AX-700

During my search, if you want a 200 watt 8 ohm test load, these should work. I need 300 watts to test some of my amps.

2x 16 ohm with 100 watts capacity

http://www.amazon.com/Green-Aluminum-Shell-Wound-Resistors/dp/B00899WKIO/ref=sr_1_3?ie=UTF8&qid=1429581314&sr=8-3&keywords=16Ohm+resistor

Bratwurst7s said:

On the other hand, I don't have any 33µF 16v caps and will have to order them. But I do have some 47µF 16v on hand. Do you think that that would be a dangerous leap to try substituting them? After all, that's what is called for in the SM, although the positions of the small & large caps are reversed.

Cheers,
James

Click to expand...

Hi James,

Hard to tell in this case, maybe because it can modify something important around input signal. Sometimes higher capacitance can be used, and sometimes it's better keep it around stock value.

I'd invite you to take a look at few really nice threads where the author (Leestereo) explains every component changed and why.

1. http://www.audiokarma.org/forums/showthread.php?t=654341

2. http://www.audiokarma.org/forums/showthread.php?t=641945

3. http://www.audiokarma.org/forums/showthread.php?t=629488

Leestereo said:

...
1. Replace all power supply electrolytic capacitors with low ESR types (increasing capacity where appropriate and physically possible).
2. Replace of all of the signal path electrolytic capacitors with film types (whenever possible) or bi-polar electrolytic types.
3. Replace of signal path ceramic capacitors with C0G types.
4. Replace failure-prone 2SA726 transistors.
5. Replace output relay and variable potentiometers for bias and DC-offset adjustment.

Click to expand...

--

Karl vd Berg said:

Hi James,

Hard to tell in this case, maybe because it can modify something important around input signal. Sometimes higher capacitance can be used, and sometimes it's better keep it around stock value.

I'd invite you to take a look at few really nice threads where the author (Leestereo) explains every component changed and why.

1. http://www.audiokarma.org/forums/showthread.php?t=654341

2. http://www.audiokarma.org/forums/showthread.php?t=641945

3. http://www.audiokarma.org/forums/showthread.php?t=629488

Click to expand...

Thanks very much Karl, This gives me lots to read tomorrow, along with a large amount of material that I downloaded today concerning:
Diodes,
Zener diodes,
Filter capacitors,
Coupling capacitors,
Capacitors in the signal path.

Trying to keep expanding on the small amount that I've learned so far. And your thoughts about the broken A-520 being in reality a good thing are right to the point. I've decided that after I get these other projects finished that I will use it as a training vehicle, as it won't matter all that much if I make some mistakes with it, and I can also try out some of the mods that you have suggested.

As far as the 33µF or 47µF caps go, I'll just use a bit of patience and make an order next week for them and some others.

To Mark and the others adding conversation and comments vis dummy loads etc, Thank You. All of this helps my learning process. Please don't stop. :thmbsp:

Now I'm off to go see Social Distortion with my son and a few friends...

Cheers,
James

I placed an order with Digi-Key today that covers what I still need for both AX-700's, most of the Kaputt A-520, and a pair of mini-grabber test leads. Digi-Key seems to be running out of stock also. They had almost no Nichicon MUSE, and FG's are starting to get scarce. I had to up the voltage on almost every cap before finding something in stock, sometimes considerably. For instance to get a 10µF (16v) FG I had to go up to 50v. Luckilly they are still small enough in diameter to fit.

Cheers,
James

OK. So I finally replaced all of the remaining caps in the black AX-700 after receiving my order on Monday. Today I started it again and rechecked the idle current with my new mini-grabber leads. I checked all 4 resistors on each channel and then chose the one that had the middle values, (both channels vairied between the 4 resistors by a total range of about 2mV (left) to 2.5mV (right)) and set the value to as close to 10mV as I could get.

Karl has been nice enough to give me a hint me on the side about the importance of measureing the DC-Offset. And that made me remember seeing a sticky from EchoWars about that subject so I read the beginning of that thread. I haven't read all 4000+ replies yet.

