Fisher 800 restoration

pixpop · 29th May 2006, 09:48 PM

I was just given a Fisher 800 receiver, and am wondering what to do with it. It basically works, and actually sounds pretty good. It has an intermittent fault that makes the sound go away for a few seconds. It has the usual scratchy pots, etc.

As far as I can tell, it's the original 800, not the 800B, or 800C.

Any recommendations? What's involved in restoration of these?

I've sent email to fisherdoctor, but no response yet.

Eli Duttman · 29th May 2006, 10:35 PM

Naughty boy!

Search for valveitude's Fisher overhaul thread.

pixpop · 29th May 2006, 10:47 PM

Well.. thanks.

I searched for fisher 800, and fisher restoration, but it didn't show up.

pixpop · 29th May 2006, 11:56 PM

.. it gets more interesting. (well, to me, at least..)

After playing for about an hour, the intermittent sound loss in the right channel morphed into an intermittent farting noise, very loud and unpleasant. Gets more frequent as time goes on. I switched it off to cool down for a while. When I switched it on again, I thought I noticed a blue flash coming from the back somewhere. Power cycled it again, and more flashes, accompanied by ths sound of arcing. Gonna leave it off now, before it goes completely south. All this makes me want to take my time and get it working properly.

While I was able to listen, was very impressed with the sound, especially vocals. Also "Lush Life" was very good. The FM sound is beautiful. Didn't try the AM. The phono stage hums in the left channel. Overall, I think it has great promise.

My only other tube experience was to build a Bottlehead kit. That went fine, and I liked the result. This thing is of course in another league entirely. So many tubes!

Eli Duttman · 30th May 2006, 12:12 AM

Valveitude's thread is here.

Tom Bavis · 30th May 2006, 02:29 AM

You will find it helpful (nay, essential!) to have a schematic and parts list. I have scans of the Fisher servce manual and the Sams Photofact folder for the 800 (also called TA-800). Copies will cost you an email - tbavis(at)rochester(dot)rr(dot)com.

pixpop · 30th May 2006, 05:09 AM

Eli,

thanks. I did find the thread by searching on Valveitude.

How should I proceed with the arcing problem? I don't know what was arcing, but am guessing it was one of the tubes. Maybe I should open it up, and power it on again so I can see what's arcing. Is the arcing likely to have damaged something?

Tom,

thanks for the offer. I sent you email. I'm not going to do anything until I see the schematic, and know what I'm looking for.

Neil Baylis

pixpop · 31st May 2006, 04:58 AM

Tom,

got the schematics today, thanks very much. Now to study a bit, and see what I can manage to get working.

Neil

pixpop · 5th October 2006, 04:07 PM

Getting back to this project after clearing up some other priorities.

I bought 4 new 7591s, but haven't tried them yet. Because of the light show in the original set, I was concerned that I might have burned up an OPT. If that was the case, I'm not sure I would want to go any further with this project, so my first order of business was to see if the OPTs were OK.

I pulled all 4 7591s, after marking which is which. I measured the resistance of the OPT primaries through the tube sockets, and they seem fine. I can see about 190 Ohms resistance between the two plates of each pair, and about 140K resistance to ground in parallel with about 220 uF. Looking at the schematic this all seems reasonable, so I think the OPTs survived the fireworks.

Next I powered up the amp (still without the output tubes) and measured the voltages in the tube sockets. The plate voltage, marked as 370V on the schematic, measured 420V. The grid measured somewhere between -9 and -10 volts.

I thought the high B+ might be because the output tubes were not there to load it down, so I picked the best looking pair of the originals, and plugged them in. The voltage came down to about 400V, so I imagine with all four plugged in it would be reasonable.

But the grid voltage is a bit weak. Later today, I'll see how far I get by replacing the selenium bridge.

I've read Valveitude's thread about a million times, and got lots of good info. Since I begin with a dead output stage, I'm going to work from the output (and power supply) back to the input.

pixpop · 6th October 2006, 04:42 AM

As expected, replacing the bridge with Shottkys did the trick. The bias is now -15V.

So I thought it would be OK to.. you know, put the new output tubes in.

Wouldn't ya know it.. I bought the wrong ones. I got the EH 7591As, and they are too big for the space available.

More anon, when my JJ tubes arrive.

29th May 2006, 09:48 PM	#1
pixpop diyAudio Member Join Date: Jan 2005 Location: Los Angeles	Fisher 800 restoration I was just given a Fisher 800 receiver, and am wondering what to do with it. It basically works, and actually sounds pretty good. It has an intermittent fault that makes the sound go away for a few seconds. It has the usual scratchy pots, etc. As far as I can tell, it's the original 800, not the 800B, or 800C. Any recommendations? What's involved in restoration of these? I've sent email to fisherdoctor, but no response yet.

