Did somebody say Red Light District? ..... I have almost manedged to get all the parts together. I never could find a "cheap" second transformer so I just bought a Hammond unit that should work. The matched resistors turned out to be alittle more trouble then expected but I think I have them sorted out. All I need now is a expertly machined top-plate and the wonderfully finished wood chasis to rest it in. I have heard in a pinch an old dynaco ST-70 top cover works just as well. ...... The project inches foward.
If anyone knows if Sy is selling extra boards for HV screen regulators please let me know.
Steve
If anyone knows if Sy is selling extra boards for HV screen regulators please let me know.
Steve
Attachments
I don't have any extras, but if you shoot me an email, I can help you get what you're looking for.
Did you note the biasing change since the original article? I'm pretty sure I posted it here- basically, I reduced the LED string length from 7 to 6.
Did you note the biasing change since the original article? I'm pretty sure I posted it here- basically, I reduced the LED string length from 7 to 6.
Yes I saw the message about cutting the number of LEDs from 7 to 6 per string.
I guess I will probably build the regulators on terminal strips as I seem to have a bunch of them.
I plead guilty in advance to stealing as much of the layout of your amp as I was able to using your posted pictures and the known size of the James transformers. I will probably get the chasis plate made by FrontPanelExpress who can do it from a CAD file for $ 50 and one week turn time. ( I hope they don't take away my DIY card for jobbing out the machine work).
How about a few hints on speakers people have reported work well with this amp.
Slightly off topic question, maybe needs its own topic.------I have seen in the pictures forum other amps and preamps that use blue or other collored LEDs to illuminate tubes for dramatic effect. Has anyone every checked that induced photo-currents (especially in head amps) are not a problem
I guess I will probably build the regulators on terminal strips as I seem to have a bunch of them.
I plead guilty in advance to stealing as much of the layout of your amp as I was able to using your posted pictures and the known size of the James transformers. I will probably get the chasis plate made by FrontPanelExpress who can do it from a CAD file for $ 50 and one week turn time. ( I hope they don't take away my DIY card for jobbing out the machine work).
How about a few hints on speakers people have reported work well with this amp.
Slightly off topic question, maybe needs its own topic.------I have seen in the pictures forum other amps and preamps that use blue or other collored LEDs to illuminate tubes for dramatic effect. Has anyone every checked that induced photo-currents (especially in head amps) are not a problem
I've looked at that. Photocurrents are normally a worry when a device is reverse biased- they modulate the leakage current. When forward biased, there's no real effect. I confirmed this by monitoring the signal across a red LED and putting a high intensity fluorescent lamp right next to it. No effect.
FPE did a great job on the top plates of my "nice" builds with the James transformers.
I've used the amps with my ESLs, the Frankenspeakers (modified NHT Super-Zeros perched on a sealed box with two Dynaudio 17W75), and LS3/5As. I'm aware of at least two other guys who are using it with high efficiency full range drivers with great success.
FPE did a great job on the top plates of my "nice" builds with the James transformers.
I've used the amps with my ESLs, the Frankenspeakers (modified NHT Super-Zeros perched on a sealed box with two Dynaudio 17W75), and LS3/5As. I'm aware of at least two other guys who are using it with high efficiency full range drivers with great success.
Slowly deconstructing the Red Light District
Well I finally to put together my copy of the red light district amp. When I started to go through the initial check out I made a most disturbing discovery. Both channels powered up normally and with a little help from Sy I got the bias set correctly but when I tried to play music one channel was very weak compared to the other. When I checked with scope I found the weak channel was fine into an open load at the output (at the 8 ohm taps of the OT) but as soon as any significant load was put on it the output voltage dropped by about 85%.
The other channel loads up with very little change in output and gives the impression it will sound quite nice when connected to a good set of speakers. I thought with one working channels how hard could it be to get the second one working, right just compare everything between them.
Well so far a have checked and all the voltages at matching points in both channels are the same and the signals are the same sizes along the signal paths..... as long as you don,t load the bad channel if you do load it the size of the AC part of the output tube plate voltage drops and the output of the channel obviously drops.
I've checked the wiring several times and have swapped the both the driver and output tubes back and forth and between channels with no change. I can also verify that all the tube filaments are lit up.
I'm at a loss to understand how everything could seem to work right when the (bad) channel is unloaded but it still will barely drive a speaker. The only good news is since I'm not a tube guy it might still be something obvious.
Anyone seen these symptoms before. TNX in advance
Steve
Well I finally to put together my copy of the red light district amp. When I started to go through the initial check out I made a most disturbing discovery. Both channels powered up normally and with a little help from Sy I got the bias set correctly but when I tried to play music one channel was very weak compared to the other. When I checked with scope I found the weak channel was fine into an open load at the output (at the 8 ohm taps of the OT) but as soon as any significant load was put on it the output voltage dropped by about 85%.
The other channel loads up with very little change in output and gives the impression it will sound quite nice when connected to a good set of speakers. I thought with one working channels how hard could it be to get the second one working, right just compare everything between them.
