I'd give it some TLC before attempting anything - there appears to be corrosion on the TO-220's leads. I would replace transistors with corroded leads - if the metal/epoxy seal gets compromised, moisture will find its way inside the transistor case. Some versions of these amps have the heatsink HOT at full DC rail voltage so be careful. The CA's are isolated - but on the old ones that was not always the case. That REALLY accelerated the corrosion issues.
The 8001 is bigger than a CA12, but smaller than a CA18. The 9001 is a bit bigger than an 18, but not by much. The implementation of the class H is different between the two series. In the old ones, the upper transistor bank is bipolar, and varies the rail voltage to the lower bank linearly once more than the lower rail is needed. The newer ones use HEXFETs in the upper bank that turn on and off like a switch when you need more than the lower rail voltage. The older type can technichally sound 'better', but at these power levels you end up with about the same result either way.
A lost neutral can be a real SOB to find - especially if it's not on your property. I had one on the POLE. It took two years of complaints to the power company, with them coming out repeatedly to test it, for them to get to the bottom of it. Voltage between "ground" and neutral measured good - even when I was getting like 150/100 between the two legs. Voltage between the ground on the pole (200 feet away) and neutral in my box measuring dangerously high was what it took to convince the power company to send somebody up the the bucket to change out a corroded connector. Which took him all of 10 minutes to do, hot. Now you see why I'd go after corroded transistors before even turning that amp on.
Unlike most "environmentally friendly" citrus acid based degreasers, Grez-Off is a very mild product that will not attack paint or any other solid surface I've applied it to in 30+ years of use. Isopropyl is actually more aggressive depending on it's concentration. But it will suspend particles and goo for rinsing, where alcohol based products will not. This makes if far superior and very effective for removing nicotine/tar goo from cigarettes. Alcohols will dissolve the goo, but evaporate without removing it. Manual wiping or brushing with alcohol is only effective if you can access the surface. Usually there are parts in the way.
Degooing can be followed by cleaning with alcohol if desired, but I've found it's not as effective as a simple distilled water rinse. But yes you definitely need to clean pots and switches after.
This is a prime example of a product I won't use. It's got lye in it. It will clean quickly, but dry out paint and oxidize aluminum.
like i said I don't care how many stories you have, sorry your product just isn't used in in the electronics industry & probably for good reasons.
BTW saying alcohol does NOT suspend particles shows you fail to grasp what's happening. it's a liquid during the cleaning, the "particles" are removed by rinsing and /or absorbing with clean kim-wipes or cotton swabs. my mentioning Castrol was indeed for other tough jobs aimed at same market / industries your product is. of course it should be used diluted as required to meet the strength for the task. lye is used in process of making soap, the Castrol is a modern (highly concentrated) detergent similar to the other wannaB weaker brands like yours. look into it
BTW soaps are rarely sold anymore except for expensive body/facial cleaning products and yes those do use lye. all detergents need water to clean, infact the latest oil paints have detergents added to them for water clean up.
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If you take the time to read the MSDS sheets, you will see that your new space age Castrol product is an acid base cleaner that is corrosive to metal. It's clearly stated in the second section of the sheet. It also states it has a strong citrus odour. I've seen first hand what happens when these products are used. Aluminum turns white a couple weeks later. Paint goes dull and needs to be buffed with compound. This stuff is garbage.
If you were to read the MSDS sheet from my "wannaB" product ,which has been around for 40+ years, you would see it is water based and uses alcohol, that you keep preaching about, as the cleaning agent. If you'd ever had to remove a heavy contamination of nicotine you would realize quickly, that alcohol alone is not good for this, because it evaporates too quickly. An added liquid to suspend the goo and stop the nicotine from re-adhering to the surface is very beneficial for removal. Proper rinsing techniques, followed by a distilled water rinse will deactivate and remove the product, while drying residue free. The only reason I suggest cleaning pot and switches again after, is because solid dust particles can become caught in the contacts or wipers, stopping them from rinsing away.
I am not new at this. I have many years of experience removing nicotine residue from the interior of vehicles before customizing them including heavy trucks with millions of miles of chain smoking team operation. Cigarette smoke residue is some of the nastiest crap out there to remove. It's harder to remove than truck driver BO. I've tried just about every product out there.
oh brother get some facts< 1st you say it has Lye (strongly base) in it , now it's an acid cleaner. & no it doesn't smell citrusy either.
you should spend time reading the usage instructions and less on MSDS which you cant seem interpret into a coherent story.
all this stuff needs water , electronics knows the problems with water!
you should spend time reading the usage instructions and less on MSDS which you cant seem interpret into a coherent story.
all this stuff needs water , electronics knows the problems with water!
then you should know about alcohol based primers not water based
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all that is here-say from folks that don't follow instructions on the back of the containers, yeah it's highly concentrated you have to dilute it, much like some modern powerful laundry detergent full strength does to cloths colors! yes careless ppl can wreck stuff> have no fear, due to idiots, Castrol is off the market and their diluted replacements have re-appeared so folks are safer not to destroy their stuff. thank you very much
most folks can NOT identify common safe household cleaners from their MSDS so saying "its all in there" is a bit ingenious to say the least. Ive looked at them nothing jumps out and say woah dude this will eat my shorts off.
