Aragon 4004 Mk2 restoration
- By donf
- Solid State
- 29 Replies
Hi folks,
As suggested by Apogee I am starting this thread to explore the ins and outs of restoring my Aragon 4004 Mk 2 Amp.
I’ve just arrived on the forum with a background in electronics and electrical servicing plus a spot of design now and then. I’m also a radio amateur and restorer of vintage radios. My home stereo system consists of a pair of Thiel CS3.6 speakers, the Aragon 4004 and a Meridian 208 preamp/CD player combination (a deteriorating ergonomic nightmare that I would rather not have bought).
My original post was in the swap meet forum as I begun to look for replacement output transistors but, at the risk of some repetition, I’ll summarise my situation here.
I put the Aragon Mark 2 on the workbench to check out a faulty right channel. Two power supply fuses blown, and, on DC testing the output transistors, three of them short-circuit.
Apogee has suggested the MJ11936 and MJ11946 as alternatives to the Toshiba 2SD242 and 2SB554 which I was originally contemplating using. I will likely use these transistors when I can locate some.
He also gave me these links to other posts:
1) A Mexico forum
2) Aragon question
3) Aragon 4004 MK2 output replacements
These were all very helpful. As Apogee pointed out, the Mexican post was very detailed and “Adrian” was serious enough about restoring his amp to come up with a complete list of the often-replaced passive components, electrolytic capacitors and some resistors.
I also read a great post from mightydub about upgrading the 4004 but I will need to go over it again to see if any of his improvements can be applied to the 4004 as it it without major changes to the circuitry.
I was able to obtain some information from a very helpful contact at Indy Audio Labs – the main schematics and also the parts list and positions for the Mark 2 upgrade.
The first thing I noticed about the output transistors was that the thermal grease had dried out and was very patchy. So I will be dismounting all the transistors, cleaning off the old grease and applying some new stuff, probably the Unigrease 3000 product. When thermal grease deteriorates it's no surprise to find failing output transistors.
Secondly the two resistors on the ground board (R201 and R202) had lost their metallic paint coating due to the regular heating. They test fine at about 10 Ohms each but I will be replacing them.
Next step, I will source the MJ11936 and MJ11946.
Here’s the amp during an initial inspection and before laying down a decent electrostatic protection mat:
All suggestions and input welcome.
Kind regards
donf
As suggested by Apogee I am starting this thread to explore the ins and outs of restoring my Aragon 4004 Mk 2 Amp.
I’ve just arrived on the forum with a background in electronics and electrical servicing plus a spot of design now and then. I’m also a radio amateur and restorer of vintage radios. My home stereo system consists of a pair of Thiel CS3.6 speakers, the Aragon 4004 and a Meridian 208 preamp/CD player combination (a deteriorating ergonomic nightmare that I would rather not have bought).
My original post was in the swap meet forum as I begun to look for replacement output transistors but, at the risk of some repetition, I’ll summarise my situation here.
I put the Aragon Mark 2 on the workbench to check out a faulty right channel. Two power supply fuses blown, and, on DC testing the output transistors, three of them short-circuit.
Apogee has suggested the MJ11936 and MJ11946 as alternatives to the Toshiba 2SD242 and 2SB554 which I was originally contemplating using. I will likely use these transistors when I can locate some.
He also gave me these links to other posts:
1) A Mexico forum
2) Aragon question
3) Aragon 4004 MK2 output replacements
These were all very helpful. As Apogee pointed out, the Mexican post was very detailed and “Adrian” was serious enough about restoring his amp to come up with a complete list of the often-replaced passive components, electrolytic capacitors and some resistors.
I also read a great post from mightydub about upgrading the 4004 but I will need to go over it again to see if any of his improvements can be applied to the 4004 as it it without major changes to the circuitry.
I was able to obtain some information from a very helpful contact at Indy Audio Labs – the main schematics and also the parts list and positions for the Mark 2 upgrade.
The first thing I noticed about the output transistors was that the thermal grease had dried out and was very patchy. So I will be dismounting all the transistors, cleaning off the old grease and applying some new stuff, probably the Unigrease 3000 product. When thermal grease deteriorates it's no surprise to find failing output transistors.