29th May 2006, 10:35 PM	#2
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	Naughty boy! Search for valveitude's Fisher overhaul thread. __________________ Eli D.

30th May 2006, 12:12 AM	#5
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	Valveitude's thread is here. __________________ Eli D.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Fisher Tube Tuner Restoration Walkthrough	LinuksGuru	Tubes / Valves	7	15th November 2011 02:15 PM
Energy 22 Ref Con Restoration	bigerik	Multi-Way	87	4th May 2011 03:00 AM
Gibson EH 150 restoration	mattnorthrop	Tubes / Valves	15	26th March 2009 08:09 AM
DC Restoration -- book?	BottomTime	Chip Amps	2	20th January 2005 07:35 PM
CD Restoration	Stryder	Digital Source	5	2nd March 2003 12:06 AM

29th May 2006, 10:47 PM	#3
pixpop diyAudio Member Join Date: Jan 2005 Location: Los Angeles	Well.. thanks. I searched for fisher 800, and fisher restoration, but it didn't show up.

29th May 2006, 11:56 PM	#4
pixpop diyAudio Member Join Date: Jan 2005 Location: Los Angeles	.. it gets more interesting. (well, to me, at least..) After playing for about an hour, the intermittent sound loss in the right channel morphed into an intermittent farting noise, very loud and unpleasant. Gets more frequent as time goes on. I switched it off to cool down for a while. When I switched it on again, I thought I noticed a blue flash coming from the back somewhere. Power cycled it again, and more flashes, accompanied by ths sound of arcing. Gonna leave it off now, before it goes completely south. All this makes me want to take my time and get it working properly. While I was able to listen, was very impressed with the sound, especially vocals. Also "Lush Life" was very good. The FM sound is beautiful. Didn't try the AM. The phono stage hums in the left channel. Overall, I think it has great promise. My only other tube experience was to build a Bottlehead kit. That went fine, and I liked the result. This thing is of course in another league entirely. So many tubes!

30th May 2006, 02:29 AM	#6
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	You will find it helpful (nay, essential!) to have a schematic and parts list. I have scans of the Fisher servce manual and the Sams Photofact folder for the 800 (also called TA-800). Copies will cost you an email - tbavis(at)rochester(dot)rr(dot)com.

30th May 2006, 05:09 AM	#7
pixpop diyAudio Member Join Date: Jan 2005 Location: Los Angeles	Eli, thanks. I did find the thread by searching on Valveitude. How should I proceed with the arcing problem? I don't know what was arcing, but am guessing it was one of the tubes. Maybe I should open it up, and power it on again so I can see what's arcing. Is the arcing likely to have damaged something? Tom, thanks for the offer. I sent you email. I'm not going to do anything until I see the schematic, and know what I'm looking for. Neil Baylis

31st May 2006, 04:58 AM	#8
pixpop diyAudio Member Join Date: Jan 2005 Location: Los Angeles	Tom, got the schematics today, thanks very much. Now to study a bit, and see what I can manage to get working. Neil

5th October 2006, 04:07 PM	#9
pixpop diyAudio Member Join Date: Jan 2005 Location: Los Angeles	Getting back to this project after clearing up some other priorities. I bought 4 new 7591s, but haven't tried them yet. Because of the light show in the original set, I was concerned that I might have burned up an OPT. If that was the case, I'm not sure I would want to go any further with this project, so my first order of business was to see if the OPTs were OK. I pulled all 4 7591s, after marking which is which. I measured the resistance of the OPT primaries through the tube sockets, and they seem fine. I can see about 190 Ohms resistance between the two plates of each pair, and about 140K resistance to ground in parallel with about 220 uF. Looking at the schematic this all seems reasonable, so I think the OPTs survived the fireworks. Next I powered up the amp (still without the output tubes) and measured the voltages in the tube sockets. The plate voltage, marked as 370V on the schematic, measured 420V. The grid measured somewhere between -9 and -10 volts. I thought the high B+ might be because the output tubes were not there to load it down, so I picked the best looking pair of the originals, and plugged them in. The voltage came down to about 400V, so I imagine with all four plugged in it would be reasonable. But the grid voltage is a bit weak. Later today, I'll see how far I get by replacing the selenium bridge. I've read Valveitude's thread about a million times, and got lots of good info. Since I begin with a dead output stage, I'm going to work from the output (and power supply) back to the input.

6th October 2006, 04:42 AM	#10
pixpop diyAudio Member Join Date: Jan 2005 Location: Los Angeles	As expected, replacing the bridge with Shottkys did the trick. The bias is now -15V. So I thought it would be OK to.. you know, put the new output tubes in. Wouldn't ya know it.. I bought the wrong ones. I got the EH 7591As, and they are too big for the space available. More anon, when my JJ tubes arrive.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read