Fisher 800c popping fuses!
- Thread starter ILLINOISgoy
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century tek
Addicted Member
It's never as simple as being something like the power cord.
A quick list of some possibilities:
-Shorted power transformer
-Shorted electrolytic capacitor
-Shorted output tube
-Shorted output transformer
These are the usual suspects when fuses begin to blow.
A quick list of some possibilities:
-Shorted power transformer
-Shorted electrolytic capacitor
-Shorted output tube
-Shorted output transformer
These are the usual suspects when fuses begin to blow.
analog
Tubes Are Good
Has this receiver been recapped or is it still original? If original I say filter capacitor, if it has been upgraded shorted output tube. But as was said could be a few different things. Don't keep replacing fuses in hoping the problem goes away and of course do not use larger fuses.
And DO NOT give a Fuse a Reynold's Wrap condom. Guaranteed invitation to a fire.
What was it playing or doing when it started popping fuses? Your description is tantamount to taking your car to the shop, saying"it's broke" tossing them the keys, and walking away. The mechanics have no clue, so they start running thru systems wasting their time (and getting paid for it too)until they hit on something. Then the car gets fixed, but you end up with a general diagnostic charge for 30 or so hours (you say WTF????). They tell you because you didn't tell us what the car was or wasn't doing we had to run systems checks and diagnostics before we found the problem. And you get stuck paying the bill for your inattention to detail.
If you would please, tell us exactly it and you were doing at the time it crapped out. Funny noises?, tube lighting up like chernobyl?, smoke? distortion in one or both channels?, lack of power to sound? What? These all help narrow down troubleshooting.
As this is better covered in the FISHER FORUM and is specific to a certain model, it should be moved there.
What was it playing or doing when it started popping fuses? Your description is tantamount to taking your car to the shop, saying"it's broke" tossing them the keys, and walking away. The mechanics have no clue, so they start running thru systems wasting their time (and getting paid for it too)until they hit on something. Then the car gets fixed, but you end up with a general diagnostic charge for 30 or so hours (you say WTF????). They tell you because you didn't tell us what the car was or wasn't doing we had to run systems checks and diagnostics before we found the problem. And you get stuck paying the bill for your inattention to detail.
If you would please, tell us exactly it and you were doing at the time it crapped out. Funny noises?, tube lighting up like chernobyl?, smoke? distortion in one or both channels?, lack of power to sound? What? These all help narrow down troubleshooting.
As this is better covered in the FISHER FORUM and is specific to a certain model, it should be moved there.
ILLINOISgoy
New Member
Specifically, at location V10 one of the 7591's was red as a dog's dick when the fuse blew. Local help in Tucson is bleak
Either the tube went chernobyl due to a tube fault, or the coupling cap to the tube is bad. In any event the tube is history if it got that RED. As this is a family type forum, please tone down the language. Can you take some underside shots of the area surrounding the output tubes, and the power supply (where the big can cap is underneath), plus an overall underneath shot of the unit.
How mechanically inclined are you? Can you solder, with confidence? Do you know the difference between a selenium rectifier and a stepped or staged 2 bbl Holley/Weber Carburetor? (yes the last is a trick question, but answer it anyway, if you get it right, you can probably work on the 800c with minor help). Have you ever worked on ANY tube gear before?
google tube audio repair Tucson. Lot's of hit's in the area. https://www.google.com/search?q=tube+audio+repair+in+tuscon&ie=utf-8&oe=utf-8
1st I'd try and get info from the AZ Antique Radio Club and see who they trust and take their gear to. http://azantiqueradioclub.org/
http://stereohospital.com/
http://retronica.net/
http://dalesantiqueradio.com/
http://www.dyna-tronics.com/
http://tubeaudio.com/
You've got more in Tucson than in the Baltimore Annapolis area combined!
There are vendors that most members use. Some are Mouser, Digikey, Jim McShane (McShane Engineering) for matched output tubes, AES, and various others. Metalbone makes a starter kit for the 800c. What it lacks can be easily gotten. Stay away from EBAY for anything related to the 800c. And that includes tubes. You can get better tubes, and better matching of the tubes as needed thru the vendors listed.
