Hi all,
After getting some usefull feedback via this thread, I finished my linestage last sunday.
Sounds like a fantastic improvement over my old'n'crappy Yamaha AX-470 integrated sandamp, so one may say 'Bibster is happy'.
(ANYONE a schematic of this yamaha thinggy? I'd like to bypass the preamp, just use it as a poweramp)
Took schiller's advice by heart, replaced the NiCd's by 500R multiturn pot's, bypassed by (ordinary) 2200uF's: One for each (of the 4) cathodes.
Inserted a 22K/5W R for each (of the 4) plates.
(Replaced the output couplings for 4 2.2uF's as well, to improve the lower end)
Managed to adjust the pots, so that over each of the 4 plate resistors there's 220 V (10mA * 22K, right?). (First, rough biasing)
Listened (Heart the tales of mystery and imagination like I never heard in before!) and settled for a while.
Yesterday, I wanted to finetune the bias, and what? Couldn't get more tha about 150V over each of the plate resistors on ONE of the two tubes... while the other tube just settles at 80-something (311V minus 220V)
Having a B+ of 311 volts, that's 150 at the plate....
What could be the cause of this? Broken, this little tubey of mine?
(It glows less than the 'working'one as well...)
Kind regard, Paul
After getting some usefull feedback via this thread, I finished my linestage last sunday.
Sounds like a fantastic improvement over my old'n'crappy Yamaha AX-470 integrated sandamp, so one may say 'Bibster is happy'.
(ANYONE a schematic of this yamaha thinggy? I'd like to bypass the preamp, just use it as a poweramp)
Took schiller's advice by heart, replaced the NiCd's by 500R multiturn pot's, bypassed by (ordinary) 2200uF's: One for each (of the 4) cathodes.
Inserted a 22K/5W R for each (of the 4) plates.
(Replaced the output couplings for 4 2.2uF's as well, to improve the lower end)
Managed to adjust the pots, so that over each of the 4 plate resistors there's 220 V (10mA * 22K, right?). (First, rough biasing)
Listened (Heart the tales of mystery and imagination like I never heard in before!) and settled for a while.
Yesterday, I wanted to finetune the bias, and what? Couldn't get more tha about 150V over each of the plate resistors on ONE of the two tubes... while the other tube just settles at 80-something (311V minus 220V)
Having a B+ of 311 volts, that's 150 at the plate....
What could be the cause of this? Broken, this little tubey of mine?
(It glows less than the 'working'one as well...)
Kind regard, Paul
Kathodyne,
If I swap the tubes, the problem swaps as well...
So the tube IS defective.. Bummer...
Anyhow, it settles at about 220V over Rplate, but a few minutes after power-on, it sort of stops working correctly (Cathode stops emitting??)
I managed to settle one of the Rplates on this tube to 220V, before it went back to 150v.
If I put the cathode to ground, 162 V is all (7.36mA)
Does this sound familiar to someone?
If I swap the tubes, the problem swaps as well...
So the tube IS defective.. Bummer...
Anyhow, it settles at about 220V over Rplate, but a few minutes after power-on, it sort of stops working correctly (Cathode stops emitting??)
I managed to settle one of the Rplates on this tube to 220V, before it went back to 150v.
If I put the cathode to ground, 162 V is all (7.36mA)
Does this sound familiar to someone?
So, here I am, answering my own questions...
That one tube is indeed at the end of his life... So I orderd a pair of NOS 5687's (Phillips, a little patriotism can't do no harm
) on eBay: I'll have them by the weekend I guess, so we'll see.
Fiddled a bit around in the amp yesterday, 'cause I think it hummed way to much (50, 100 Hz). Quickly put in a switch for the heaters of the 5687's.
But turning them of did NOT reduce the hum.. pity..
I than took out (after waiting a while
) the 'defective' tube, ending up having a mono preamp: Hum seemed gone.
My (first) question is now: Can a 'at-the-end-of-life' tube induce (or pick-up or so) the 50Hz AC?
Second: I presume my PT is a bit short on the 6.3V heater's tap: I end up (SS bridge, 4700uF/0.3R/4700uF) having 5.04V on the heaters...