Well so far a have checked and all the voltages at matching points in both channels are the same and the signals are the same sizes along the signal paths..... as long as you don,t load the bad channel if you do load it the size of the AC part of the output tube plate voltage drops and the output of the channel obviously drops.
I've checked the wiring several times and have swapped the both the driver and output tubes back and forth and between channels with no change. I can also verify that all the tube filaments are lit up.
I'm at a loss to understand how everything could seem to work right when the (bad) channel is unloaded but it still will barely drive a speaker. The only good news is since I'm not a tube guy it might still be something obvious.
Anyone seen these symptoms before. TNX in advance
Steve
Hi Steve
Inspect you you haven't swapped in the bad channel, the anode for the screen grid connections , at the tube sockets .
Inspect you you haven't swapped in the bad channel, the anode for the screen grid connections , at the tube sockets .
First non-kit amp "red light district" back on track
Thanks to everyone for there suggestions. My bad, I nicked a 330 pf compensation cap on the bottom with a soldering iron shorted it out and causing the 33k resistor to run in parrallel with 133k plate resistor. Film caps burn through real easy I guess. I had to replace it with a ceramic disk I had handy till I can order something nicer but at least I have two audibly working channels now. Sounds very promising driving 25 year old Mordant Short bookshelf speakers sitting under the workbench.
After I undue the carnage I did trying to debug the poor thing I'll try and have a full report.
Steve
Thanks to everyone for there suggestions. My bad, I nicked a 330 pf compensation cap on the bottom with a soldering iron shorted it out and causing the 33k resistor to run in parrallel with 133k plate resistor. Film caps burn through real easy I guess. I had to replace it with a ceramic disk I had handy till I can order something nicer but at least I have two audibly working channels now. Sounds very promising driving 25 year old Mordant Short bookshelf speakers sitting under the workbench.
After I undue the carnage I did trying to debug the poor thing I'll try and have a full report.
Steve
about the leds people,
i have been building the broertjes I/V stage, and a lot was going on about the noise in the leds,
well somebody told me me that
Kingbright red diffused LED,L-53HD 25mA 5mm
are very fine leds for this application, so i think they will perform very well in this amp (which i'm going to build, yeehaa)
ps: the rs number of this component is
2285988
voila
i have been building the broertjes I/V stage, and a lot was going on about the noise in the leds,
well somebody told me me that
Kingbright red diffused LED,L-53HD 25mA 5mm
are very fine leds for this application, so i think they will perform very well in this amp (which i'm going to build, yeehaa)
ps: the rs number of this component is
2285988
voila
So far, I've not run into any noise problems from forward biased LEDs; I have some cheap Radio Shack ones in the cathodes of my phono stage. And, of course, in this application, they're used in an insensitive stage where they have the additional benefit of common mode rejection.
Good luck with the build!
Good luck with the build!
thanx SY,
well the one i'm refering to are 5 cent each, not really that expensive i think.
a small question for the knowledge: if i should use 6bq5 then i suppose 320 will be a tad to high ? abusing el84 at 320 is a bit over the edge, putting 320 on a pair of 6bq5 could be a bit to much over the edge ?
well the one i'm refering to are 5 cent each, not really that expensive i think.
a small question for the knowledge: if i should use 6bq5 then i suppose 320 will be a tad to high ? abusing el84 at 320 is a bit over the edge, putting 320 on a pair of 6bq5 could be a bit to much over the edge ?
FWIW, Dynaco abused the 6BQ5 exactly the same way; I've never seen an SCA35 where the plate voltage was within the tubes' max ratings. If you keep the screen voltage down to 250-270 and watch plate dissipation, I suspect there won't be any problems.
Cheap LEDs are really the best for this application.
Cheap LEDs are really the best for this application.
hello SY,
i wonder if that wouldn't shorten the tube's lifespan ?
luckily they come cheap as chips, the el84 or 6bq5, still i wonder.
another question about the design. i have red your article: quite impressive, i try to learn a bit (well a lot actually).
1)suppose you have an perfect B+ rail at 320, could you connect the 295+ screen on it by a resistor ? under the conditions that the 320+ rail is perfect stabil.
2)if you do that, you make a triode out of it ? yes ?
3)if you make a triode el84 out of it, does it necessairy run in A class ? so a pentode coupeld as triode does it always run in class A ?
thanx a lot
ps: how does the amp hold itself against a pure class a amp ? i have only heard my headphone class a, and must say i'm impressed. still i think i need a bit more then 5 watts, so i need to go with the pp; (probably i will not always have a fullrange in front of it; i'm an esl lover too).
greetz
i wonder if that wouldn't shorten the tube's lifespan ?
luckily they come cheap as chips, the el84 or 6bq5, still i wonder.
another question about the design. i have red your article: quite impressive, i try to learn a bit (well a lot actually).
1)suppose you have an perfect B+ rail at 320, could you connect the 295+ screen on it by a resistor ? under the conditions that the 320+ rail is perfect stabil.
2)if you do that, you make a triode out of it ? yes ?