So, the measurements. The right channel drifted from about 12.6mV to 14.8mV. The left channel was a little higher, from a low of 17.9 to a high of 19.8. The amp had been running idle for about a half hour before taking the measurements, I hope that's long enough.

At this point I'm willing to call this amp finished. Tomorrow I'll be bringing it, my A-520 and A-S201 into the living room and letting them run with the Canton Karat 60's for a listening test and comparison. Also tomorrow I hope to finish the silver 700. It only needs 5 more caps (2x 33µF and 3x 10µF), that shouldn't take long.

Cheers,
James

DC offset

Bratwurst7s said:

So, the measurements. The right channel drifted from about 12.6mV to 14.8mV. The left channel was a little higher, from a low of 17.9 to a high of 19.8. The amp had been running idle for about a half hour before taking the measurements, I hope that's long enough.

Cheers,
James

Click to expand...

The numbers are good. Nothing to worry about. :thmbsp:

Karl vd Berg said:

The numbers are good. Nothing to worry about. :thmbsp:

Click to expand...

Good to know. Thanks for the continued advice and support! If the finances look OK after at the weekend I'll be ordering one of those LCR ESR transistor/diode/cap testers that you pointed out. I'll be glad to have one of them to play with.

Cheers,
James

I just finished the silver 700. Again I measured all 4 emmitor resistors on each channel, chose the one closest to the middle value and re-adjusted the idle current. On the right channel setting it to 10.3mV gave me a high-low spread of ca 11mV-9mV on the others. With the left going dead on 10mV was best.

For DC-Offset the left ranged from about a low of 17.6mV to a high of 19.7, the right was a bit higher ranging from ca 22mV to 24.5mV. These numbers seem to be in what was described as "acceptable" rather than "good" but for now I'm leaving things as they are. I'll ask my friend that it's going to if he would like me to look deeper but I suspect that he will want to just start using it for now.

In any case I'll need to order that transistor testor before attempting to go any farther.

Working on these amps has been a lot of fun and educational, I feel like I've reached the point where I'm just ignorant rather than being stone cold completely ignorant.

Cheers,
James

Hi James,

Could you please tell the part number of the (blue) relay in the AX-700? You probably have put it in the parts list previously. I think I need to order the same kind of relay. Thanks a lot!

P.S.: Yes, with that gain (hFE) tester, it will help you to find the matched pairs of trannies to help reducing distortion even further.
Excellent work, btw!

Karl vd Berg said:

Hi James,

Could you please tell the part number of the (blue) relay in the AX-700? You probably have put it in the parts list previously. I think I need to order the same kind of relay. Thanks a lot!

P.S.: Yes, with that gain (hFE) tester, it will help you to find the matched pairs of trannies to help reducing distortion even further.
Excellent work, btw!

Click to expand...

Finder 40.52 @ 24vDC 8A. They measure 890 ohms across the coil. I've used them in 3 amps now. I also used the white Finder 41.52.9.024.0010 in 2 amps with no problems. If memory serves they measured 1.2kohms across the coil.

I'll be ordering the tester tonight or tomorrow. But for now a friend is coming over and we are going to give these various amps a workout. :yes:

Cheers,
James

OK! We just gave the black 700 a serious workout. Gywn Ashton, Led Zeppelin, ZZ Top, Robin Trower, Triumvirat, Kenny Wayne Shepherd.

The combo of this amp and the Canton Karat 60's is very very good. This is the first time that I've given either of them an extended run in the front room and they sound fantastic together. Very clean and tight, great bass without being boomy. Open and clear mids and highs withought being cold sounding and very good imaging. That was fun. This setup is ready to go to my daughter.

Cheers,
James

Bratwurst7s said:

Finder 40.52 @ 24vDC 8A. They measure 890 ohms across the coil.

Click to expand...

Super! Thanks a lot! :thmbsp:

Karl vd Berg said:

P.S.: Yes, with that gain (hFE) tester, it will help you to find the matched pairs of trannies to help reducing distortion even further.
Excellent work, btw!

Click to expand...

Karl vd Berg said:

Super! Thanks a lot! :thmbsp:

Click to expand...

