (<10% out anyway). I used the "standard" feedback - I'll try the second scheme at some point.
My PSU is a little different to Broskie's. I have a full bridge made from those nice fairchild stealth diodes, into 470uF-52r-100uF-15h-100uF with a 0.68uF bypass at the end of that chain. I also added 33uF//.33uF bypass as decoupling at the PS feed into the phase splitter. I'm using a twisted pear LCDPS for the 6SN7 heaters and AC heaters for the EL34s. The CT of the heater is tied to star ground, 6SN7 heaters elevated to 1/4 B+. LM317ccs on the EL34 cathode running at 83mA.
ckgpkg: the cathodes of the EL34s are sitting ~40V off ground, which gives a heater to cathode diff of ~35V. If you elevate these heaters to 1/4 B+ (~110V) they are now up at 70V off the cathode so still well within the 100V rating.
I kept the 2 red leds on the input cathode.
Fran
Quick question, The schematic on the Broskie website shows the EL34 triode connected with the G3 connected to the plate as well. The extremely comprehensive Mullard datasheet at Franks shows only conditions for G3 connected to the cathode. My question is will the triode curves be drastically different for this mode of operation and has anybody charted the difference?
Mctavish: I don't know....
Btw, I had a little bit of motorboating at turn off on this amp - soft thumping lasting 5-8secs. I had to add a little extra decoupling for the input valve.
Hoping to hear it in earnest tonight...
Fran
Btw, I had a little bit of motorboating at turn off on this amp - soft thumping lasting 5-8secs. I had to add a little extra decoupling for the input valve.
Hoping to hear it in earnest tonight...
Fran
Hi,
I'm also interested in building this 'Broskie' EL34/PP. So it's nice to read about your projects. But
there's one thing that makes me a bit confused, Why put a CCS in the output cathodes? Wouldn't
a constant Voltage be what one will have there? I know that one can use a CCS to make the output pair
act a self splitting stage. But in this amp we have a phase splitter.
I'm trying to learn this.
Rolf
I'm also interested in building this 'Broskie' EL34/PP. So it's nice to read about your projects. But
there's one thing that makes me a bit confused, Why put a CCS in the output cathodes? Wouldn't
a constant Voltage be what one will have there? I know that one can use a CCS to make the output pair
act a self splitting stage. But in this amp we have a phase splitter.
I'm trying to learn this.
Rolf
A CCS regulates the current flow very closely. It allows the voltage to vary while keeping the current constant. I always took it that the CCS helped out by being more linear, plus that it presented a better load (although I think thats more in plate load CCS).
Anyway, the amp si doing very nice duty here tonight in the main system. The sound is dynamic, with very good detail. There is a touch of warmth - probably more so than the EL84 version from the tubecad page, but with a real sweetness too. Its a vibrant sound.....
Overall a good result I think. I imagine I'll be keeping this one. Now that I know it works well, I need to go back and tweak a few more things. I need larger wattage plate resistors (anyone got any 1W 20k they want to pass on?), of course try the alternative feedback scheme, and maybe try a CCS on the plate of the input 6SN7.
************************
errr, mid-post change of plan!!!!
Following a nice hisssssssss sound, it seems some of the magic smoke has escaped from the amp!!! Just opened her up and the main reservoir cap is gone. It was a second hand cap, maybe it was just dried out, but it spewed its contents over the inside. Doesn't look like any other damage was done......
Eeeek!
Fran
Fran
Anyway, the amp si doing very nice duty here tonight in the main system. The sound is dynamic, with very good detail. There is a touch of warmth - probably more so than the EL84 version from the tubecad page, but with a real sweetness too. Its a vibrant sound.....
Overall a good result I think. I imagine I'll be keeping this one. Now that I know it works well, I need to go back and tweak a few more things. I need larger wattage plate resistors (anyone got any 1W 20k they want to pass on?), of course try the alternative feedback scheme, and maybe try a CCS on the plate of the input 6SN7.
************************
errr, mid-post change of plan!!!!
Following a nice hisssssssss sound, it seems some of the magic smoke has escaped from the amp!!! Just opened her up and the main reservoir cap is gone. It was a second hand cap, maybe it was just dried out, but it spewed its contents over the inside. Doesn't look like any other damage was done......
Eeeek!