With quite a lot of ripple: 1Vtt. This WILL lengthen the life of my tubes, but isn't it a bit TOO low? (Or should I go for AC heating, lust to get rid of the voltage drop, thus to end up near(er) to the desired 6.3V?)
Thanks, Paul
PS: Burnedfingers: I did redo my soldering I redid everything as a matter of fact...
That one tube is indeed at the end of his life... So I orderd a pair of NOS 5687's (Phillips, a little patriotism can't do no harm
) on eBay: I'll have them by the weekend I guess, so we'll see.Fiddled a bit around in the amp yesterday, 'cause I think it hummed way to much (50, 100 Hz). Quickly put in a switch for the heaters of the 5687's.
But turning them of did NOT reduce the hum.. pity..
I than took out (after waiting a while
) the 'defective' tube, ending up having a mono preamp: Hum seemed gone.My (first) question is now: Can a 'at-the-end-of-life' tube induce (or pick-up or so) the 50Hz AC?
Second: I presume my PT is a bit short on the 6.3V heater's tap: I end up (SS bridge, 4700uF/0.3R/4700uF) having 5.04V on the heaters...
With quite a lot of ripple: 1Vtt. This WILL lengthen the life of my tubes, but isn't it a bit TOO low? (Or should I go for AC heating, lust to get rid of the voltage drop, thus to end up near(er) to the desired 6.3V?)
Thanks, Paul
PS: Burnedfingers: I did redo my soldering
I redid everything as a matter of fact...i have no idea...haven't had any strange behaving tubes yet....did have tubes which did not glow anymore on startup
you can only get 6,3vdc from a 6,3v winding if you use something ike a low-drop regulator...
5,04 is too low (you have to be within 5%), low heater voltage might be able to lenghthen the filament's life, but surely the tube will not live longer as the cathode will get poisoned and isn't able to emit anymore.....
6,3vac is mostly sufficient....build a decent dc filament supply if going for DC heating
greets!
you can only get 6,3vdc from a 6,3v winding if you use something ike a low-drop regulator...
5,04 is too low (you have to be within 5%), low heater voltage might be able to lenghthen the filament's life, but surely the tube will not live longer as the cathode will get poisoned and isn't able to emit anymore.....
6,3vac is mostly sufficient....build a decent dc filament supply if going for DC heating
greets!
Actually heating the cathodes of 5687 at much lower than the rated voltage is likely to greatly shorten the life of the tube, particularly since they run at relatively high cathode currents. For good life they need to run within their nominal rating of 6.3V +/- 5% otherwise cathode poisoning is a possibility.
It is also quite likely that your bad 5687 has low emission at ~5V, as this over 20% below the correct filament voltage and may not be bad at all. (These are not specified for emission at 5V!!)
A very ripple laden DC filament supply is far worse for hum pickup than any AC supply I have encountered by virtue of the shape of the ripple waveform which is 2X your line frequency and loaded with mostly low order harmonics, this rich spectra of harmonics is injected into the vicinity of the cathode and grid both capacitively and magnetically as well.
If you still want to use dc filament supply you will need low loss schottky rectifiers and a lot of capacitance, a high current x-over inductor of several mH will help as well in a pi-filter configuration. Provided your transformer is not too lossy you might make it to the vicinity of 6.3V.
I recommend 6.3VAC filament supply biased up to maybe 20Vdc using a resistive voltage divider off of your B+. You can use high value resistors and a smallish electrolytic cap to provide a low impedance to ground. Assuming a 450V supply and 1mA this implies about 430K/20K divider and maybe 10uF across the 20K which should be 50V for safety.
I would replace those multi-turn pots with fixed resistors once you know what the right value is for them. Fixed resistors are much more reliable long term, and I would replace those large 2200uF bypass caps with a Black Gate in the range of 220uF - 470uF, with about a 16V rating, even the less expensive grades are still a huge improvement over most anything else I have tried.
Incidentally those Philips 5687 are most likely to have been made in one of the former Sylvania ECG plants acquired by Philips in the early 1980's. (I worked for GTE Labs at the time, GTE was Sylvania's parent company. I remember our lamentations about the sale, but it did give us access to Philips products at low prices in our company store where I bought my first Philips/Magnavox CD player in 1984.) I'm not aware of this tube ever having been made anywhere else except in the USA.