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I've had lots of experience with automotive type cleaners and cleaners in general. They won't come right out and say it, but there are phrases in there that should raise some red flags. It states flat out, corrosive to metal. It also state strong citrus odor, which usualy = citrus acid based product. Those two statements alone says to me, it will go above and beyond what is required as a degreaser. It will completely remove any protective lubricants from the metal, particularly aluminum. This is why it causes oxidization in aluminum. If you are going to use this stuff, do yourself a huge favor, and coat any raw aluminum with light oil after drying. Also avoid contact with paint. Also avoid contact with your skin. Most citrus based cleaners will dry your skin badly as well. It won't eat your shorts off, but it will eat your hands.
As you've stated, alcohol as a cleaner isn't as much of a concern.
As you've stated, alcohol as a cleaner isn't as much of a concern.
once we were having cleaning issues with a new PCB assembly shop and one of the techs took it upon himself without asking and brought in an automotive style parts cleaner basin to do it in-house. LOL I didn't ask what cleaning solution he planned on using cuz that was a complete fail.
I'd pass on dunking anything in those solvent tanks. Varsol used to be terrible. I have no idea what that recycle stuff is in them now, but it's much worse. I've got a Walter Bio-circle enzyme based wash tank in my shop. I haven't seen anything published, but the Walter rep suggested I try it on new circuit boards as a flux remover. The little bugs eat the flux right up but don't seem to touch anything else. I give it a quick cleaning with distilled water and Isopropyl after and they're ready for service.
Thanks guys;
I promise, no more cleaning questions!
I have attached a section of the CA-18 output schematic. Are those HEXFETS? Are they similar to triacs, (either on or off)?
Also, am I correct in assuming that the volume pots vary a control voltage or do they carry the audio signal?
I promise, no more cleaning questions!
I have attached a section of the CA-18 output schematic. Are those HEXFETS? Are they similar to triacs, (either on or off)?
Also, am I correct in assuming that the volume pots vary a control voltage or do they carry the audio signal?
Attachments
BTW;
The 8001 has bi-polar transistors in both tiers. I have heard about live heat sinks in Crest amps, but the CA-18 sinks are mounted directly to the chassis floor, the 8001 has an insulating strip under all of the visible devices, but I will double check.
Question; I understand that live heat sinks allow direct device mounting for better heat transfer, but does this require a separate heat sink for each rail?
The 8001 has bi-polar transistors in both tiers. I have heard about live heat sinks in Crest amps, but the CA-18 sinks are mounted directly to the chassis floor, the 8001 has an insulating strip under all of the visible devices, but I will double check.
Question; I understand that live heat sinks allow direct device mounting for better heat transfer, but does this require a separate heat sink for each rail?
hehe at least you know who to ask when it comes time to have your amp "detailed" and smelling spring fresh.
yes MOSFETs. but "HEX" is IRF marketing name for it . most times they work best on or off ( ones and zeros) , but for this I think they are used in linear mode.
most volume pots adjust the signal towards the amps input. Its hard to say anything concrete without a schematic.
Volume pots are control the input voltage, right after the balanced/unbalanced converter.
Sajti
It's a special trick by Crest. Something like "semilinear". In the linear mode, the upper semiconductors, has unity gain (emitter followers), and they are driven from the output voltage, if it reach the treshold level. But in CA18 there is a gain of 1.66 for the MOSFET stage, which means, that it's saturate earlier, than the linear solution, and it reduce the voltage across this section. This gives better efficiency, and the they can mounted to the heatsink without insulator, together with the output devices.
Sajti
Thanks guys;
I now have the data sheet and your info. They are power mosfets in the second tier of the CA-18. I am guessing that faster switching speed (cooler operation) was one of Crest's motives for using this device. Thanks, infinia, Andrew, sajti. So far, the output sections of the CA-18 and the 8001 seem to be holding together. Fingers crossed, with all those devices, failures in this area must be catastrophic!
My concern is still in the front end of the CA-18, in light of the previous problem; channel B clip light stayed on and output muted. I have re-attached the schematic. I think I need to print this schematic in poster size and trace the signal path with high-lighters! Circuit paths seem to disappear through 'wormhole' paths. I need to become familiar with the tabs and symbols.
** My primary question (at the moment) is; what voltage is controlled by the volume pots? A DC voltage or the actual audio signal?
Crest claims that all the protection circuits do not affect the signal in normal operation. I would like to acquire enough knowledge to verify this. I would never attempt this, (at this point) but I have these 'purist' thoughts of eliminating all these limiter circuits and connect an audio signal as directly as possible to the amplifier to avoid any possible compression and improve S/N ratio. I would never attempt this, I would need stacks of amps and voice coils to burn!
I now have the data sheet and your info. They are power mosfets in the second tier of the CA-18. I am guessing that faster switching speed (cooler operation) was one of Crest's motives for using this device. Thanks, infinia, Andrew, sajti. So far, the output sections of the CA-18 and the 8001 seem to be holding together. Fingers crossed, with all those devices, failures in this area must be catastrophic!
My concern is still in the front end of the CA-18, in light of the previous problem; channel B clip light stayed on and output muted. I have re-attached the schematic. I think I need to print this schematic in poster size and trace the signal path with high-lighters! Circuit paths seem to disappear through 'wormhole' paths. I need to become familiar with the tabs and symbols.
** My primary question (at the moment) is; what voltage is controlled by the volume pots? A DC voltage or the actual audio signal?
Crest claims that all the protection circuits do not affect the signal in normal operation. I would like to acquire enough knowledge to verify this. I would never attempt this, (at this point) but I have these 'purist' thoughts of eliminating all these limiter circuits and connect an audio signal as directly as possible to the amplifier to avoid any possible compression and improve S/N ratio. I would never attempt this, I would need stacks of amps and voice coils to burn!
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