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Fisher 800-B Restore Questions and Advise
- Thread starter TubeJunkie
- Start date
Sounds like a perfect test set to me. Checking fundamental work, NOT fine tuning at the end.
If you do not want to use those tubes, PLEASE GIVE THEM TO ME :yes: Seriously!
So what's the hurry on outputs? Relax and get busy on that parts order from Mouser! You could very well have it all ready for fine tuning by the time Jim gets you some tubes.
I was just ragging on you, I don't/didn't know if you were a kid or what. Now days everybody's always in a hurry but don't seem willing to put in the time to get the desired results, then cry when things don't turn out so well. Just giving you a hard time but I still stand by the advice, you know, why do it if you ain't gonna do it right.
And you KNOW the first thing you're going to do when you get those new tubes is plug 'em in, whether you've had time to work on the amp or not :yes:
Sorry about being unable to do much, know the feeling my friend.
Thomas
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TubeJunkie
Master of None
Hey Thomas,
No problem. I wasn't offended is the slightest. I placed the Mouser order a few days ago. I already have the resistors. But, you are right, I do need to get busy on what parts I have on hand. I would be tempted to plug in the new tubes, but I wouldn't. Patience is something I'm still learning............ Even though I'm 41. Thanks Again. And for those old Fisher 7591's, better hang on to them. Good try though.........
Overhaul Question: Should I go up in value on the coupling caps, since I'll be running the EH 7591's? If & when I ever get any..........lol I think I ordered both, .047 & .1uf....
No problem. I wasn't offended is the slightest. I placed the Mouser order a few days ago. I already have the resistors. But, you are right, I do need to get busy on what parts I have on hand. I would be tempted to plug in the new tubes, but I wouldn't. Patience is something I'm still learning............ Even though I'm 41. Thanks Again. And for those old Fisher 7591's, better hang on to them. Good try though.........
Overhaul Question: Should I go up in value on the coupling caps, since I'll be running the EH 7591's? If & when I ever get any..........lol I think I ordered both, .047 & .1uf....
As of this writing (and still using the well traveled G.E.s that came in mine) I left all the topology dead stock, except for the "fusitors" and obvious PS rebuild. I replaced all the molded, random small value electrolytics and mylar caps too, again with stock values.
But like you, I ordered the parts for the popular mods as well.
I did want to run the receiver dead stock, but safe and sound, first, to have a meaningful baseline and reference.
Then I would have a meaningful appreciation as I added/performed the mods and upgrades.
Wanted to hear it as close as Avery made it first.
Be happy to take those old cracked Fishers off your hands though, any time.
Good luck with your project; you'll be glad you did.
Thomas
This will fix those cracked bases good as new:
http://www.amazon.com/Insta-Flex-Rubber-Toughened-Adhesive-Glue/dp/B002N4UD3U
You can get it at HobbyTown USA if you have one nearby.
Just flow it in the cracks, let capillary action do it's thing. This blend of cyanoacrylate blends well, won't dry white and won't crack with pulling and pushing. Good gap filler characteristics and sandable.
Bob Smith makes good stuff.
http://www.amazon.com/Insta-Flex-Rubber-Toughened-Adhesive-Glue/dp/B002N4UD3U
You can get it at HobbyTown USA if you have one nearby.
Just flow it in the cracks, let capillary action do it's thing. This blend of cyanoacrylate blends well, won't dry white and won't crack with pulling and pushing. Good gap filler characteristics and sandable.
Bob Smith makes good stuff.
Yep, running 4 G.E.s as I write this line; getter flash is brown to black.
I am certain the top end of their output range is is more than truncated, but still going strong within reasonable and very satisfying SPL levels; they still sound very very good, cooked and brittle bases and all. 90dB or better at times, currently pushing (and no pile ons here) a pair of L100s. I have better speakers to match with this amp it's just currently impractical to make the change.
Since my new power supply I can touch them comfortably, albeit briefly, even after several hours of play.
I think these G.E.s were installed in the '70s when this one got the microscopic Motorola bridge; only work this one ever had as far as I can see aside from an IEC Mullard installed in the MPX.
Thomas
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TubeJunkie
Master of None
Another 800-B Restore Question ???
