Fisher 1800 Stereo Beacon Performance

Dave451

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I obtained and 'polished up' a Fisher 1800 recently, described at RSSteve's "1800 Roll Call and Information" thread:

http://audiokarma.org/forums/index....iver-information-thread-and-roll-call.724824/

I'm quite happy with the overall condition of this receiver and it sounds very good. Still puzzling over the relay-controlled "Stereo Beacon" control, though. It didn't work at all in "FM Automatic" mode when I first got it. After an FM IF/Ratio Detector alignment, it started working again. I also cleaned the contacts on the relay while doing various work in the unit.

Now that the 1800 is playing in the listening room, I'm impressed with the sensitivity of the receiver with just a wire dipole antenna. I live about 35 miles from Philadelphia 'as the crow flies' and there are plenty of strong stereo stations, as well as a few even closer in Wilmington DE. These stations put the signal meter at or well past 4 out of 5 and come in with very little noise in "Stereo Filter" mode (full time FM multiplex).

However, the Beacon light only lights in Automatic mode on 3 or 4 of the very strongest stations. Looking at the schematic, there appears to be no way to adjust the circuit. The 6GK5 SB amp tube tests strong (mutual conductance). I performed Dave Gillespie's "800C Service Bulletin" to change out B+ supply resistors to the diode matrix that controls this circuit.

I did not try to align the multiplex decoder, as it showed good stereo operation and separation when driven with my Sencore SG-165 (if it ain't broke…..). There is good apparent separation when listening as well. No distortion in stereo on moderately strong to strong signals. The signal meter shows 4+ with strong signals, about 3 between signals and close to zero or 1 with no antenna connected.

So, the question: should the Beacon be operating on more stations? If so, what should I look at to achieve it? MPX decoder alignment? Other?

Thanks!
Dave
 

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IIRC and I don't have access to either of my 800c's, the Beacon lamp has one wire to it. If so it grounds thru the chassis. 1st thing I'd do is Make absolutely sure the chassis, the mount and the inside of the socket for the #47 bulb are absolutely clean and make tight connections. If it still isn't right, and you're sure you're getting a good 19kc signal out of the discriminator, then the MPX will probably need some alignment tweaking. Dave can get into the details there. I don't touch them, and for good reason. I like what little I have of Stereo, but they do light up across the dial on all but 2 stations here in B'more/Wash D.C. area.

I'd also check all 3 of the 12ax7's. I had one on a MPX-125 that showed good on GM and Emissions on both sides, but it wouldn't pass a signal in the V100 position. Also swap the 6GK5 beacon tube with the RF Amp (V1) and see if that helps.
 
Thanks to you both! I'll check all these things and get back to you. May be a little while as I listen to the 1800 and let everything play in. Plus, the dang thing is so heavy that I don't want to carry it up and down the stairs more than I have to, so I'll see if any other bugs are evident and then get it back on the bench.
Dave
 
That's where Adult Children come in.:naughty::naughty: Bribe them with a beer:beerchug: or something stronger for use of their back! :whip:
 
More work on the checklist for the 1800. First, I'm hearing some distortion in loud music passages on high-pitched instruments, even with the tuner carefully tuned to the highest signal strength. Looks like a visit to the MPX decoder is in order for alignment. Second, and I don't know how I missed it on the bench, but both of the faceplate lamps are burned out, so I'll be searching in the stickies for replacements when she goes back on the bench.

After tending to the MPX decoder, I'll see how the Stereo Beacon is operating (after completing the checks above) and take it from there.

Larry, both of my adult children are daughters and, although sturdy, probably couldn't manage the 1800 up and down the stairs no matter how much beer or wine I gave them! However, my son-in-law is a strapping 6 foot 3" lad who can help in that regard and actually takes some interest in my benchwork.

Dave
 
Dave, you must be awful close to me. I'm also relatively close to Philly, and Wilmington is closer. If you can see a steam cloud from a nuclear plant from your place, we're definitely close.