Secondly the two resistors on the ground board (R201 and R202) had lost their metallic paint coating due to the regular heating. They test fine at about 10 Ohms each but I will be replacing them.
Next step, I will source the MJ11936 and MJ11946.
Here’s the amp during an initial inspection and before laying down a decent electrostatic protection mat:
All suggestions and input welcome.
Kind regards
donf
KEF LS50 playground - measurements of raw drivers in factory cabinets and simulations
I'm posting .txt files that you can convert to .frd or .zma if your simulator needs it. I derived frequency files with about 10ms gate time. I didn't merge it to get low frequency response of woofer (under 120Hz) because i'm not interested in it. In the .zip file that is available for download from my DB account there is another .zip file that can be uploaded to HolmImpulse if you are not satisfied how i extracted sim files so you can do it as you see fit. All measurements are done from about 108cm on axis and approximately 30 degrees off axis. It is not good as 0-180 in 10 degrees increments but if you cross it over between 2000-2800Hz you won't get into trouble. Any fine tuning i recommend to be done by measuring and listening of your drivers.
If there's anything that you want me to do (other than measuring TS for woofers because i'm not doin' it 🙂 ) feel free to ask.
Dropbox - Kef LS50 measurements and sim files.zip - Simplify your life
Measurements done with calibrated Behringer ECM8000, M-audio FastTrack USB, Holmimpulse.
Measurement conditions
https://i.postimg.cc/B68BsJQX/IMG-2671.jpg
Midwoofer and tweeter
https://i.postimg.cc/gkbHFF92/50-a.png
https://i.postimg.cc/1RqrjRjd/50.png
Simulation of Kef's factory crossover: frequency, impedance and phase response
https://i.postimg.cc/yxchgnRK/LS50.png
https://i.postimg.cc/QtRkdvHS/LS50.png
https://i.postimg.cc/QNyvpMWn/50.png
Few comments:
In Kef LS50 they've seem to have done around 8dB baffle step compensation for midwoofer. That sounds like a lot but surprisingly it doesn't sound that bad at all. I guess that it doesn't go much low so it kinda evens out. Tweeter level is set, as can be seen, a 1.5-2dB higher than midwoofer. Again, i'm surprised that it isn't perceived like overly bright. You can hear it being louder but it doesn't make you want to turn the volume down - quite strange actually, unlike any metal dome i've listened so far. Also, good thing i've prepared and measured both cabinets because there are few measured differences between drivers. You'll see.
So, that being said, feel free to share what you've achieved with this or with your LS50's. I know i will.
EDIT: Couple of guys chimed in also so this is our take on KEF LS50 ALTERNATIVE CROSSOVER:
Zvu PSM XO
Göran
XMechanik
Enjoy and have fun.
If there's anything that you want me to do (other than measuring TS for woofers because i'm not doin' it 🙂 ) feel free to ask.
Dropbox - Kef LS50 measurements and sim files.zip - Simplify your life
Measurements done with calibrated Behringer ECM8000, M-audio FastTrack USB, Holmimpulse.
Measurement conditions
https://i.postimg.cc/B68BsJQX/IMG-2671.jpg
Midwoofer and tweeter
https://i.postimg.cc/gkbHFF92/50-a.png
https://i.postimg.cc/1RqrjRjd/50.png
Simulation of Kef's factory crossover: frequency, impedance and phase response
https://i.postimg.cc/yxchgnRK/LS50.png
https://i.postimg.cc/QtRkdvHS/LS50.png
https://i.postimg.cc/QNyvpMWn/50.png
Few comments:
In Kef LS50 they've seem to have done around 8dB baffle step compensation for midwoofer. That sounds like a lot but surprisingly it doesn't sound that bad at all. I guess that it doesn't go much low so it kinda evens out. Tweeter level is set, as can be seen, a 1.5-2dB higher than midwoofer. Again, i'm surprised that it isn't perceived like overly bright. You can hear it being louder but it doesn't make you want to turn the volume down - quite strange actually, unlike any metal dome i've listened so far. Also, good thing i've prepared and measured both cabinets because there are few measured differences between drivers. You'll see.