If you take it to a shop, MARK THE TUBES! Especially if they are FISHER BRANDED! Most shops are honest, but there are always a few that are less than scrupulous. Ask the shop if you can supply needed parts. Then mark them all so you can verify they actually went in the unit. Take pictures of the unit (both top and bottom with the lids off) BEFORE and AFTER for comparison. I'm not saying that shops are trying to steal you blind, but an ounce of prevention............. I've seen too many guys get burned, too often. get a written estimate 1st. Then compare the estimate with actual work done. If the guy calls 1/2 way thru and tells you it's gonna need X and y , tell him you want a revised WRITTEN estimate before ok'ing the work.
Discuss exactly what you want done to the unit.
1.) Basic, get it running reliably. Couple Hundred minimum plus output tubes.
2.) Update all coupling caps, and Can Caps (including Bias caps) along with #1 a bit more.
3.) Full up restoration with Alignment of AM, FM, and Multiplex sections of tuner. to include #1 and #2 . Lot more than #1.
Get price estimate on all 3. It ain't gonna be cheap. Look for a full up Restoration to be >$600-$700 in Labor. Can caps are NOT Cheap.
If you decide you want to go ahead and do the work yourself, you have a knowledge base of at least 1 to 2 CENTURIES worth of experience in the 800c. There are planty of 800c rehab and restoration threads in the forum. All you need to do is look them up. ASK QUESTIONS! Failure to ask a question because it sounds lame, can result in damage to the unit, and or injury to yourself or death from hi voltages. We've all BTDT, and got the faded and holey T-Shirts. There are NO DUMB QUESTIONS here. We might ride ya a little on a gaff, but it's all in good fun.
Service manuals can be had on www.FISHERCONSOLES.com for the 800c. Get the one that your 800c's serial number falls into. Take it down to Office Depot and ask them to combine the schematic pages, then blow it up to 24"x36". As you replace a part, check it off. Do one section at a time. Do the Amplifier 1st (with some added Safety parts we'll discuss later when you start on it.) Then the Power Supply. The Bias circuit will throw you as it's Negative Voltage so be prepared to ask questions.
Hayseed HAmfest has an 800c can cap kit for about $120.95 https://hayseedhamfest.com/collections/audio/products/fisher-800-c-re-cap-kit-4-cans These are custom made can's stuffed with Nichicon Hi Temp (105*C) rated caps. New bases, and basically plug and solder in.
Jim McShane has EH 7591's for $89.50 a quad. or the Small Bottle Tung-Sol Re-Issues. Limited Quantities. Apparently New Sensor ( the Russian Co) is having some kind of problem getting them out the door. They usually go for about $125 or so a quad. Both are tested by JIM at operating voltages, and matched while at those voltages. Lot better matches than the factory does.
Metalbone has the restoration starter kit http://www.metalbone.net/fisher.html here. for $85.00 plus shipping of $9.00.
Any questions? Clear as Water? or Mud?
Larry
How mechanically inclined are you? Can you solder, with confidence? Do you know the difference between a selenium rectifier and a stepped or staged 2 bbl Holley/Weber Carburetor? (yes the last is a trick question, but answer it anyway, if you get it right, you can probably work on the 800c with minor help). Have you ever worked on ANY tube gear before?
google tube audio repair Tucson. Lot's of hit's in the area. https://www.google.com/search?q=tube+audio+repair+in+tuscon&ie=utf-8&oe=utf-8
1st I'd try and get info from the AZ Antique Radio Club and see who they trust and take their gear to. http://azantiqueradioclub.org/
http://stereohospital.com/
http://retronica.net/
http://dalesantiqueradio.com/
http://www.dyna-tronics.com/
http://tubeaudio.com/
You've got more in Tucson than in the Baltimore Annapolis area combined!
There are vendors that most members use. Some are Mouser, Digikey, Jim McShane (McShane Engineering) for matched output tubes, AES, and various others. Metalbone makes a starter kit for the 800c. What it lacks can be easily gotten. Stay away from EBAY for anything related to the 800c. And that includes tubes. You can get better tubes, and better matching of the tubes as needed thru the vendors listed.
If you take it to a shop, MARK THE TUBES! Especially if they are FISHER BRANDED! Most shops are honest, but there are always a few that are less than scrupulous. Ask the shop if you can supply needed parts. Then mark them all so you can verify they actually went in the unit. Take pictures of the unit (both top and bottom with the lids off) BEFORE and AFTER for comparison. I'm not saying that shops are trying to steal you blind, but an ounce of prevention............. I've seen too many guys get burned, too often. get a written estimate 1st. Then compare the estimate with actual work done. If the guy calls 1/2 way thru and tells you it's gonna need X and y , tell him you want a revised WRITTEN estimate before ok'ing the work.