Also worth a look, is the lamp the correct one? Don't pretend to know the circuit at all but sometimes they are designed for a specific lamp and using the wrong one will mess it up. Subbing a #44 for a #47 happens by accident sometimes.
 
Yep, on a clear winter day you can see the steam risking from Salem 1! Chester County, PA. As for the lamps, the burned out ones are the 'festoon' ones on the sides of the dial plate that look more like fuses. There's a good tread on replacing these lamps and a guy on ebay has LED replacements that I will probably try. These are the first ones I've seen burned out. Both were good in the 400 and 500B Fishers I had. The two FM bulbs with the hoods on the chassis are both good.
 
Its Hope Creek with the tower but close enough. Salem 1 and 2 are river cooled. they're the next town over from me.

I meant the stereo beacon lamp. Is that the one the circuit wants?
 
Ah--got it. I'll check it for the proper bulb in the beacon lamp. Carried it down to the workbench and will look tonight. Any particular recommendations on replacing the festoon side lamps?
Thanks!
Dave
PS Stream rising from Salem 1 would be pretty bad, I guess!
 
no idea about the festoons. The one Fisher I own has one original and one donated out of my parts chassis.
 
Did you check the phase inverter balance? It could be off and getting rid of the "noose" might be a worthwhile effort (clip out 1 resistor per)while you're in there. See this thread for details . http://audiokarma.org/forums/index.php?threads/fisher-400-service-bulletin.671281/
Also the 800 service bulletin thread in the stickies about 2 resistors that are way undersized for the job and can screw with fm reception quality. Dave details the problem here....... http://audiokarma.org/forums/index.php?threads/service-bulletin-800c.796896/

Make sure you get the length of the festoons on the 1800. They aren't the normal length of fuse or festoon lamps available. They are longer by 2 end caps from fuse lamps.
 
Thanks very much for the input, Larry. I have not checked the PI balance settings and I will. The distortion seems to be coming on FM reception only, leading me to suspect the MPX decoder, since the front end of the FM receiver has been aligned, but I'll definitely check the PI's. I did Dave G's mods on my 400 receiver, including 'de-noosing' and it sounds very, very good. I'm studying on how much, if any, I want to mod the 1800.

I did do Dave's suggested "800C Service Bulletin," replacing the two resistors with 1/2 W metal film of the same values. And, thanks for the suggestion on the lamps. I was about to order something, but I'll take a close look at the current ones and measure the length before I buy anything.

I'll report on what I find on all of the above as I get back to the bench next day or so.
 
I found something that works great to clean tube socket leaves. It's a LINCOLN Torch tip cleaning kit. About 7-8 different sized brushes on a carrier similar to a hex key set. About $4.00-$5.00 @ Home Depot. In the section with the Welding/Burning Equipment.

Lincoln Electric TIP CLEANER. Part # KH575 Contains File and Tip cleaner for Drill sizes 45 to 77. Works great on the 7 and 9 pin small tubes. For the Larger Octal or Noval/Novar tubes you got to work it sideways a bit to get all surfaces but it does really nice. Beats those plastic Dental brace brushes by a couple orders of magnitude.
 
Going to pick one up, Larry--thanks for the tip. I've been looking for something better than the dental brushes.
 
Finished up the work on the MPX decoder and Stereo Beacon indicator (following your suggestions) all is working very well now, to wit:
1. The lamp in the SB indicator was a non-descript one (Taiwan 1616) with a GE #47 pull I had on hand. The lamp assembly is not grounded to the chassis. Two wires come from the assembly; one goes to the SB relay and the other to the small tube filament circuit as per schematic and both were connected securely.

2. I pulled the front panel and one festoon lamp was missing and the other didn't work (loose end cap). These are the 1/4 inch by 42 mm (1 5/8") size. I ordered warm white LED replacements from an ebay vendor that hopefully should do the trick.

3. This is the only vintage unit that I've had where the 'light control' polyurethane foam around the front glass was still intact. Nice not to have to replace it this time!