I installed the safety resistor's (removed short wire on pin 5 of each 7591 output tube socket, & replaced with 10 ohm 1/4 watt resistor). Should i have used 1/2 watt resistor's instead of 1/4 watt? I read somewhere on another thread here on AK to use 1/4 watt. But I just found an upgrade instruction manual that comes in those upgrade/restore kits, and it says to 1/2 watt. I don't think it's a problem, using the (10 ohm)1/4 watt resistors, just want to get some of you more experienced guy's opinion.
Also, what are your thought's on changing R126 (5.6k 1/2 watt), bias feed resistor to a 2.7k 1/2 watt resistor? I will be running the Electro-Harmonix 7591a tubes. I seen a video on YouTube, a guy has both installed in his, and can switch the resistor, via a flip switch. Thanks for reading.
I installed the safety resistor's (removed short wire on pin 5 of each 7591 output tube socket, & replaced with 10 ohm 1/4 watt resistor). Should i have used 1/2 watt resistor's instead of 1/4 watt? I read somewhere on another thread here on AK to use 1/4 watt. But I just found an upgrade instruction manual that comes in those upgrade/restore kits, and it says to 1/2 watt. I don't think it's a problem, using the (10 ohm)1/4 watt resistors, just want to get some of you more experienced guy's opinion.
Also, what are your thought's on changing R126 (5.6k 1/2 watt), bias feed resistor to a 2.7k 1/2 watt resistor? I will be running the Electro-Harmonix 7591a tubes. I seen a video on YouTube, a guy has both installed in his, and can switch the resistor, via a flip switch. Thanks for reading.
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The 1/4 watt is preferred. They are intended to function as a safety device and pop open in case an output tube starts to carry excessive current. A 1/2 watt will also work, but the 1/4 watt will open a bit faster.
TubeJunkie
Master of None
Thanks Fisherdude,
That's what I thought, just wanted some reassurance. I appreciate your advise, and taking the time to answer my question.
I updated/added another question to that same post. I would like your thoughts on it, as well. If you don't mind. Again, much appreciated.
That's what I thought, just wanted some reassurance. I appreciate your advise, and taking the time to answer my question.
I updated/added another question to that same post. I would like your thoughts on it, as well. If you don't mind. Again, much appreciated.
Oops, missed that other question!
When you change from the old selenium rectifier to a new one, the circuit values will change a bit, and the grid bias voltage and then the plate current will go up a bit. Since those numbers were on the high side when the unit was new, this can be a problem. Changing the resistor value will help bring it back in line.
So, since you've done the 1/4 watt 10 ohm resistor work, you can now check the plate current, which is the most important number. Take a voltage reading across each 10 ohm resistor. Ideally, you should be reading around 0.30-0.35 volts, or 300-350 millivolts. Since that's the voltage drop across 10 ohms, then Ohm's Law: I = V/R, will tell you that 300mv/10 ohms = 30 milliamps. You want the current to be in the 30-35 milliamp range. If this number gets too high, you'll see the plates on the output tubes start to glow a dull red due to the excessive current. That's bad.
Take the measurements when you get a chance and let us know what it is for each tube.
When you change from the old selenium rectifier to a new one, the circuit values will change a bit, and the grid bias voltage and then the plate current will go up a bit. Since those numbers were on the high side when the unit was new, this can be a problem. Changing the resistor value will help bring it back in line.
So, since you've done the 1/4 watt 10 ohm resistor work, you can now check the plate current, which is the most important number. Take a voltage reading across each 10 ohm resistor. Ideally, you should be reading around 0.30-0.35 volts, or 300-350 millivolts. Since that's the voltage drop across 10 ohms, then Ohm's Law: I = V/R, will tell you that 300mv/10 ohms = 30 milliamps. You want the current to be in the 30-35 milliamp range. If this number gets too high, you'll see the plates on the output tubes start to glow a dull red due to the excessive current. That's bad.
Take the measurements when you get a chance and let us know what it is for each tube.
