"this what it has"
Gee, a house numbered RCA 1B04, how novel !
http://www.partsolver.com/Product.a...6&SubstitutePart=0&OrgPartNum=&OrgPartMfg=RCA
BOHICA pricing applies.
Gee, a house numbered RCA 1B04, how novel !
http://www.partsolver.com/Product.a...6&SubstitutePart=0&OrgPartNum=&OrgPartMfg=RCA
BOHICA pricing applies.
http://www.area51esg.com/search.asp
Status Qty Part Mfg D/C
In Stock 10 RCA1B05 RCA 7822
Available 36 RCA1B04 HAR
Available 36 RCA1B04 HAR
Status Qty Part Mfg D/C
In Stock 10 RCA1B05 RCA 7822
Available 36 RCA1B04 HAR
Available 36 RCA1B04 HAR
SVI2004A
I'd agree with djk, use MJ15024's. You don't get much more indestructable than those with an audio transistor. Replace the entire channel, match them if you can. House numbered parts are quite normal in audio equipment. Like it's a big secret. I guess more for warranty purposes back then.
deadsled
When the amp delivers any current, the protection trips on that channel. Have you checked the emitter resistors and emitter-base drops on the outputs? What are the DC offset voltages?
-Chris
I'd agree with djk, use MJ15024's. You don't get much more indestructable than those with an audio transistor. Replace the entire channel, match them if you can. House numbered parts are quite normal in audio equipment. Like it's a big secret. I guess more for warranty purposes back then.
deadsled
When the amp delivers any current, the protection trips on that channel. Have you checked the emitter resistors and emitter-base drops on the outputs? What are the DC offset voltages?
-Chris
DJK is correct use the MJ 15024 outputs. I have used these in a number of 16's with 100% success. Replace the entire channel! Do NOT try to mix with house transistors.
Current problems?
In addition to above post check the driver transistors. I suggest replacement of these in addition to the outputs. Heck, its only a few bucks to do it right.
Joe
Current problems?
In addition to above post check the driver transistors. I suggest replacement of these in addition to the outputs. Heck, its only a few bucks to do it right.
Joe
Well, me again!
Haha, I got the monster working, and what a trick it was.
I tested parts until I began to pull hair out (not literally) and couldn't find a single thing wrong so I definitely suspected the opamps by then.
Just today, I decided firmly that it was the opamps when I found that they were pulling the + input negative by 2.3V, which, as far as I know, an opamp input should not pull its loading resistors away from zero like that no matter what.
I did a really nasty quick fix, since I had some LM358P chips sitting here, I put them into the circuit. It is only a basic opamp, not like the original µA739PC that was in there in the first place, however it worked well.
There were no more input and output lag connections anymore, however, as far as the circuit design goes, I was certain that a normal opamp would work just as well.
Upon powering up I had a slight DC offset (less than 2V) which made me ecstatic after all I could get before was -63V haha.
I adjusted the nulling pot and got both outputs down to +-1mV which is certainly an acceptable offset by my standards.
The amplifier works very well, though, I'm wondering if it'd sound a little bit sweeter with the original types of opamps in? I am certainly ordering original type replacements but for now these cheap little 358s work rather nicely.
Haha, I got the monster working, and what a trick it was.
I tested parts until I began to pull hair out (not literally) and couldn't find a single thing wrong so I definitely suspected the opamps by then.
Just today, I decided firmly that it was the opamps when I found that they were pulling the + input negative by 2.3V, which, as far as I know, an opamp input should not pull its loading resistors away from zero like that no matter what.
I did a really nasty quick fix, since I had some LM358P chips sitting here, I put them into the circuit. It is only a basic opamp, not like the original µA739PC that was in there in the first place, however it worked well.
There were no more input and output lag connections anymore, however, as far as the circuit design goes, I was certain that a normal opamp would work just as well.
Upon powering up I had a slight DC offset (less than 2V) which made me ecstatic after all I could get before was -63V haha.
I adjusted the nulling pot and got both outputs down to +-1mV which is certainly an acceptable offset by my standards.
The amplifier works very well, though, I'm wondering if it'd sound a little bit sweeter with the original types of opamps in? I am certainly ordering original type replacements but for now these cheap little 358s work rather nicely.
Well, after setting the bias to that amount, I found that the heatsinks were quite warm upon stability.
I didn't see anything wrong with the heatsink temperature, however, once the transformers reached their operating temperature, they got so hot I almost couldn't hold my hand against the core steadily..
Is this supposed to be normal here? Or do you figure something is wrong if that's happening with 15mV across each emitter resistor?
I didn't see anything wrong with the heatsink temperature, however, once the transformers reached their operating temperature, they got so hot I almost couldn't hold my hand against the core steadily..
Is this supposed to be normal here? Or do you figure something is wrong if that's happening with 15mV across each emitter resistor?
Hi Duo,
Try to reduce the bias current a bit, or measure the entire stage current. Do this by measuring across a 2W 1 ohm resistor in series with the DC supply in a fuse position. Let the amp settle down and measure the bias current again, reduce if needed. Do not hook up to speakers with the 1 ohm resistors in circuit.
The uA739 / 749 amps where noisy at best. I forget which one had an internal pulldown resistor. The other one normally used a pull down current source. Watch for a resistor or current source to the negative supply. Remove if these exist.
