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Techs or other could you help please.
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Some say amps as old as 800's are at about that age where they could use new capacitors and transformers. It may not be completely necessary yet but something to think about.
A good once over would be to check all valves, maybe swapping in a set that you know is solid first.
Cleaning all jacks and sockets since corrosion could have built up over the years.
Corrosion can also build up in the pots too and you can clean those with contact cleaner as well.
That's where I would start. Hope you get it straight.
A good once over would be to check all valves, maybe swapping in a set that you know is solid first.
Cleaning all jacks and sockets since corrosion could have built up over the years.
Corrosion can also build up in the pots too and you can clean those with contact cleaner as well.
That's where I would start. Hope you get it straight.
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I'll start cleaning the sockets etc.. is there a spray cleaner that you can suggest?
I know how to bias my JVM's but is there a thread here on how to bias the JCM800 2203?
I don't know if there is a specific thread on biasing 2203's but it is the same process for most amplifiers. Do you have access to bias probes and a multimeter? This is the method I use which is one of the simpler ones, there is also the 1ohm resistor method which I don't use personally and couldn't tell you how right off the top of my head.
eurotubes.com has a video where they bias a 2203 right in front of you, but you need probes to do it like they show. I recommend getting some sort of probe if you don't already have one. You only need one for a 2203 as all four valves are adjusted via a single trim pot.
As far as the contact cleaner goes, I never actually paid attention to any brand as long as it was contact cleaner for electronics.
If you need any more help on biasing the 800 let me know and I can walk you through it.
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I didnt get enough info on the Eurotubes video to be able to bias, so if you dont mind giving me the speps on how to bias the amp that would be great.
Thanks
Thanks
core
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Yeah the problem I've noticed on Eurotubes is no matter what computer I've used those videos stop playing at the same time in the video, right before he actually gets to the trim pot part for say the 800. You can never get past that point in the video because of a buffering problem.
Not sure how many people have that problem but being the only source out there right now it would be awesome if someone could take up the mantle to get the info out there in another format, even if it's just pictures and text.
If I was able to get them to work I could record them and convert them to another format because I think part of the problem is they are in windows media format and are not buffering properly from his site.
Who knows it may even be a simple fix on his server. I've only noticed one of his videos on Youtube so far for a DSL100. Does anyone know if there are more of his videos for other amps on Youtube?
Thanks!
Not sure how many people have that problem but being the only source out there right now it would be awesome if someone could take up the mantle to get the info out there in another format, even if it's just pictures and text.
If I was able to get them to work I could record them and convert them to another format because I think part of the problem is they are in windows media format and are not buffering properly from his site.
Who knows it may even be a simple fix on his server. I've only noticed one of his videos on Youtube so far for a DSL100. Does anyone know if there are more of his videos for other amps on Youtube?
Thanks!
There are some of his videos on youtube if you can find them. I'm not sure the exact titles but that is the first place I saw them.
To bias the 800 is relatively easy, I'll try to give you the quickest and simplest answer.
1. Got to have a cheap bias probe and a multimeter, if not, then a more expensive unit like a Weber Bias Rite would be a little easier but I'll just explain it using a simple probe.
2. Take the amp out of the head cabinet, have everything unplugged of course, insert the probe into any of the tubes and place the amp upside down, you'll have to get some kind of blocks like a 2x4 or something and put them underneath the transformers to hold it up since the probe elevates the height of the tube.
3. (Here's where it pays to have two multimeters or the Bias Rite) Turn the amp On and let it warm up in Standby for a couple minutes. Make sure you have a load (speaker) connected to the amp. Turn the Standby switch off so now you are in Play Mode. Set your multimeter to the highest DCV setting, at least 600 or better, clip the neutral lead to the chassis and touch the positive lead to pin#3 of any power tube to read the plate voltage. For 2203's it should be in the 400's. Once you have that number, write it down. If you have your probe hooked up to a second meter, good, if not, now you have to shut everything down and plug in the probe to the meter. If you switch the meter on with the probe in and the amp on it will blow the meter.
4. Now that you have the plate voltage, your probe in your meter and the meter is now set to at least the 100 scale in DCA you are ready to adjust the bias. Let's say your plate voltage was 460 and you are using EL34 tubes. Your formula would look like this...
(plate dissipation of tube / plate voltage) x 0.7 = bias in mA
25 / 460 = 0.054 x 0.7 = 0.038
So in this case you would want to start the bias at 38 mA.
That's pretty much it.
Now of course the main reason for biasing tubes in the first place is mainly to eliminate crossover distortion by applying the safe and proper operating voltages and current to the tubes. The little formula I showed you is not the guaranteed location but is the most typical area of where the bias should be. Everyone will agree that crossover distortion generally ends at 70% bias. Also, the plate dissipation of the tubes will differ from whatever tube type you may have, 25 for EL34, KT77, E34L. 30 for 6L6GC and 35 for KT88, 6550. 6L6's, KT66's and 6V6's are kind of funny and the plate dissipation on those really depends on the manufacturer. It's good to be able to read a spec sheet if you ever go with those tubes. I've seen KT66's with plate dissipation as low as 17 before. I don't even know why I mentioned 6V6's because you do not want those in your 2203 whatsoever. Could be bad news from what I'm told
Anyway, hope this helps you out.
To bias the 800 is relatively easy, I'll try to give you the quickest and simplest answer.
1. Got to have a cheap bias probe and a multimeter, if not, then a more expensive unit like a Weber Bias Rite would be a little easier but I'll just explain it using a simple probe.