TubeJunkie
Master of None
Hey Fisherdude,
Getting an average .300 volts DC, across the 10ohm resistors (Pin 5 of 7591 tubes). This is also after changing the bias resistor (R126) to a 2.7k. and changed the old Siemans selenium rectifier and top-hat diodes. And that's with the original tubes too. And, NO, you can't have my old Fisher 7591's...............lol...... But if I ever throw them away, I'll throw them AT you.......... Just kidding.... lol again ............And:
7591's Pin #3 Avg. 410 vdc.
7591's Pin #6 Avg. -17.1 vdc.
Seems to be running pretty smoothly. Thanks for your advise, help, and giving me a hard time. Sometimes, we all need a little fire built up under our ass.
I think I'll replace the dual section 1000uf can thats underneath the chassis. And later the ones on top of the chassis. I'm still waiting for my two dial lamp fuse-bulbs to come in. If there's anything else I did to check or do, please let me know. Thanks Again. Take Care.......
TubeJunkie
Getting an average .300 volts DC, across the 10ohm resistors (Pin 5 of 7591 tubes). This is also after changing the bias resistor (R126) to a 2.7k. and changed the old Siemans selenium rectifier and top-hat diodes. And that's with the original tubes too. And, NO, you can't have my old Fisher 7591's...............lol...... But if I ever throw them away, I'll throw them AT you.......... Just kidding.... lol again ............And:
7591's Pin #3 Avg. 410 vdc.
7591's Pin #6 Avg. -17.1 vdc.
Seems to be running pretty smoothly. Thanks for your advise, help, and giving me a hard time. Sometimes, we all need a little fire built up under our ass.
I think I'll replace the dual section 1000uf can thats underneath the chassis. And later the ones on top of the chassis. I'm still waiting for my two dial lamp fuse-bulbs to come in. If there's anything else I did to check or do, please let me know. Thanks Again. Take Care.......
TubeJunkie
TubeJunkie
Master of None
Phono Stage Hum in Fisher 800-B
Hey guys,
(Fisher 800-B) I have a slight hum in my phono section. When I unplug the TurnTable, the hum stops. I tried different TT's, and I found one that was a little quiter. Got to be a ground issue, I'm thinking. I reversed the AC plug in the outlet, no change. I've rolled a few 12ax7 tubes in the phono section, with a little success. But, it's still there. Is there any specifics I should check? I hope to replace and/or rebuild all the multi-section can caps soon. When I can more afford it. Ya think Santa and his elves makes Electrolytics? Thanks in advance for any and all suggestions, comments, and rig-a-mo-roll..........
Gave the dial glass a good cleaning, and orange oiled the wood cab. Man, this 800-B is gorgeous. Thank You Fisher GODS for shining on me........lol. I'm lucky to have found this beauty. Gotta solve the hum, though. I love my records, too, and got to play them through this reciever. Let me know what you all think about the hum issue, mentioned above. Thanks Again,
TubeJunkie
Hey guys,
(Fisher 800-B) I have a slight hum in my phono section. When I unplug the TurnTable, the hum stops. I tried different TT's, and I found one that was a little quiter. Got to be a ground issue, I'm thinking. I reversed the AC plug in the outlet, no change. I've rolled a few 12ax7 tubes in the phono section, with a little success. But, it's still there. Is there any specifics I should check? I hope to replace and/or rebuild all the multi-section can caps soon. When I can more afford it. Ya think Santa and his elves makes Electrolytics? Thanks in advance for any and all suggestions, comments, and rig-a-mo-roll..........
Gave the dial glass a good cleaning, and orange oiled the wood cab. Man, this 800-B is gorgeous. Thank You Fisher GODS for shining on me........lol. I'm lucky to have found this beauty. Gotta solve the hum, though. I love my records, too, and got to play them through this reciever. Let me know what you all think about the hum issue, mentioned above. Thanks Again,
TubeJunkie
Attachments
TubeJunkie
Master of None
Hi don,
Yes the ground wire from the TT is connected to the chassis. Did not try it unhooked. I've tried 2 different ground locations on the chassis, same difference. And, yes, I'm using a modern TT cartridge (MMC). Not sure what you mean by the phono low input. I know the 800-B has phono level adjustment pots. Did you mean that? Anything else I can check or try? Thanks for your help. TubeJunkie
Yes the ground wire from the TT is connected to the chassis. Did not try it unhooked. I've tried 2 different ground locations on the chassis, same difference. And, yes, I'm using a modern TT cartridge (MMC). Not sure what you mean by the phono low input. I know the 800-B has phono level adjustment pots. Did you mean that? Anything else I can check or try? Thanks for your help. TubeJunkie
Steve Hoffman
Mac and Roundie TV lover
TubeJunkie,
Audiodon forgot, I think, that only the Fisher "C" series receivers have a "Phono Low" and Phono High" choice on inputs. On our 800B's we just have the one phono input.