4. I installed the Dave Gillespie mod to lower the noise detection threshold in the MPX; i.e. a 47K 1/4 W resistor across the 1Meg R204. The beacon started working much better even before MPX alignment, allowing stereo reception and lighting the lamp on any reasonable signal, not just the two or three strongest. Great tip, Dave!

5. The MPX alignment went very well. All the practice with the 400 and 500B before really helped (as well as a close review of my notes and Dave G's coaching). It was pretty well out of whack and required a fair amount of adjustment. For one thing, the phase was wrong (left MPX input coming through right channel) and the separation adjustments were well off. The 80kHz subcarrier adjustment was, as always, very broad but there was a slight minimum. 19 kHz pilot was pretty close, but touched it up. 38 kHz adjustment needed some work (see above on phase problem), but dialed right in with stable Lissajou figure over my full range of RF output from the Sencore SG-165. The separation ended up well above the 33.5 dB minimum (could barely measure the off-channel RMS voltage), both with the MPX directly driven and through the receiver from the antenna terminals.
6. I adjusted the phase inverters for the power amp and tested the amp. Initial checks had the right channel starting to clip fairly early and unsymmetrically. I changed out the V15 PI/Driver Philips 12AX7 with a tested good Sylvania (avoided a Russian tube) and got much better symmetry at clipping, measurably less distortion (as seen on my scope FFT output) and more output from the right side. I followed the Service Manual procedure for PI adjustment at 25W output, except into an 8 ohm load instead of the 4 ohms specified (would that make much of a difference?).

I ended up with 32 and 34 WRMS at 1 kHz R and L, respectively, single channel driven. I got 30 WRMS per channel with both driven (speaks well for the power supply, I guess) with good tracking between channels and balance of the controls.

Finally, a prior tech/owner changed out the volume control and PS switch. The volume control acts a bit odd in the first part of the turn: volume rises at first, then doesn't change for a little bit, then begins rising again. Does this for both channels, so I'm not sure what's going on with it, but there's no noise in the control, it has volume control taps and the Loudness function works well. Thoughts?

Anyway, the whole rig is working very well now; crystal-clear FM stereo audio and all is good in "stereo beacon land." Waiting for the festoon lamps to come in, cleaning her up a little, and then back to the listening room again.
Dave
 
Great job, Dave!! Glad you got it going. No doubt that the pause in volume control action is occurring right at the point where the loudness tap is attached to the carbon track. Such a pause at this point is hardly uncommon, with some controls showing more pause than others.

The 800C (1800) receiver is such a statement of Fisher engineering and American manufacturing of the day. When they're "right", they are truly an amazing machine, being one of the best executed and best looking entertainment centers of its day. Maybe you've seen the thread on my own 800C when I first got it -- pristine looking, and advertised as working perfectly, with of course most of it hardly working correctly at all when I received it. But I went completely through it and did all the goodies to mine, including one that turns the the Signal Strength meter lamp off when none of the tuner functions are selected, which I think really completes the look of the unit when an external source is selected. I enjoy the heck out of mine, and I have no doubt you'll will enjoy your 1800 as well.

Congrats on a job well done!

Dave
 
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Thanks, Dave. I have looked at your 800C thread a while back but I'm going back for another look as long as I have the 1800 on the bench. I've had to do more work on this one that I might have thought when I bought it, but it's fundamentally quite sound and in very good condition and the work just makes it more mine. As the pinnacle of Fisher design and construction, it's a keeper for sure!
 
Dave G,
I re-read your post (great as always) and saw that you had been requesting information on output transformers, so I thought I'd add this to the pile:

Fisher 1800 S/N 52468T (Originally wired for 220-240 VAC)
OPTS: T991-116-2C and T991-116-1C, both also stamped 1005702

I'll also post this on RSSteve's 1800 call for info thread.
Dave
 
Thanks Dave -- My 800C came with one output transformer having some off measurements and a possibly a different number (it's been a while), but I've since replaced it with a normally performing replacement that now produces matched performance in both channels. It was just another one of those things that was "off" about my unit when I purchased it.

Dave
 
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