It is also quite likely that your bad 5687 has low emission at ~5V, as this over 20% below the correct filament voltage and may not be bad at all. (These are not specified for emission at 5V!!)
A very ripple laden DC filament supply is far worse for hum pickup than any AC supply I have encountered by virtue of the shape of the ripple waveform which is 2X your line frequency and loaded with mostly low order harmonics, this rich spectra of harmonics is injected into the vicinity of the cathode and grid both capacitively and magnetically as well.
If you still want to use dc filament supply you will need low loss schottky rectifiers and a lot of capacitance, a high current x-over inductor of several mH will help as well in a pi-filter configuration. Provided your transformer is not too lossy you might make it to the vicinity of 6.3V.
I recommend 6.3VAC filament supply biased up to maybe 20Vdc using a resistive voltage divider off of your B+. You can use high value resistors and a smallish electrolytic cap to provide a low impedance to ground. Assuming a 450V supply and 1mA this implies about 430K/20K divider and maybe 10uF across the 20K which should be 50V for safety.
I would replace those multi-turn pots with fixed resistors once you know what the right value is for them. Fixed resistors are much more reliable long term, and I would replace those large 2200uF bypass caps with a Black Gate in the range of 220uF - 470uF, with about a 16V rating, even the less expensive grades are still a huge improvement over most anything else I have tried.
Incidentally those Philips 5687 are most likely to have been made in one of the former Sylvania ECG plants acquired by Philips in the early 1980's. (I worked for GTE Labs at the time, GTE was Sylvania's parent company. I remember our lamentations about the sale, but it did give us access to Philips products at low prices in our company store where I bought my first Philips/Magnavox CD player in 1984.) I'm not aware of this tube ever having been made anywhere else except in the USA.
Kevin, Kathodyne,
Thanks for these encouraging words! Tonite, I'll heat my soldering rod, and get rid of that rectumfrier and filter. As Kevin states: the rectified and (pooly) filtered DC is way worse than 'clean' AC. Thanks for reminding me
I think my PT will make it to 6.3@2A, ' cause that's how I ordered hem (her?).
I'll try to 'float' them tomorry (No parts in stock here...): Having a B+ a about 305V, I'll use (Correct me if I'm wrong) 220K+20K (Both 5W cemented thingies?), and putting a 100uF/160V cap in // with the 20K: That'll make some 25V. Is this too much? Also: Can I pick this up from any of the two 'last' RC's of my B+?
Do I need some 300R from my thus created virtual CT to each leg of the heaters suppy, or can I just tie this 'ground' to one of the heater supply's legs?
Also, I had this thought flashing through my (lack of)brain that this 'doomed' tube *might* turn out not te be that bad! (Crossed fingers... quick wife hurry up with the food, so I can get to start!)
So these ' Philips' end up being Sylvania's? Don't know enough about tubes yet to tell me if that's good or bad My ears will tell me!
Thanks, I'll keep you informed about this li'l project!
Paul
Thanks for these encouraging words! Tonite, I'll heat my soldering rod, and get rid of that rectumfrier and filter. As Kevin states: the rectified and (pooly) filtered DC is way worse than 'clean' AC. Thanks for reminding me
I think my PT will make it to 6.3@2A, ' cause that's how I ordered hem (her?).
I'll try to 'float' them tomorry (No parts in stock here...): Having a B+ a about 305V, I'll use (Correct me if I'm wrong) 220K+20K (Both 5W cemented thingies?), and putting a 100uF/160V cap in // with the 20K: That'll make some 25V. Is this too much? Also: Can I pick this up from any of the two 'last' RC's of my B+?
Do I need some 300R from my thus created virtual CT to each leg of the heaters suppy, or can I just tie this 'ground' to one of the heater supply's legs?
Also, I had this thought flashing through my (lack of)brain that this 'doomed' tube *might* turn out not te be that bad! (Crossed fingers... quick wife hurry up with the food, so I can get to start!)
So these ' Philips' end up being Sylvania's? Don't know enough about tubes yet to tell me if that's good or bad
My ears will tell me!Thanks, I'll keep you informed about this li'l project!