Fran
Fran
Okej,I see.
of what you did when you buildt the 'Red Light District' Anyway I'm glad it works. And I
have no intention to spoil the fun with my dumb questions😉
Regards
Rolf
Here lies my confusion, I don't want the cathode voltage to vary at all. It's the oppositeYou said:
of what you did when you buildt the 'Red Light District' Anyway I'm glad it works. And I
have no intention to spoil the fun with my dumb questions😉
Regards
Rolf
I've gone back over the PS in my amp. I ended up taking out the choke (eventually found the info that the choke was only rated for 100mA - no wonder it was getting hot!
So I've gone back to a CRCRC set up, and because my Tx is putting out ~450 or so I have >510V at the first C, ending up with 440 at the main B+. I'm using stacked caps to get the voltage rating...... one of the issues when using a salvaged Tx!!!
So the whole amp gets quite warm!!
Sound is good though......
So I've gone back to a CRCRC set up, and because my Tx is putting out ~450 or so I have >510V at the first C, ending up with 440 at the main B+. I'm using stacked caps to get the voltage rating...... one of the issues when using a salvaged Tx!!!
So the whole amp gets quite warm!!
Sound is good though......
Shuguang EL34
hi,
this is my EL34 pp amp, ultra-linear output, based on the Mullard 5-20 and HK Citation V amps....sounds fantastic, bass is tight and controlled which is a revelation.....
input tubes are Russian 6J9 pentode, Hitachi 6CG7 LTp drivers....
SS rectification, using a common mode choke and generous filtering, fast rectifiers isolate the 2 channels with its own filter caps.....B+ at OPT center lead is 445 volts, tubes are biased at 33mA each.....so that they are idling at about 15 watts each.....
hi,
this is my EL34 pp amp, ultra-linear output, based on the Mullard 5-20 and HK Citation V amps....sounds fantastic, bass is tight and controlled which is a revelation.....
input tubes are Russian 6J9 pentode, Hitachi 6CG7 LTp drivers....
SS rectification, using a common mode choke and generous filtering, fast rectifiers isolate the 2 channels with its own filter caps.....B+ at OPT center lead is 445 volts, tubes are biased at 33mA each.....so that they are idling at about 15 watts each.....
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Thats a very nice build Tony. Very neat inside. Mine is like a bag of snakes by comparison!! Its quiet though, so I'm happy enough! Will take a pic tomorrow....
Fran
Fran
thanks, pin3 leads should be clear of nearby pin2, i suffered a spark over because of the very close proximity of the opt leads to pins, fixed that and everything is fine.......
the Russian 6J9 is likewise a revelation......very quiet and clear sounding.....
i've used Aerovox 1000ufd/250 volt caps is series per channel, 2 x 1100uf/300volt caps in series after the common mode choke, the negative of 0volts is taken from this cap, then 2 x 220uf/400volt caps also in series before the common mode choke...no film type bypass were used in any of these caps....and all of these caps were harvested from discarded computer psu's.......
the Russian 6J9 is likewise a revelation......very quiet and clear sounding.....
i've used Aerovox 1000ufd/250 volt caps is series per channel, 2 x 1100uf/300volt caps in series after the common mode choke, the negative of 0volts is taken from this cap, then 2 x 220uf/400volt caps also in series before the common mode choke...no film type bypass were used in any of these caps....and all of these caps were harvested from discarded computer psu's.......
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Very similar here. The sound from the tubecad amp is very dynamic, clean and with a touch of warmth. Punchy bass too, which is always nice. I was thinking of picking up a pair of 6L6 or KT66 and seeing how they sound. Running some JJ EL34 and a mix f shuguang 6SN7 and russian 6H8S at the moment.
Fran
Fran
I went back today and fitted the "alternate" feedback resistors - 3.2k from each side of the OPT secondary to the cathodes of the drivers:
I'm listening to it now as I type - very hard to tell any difference at all from the standard one with the 2 x 1K divider to the driver stage ground. I think it seems a little "duller" sound.....
So it might be that the values need to be adjusted, or maybe the other way is better?
Fran
I'm listening to it now as I type - very hard to tell any difference at all from the standard one with the 2 x 1K divider to the driver stage ground. I think it seems a little "duller" sound.....
So it might be that the values need to be adjusted, or maybe the other way is better?
Fran
I dropped that feedback resistor to 2k - and while I have a lot more gain now, the sound is also livelier, more dynamic sounding. I'll go back and try ~2.5k next as a mid way point.
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