Read some other threads and I have decided to replace the parts in this shopping list. Please check my math on this but I thought others might find useful. Remember I'm a real newbie on electronics. I can solder but electronics is a language I'm learning.
In the other picture there is a gray colored glue (I think) covering the transistor. What is that glue? What will I find under this glue? Is there some type of a connection the wires attach to?
Also I assume these gray capacitors are in need of replacement? Check that I have the right ones. See XLS shopping list and pic of round orange cap and pic of old gray cap.
Mucho Thanks!
Ps The quantity on the transistor that say 4 should be 8.
In the other picture there is a gray colored glue (I think) covering the transistor. What is that glue? What will I find under this glue? Is there some type of a connection the wires attach to?
Also I assume these gray capacitors are in need of replacement? Check that I have the right ones. See XLS shopping list and pic of round orange cap and pic of old gray cap.
Mucho Thanks!
Ps The quantity on the transistor that say 4 should be 8.
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You first picture shows a transistor top body covered with ( which I take to be ) heat-sink paste ,its probably there to help diffuse the heat running down the legs and melting the solder underneath .
As such --just leave it.
Yes your second picture is an old school ceramic disc capacitor , they are usually quite reliable but you can change them for the COG variety you show in picture three just make sure its near the same value, they are usually fitted for stability purposes.
As such --just leave it.
Yes your second picture is an old school ceramic disc capacitor , they are usually quite reliable but you can change them for the COG variety you show in picture three just make sure its near the same value, they are usually fitted for stability purposes.
Hi OldMarantzGear! You sent me an email about this, sorry I didn't get to answer yet.
Anyways.
The grey glue just bonds the thermal compensation thermistor the transistor body. Remove with a razor blade, and re-glue it on the new one with silicone.
The original compensation capacitors in the early production GFA-555's were 22pF, and 68pF for the later ones. There is no other difference in the circuit, so I figure Adcom changed it for a good reason. So I include these 68pF C0G capacitors as replacements.
The new transistors are included because they are a common failure mode on GFA-555's. (Not that they are unreliable, they are generally speaking extremely reliable.) The original transistors have barely sufficient Vce. This wasn't Adcom being cheap. Back in the day, there were not many choices for driver transistors with high Vce, high Hfe and low capacitance.
Anyways.
The grey glue just bonds the thermal compensation thermistor the transistor body. Remove with a razor blade, and re-glue it on the new one with silicone.
The original compensation capacitors in the early production GFA-555's were 22pF, and 68pF for the later ones. There is no other difference in the circuit, so I figure Adcom changed it for a good reason. So I include these 68pF C0G capacitors as replacements.
The new transistors are included because they are a common failure mode on GFA-555's. (Not that they are unreliable, they are generally speaking extremely reliable.) The original transistors have barely sufficient Vce. This wasn't Adcom being cheap. Back in the day, there were not many choices for driver transistors with high Vce, high Hfe and low capacitance.
Thanks for reply’s. Duncan and Chris
Chris
I decided I’d give it a try replacing these parts before putting on your parts. Since I’m such a knob newbie on electronics, just posted here for some confirmation before I warm up solder iron and solder sucker. Your parts look beyond my skills.
I was able from other posts with 555II to see these are the parts people commonly replace....so I’ll give that a try. I know I should probably teach myself how to use my multimeter to figure exactly which component is broken. But if I replace all these and if it works...great. I just don’t have a need to do a lot of this type of learning (using multi) to spend the time but I’m cheap since electronic repair here in SLC is expensive. I’m waiting for parts and hope to start this Saturday.
So the round orange caps are to replace the small gray ones?
Chris
I decided I’d give it a try replacing these parts before putting on your parts. Since I’m such a knob newbie on electronics, just posted here for some confirmation before I warm up solder iron and solder sucker. Your parts look beyond my skills.
I was able from other posts with 555II to see these are the parts people commonly replace....so I’ll give that a try. I know I should probably teach myself how to use my multimeter to figure exactly which component is broken. But if I replace all these and if it works...great. I just don’t have a need to do a lot of this type of learning (using multi) to spend the time but I’m cheap since electronic repair here in SLC is expensive. I’m waiting for parts and hope to start this Saturday.
So the round orange caps are to replace the small gray ones?
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Looking at the schematic some of those low value capacitors are used for local feedback as such yes you can change them but only for the same values the orange round COG capacitors in your photo have a different value ,have a look and read of -
Understanding Ceramic Disc Capacitor Values – Kitronik Ltd
I know this website makes great play of replacing capacitors but that is the larger electrolytic types , again looking at the schematic I personally would not replace the original ceramic and/or mica types as they have a very long life time as compared to electrolytics .