So, that being said, feel free to share what you've achieved with this or with your LS50's. I know i will.
EDIT: Couple of guys chimed in also so this is our take on KEF LS50 ALTERNATIVE CROSSOVER:
Zvu PSM XO
Göran
XMechanik
Enjoy and have fun.
Linear Audio HV Time Delay / Soft Start and Speaker Turn-On Delay and DC protection
- By Tubenstein
- Power Supplies
- 0 Replies
Attachments
Black Gate 33uf 16volt
I have a pair of Black Gate 33uf 16 volt capacitors that I purchased for a project that never took shape. Asking $50.00 $U.S. free shipping to lower U.S.48 via USPS.
What is 6HV5 really capable of?
- By Sch3mat1c
- Tubes / Valves
- 4 Replies
I set up a very fast pulse driver to investigate high-Vg1 operation.
Approximate circuit. There are two pins for each grid; both are connected. G2 was tested with direct shorts to ground, and 47 ohm resistors each pin, without much difference. Heater (not shown) is bypassed at the base with a pair of 10nF ceramics, then a twisted pair with ferrite beads comes back to the breadboard.
What's that heresy on the left? When you overvoltage a BJT, it draws current exponentially, much like a zener diode does. It happens to depend upon base connection. When base is open, you get a limit of Vceo (measured C-E). When emitter is open, Vcbo (measured C-B, and is higher). It stands to reason, there's a region connecting these, for intermediate values of base/emitter current: this is where R2 comes into play.
If you've ever biased a zener diode at light currents and measured it, you've probably noticed it has a very noisy level, that seems to act like rising ramps and random height discharges. This is avalanche breakdown, the avalanche being multiplied randomly by charges accelerated by the high voltage, impacting atoms or impurities in the junction. Well, BJTs exhibit the same behavior, but in this region of operation, it's turned up to eleven: the avalanche can go all the way to zero. And it happens very quickly: it can take but a fraction of a nanosecond! (2N2369 is the classic type used for this, e.g. Linear Technology AN-47, Jim Williams' favorite pulse generator circuit. There are also purpose-tested parts available, e.g. FMMT417TD -- pricey, but you pay for testing, parts that are reliable in this otherwise undocumented operating mode.)
So, simply read this as a fast switch pulling the left end of C2 up to GND momentarily. Much like a gas discharge tube. The '3904 breaks down around 100-120V.
Mind, it's not an ideal switch; internal resistance is still present. For the '3904, this is about 10-20 ohms, not great. It's just what's handy.
Anyway, this pulse is coupled through C2 into the grid, which is biased and terminated. R4-L1 discharges the grid relatively quickly after a pulse (along with C2 and Cin, they set the pulse duration). C- is typically -20V or so, enough to keep the tube in cutoff at 2kV.
C1 is a fairly large ceramic disc cap, and R3 is a TO-220 thin-film resistor -- may be noteworthy because their parasitics aren't exactly negligible here.
Photo:
Breadboard for convenience. Left module is a 12:140V isolated supply, positive grounded. Middle is a 2000V modest-current supply (up to 10mA or so). (You maybe can't tell in the photo, but the 100k carbon-comp plate resistor is swollen from running it at zero bias a little too long. So, it has at least enough power to do that.) Red and blue wire coming up from the bottom are a ballast resistor for the heater; bench supply is 12V, and it's just dropped down to get a nice 6.3V here.
And the test circuit / module on the right. The avalanche pulser is in the bottom front, Manhattan style with SMTs and axials. Two red wires snake up the riser board, connecting to both grid pins. Tube is contained in the cage (shielding to keep plate voltage contained -- these waveforms are like weak ESD, the fast edges get everywhere). A PCB socket provides connection.
Sitting on top of the test circuit, a hand made 100x probe. It's... not great at these edge rates, but it seems to be doing alright here.
I built it this way to get minimum distance, stray inductance, whatever, to the base of the tube. I can't do anything about what's inside it (in particular, the thin wire links to electrodes, and the overall height of the electrode structure), and I think that's a big part of the ringing waveform. Basically, to see what can be done, within those limitations.