Happy to be able to return the help in a small way. Some feedback for you, regarding what your continued help has accomplished. My friend picked up the silver 700 a few hours ago and he just called me a few minutes ago with his first impressions after hooking it up to his Quadral's. "A day and night improvement over his old 30 watt Sony amp." He is now happily turning it up and is surprised that his speakers are a lot better than he previously thought. :thmbsp:

I ordered the tester yesterday and it has now shipped. I assume that it's coming by way of sailboat and horse cart because the estimated delivery date is 18 June. But at least it's on the way.

Cheers,
James

When I did the listening session in post # 91 a good friend was over and he tasked me with finding him an amp to replace his current Pioneer A-305R. So last Sunday I snagged another black AX-700 on the auction site. It arrived today.

The seller did a nice job of packaging and it arrived without any damage. The amp is in extremely good condition optically, only a very few small sctatches, almost mint. Functionally it has scratchy switches and pots, has some channel bleed through, the left channel doesn't go completely down, low bass in left channel and high in the right. It's extremely dusty inside but has no signs of smokers glop. Nothing serious. I'll be starting the clean up and deox tomorrow.

From the condition of the cover screws I don't believe anyone has ever been inside of the amp, that's nice. Everything looks original inside. I have almost all of the caps that I need, as well as the relay and trim pots. I'll be making an order with Digi-Key and Bonzai tomorrow for the rest and extra. This will be fun. And my little transistor checker arrived so I have that to use to check the old parts. It will be interesting to be able to check ESR on the caps for the first time.

Cheers,
James

Bratwurst7s said:

...

And my little transistor checker arrived so I have that to use to check the old parts. It will be interesting to be able to check ESR on the caps for the first time.

Cheers,
James

Click to expand...

That's pretty fast. Faster than the one I received (took +6 weeks).

The tester is very handy. It's also fun with caps, trannies, inductors, etc...

If you do a search "typical ESR capacitor values", you'll see few handy ESR tables...

Hi Karl. I was surprised by how quickly it got here, the seller stated something like 3 to 4 weeks and it only took about 1 week.

Thanks for the link/info. Once again interesting and usefull. :thmbsp:

Cheers,
James

Bratwurst7s said:

Hi Karl. I was surprised by how quickly it got here, the seller stated something like 3 to 4 weeks and it only took about 1 week.

Thanks for the link/info. Once again interesting and usefull. :thmbsp:

Cheers,
James

Click to expand...

If you have time, please track the large filter caps that you replace.

The reports are that they are "in spec for capacitance and ESR" even after 30-40 years. If true, this is very impressive.

Bubo said:

If you have time, please track the large filter caps that you replace.

The reports are that they are "in spec for capacitance and ESR" even after 30-40 years. If true, this is very impressive.

Click to expand...

I'll be happy to check them on this newest amp and post the results. And now that I have a meter that can check for ESR I can also go back and look at the other caps from the previous again as I haven't thrown them out yet. They are all mixed up in a container now though (A-1020, A-520 and 2x AX-700).

If you look at the earleir results that I posted it seems to me that it's the smaller value caps that held their values quite well while the larger ones had dropped, sometimes considerably.

Cheers,
James

Bratwurst7s said:

I'll be happy to check them on this newest amp and post the results. And now that I have a meter that can check for ESR I can also go back and look at the other caps from the previous again as I haven't thrown them out yet. They are all mixed up in a container now though (A-1020, A-520 and 2x AX-700).

If you look at the earleir results that I posted it seems to me that it's the smaller value caps that held their values quite well while the larger ones had dropped, sometimes considerably.

Cheers,
James

Click to expand...

Thanks, if the large filter caps are not immortal, as many seem to think, then shattering the myth is a good idea.

Bubo said:

Thanks, if the large filter caps are not immortal, as many seem to think, then shattering the myth is a good idea.

Click to expand...

Well, wait a sec, the only ones that I have not pulled are the main 18,000µF filter caps, so I'm probably miscommunicating. I haven't wanted to risk damaging one of them by pulling them without having a suitable replacement on hand. Sorry if I got that wrong.

Cheers,
James