3)if you make a triode el84 out of it, does it necessairy run in A class ? so a pentode coupeld as triode does it always run in class A ?
thanx a lot
ps: how does the amp hold itself against a pure class a amp ? i have only heard my headphone class a, and must say i'm impressed. still i think i need a bit more then 5 watts, so i need to go with the pp; (probably i will not always have a fullrange in front of it; i'm an esl lover too).
greetz
In no particular order:
I'm not a huge fan of pure class A. It can have its virtues, but greater efficiency means greater dynamic range.
I don't think tube life will be an issue at 320V. First, it's only about 10V over the ratings (cathodes are at +10V). Second, I've pulled two sets of long hours 6BQ5 out of some veteran SCA35s, which run them at 340-350V anode. Despite at least a thousand hours of this abuse, the tubes test and sound fine. My prototype has more than a year of daily use and the output tubes still test as new.
You can triode the output stage, but you'll have to modify the grid circuit (bypass part of the current limiter/grid stoppers) and figure out how to set the idle current, since the screen will no longer be adjustable. I don't think it's worth it for this circuit- a triode circuit ought to be designed from scratch, and of course it will have significantly less power and headroom.
Glad you liked the article- I try to make these things teaching tools.
I'm not a huge fan of pure class A. It can have its virtues, but greater efficiency means greater dynamic range.
I don't think tube life will be an issue at 320V. First, it's only about 10V over the ratings (cathodes are at +10V). Second, I've pulled two sets of long hours 6BQ5 out of some veteran SCA35s, which run them at 340-350V anode. Despite at least a thousand hours of this abuse, the tubes test and sound fine. My prototype has more than a year of daily use and the output tubes still test as new.
You can triode the output stage, but you'll have to modify the grid circuit (bypass part of the current limiter/grid stoppers) and figure out how to set the idle current, since the screen will no longer be adjustable. I don't think it's worth it for this circuit- a triode circuit ought to be designed from scratch, and of course it will have significantly less power and headroom.
Glad you liked the article- I try to make these things teaching tools.
thanx a lot SY,
i will make the PP anyway, but i was thinking about it. dynamic range is something which is quite important.
well that's a good sign that the tubes hold them so well even with 340 volt on them. i will run my tubes daily for like ten hours. music is always on. so it is a bit of an issue not to wear out to much tubes, and certainly no expensive ones. if you have to change every year an expensive pp 2a3, or 300b, then it's a no go for me.
indeed, a triode has to designed from scratch. i'll not try to even make it mathematicily work, cause i don't know any equations 🙄
if you have any other fine articles written, i'll be happy to read them more than once.
greetz
oh yes, maybe i have asked this question before, i'm going a bit crazy i think; but euuu; the resistor value. i'm using the advised metal film resistors, since they are so cheap.
the 10k/133k and the 45k3/45k3 that needs 2 watt,
what about the rest of the resistors in the amp ?
and about the psu ? what are save values ?
thanx again
i'm gonna give it a try: (looking at the scheme for left to right)
100k : 1/8w
1k0 ;6k8 : 1/8w
47k: 1/4w
270k:1/8w
1r0: 1/8w : 0.12²*1
i will make the PP anyway, but i was thinking about it. dynamic range is something which is quite important.
well that's a good sign that the tubes hold them so well even with 340 volt on them. i will run my tubes daily for like ten hours. music is always on. so it is a bit of an issue not to wear out to much tubes, and certainly no expensive ones. if you have to change every year an expensive pp 2a3, or 300b, then it's a no go for me.
indeed, a triode has to designed from scratch. i'll not try to even make it mathematicily work, cause i don't know any equations 🙄
if you have any other fine articles written, i'll be happy to read them more than once.
greetz
oh yes, maybe i have asked this question before, i'm going a bit crazy i think; but euuu; the resistor value. i'm using the advised metal film resistors, since they are so cheap.
the 10k/133k and the 45k3/45k3 that needs 2 watt,
what about the rest of the resistors in the amp ?
and about the psu ? what are save values ?
thanx again
i'm gonna give it a try: (looking at the scheme for left to right)
100k : 1/8w
1k0 ;6k8 : 1/8w
47k: 1/4w
270k:1/8w
1r0: 1/8w : 0.12²*1
WATT'S WHAT?
Hi,
How can say, a 50W class AB amp be more dynamic than a 50W class A amp?
IOW, how pleasant can a distorted dynamic swing be? 😀
Cheers, 😉
P.S. Glad to see you survived the by now beer-deprived city of Mechelen, BTW. 😉
Hi,
How can say, a 50W class AB amp be more dynamic than a 50W class A amp?
IOW, how pleasant can a distorted dynamic swing be? 😀
Cheers, 😉
P.S. Glad to see you survived the by now beer-deprived city of Mechelen, BTW. 😉
We quite impressed the saleslady at Het Anker by how much beer we loaded in the car. The suspension was actually bottomed, so we had to proceed VERY carefully to Biezenmortel, where the beer was consumed... rapidly.
The comparison I had in mind was the same set of outputs and power supply capability. Two EL84 can give you 17W in class AB, but maybe 6-7W in Class A. That seems like extra dBs to me.
The comparison I had in mind was the same set of outputs and power supply capability. Two EL84 can give you 17W in class AB, but maybe 6-7W in Class A. That seems like extra dBs to me.