Discuss exactly what you want done to the unit.
1.) Basic, get it running reliably. Couple Hundred minimum plus output tubes.
2.) Update all coupling caps, and Can Caps (including Bias caps) along with #1 a bit more.
3.) Full up restoration with Alignment of AM, FM, and Multiplex sections of tuner. to include #1 and #2 . Lot more than #1.
Get price estimate on all 3. It ain't gonna be cheap. Look for a full up Restoration to be >$600-$700 in Labor. Can caps are NOT Cheap.
If you decide you want to go ahead and do the work yourself, you have a knowledge base of at least 1 to 2 CENTURIES worth of experience in the 800c. There are planty of 800c rehab and restoration threads in the forum. All you need to do is look them up. ASK QUESTIONS! Failure to ask a question because it sounds lame, can result in damage to the unit, and or injury to yourself or death from hi voltages. We've all BTDT, and got the faded and holey T-Shirts. There are NO DUMB QUESTIONS here. We might ride ya a little on a gaff, but it's all in good fun.
Service manuals can be had on www.FISHERCONSOLES.com for the 800c. Get the one that your 800c's serial number falls into. Take it down to Office Depot and ask them to combine the schematic pages, then blow it up to 24"x36". As you replace a part, check it off. Do one section at a time. Do the Amplifier 1st (with some added Safety parts we'll discuss later when you start on it.) Then the Power Supply. The Bias circuit will throw you as it's Negative Voltage so be prepared to ask questions.
Hayseed HAmfest has an 800c can cap kit for about $120.95 https://hayseedhamfest.com/collections/audio/products/fisher-800-c-re-cap-kit-4-cans These are custom made can's stuffed with Nichicon Hi Temp (105*C) rated caps. New bases, and basically plug and solder in.
Jim McShane has EH 7591's for $89.50 a quad. or the Small Bottle Tung-Sol Re-Issues. Limited Quantities. Apparently New Sensor ( the Russian Co) is having some kind of problem getting them out the door. They usually go for about $125 or so a quad. Both are tested by JIM at operating voltages, and matched while at those voltages. Lot better matches than the factory does.
Metalbone has the restoration starter kit http://www.metalbone.net/fisher.html here. for $85.00 plus shipping of $9.00.
Any questions? Clear as Water? or Mud?
Larry
primosounds
Powered with pure tube sounds.
As Larry said, Just a single tube red plating would most likely indicate a bad coupling cap or weak tube. With your DMM , you can test to see what the DCV is on the output tube side of the coupling cap. You can move a good tube to the socket where the bad tube went off, and put the bad tube in its socket. And with one hand on the on/off switch watch what happens to the output tubes and also listen to your speakers as usually when an output tube goes ballistic it starts to make a loud hum or other noises. The bad tube will take a minute of 2 to runaway if it is trash so you need to work quickly to measure the volts of the output tube side of the coupling cap. So, if the test shows that the output tube in the socket where the other tube went runaway operates normally that would point to the tube. If the suspect tube goes away again in the "good" socket you need to get a replacement. If the good tube starts to redplate turn off the amp and check for problems. Hopefully , you had enough time to get the voltage readings from each input grid of the power tubes. Ideally, they would be very close and any large deviation indicates a problem. Please remember that you are risking electrocution when checking voltages in a tube amp so if you don't know proper safety procedures you need to read about them. Good luck.
Because the fuse was blowing there's a simple test that can be done to divide and conquer. The goal in this case is to find out if the supply is bad or not.
- Pull all of the tubes out except the rectifier.
- With a good CORRECT VALUE fuse, turn it on and see if it blows again.
a) If it doesn't blow then you have an opportunity to measure the power supply voltages. In this case your tubes are pulling too much current and further testing is needed.
b) If it blows again then your power supply is toast and needs to be repaired.
- Pull all of the tubes out except the rectifier.
- With a good CORRECT VALUE fuse, turn it on and see if it blows again.
a) If it doesn't blow then you have an opportunity to measure the power supply voltages. In this case your tubes are pulling too much current and further testing is needed.
b) If it blows again then your power supply is toast and needs to be repaired.
The 800c is SS rectified. So no rectumfrier tube to worry about. But there IS a votlage doubler in the P.S.