2. Take the amp out of the head cabinet, have everything unplugged of course, insert the probe into any of the tubes and place the amp upside down, you'll have to get some kind of blocks like a 2x4 or something and put them underneath the transformers to hold it up since the probe elevates the height of the tube.
3. (Here's where it pays to have two multimeters or the Bias Rite) Turn the amp On and let it warm up in Standby for a couple minutes. Make sure you have a load (speaker) connected to the amp. Turn the Standby switch off so now you are in Play Mode. Set your multimeter to the highest DCV setting, at least 600 or better, clip the neutral lead to the chassis and touch the positive lead to pin#3 of any power tube to read the plate voltage. For 2203's it should be in the 400's. Once you have that number, write it down. If you have your probe hooked up to a second meter, good, if not, now you have to shut everything down and plug in the probe to the meter. If you switch the meter on with the probe in and the amp on it will blow the meter.
4. Now that you have the plate voltage, your probe in your meter and the meter is now set to at least the 100 scale in DCA you are ready to adjust the bias. Let's say your plate voltage was 460 and you are using EL34 tubes. Your formula would look like this...
(plate dissipation of tube / plate voltage) x 0.7 = bias in mA
25 / 460 = 0.054 x 0.7 = 0.038
So in this case you would want to start the bias at 38 mA.
That's pretty much it.
Now of course the main reason for biasing tubes in the first place is mainly to eliminate crossover distortion by applying the safe and proper operating voltages and current to the tubes. The little formula I showed you is not the guaranteed location but is the most typical area of where the bias should be. Everyone will agree that crossover distortion generally ends at 70% bias. Also, the plate dissipation of the tubes will differ from whatever tube type you may have, 25 for EL34, KT77, E34L. 30 for 6L6GC and 35 for KT88, 6550. 6L6's, KT66's and 6V6's are kind of funny and the plate dissipation on those really depends on the manufacturer. It's good to be able to read a spec sheet if you ever go with those tubes. I've seen KT66's with plate dissipation as low as 17 before. I don't even know why I mentioned 6V6's because you do not want those in your 2203 whatsoever. Could be bad news from what I'm told
Anyway, hope this helps you out.
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Thanks viking. Ive ordered a bias rite so that i can go through the steps alot easier i figured it would be a good investment for my amps.
Good man. The Bias Rite is going to make the process pretty painless. Just the fact alone you can read the plate voltage with the flick of a switch makes all the difference in the world.
core
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Awesome thank you Viking this will help out tremendously. I think I'm going to go with a Weber as well as it seems to be the easiest one to use for a beginner. Being a car guy I'm with you on being able to know the basics and do minor service on amps.
Good luck Australian!
Good luck Australian!
RobS
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DickSmith and Jaycar sell contact cleaner, CRC make one as well, available at most auto shops.
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Re: Techs or other could you help please.JCM800 Bias
Viking mentioned this video in a previous post. This is the link that downloads the whole video from eurotubes and doesn't have the problem of stopping half way through playing the video.
http://www.eurotubes.com/video/Generic-Bias.wmv
Viking mentioned this video in a previous post. This is the link that downloads the whole video from eurotubes and doesn't have the problem of stopping half way through playing the video.
http://www.eurotubes.com/video/Generic-Bias.wmv
pacAir
Member
An extremely good professional contact & potentiometer cleaner and contact enhancer is DeOxit 5 from Caig Laboratories. I used the first version of their product (called Cramolin) for over 20 years and DeOxit 5 is an even better product! 
You can use it on pots, jacks, relay contacts, switches and tube sockets/pins and it can solve a LOT of problems caused by corrosion and dirt/dust.
Highly recommended and available in many electronics and music stores (Hosa also sells it on a card in Guitar Centers here in the states). It is available in spray, pen, liquid and wipes. It isn't cheap, but it only takes a very thin film to do the job.
Steve
You can use it on pots, jacks, relay contacts, switches and tube sockets/pins and it can solve a LOT of problems caused by corrosion and dirt/dust.
Highly recommended and available in many electronics and music stores (Hosa also sells it on a card in Guitar Centers here in the states). It is available in spray, pen, liquid and wipes. It isn't cheap, but it only takes a very thin film to do the job.
Steve
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I've got a few questions about this:
4. Now that you have the plate voltage, your probe in your meter and the meter is now set to at least the 100 scale in DCA you are ready to adjust the bias. Let's say your plate voltage was 460 and you are using EL34 tubes. Your formula would look like this...
(plate dissipation of tube / plate voltage) x 0.7 = bias in mA
25 / 460 = 0.054 x 0.7 = 0.038
So in this case you would want to start the bias at 38 mA.
That's pretty much it.
1.First question-What is plate dissipation? Is it just another way of saying plate voltage?
Second Question is could you simplify this because I get lost on this point.-25 / 460 = 0.054 x 0.7 = 0.038
So in this case you would want to start the bias at 38 mA.
That's pretty much it.
4. Now that you have the plate voltage, your probe in your meter and the meter is now set to at least the 100 scale in DCA you are ready to adjust the bias. Let's say your plate voltage was 460 and you are using EL34 tubes. Your formula would look like this...
(plate dissipation of tube / plate voltage) x 0.7 = bias in mA
25 / 460 = 0.054 x 0.7 = 0.038
So in this case you would want to start the bias at 38 mA.
That's pretty much it.
1.First question-What is plate dissipation? Is it just another way of saying plate voltage?
Second Question is could you simplify this because I get lost on this point.-25 / 460 = 0.054 x 0.7 = 0.038
So in this case you would want to start the bias at 38 mA.
That's pretty much it.