On to the most important part, the waveform:
Ch1: 100x probe, across R3.
Ch3: 10x probe, G1 voltage.
Bias has been adjusted up here, for the biggest possible pulse. So, that's about 2A peak plate current, and 60V peak grid voltage.
Not shown: the cathode voltage shows a bit over 10V peak, or about 4.5A. Presumably the difference (2.5A) is grid current.
(The beam plates (G2, with 2 x 47 ohm resistors to GND) also show a significant peak of -15.6V, followed by a rebound to +9V, then lumpy decay. This seems in the right ballpark for Cg2a ~ 10pF.)
I'm a bit surprised the peak current isn't higher, or, the plate current isn't; limited by the, hFE so to speak, which seems to be pretty poor at this point.
Also wonder how it varies with pulse width. Radar modulator tubes are rated for pulses of microseconds, sweeps tens of microseconds; maybe there just isn't much space charge available on a nanosecond basis?
Tim
Approximate circuit. There are two pins for each grid; both are connected. G2 was tested with direct shorts to ground, and 47 ohm resistors each pin, without much difference. Heater (not shown) is bypassed at the base with a pair of 10nF ceramics, then a twisted pair with ferrite beads comes back to the breadboard.
What's that heresy on the left? When you overvoltage a BJT, it draws current exponentially, much like a zener diode does. It happens to depend upon base connection. When base is open, you get a limit of Vceo (measured C-E). When emitter is open, Vcbo (measured C-B, and is higher). It stands to reason, there's a region connecting these, for intermediate values of base/emitter current: this is where R2 comes into play.
If you've ever biased a zener diode at light currents and measured it, you've probably noticed it has a very noisy level, that seems to act like rising ramps and random height discharges. This is avalanche breakdown, the avalanche being multiplied randomly by charges accelerated by the high voltage, impacting atoms or impurities in the junction. Well, BJTs exhibit the same behavior, but in this region of operation, it's turned up to eleven: the avalanche can go all the way to zero. And it happens very quickly: it can take but a fraction of a nanosecond! (2N2369 is the classic type used for this, e.g. Linear Technology AN-47, Jim Williams' favorite pulse generator circuit. There are also purpose-tested parts available, e.g. FMMT417TD -- pricey, but you pay for testing, parts that are reliable in this otherwise undocumented operating mode.)
So, simply read this as a fast switch pulling the left end of C2 up to GND momentarily. Much like a gas discharge tube. The '3904 breaks down around 100-120V.
Mind, it's not an ideal switch; internal resistance is still present. For the '3904, this is about 10-20 ohms, not great. It's just what's handy.
Anyway, this pulse is coupled through C2 into the grid, which is biased and terminated. R4-L1 discharges the grid relatively quickly after a pulse (along with C2 and Cin, they set the pulse duration). C- is typically -20V or so, enough to keep the tube in cutoff at 2kV.
C1 is a fairly large ceramic disc cap, and R3 is a TO-220 thin-film resistor -- may be noteworthy because their parasitics aren't exactly negligible here.
Photo:
Breadboard for convenience. Left module is a 12:140V isolated supply, positive grounded. Middle is a 2000V modest-current supply (up to 10mA or so). (You maybe can't tell in the photo, but the 100k carbon-comp plate resistor is swollen from running it at zero bias a little too long. So, it has at least enough power to do that.) Red and blue wire coming up from the bottom are a ballast resistor for the heater; bench supply is 12V, and it's just dropped down to get a nice 6.3V here.
And the test circuit / module on the right. The avalanche pulser is in the bottom front, Manhattan style with SMTs and axials. Two red wires snake up the riser board, connecting to both grid pins. Tube is contained in the cage (shielding to keep plate voltage contained -- these waveforms are like weak ESD, the fast edges get everywhere). A PCB socket provides connection.
Sitting on top of the test circuit, a hand made 100x probe. It's... not great at these edge rates, but it seems to be doing alright here.