Wholesale changing of compensation/stability capacitors to different values can actually cause instability or frequency response/bandwidth problems as the designer of the circuit fitted them to allow the amplifier to work properly without insipid high frequency oscillation .
So--IMHO- leave them be .
Understanding Ceramic Disc Capacitor Values – Kitronik Ltd
I know this website makes great play of replacing capacitors but that is the larger electrolytic types , again looking at the schematic I personally would not replace the original ceramic and/or mica types as they have a very long life time as compared to electrolytics .
Wholesale changing of compensation/stability capacitors to different values can actually cause instability or frequency response/bandwidth problems as the designer of the circuit fitted them to allow the amplifier to work properly without insipid high frequency oscillation .
So--IMHO- leave them be .
Thanks Duncan.
Duncan
OT but....How's the opening of the UK and Germany going in regards to covid? My wife and I have a Porsche driving trip planned for Germany in late Aug early Sept. We both are vaccinated. Had to cancel this trip last summer. Hoping things are opened up so we can make it this year. Thanks for any info.
Duncan
OT but....How's the opening of the UK and Germany going in regards to covid? My wife and I have a Porsche driving trip planned for Germany in late Aug early Sept. We both are vaccinated. Had to cancel this trip last summer. Hoping things are opened up so we can make it this year. Thanks for any info.
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If I was you I would head to Las Vegas, its just been announced that the EU will let in American citizens who can---PROVE -- they have had all their vaccinations ---OTOH--- Germany is heading for another "crackdown " .
European Union will let vaccinated Americans visit this summer: official | Fox News
European Union will let vaccinated Americans visit this summer: official | Fox News
The USA is doing much more progress in vaccinating people, the EU simply does not have the numbers in terms of doses.
And Germany and Italy are among the worst affected, the medical systems are reported to be overwhelmed.
Better stay away, and safe.
And Germany and Italy are among the worst affected, the medical systems are reported to be overwhelmed.
Better stay away, and safe.
Naresh could you explain the logic --? are you saying US citizens who have had both vaccinations using USA chemicals are still not safe ?
Looking at India I can see why you think that way but Germany isn't India.
India suffers worst day of pandemic with record number of cases and deaths | India | The Guardian
Looking at India I can see why you think that way but Germany isn't India.
India suffers worst day of pandemic with record number of cases and deaths | India | The Guardian
What I meant is that the USA is a lot safer to travel in than the cities in Europe, there was a news item that the USA government officials say that masks are not needed if it is 2 weeks past your second dose.
Off hand, as I do not keep track, the situation in Germany is that they are a lot slower in vaccinating the general public, they are at the first dose stage.
In India, the first batch was given to doctors, nurses, hospital staff, ambulance drivers and so on. This was in February.
The second phase, in March, was those above 60, and later people with certain issues like blood pressure and diabetes were vaccinated after proving they were sick.
From 1 April, those above 45 are being done, and from 1 May the age group 18 to 45 will also get the vaccine.
Here another issue is that people have gone back to their home towns and villages, and are getting sick in remote places with poor facilities.
And the disease is such that the infected person is asymptomatic for up to 2 weeks. So it is easy to pick up infections during travel.
So please avoid contact with people as much as you can, avoid visitors, bear in mind the virus can linger for up to 48 hours in air conditioned places...mask up and get vaccinated, please.
I apologize in advance for this long and off topic post.
Off hand, as I do not keep track, the situation in Germany is that they are a lot slower in vaccinating the general public, they are at the first dose stage.
In India, the first batch was given to doctors, nurses, hospital staff, ambulance drivers and so on. This was in February.
The second phase, in March, was those above 60, and later people with certain issues like blood pressure and diabetes were vaccinated after proving they were sick.
From 1 April, those above 45 are being done, and from 1 May the age group 18 to 45 will also get the vaccine.
Here another issue is that people have gone back to their home towns and villages, and are getting sick in remote places with poor facilities.
And the disease is such that the infected person is asymptomatic for up to 2 weeks. So it is easy to pick up infections during travel.
So please avoid contact with people as much as you can, avoid visitors, bear in mind the virus can linger for up to 48 hours in air conditioned places...mask up and get vaccinated, please.
I apologize in advance for this long and off topic post.
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The Pacific coastal highway and parts of the inter state system are worth the road trip...
Here the current experience is that you can still get infected after 4 weeks of dose two, only the infection is milder.
So please act as if every body you meet is a potential carrier.
Better to be paranoid and safe than gasping for oxygen in a hospital far away from your home and family.
Here the current experience is that you can still get infected after 4 weeks of dose two, only the infection is milder.
So please act as if every body you meet is a potential carrier.
Better to be paranoid and safe than gasping for oxygen in a hospital far away from your home and family.