Try a better op amp now, like an NE5532A or better. Watch the supply voltages on the op amp. May as well replace the decoupling caps in the op amp supplies now.
-Chris
Try to reduce the bias current a bit, or measure the entire stage current. Do this by measuring across a 2W 1 ohm resistor in series with the DC supply in a fuse position. Let the amp settle down and measure the bias current again, reduce if needed. Do not hook up to speakers with the 1 ohm resistors in circuit.
The uA739 / 749 amps where noisy at best. I forget which one had an internal pulldown resistor. The other one normally used a pull down current source. Watch for a resistor or current source to the negative supply. Remove if these exist.
Try a better op amp now, like an NE5532A or better. Watch the supply voltages on the op amp. May as well replace the decoupling caps in the op amp supplies now.
-Chris
I have tried to replace the stock opamp in a Cit-16 and it gave me fits. Would oscillate at the drop of a hat, no matter what I did. Stuck the stock chip back in and said "screw it!" There are at least two feedback loops in that thing, and the feedback for the opamp encompasses the entire amp. I could not make it happy.
Duo...put a scope on that puppy and make sure that it isn't trying to self-destruct with oscillations.
Duo...put a scope on that puppy and make sure that it isn't trying to self-destruct with oscillations.
How rude of you to drop by and peer over my shoulder without announcing yourself, or bringing the beer...
i.e., you're making false assumptions on my attempt with too little info
I had set up the input section to accomodate the opamp, but the gain is set not locally, but globally by R7 and R8. I had a spec sheet on the uA739 but cannot seem to find it now (no great loss in my book), but I recall that is was nothing more than a dual opamp with input and output lag connections. The 5534 was one IC I tried, and if it had been running open loop, I'd think the output probably would have either been stuck on a rail, or been oscillating rail-to-rail. Instead, it almost worked, but I had a high frequency oscillation of perhaps 10V P-P at the output.
I fooled with it for a few days, and decided that I had to neuter the 5524 so much with external compensation to get rid of the HF crud that I was essentially wiping out any gains I might achieve by using it. The uA739 went back in and I got on with my life.
i.e., you're making false assumptions on my attempt with too little info
I had set up the input section to accomodate the opamp, but the gain is set not locally, but globally by R7 and R8. I had a spec sheet on the uA739 but cannot seem to find it now (no great loss in my book), but I recall that is was nothing more than a dual opamp with input and output lag connections. The 5534 was one IC I tried, and if it had been running open loop, I'd think the output probably would have either been stuck on a rail, or been oscillating rail-to-rail. Instead, it almost worked, but I had a high frequency oscillation of perhaps 10V P-P at the output.
I fooled with it for a few days, and decided that I had to neuter the 5524 so much with external compensation to get rid of the HF crud that I was essentially wiping out any gains I might achieve by using it. The uA739 went back in and I got on with my life.
Attachments
Hi EchoWars,
Ahhh, the old brain fart strikes. Sorry 'bout not bringing any beer. I got confused in memory between this and another chip.
I did have problems replacing this in a Marantz 3600 many years ago. The Marantz used the uA749, external current sink. This unit uses an internal resistor to the negative supply from the output. The Crown DC-60 and DC-300A used uA 749. I can send you the schematic of the D-60 if you want (PDF). It has an internal equiv diagram. Some units used uA739 and they show how to use either one. This may or may not help you out.
You know, even slowing down the new chip would improve the sound. As I recall, this chip was very noisy. The noise level should drop. I'm sure the THD would drop as well.
Please accept my apologies
-Chris
Ahhh, the old brain fart strikes. Sorry 'bout not bringing any beer. I got confused in memory between this and another chip.
I did have problems replacing this in a Marantz 3600 many years ago. The Marantz used the uA749, external current sink. This unit uses an internal resistor to the negative supply from the output. The Crown DC-60 and DC-300A used uA 749. I can send you the schematic of the D-60 if you want (PDF). It has an internal equiv diagram. Some units used uA739 and they show how to use either one. This may or may not help you out.
You know, even slowing down the new chip would improve the sound. As I recall, this chip was very noisy. The noise level should drop. I'm sure the THD would drop as well.
Please accept my apologies
-Chris
Don't be silly...you have nothing to apologise for, except for forgetting the Moosehead (call me wierd, but I like that stuff).anatech said:
The amp was sold as it was...worked pretty well, but you are right about noise. It certainly needed help in that department. Always liked the way it looked, but besides the opamp input, I also never had a big love of quasi-comp designs.
Duo...
There is a way to get, say, a NE5534 to work in that amp, and if I had been determined to do it I probably could have. I suggest the 5534 because of its easy way of controlling HF response with external compensation. Regardless of the battle you might endure to get it functional, it will be 1/10th of what you might go through to make a discrete stage work (and partly because it will mean the fewest changes in the original circuit. To me, if you gotta rebuild the whole bloody amp to feel good about it, go buy another amp.)
You had mentioned the output trannies getting rather warm. If you haven't yet, you really need to examine the output from the amp on a scope, and a square wave test is also in order.
If it looks good, then I'd call it a day, as this isn't really the type of amp to be auditioning opamps in. If stability is an issue, you got some work to do.
If it looks good, then I'd call it a day, as this isn't really the type of amp to be auditioning opamps in. If stability is an issue, you got some work to do.
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