I built it this way to get minimum distance, stray inductance, whatever, to the base of the tube. I can't do anything about what's inside it (in particular, the thin wire links to electrodes, and the overall height of the electrode structure), and I think that's a big part of the ringing waveform. Basically, to see what can be done, within those limitations.
On to the most important part, the waveform:
Ch1: 100x probe, across R3.
Ch3: 10x probe, G1 voltage.
Bias has been adjusted up here, for the biggest possible pulse. So, that's about 2A peak plate current, and 60V peak grid voltage.
Not shown: the cathode voltage shows a bit over 10V peak, or about 4.5A. Presumably the difference (2.5A) is grid current.
(The beam plates (G2, with 2 x 47 ohm resistors to GND) also show a significant peak of -15.6V, followed by a rebound to +9V, then lumpy decay. This seems in the right ballpark for Cg2a ~ 10pF.)
I'm a bit surprised the peak current isn't higher, or, the plate current isn't; limited by the, hFE so to speak, which seems to be pretty poor at this point.
Also wonder how it varies with pulse width. Radar modulator tubes are rated for pulses of microseconds, sweeps tens of microseconds; maybe there just isn't much space charge available on a nanosecond basis?
Tim
Comparing LME49810, 49830 and 49811
Now I have enough plug-in driver boards to do LME498xx comparison efficiently. Three driver boards will be prepared for working with two pairs of NJL3281D/1302D. I will see do we need driver stage for 49830 and 49811, and more.
wire bridge / separators
- By Subuckethead
- Room Acoustics & Mods
- 1 Replies
If your like me and fix engines up doing things like sticking very high voltage ignition coil amplifiers in them. You might of been unlucky enough to experience a crossfire situation leading to detonation. It can happen without touching your wallet. Or lead to several grand for a new engine 
😱
For stereo purposes, I can visualize power wires arcing if it were any, crossing in to one of many other lines. High current down the path of least resistance...it seems often likely. Effective insulation can do so much to resist it.
If it were more like a constant source of audible interference/ colouration it would be easier to determine how much bridges might offer positives. Reasons we would like them to in this hobby.
I went on a wire quest several months ago. If anything if bridges maintain them better they last longer/ look better.
Thats a good enough reason.
If I wasn't busy burning off pandemic bordom....chances are I wouldnt be qite as meticulous, ha!
I always liked nice quality wire sounds. I always kept it tucked in and took care of it my in mobile audio. I would route wire down through its custom junctions. It made changing parts very simple. Better than wresting wire to change an amp or speakers.
Another plus. But the reason I am here. A question of materials, suited non magnetic, just oak and walnut wood and aluminum this time.
I would of opted for glass cube (next time). Heavy sturdy, doesn't carry or store current. Stick on some 3M sticky loops, done, super fast super easy. (unless you trip on wires, use caution walking always)
Question, is acrylic conductive?
If you build it, you should at least build it correctly, lol!. Keeping in mind there is no "correct way" if something does not work either way :wave.
😱For stereo purposes, I can visualize power wires arcing if it were any, crossing in to one of many other lines. High current down the path of least resistance...it seems often likely. Effective insulation can do so much to resist it.
If it were more like a constant source of audible interference/ colouration it would be easier to determine how much bridges might offer positives. Reasons we would like them to in this hobby.
I went on a wire quest several months ago. If anything if bridges maintain them better they last longer/ look better.
Thats a good enough reason.
If I wasn't busy burning off pandemic bordom....chances are I wouldnt be qite as meticulous, ha!
I always liked nice quality wire sounds. I always kept it tucked in and took care of it my in mobile audio. I would route wire down through its custom junctions. It made changing parts very simple. Better than wresting wire to change an amp or speakers.
Another plus. But the reason I am here. A question of materials, suited non magnetic, just oak and walnut wood and aluminum this time.
I would of opted for glass cube (next time). Heavy sturdy, doesn't carry or store current. Stick on some 3M sticky loops, done, super fast super easy. (unless you trip on wires, use caution walking always)
Question, is acrylic conductive?
If you build it, you should at least build it correctly, lol!. Keeping in mind there is no "correct way" if something does not work either way :wave.
