Well, I hooked up the scope. Here is where your sig line is especially true SY!
As far as I can see there is a slight sine wave, but thats with the volt div at 20mV. It seems very "small" if you know what I mean. I don't see any major waves etc. If someone can tell me what I should have the volts and time divs set at and what to watch out for, I can do that. If I measure AC at the output Tx with my DMM I get <3mV, slowly going down.
Valves are indeed russian 6n14n and there is a bit of blue glow inside the black plates. They appear brand new and have a code on them 0480 (april 1980?)
Both channels settle to 65-70mV after being on for a few minutes. Screen voltage stays at 293V.
Going to listen now - reports later!
Fran
As far as I can see there is a slight sine wave, but thats with the volt div at 20mV. It seems very "small" if you know what I mean. I don't see any major waves etc. If someone can tell me what I should have the volts and time divs set at and what to watch out for, I can do that. If I measure AC at the output Tx with my DMM I get <3mV, slowly going down.
Valves are indeed russian 6n14n and there is a bit of blue glow inside the black plates. They appear brand new and have a code on them 0480 (april 1980?)
Both channels settle to 65-70mV after being on for a few minutes. Screen voltage stays at 293V.
Going to listen now - reports later!
Fran
OK,
listening:
Sound is good and all that - everything is as it should be, soundstage, bass mids and treble. All good and transients OK etc. Does sound different to my other amp, but then thats to be expected.
I do have some buzz - and its intermittent. Comes and goes, but I think its from the 24V aikido pre. When I mute the inputs, I get silence.
With the other amp hooked in, I had hum, stronger in the right channel. Now I have buzz, again, stronger in the right channel, and as I said a bit intermittent. Its independent of volume setting. Not terribly loud, but you would notice it in quiet passages.
Probably what I need to do is hook up a source with a built in volume control and use it for a while and see how the amp goes. If its OK (and it was in the workshop) then its the pre.
So more testing needed, but sonically the amp seems to perform well.
Fran
listening:
Sound is good and all that - everything is as it should be, soundstage, bass mids and treble. All good and transients OK etc. Does sound different to my other amp, but then thats to be expected.
I do have some buzz - and its intermittent. Comes and goes, but I think its from the 24V aikido pre. When I mute the inputs, I get silence.
With the other amp hooked in, I had hum, stronger in the right channel. Now I have buzz, again, stronger in the right channel, and as I said a bit intermittent. Its independent of volume setting. Not terribly loud, but you would notice it in quiet passages.
Probably what I need to do is hook up a source with a built in volume control and use it for a while and see how the amp goes. If its OK (and it was in the workshop) then its the pre.
So more testing needed, but sonically the amp seems to perform well.
Fran
Just to say the amp seems pretty stable. The buzz is definitely coming from the preamp, and is independent of volume. When I connected my squeezebox up directly to the RLD it is dead silent. It seems to be settling in nicely, been on today for about 4 hours so far and no hisses pops bangs or wallops.
So I seem to remember a link around here for diagnosing buzzes and hums (and this is raspy buzz, not hum). I searched but can't find. I think it was along the lines of buzzes come from one place and hum from somewhere else, but dang if I can't remember or find the link now. Anyone know where it is?
Fran
So I seem to remember a link around here for diagnosing buzzes and hums (and this is raspy buzz, not hum). I searched but can't find. I think it was along the lines of buzzes come from one place and hum from somewhere else, but dang if I can't remember or find the link now. Anyone know where it is?
Fran
ello,
I am building this amp and recently i saw the the electronic crossover at your website. Is there a convenient way that i can inplement those two in the same box. I mean, the ecc88 buffers are at ca 100 plate voltage which means that i need a third hv-supply. If possible, how would you implement adecuate buffers using for example the 400V supply for the ecc81 in the rld?
In my hand i have two altec 15335A bridging transformers (1:1, 15kohm/15kohm). In the datasheet, these units response are flat to about 40khz but the phase response are beginning to drift at 10khz and are -50degrees at 40 khz. Would these units compromise performace as input transformers?
Also i would like to say thanks for sharing your expertise and it has been a pleasure reading the article!
Axel
I am building this amp and recently i saw the the electronic crossover at your website. Is there a convenient way that i can inplement those two in the same box. I mean, the ecc88 buffers are at ca 100 plate voltage which means that i need a third hv-supply. If possible, how would you implement adecuate buffers using for example the 400V supply for the ecc81 in the rld?
In my hand i have two altec 15335A bridging transformers (1:1, 15kohm/15kohm). In the datasheet, these units response are flat to about 40khz but the phase response are beginning to drift at 10khz and are -50degrees at 40 khz. Would these units compromise performace as input transformers?
Also i would like to say thanks for sharing your expertise and it has been a pleasure reading the article!
Axel
No reason why not. Just be careful to keep it away from the transformers. As a practical matter, I'd probably substitute an ECC81 for the ECC88 and increase the B+ to 250V, just to reduce dissipation in the regulator- after all, you've got about a 40mA draw, so there's 4W per 100V to be dropped.