Paul
I don't have one, but my guess is that the tone controls are wrapped around the power amplifier, in the NFB loop as a lot of the newer (80's and up) Japanese integrated amps are. If so there isn't a tone control amp proper that can be bypassed. It can be done by removing the associated tone control circuitry and replacing it 2-resistors and a cap or two of the correct values.
I've never liked the sound of sand amps that had their tone control circuit designed as such. Very boomy-muddy sounding little critters. It's CHEAPER not BETTER! This means the power amp has a little extra gain to give the extra 20dB plus what's left over to hammer it into submission.
If the tone controls are in a 'separate' circuit, just find the 1st (input) differential pair and the associated input cap, usually a 1uF - .47uF/50V electrolytic cap, possibly an Elna LR cap, orange or 'peach' in color. This assuming it's not an IC amp! Then just find the input cap.
Hope this helps a little.
Cheers
Wayne
Hi,
Got rid of the sand + filter in the heater PS: Ended up having 6.1V (loaded)
And all of a sudden, both tubes are able to settle @ 10mA!
(Alltough the 'supposed-to-be-dead-but-still-alive' tube is biased at only 1.35V, versus 2.47 for the other one... That'll be better with the 'new' tubes I ordered)
There's still some 50Hz in this project (RMAA said something like -80dB) ... might lifting the heaters to ~25V help? (And is the way I proposed to do it, the way to go?)
Paul
Got rid of the sand + filter in the heater PS: Ended up having 6.1V (loaded)
And all of a sudden, both tubes are able to settle @ 10mA!
(Alltough the 'supposed-to-be-dead-but-still-alive' tube is biased at only 1.35V, versus 2.47 for the other one... That'll be better with the 'new' tubes I ordered)
There's still some 50Hz in this project (RMAA said something like -80dB) ... might lifting the heaters to ~25V help? (And is the way I proposed to do it, the way to go?)
Paul
Shoog,
I does help! I approve (I used 220K+22K, the latter in // with a 100uF, both R's are 1W: Is that sufficiant?)
I got the signal wires as far as possible away from both the Self and the PT as well: Helped a lot as well
There's some left, so I'll make it through the weekend ;-)
Another (simple?) question, to which as yet I've found it rather difficult to find the answer, as I might not (yet) understand the whole of the matter:
Operating points, sweet spots and such: I've adjusted my (4) cath. resistors SO that there's 220V over my 22K plate resistors (==> 10mA). Reading than 66V at the plate (~ 286 V B+), and some 2.3V cathode.
Is this 'sweet'? Should I take smaller Rplate's to achive higher Vplate? Or the other way around?
I just can't figure where I should settle the operating point.
Anyone some ideas, or some suggested reading?
Paul
I does help! I approve
(I used 220K+22K, the latter in // with a 100uF, both R's are 1W: Is that sufficiant?)I got the signal wires as far as possible away from both the Self and the PT as well: Helped a lot as well
There's some left, so I'll make it through the weekend ;-)
Another (simple?) question, to which as yet I've found it rather difficult to find the answer, as I might not (yet) understand the whole of the matter:
Operating points, sweet spots and such: I've adjusted my (4) cath. resistors SO that there's 220V over my 22K plate resistors (==> 10mA). Reading than 66V at the plate (~ 286 V B+), and some 2.3V cathode.
Is this 'sweet'? Should I take smaller Rplate's to achive higher Vplate? Or the other way around?
I just can't figure where I should settle the operating point.
Anyone some ideas, or some suggested reading?
Paul
I have mine operating with about 4V over the cathode (I use two green LEDs to set this) I have a CCS on the plate and it settles at about 100V on the anode. Sounds sweet to me and should pass about 10mA.
I would guess that your 65V volts on the anode is a little low. If your using the DIYPARADISE schematic then you have a little bit low +B, the easy solution is to reduce your plate resistor a tad.
Finding the sweet spot is a matter of slavishly copying someones tuned design - or experimenting till your happy.
Shoog
I would guess that your 65V volts on the anode is a little low. If your using the DIYPARADISE schematic then you have a little bit low +B, the easy solution is to reduce your plate resistor a tad.
Finding the sweet spot is a matter of slavishly copying someones tuned design - or experimenting till your happy.