I think a slight hum is pretty normal for these units (I could be wrong). I usually play my Thorens TT through a PrimaLuna phono stage and in to my 800B so I bypass the Fisher phono section (which I have found to be a bit lacking in dynamics). When I play a turntable (usually a Thorens TD-160) directly into the 800B and a record is playing, the music and surface noise mask out any low level hum that is lurking around. I try not to stress over it too much...
Hope this helps.
Audiodon forgot, I think, that only the Fisher "C" series receivers have a "Phono Low" and Phono High" choice on inputs. On our 800B's we just have the one phono input.
I think a slight hum is pretty normal for these units (I could be wrong). I usually play my Thorens TT through a PrimaLuna phono stage and in to my 800B so I bypass the Fisher phono section (which I have found to be a bit lacking in dynamics). When I play a turntable (usually a Thorens TD-160) directly into the 800B and a record is playing, the music and surface noise mask out any low level hum that is lurking around. I try not to stress over it too much...
Hope this helps.
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TubeJunkie
Master of None
Thanks Steve,
I appreciate your insight. I have replaced all electrolytics with the exception of the multi-section caps, and the two cardboard covered caps. You think if I replaced all of the above mentioned caps, that it would eliminate the hum. I noticed on AUX, that there is a very slight noise (hum) in the background. I intend to replace those E_caps, when the finances alows for it. Let me know your thoughts. Thanks Again.
I appreciate your insight. I have replaced all electrolytics with the exception of the multi-section caps, and the two cardboard covered caps. You think if I replaced all of the above mentioned caps, that it would eliminate the hum. I noticed on AUX, that there is a very slight noise (hum) in the background. I intend to replace those E_caps, when the finances alows for it. Let me know your thoughts. Thanks Again.
Steve Hoffman
Mac and Roundie TV lover
I'm not a techie but you should leave your volume control at a normal level and not worry too much about hum. After all, your Fisher is almost 50 years old. It's not going to have (and wasn't designed to have) the signal to noise ratio of modern gear.
Personally, I only replace what really needs replacing. Everything else stays vintage. The only vintage tube gear I have that has totally NO noise or hum is my McIntosh MC30 monoblocks. When you put a preamp in there the noise and hum comes into play. If you worry about getting rid of all noise and hum, you're going to modernize your gear so much there will be no point in having a nice, vintage piece any more. My thoughts, anyway!
Personally, I only replace what really needs replacing. Everything else stays vintage. The only vintage tube gear I have that has totally NO noise or hum is my McIntosh MC30 monoblocks. When you put a preamp in there the noise and hum comes into play. If you worry about getting rid of all noise and hum, you're going to modernize your gear so much there will be no point in having a nice, vintage piece any more. My thoughts, anyway!
TubeJunkie
Master of None
Ironic that you mention mono block amps. My pair of Fisher 100AZ amps and Dynaco PAS3 preamp, have no hum. So, maybe you have a point there. I think it's more about, less crosstalk. Everything is more seperated from each other. This is my first Fisher reciever, but I just can't accept that it's supposed to have a little hum. No offense, I respect your insight but, Avery Fisher wouldn't alow for that, surely????? lol..... I did have a Sherwood S-5000 intergrated amp, and it had no hum. Wish I hadn't have sold it. So, I don't know....... Thanks for chiming in. Much Appreciated. I always enjoy talking tube anything, and listening to others thoughts on the subject.
Steve Hoffman
Mac and Roundie TV lover
Next time I fire my 800B up I'll crank it and give a listen, see what it's doing without music. I'll try the phono stage as well.. I'm curious!
I'll let you know..
I'll let you know..