I put mine into the Heretical box, using the original Heretical board as the second cathode follower and a modified Heretical board as the first cathode follower. At some point soon, I'll finish the next part of the article and show some photos.
I'm not a believer is excessive bandwidth, so the 40kHZ pole wouldn't scare me too much.
I put mine into the Heretical box, using the original Heretical board as the second cathode follower and a modified Heretical board as the first cathode follower. At some point soon, I'll finish the next part of the article and show some photos.
I'm not a believer is excessive bandwidth, so the 40kHZ pole wouldn't scare me too much.
I changed my mind. 
Thinking it through, 250V at 10mA for the ECC81 takes you to 2.5W per section, a bit higher than that tube should be run. It's better to put in an extra transformer for the crossover bit or uprate the PS already there to handle the extra 40mA for the crossover and live with the 4 or 5 watts that the regulator will need to dissipate.
Don't forget the +/-12V that the opamps will require.
Thinking it through, 250V at 10mA for the ECC81 takes you to 2.5W per section, a bit higher than that tube should be run. It's better to put in an extra transformer for the crossover bit or uprate the PS already there to handle the extra 40mA for the crossover and live with the 4 or 5 watts that the regulator will need to dissipate.Don't forget the +/-12V that the opamps will require.
Hi again,
I was rereading the heretical article. You write that 6sn7 is an equally good choice as ecc88 but requires higher plate voltage. Therefore I speculate that 6sn7 could be a a good choice for me?
Anyhow, the ps part will be extensive with the 12V supplys and possibly a third hv supply. I probably need to make a pcb for that.
I was rereading the heretical article. You write that 6sn7 is an equally good choice as ecc88 but requires higher plate voltage. Therefore I speculate that 6sn7 could be a a good choice for me?
Anyhow, the ps part will be extensive with the 12V supplys and possibly a third hv supply. I probably need to make a pcb for that.
Yes, you write that the ecc88 a better performer, but I understod it as if both tubes fulfilled the design criteria hence i interpreted both tubes as equally good choices in the application.
i am referring to this section:
"We’re now in a position to select a tube. There are a lot of candidates which are happy at the desired current, two very common ones being the 6SN7 and the 6DJ8/ECC88. These also have the considerable virtue of being cheap and easy to find. Recalling that the output impedance of a cathode follower is about 1/gm, we can check the suitability. The 6SN7 has a transconductance of 2.5-3 mA/V, which translates to an output impedance of 300-400 ohm. Add a cathode stopper (more about that later) and we’re up to roughly 1K, well within what we need. Similarly, a 6DJ8/ECC88 at 10mA will have a transconductance about three times higher, resulting in a base source impedance of roughly 100-150 ohm. So from this standpoint, either will work. The 6SN7 is a lower distortion tube, but with the inherent feedback of a cathode follower, both tubes are likely to have exceptionally low distortion at these signal levels.
The ECC88 is a winner in this application because of its plate voltage requirements: less than half what is needed for the 6SN7. So low, in fact, that the B+ supply can be made with a standard isolation transformer, and still have enough headroom for active regulation. As a bonus, the higher transconductance translates into a lower noise floor."
i am referring to this section:
"We’re now in a position to select a tube. There are a lot of candidates which are happy at the desired current, two very common ones being the 6SN7 and the 6DJ8/ECC88. These also have the considerable virtue of being cheap and easy to find. Recalling that the output impedance of a cathode follower is about 1/gm, we can check the suitability. The 6SN7 has a transconductance of 2.5-3 mA/V, which translates to an output impedance of 300-400 ohm. Add a cathode stopper (more about that later) and we’re up to roughly 1K, well within what we need. Similarly, a 6DJ8/ECC88 at 10mA will have a transconductance about three times higher, resulting in a base source impedance of roughly 100-150 ohm. So from this standpoint, either will work. The 6SN7 is a lower distortion tube, but with the inherent feedback of a cathode follower, both tubes are likely to have exceptionally low distortion at these signal levels.
The ECC88 is a winner in this application because of its plate voltage requirements: less than half what is needed for the 6SN7. So low, in fact, that the B+ supply can be made with a standard isolation transformer, and still have enough headroom for active regulation. As a bonus, the higher transconductance translates into a lower noise floor."
SY,
Looking at this design, you almost have me convinced, but I think I am being lost at the extra power supply. How about a CCS on first stage to lower its B+ requirement. This leaves the cathodyne running at 320V, but saves a second PS. Maybe a small saving grace is that by making the CCS adjustable, the voltage on the cathodyne's grid can be set with some precision. Any objections to this?
Looking at this design, you almost have me convinced, but I think I am being lost at the extra power supply. How about a CCS on first stage to lower its B+ requirement. This leaves the cathodyne running at 320V, but saves a second PS. Maybe a small saving grace is that by making the CCS adjustable, the voltage on the cathodyne's grid can be set with some precision. Any objections to this?
Well, it's not like 20mA at 400V is going to break that bank...
I had considered doing just that, but was alarmed by bench measurements of an ECC81 with a 1k cathode resistor and the CCS plate load. Distortion was shockingly high. Now, adding the feedback connection at the cathode may change things, and I haven't tried it in the actual amp, so I won't say that it's undo-able.