Shoog
P*taing bord*l
Hi,
Shoog: I reduced my Rplate's to 11K (2*22K in //) just now, ajusted the Vk to 4v.
Working okay now, sounding a bit better as well, hard to express 'how'...
But I still can't get rid of this last bit of hum....
This last bit, is (I think it's odd) independant of the volume-pot setting: Hi of at - infinite: Still the same hum.
It defenitly comes from the PS, 'cause if I cut the power, it's gone (that is: cutting L, Leaving the Neutral + PE).
As I've allready checked the heaters (by switching them off), I guess it's the B+, or the 220V coming in????
Or something else?
Tomorrow I'll try to post a spectrogram, if that might help????
Merci, Paul
Hi,
Shoog: I reduced my Rplate's to 11K (2*22K in //) just now, ajusted the Vk to 4v.
Working okay now, sounding a bit better as well, hard to express 'how'...
But I still can't get rid of this last bit of hum....
This last bit, is (I think it's odd) independant of the volume-pot setting: Hi of at - infinite: Still the same hum.
It defenitly comes from the PS, 'cause if I cut the power, it's gone (that is: cutting L, Leaving the Neutral + PE).
As I've allready checked the heaters (by switching them off), I guess it's the B+, or the 220V coming in????
Or something else?
Tomorrow I'll try to post a spectrogram, if that might help????
Merci, Paul
If your've definately got +B hum then adding an extra stage of RC or LC is the only way to go. I found the 5687 prone to heater hum, but I think this is largeley dependant on the brand of valve. If the volume control alters the amount of hum then its probably not +B induced hum - but something to do with layout. Its very difficult to sort this out at a distance. Are your input phono sockets isolated from the case. Hows your grounding arranged. Is your main safety ground isolated from your circuit ground? These are the type of questions which are likely to lead to the problem.
Shoog
Shoog
Hi,
Well....
Here's my schematic...
And here's a picture of the inside. (Yes I know, I'm no soldering-expert...)
All input+output sockets are in the wooden back of the case.
All their GND's are linked together.
From these input/output-ground-rail, ONE wire goes to the U shaped ground-rail inside.
All signal wires are shielded, shield connected ONLY to the phono-input/output sockets.
Between the input-selector and the volume-pot, the shield is connected ONLY to vol.pot. Between the gridresistor and the pot, the shield is connected to the pot AND the ground-rail.
The shield of the output are for the moment floating around: They WERE connected to the rail, but this was replaced yesterdaynight by a single (White) wire coming from the input/output-ground-rais-thinngy.
Regards, Paul
Well....
Here's my schematic...
And here's a picture of the inside. (Yes I know, I'm no soldering-expert...)
All input+output sockets are in the wooden back of the case.
All their GND's are linked together.
From these input/output-ground-rail, ONE wire goes to the U shaped ground-rail inside.
All signal wires are shielded, shield connected ONLY to the phono-input/output sockets.
Between the input-selector and the volume-pot, the shield is connected ONLY to vol.pot. Between the gridresistor and the pot, the shield is connected to the pot AND the ground-rail.
The shield of the output are for the moment floating around: They WERE connected to the rail, but this was replaced yesterdaynight by a single (White) wire coming from the input/output-ground-rais-thinngy.
Regards, Paul
hmmm....can't help but notice that there are very long lines in your layout.....230v wire running across your input....230v wire running || with HT for a while. try to rearrange stuff (your chassis is not logical.....creates long 'feeding' lines). place capacitors (they uper ones) where they are needed...and turn them around...now they are crossing the ground line....
i'm not entirely sure....but doesn't the transformer shield need the same ground level as the circuit ground??
why no grid leak?...(yeah the pot...but now it is dependant)
i'm not entirely sure....but doesn't the transformer shield need the same ground level as the circuit ground??
why no grid leak?...(yeah the pot...but now it is dependant)
Its not entirely clear from your description, but I believe you need to connect a lead from your input/output phonos to your earth bar. Otherwise all your inputs/outputs are referenced to the earth of your sources and not to the preamp. This will inevitably lead to earth hum loops - of just the volume sensitive type you describe.
Shoog
Shoog
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.