Yes, 6SL7 for the input tube, 6DJ8/ECC88 for the phase splitter. Set the CCS for the input tube to 1.2mA. Replace the "bottom" red LED in the 6SL7 cathode with a 47 ohm resistor, the feedback resistor with a 300R/1W, then bring the feedback to the junction of the 47R and red LED.
I've got one on the bench at the moment for measurement using one of the cool boards you sent me.
I've got one on the bench at the moment for measurement using one of the cool boards you sent me.
A la: luciole rouge
It sims to about 0.024% THD@10W. Haven't yet put solder to copper so I can't verify.
An externally hosted image should be here but it was not working when we last tested it.
It sims to about 0.024% THD@10W. Haven't yet put solder to copper so I can't verify.
Yves,
Off Topic - do you have link to that RCA PhotoPhone. Bootstrapping the anode load of a CC stage as you suggest is something I've wanted to try. I recall from my days of playing in the Sand Pit that boostrapping the VAS load imparted "sonic magic" compared to a CCS load (and a degraded CCS with parallel resistor was sonically better than a straight CCS). I'm wondering if that same "magic" will result with tubes?
Appologies for the off topic.
Cheers,
Ian
Off Topic - do you have link to that RCA PhotoPhone. Bootstrapping the anode load of a CC stage as you suggest is something I've wanted to try. I recall from my days of playing in the Sand Pit that boostrapping the VAS load imparted "sonic magic" compared to a CCS load (and a degraded CCS with parallel resistor was sonically better than a straight CCS). I'm wondering if that same "magic" will result with tubes?
Appologies for the off topic.
Cheers,
Ian
Are there any circuit boards available for this project? I have a perfect donor amp to build this...
Nope, but the circuit is so simple, point-to-point should be easy- I have photos on my website (and downloadable drilling diagrams for the top plate) illustrating the layout. If someone wants to design boards and sell them, I have no problem with that.
You don't really get less distortion. With UL, the open loop gain is lower, so there's less feedback. That tends to raise distortion. Now, we're talking about pretty small differences, but why not enjoy the extra power if it costs nothing in linearity?
In a spare time during weekend I made a couple mods to my RDL.
1. Replaced 4 coupling caps of 0.1uF with 1,8uF.
2. Replaced bias resistor for input tube with red LED and 15 ohm resistor in series. NFB resistor connected to LED and bias resistor junction is 100 ohm. That change is significant to reproducing details in highs and "attack" of bass.
3. Bypassed PSU caps with 20nF styroflex.
There has been continuous debate over phase splitter in another thread, so I cannot tell if 1. is correct value
1. Replaced 4 coupling caps of 0.1uF with 1,8uF.
2. Replaced bias resistor for input tube with red LED and 15 ohm resistor in series. NFB resistor connected to LED and bias resistor junction is 100 ohm. That change is significant to reproducing details in highs and "attack" of bass.
3. Bypassed PSU caps with 20nF styroflex.
There has been continuous debate over phase splitter in another thread, so I cannot tell if 1. is correct value
Those values will work fine. My data clearly show that the cathodyne will give nearly perfectly balanced outputs when set up as described in my article.
One more thing to try if you can- raise B+ to 500V, drop idle current to 20mA per tube (that will greatly reduce screen voltage), and connect your speaker to the 4 ohm tap of the output transformer. It's crazy, but it gives more power with no discernible distortion penalty and (at least with JJ output tubes) the amp seems to stay cool and stable. I have about 300 hours on my current set of tubes run this way and they test/act as new.
edit: Roger Modjeski suggests that the plate voltage can be run as high as 700V, with the idle current reduced to keep dissipation down.
One more thing to try if you can- raise B+ to 500V, drop idle current to 20mA per tube (that will greatly reduce screen voltage), and connect your speaker to the 4 ohm tap of the output transformer. It's crazy, but it gives more power with no discernible distortion penalty and (at least with JJ output tubes) the amp seems to stay cool and stable. I have about 300 hours on my current set of tubes run this way and they test/act as new.
edit: Roger Modjeski suggests that the plate voltage can be run as high as 700V, with the idle current reduced to keep dissipation down.
I have been running a Tubelab Simple P-P in fixed bias (similar design) with 460 volts on B+, 320 volts on the screens, idle current set for minimum THD and an unknown load impedance (probably 6600 ohms). I am not home to see which tap the speakers are on. This set up gives me about 30 WPC and great dynamic punchy sound. It works great with new production JJ, NOS or crusty old used GE, RCA or Sylvania tubes. Any Russian tube I have tried will run away within a few days. So will my (possibly counterfit) Ei 7189A's.
I have two of these. One is running JJ tubes and is used for HiFi. The other has both channels paralleled through a common OPT and I play my guitar through it. It makes 55 watts at 3% distortion. The 8903 reads 70 watts when I turn all the knobs to 11 and let it scream (25+% distortion). It is using some very old used Baldwin branded Sylvania 6BQ5's that I pulled from a church organ that was being scrapped. Both have been running for over a year and show no signs of distress.
hi guys. noticed a few new postings on this thread so i thought id search for some advice here.
id like to build the red light district this winter to pass the time indoors (living in Michigan). i built my first amp last winter. a pentode spud kit for first time builders. it was a blast so now im craving more. with the RLD though, my inexperience in choosing parts is a bit of a problem. right now im trying to decide which power and output transformers to purchase. im going to have to source everything as i dont have a scrap pile yet.
it happens that ive got a friend with a used hammond 273bx power supply that i could pic up. being a total beginer, i have no idea if that supply could be put to use in the RLD??? for the driver stage maybe??? i figure its a long shot. also if its a bust, any advice on the ideal power and output transformers would be a HUGE help.
also, im not sure if i've found all the availible info on the RLD? all ive found is this thread and SY's actual write up on it using google. couldn't find the DIYMAG write up. any other recources?
peace
phil
id like to build the red light district this winter to pass the time indoors (living in Michigan). i built my first amp last winter. a pentode spud kit for first time builders. it was a blast so now im craving more. with the RLD though, my inexperience in choosing parts is a bit of a problem. right now im trying to decide which power and output transformers to purchase. im going to have to source everything as i dont have a scrap pile yet.
it happens that ive got a friend with a used hammond 273bx power supply that i could pic up. being a total beginer, i have no idea if that supply could be put to use in the RLD??? for the driver stage maybe??? i figure its a long shot. also if its a bust, any advice on the ideal power and output transformers would be a HUGE help.
also, im not sure if i've found all the availible info on the RLD? all ive found is this thread and SY's actual write up on it using google. couldn't find the DIYMAG write up. any other recources?
peace
phil
You can always ask here.
There's lots of good transformers out there- if you can't find my favorites (James), the Dynaclones look very nice. Plenty of old SCA-35s out there as well, ripe for salvage. I've had very good luck with the Allied-branded Hammond power transformers. Haven't tried Edcor, but Pete Millett uses them and he knows what he's doing- I think that's low risk. In fact, you could use the transformer package sold for the Engineer's Amp at a very reasonable price.
There's lots of good transformers out there- if you can't find my favorites (James), the Dynaclones look very nice. Plenty of old SCA-35s out there as well, ripe for salvage. I've had very good luck with the Allied-branded Hammond power transformers. Haven't tried Edcor, but Pete Millett uses them and he knows what he's doing- I think that's low risk. In fact, you could use the transformer package sold for the Engineer's Amp at a very reasonable price.