If you try it, though, be prepared with an extra power transformer, just in case.
feppe, I'm sorry, I hadn't seen your previous post. Yes, 6SN7 will work, but ECC88 is better, cheaper, and easier to supply. That was the point I was trying to make.
I had considered doing just that, but was alarmed by bench measurements of an ECC81 with a 1k cathode resistor and the CCS plate load. Distortion was shockingly high. Now, adding the feedback connection at the cathode may change things, and I haven't tried it in the actual amp, so I won't say that it's undo-able.
If you try it, though, be prepared with an extra power transformer, just in case.
feppe, I'm sorry, I hadn't seen your previous post. Yes, 6SN7 will work, but ECC88 is better, cheaper, and easier to supply. That was the point I was trying to make.
SY said:
Interesting. Perhaps using one of the Antek power toroids which have dual HV secondaries would work. One of them used with a solid state bridge for the driver, the other with a hybrid bridge to drop a few volts for the output section. These things are cheap and have super high VA ratings, so this wouldn't stress it at all.
The 300V (2T300) version, with a C (220u) L (9H/300R) C (220u) gives about 405V @ 20mA with 500 micro volts of ripply on one winding (thats a Hammond 156G choke), and the other, with C (10u) L (1.5H/56R) C (100u) and a hybrid rectifier using a EZ81 gives 320V @ 170mA with about 1V or ripple.
The EZ81 rectifier can share the 6.3V winding with the drivers and will add the benefit of a slow startup to the output section. The cost is an extra $12 tube.
My goal here is to put one of these together for under $150 or so. With the Antek, some $20 Edcor OPTs, and a single Zener + 10M45 shunt reg for the screens, I think this should be doable.
Adding up the parts, it looks like even a super budget version of the RLD is in the $350 ball park, and really the only "savings" are in the OPTs. Not a bad deal, and on a watt per dollar basis, beats my 300B's by quite a bit. But, I already have those and there is a recession on which means this probably won't get done for a while -- unless I can find a friend in need of a new amp.
I reckon mine stood me about $400 or so. Worked perfectly once I found my mistakes!I did bias it fairly low IIRC - maybe it could be improved on by running the EL84s a bit harder. Used some replacement dynaco output Tx from triode electronics when they were on sale.
BTW a funny thing happened. SY recommended some JJ 12AT7. Which I duly went and bought (not dear). But after a while, of a sudden, one of them started to make a funny noise through the speakers, kinda like what motorboating has been described as. If I gave the tube a good flick with a fingernail, it went away, but then returned later.
Anyone ever had this?
Fran
BTW a funny thing happened. SY recommended some JJ 12AT7. Which I duly went and bought (not dear). But after a while, of a sudden, one of them started to make a funny noise through the speakers, kinda like what motorboating has been described as. If I gave the tube a good flick with a fingernail, it went away, but then returned later.
Anyone ever had this?
Fran
Power supply
I read from the schematic of the PSU that 2 EL84s and 4 ECC81 filaments are powered. Similarly, only 1 regulator is presented. I have looked at the pictures of SY's amp and spotted only 1 power xformer and 1 big choke.
Does it mean there is only 1 PSU for HV, reg'd screen voltage and fils?
I read from the schematic of the PSU that 2 EL84s and 4 ECC81 filaments are powered. Similarly, only 1 regulator is presented. I have looked at the pictures of SY's amp and spotted only 1 power xformer and 1 big choke.
Does it mean there is only 1 PSU for HV, reg'd screen voltage and fils?
No, there's two power supplies. In my crummy-looking prototype, the driver power transformer was under the chassis. In my nicer builds, it's right next to the main power transformer which runs the output tube plates and screens. In both cases, the driver supply choke is small so is mounted right on the raw power supply board.
Fran, check your solder connections on that tube socket (even if they look OK, reflow them). And replace that tube anyway- they're cheap.
Fran, check your solder connections on that tube socket (even if they look OK, reflow them). And replace that tube anyway- they're cheap.
I was not precise in what I had written in the previous post, perhaps because of my sweet 4 years old son and semi dry 2 year old Chardonnay 
So ... I know there are actually 2 PSU: 1 for power tubes and drivers the other for input tubes. Yet I had had problem to count filaments. Checked the other PSU schematic with elements description and power xformer specs. Am I correct that those 4 heaters are for EL84 and the remaining 2 stand for 2 connected in series pairs of heaters of ECC81s?
If I replace 2 x 6,3 V w/CT with only 6,3-0 V or 3,15-0-3,15V what heater supply might look like and what I would miss?
Is the BOM hosted anywhere for download?
So ... I know there are actually 2 PSU: 1 for power tubes and drivers the other for input tubes. Yet I had had problem to count filaments. Checked the other PSU schematic with elements description and power xformer specs. Am I correct that those 4 heaters are for EL84 and the remaining 2 stand for 2 connected in series pairs of heaters of ECC81s? If I replace 2 x 6,3 V w/CT with only 6,3-0 V or 3,15-0-3,15V what heater supply might look like and what I would miss?
Is the BOM hosted anywhere for download?