Discussion in 'Fisher' started by mrphilco, Jun 11, 2017.
No problem Ron. I get gun-shy at times too with this stuff.
Could you measure the diameter of the knobs on your tuner? I see some on eBay that look correct, but am not sure about the diameter. One set appears to be showing at 20.4mm? with a dial caliper around it. I know there are at least two sizes, perhaps even three which includes some used on consoles as well as component designs. I need to get at least one to replace a knob on the tuner I bought that is missing its cap.
Thanks in advance.
Glad to, but it may not happen for a day or two. I don't have a lot of spare time in the evenings after work, unfortunately.
So...I decided to only mow 75% of the yard this evening instead of all of it so I have a little extra time now. Joe, here are your measurements:
Height - 0.74"
Diameter - 0.725"
Now, my micrometer is hardly a laboratory standard, but I think those measurements are close enough for Govt. work. All eight knobs are the same size and same style save for the fact that the AM and FM tuning knobs have no triangles (pointers) on the face.
Thank you for taking the time to measure the knobs for me. I understand about getting home from work. You are already tired and as you said, there are not that many hours before it is time to retire for the night.
Your measurements confirmed what I thought about some Fisher knobs I saw on eBay. The 20.4mm dimension tags it as being a larger knob that likely was used on one of the Fisher console models. It is larger than the ones normally used on the front of the 202-R and the FM-200-B. The 202-R uses a different knob cap than the later Fisher tuners and amplifiers. They have a brass outer ring with a Fisher Brown center and an exposed brass arrow pointer. The later Fisher products used brushed brass knob caps with a black dash pointer.
Now I will know exactly what size knobs to look for on the 202-R tuner.
How high does the signal level meter of your tuner rise on a strong local FM station? Dave Gillespie mentions that on the 500-C and 800-C if it does not go over level 4 it indicates one or more IF stages with issues - likely silver mica disease in and IF transformer. My 500-C has this problem and needs attention to improve its FM MPX operation. It picks up the station I like, but its MPX lock is poor and as I tune across the station there is a background oscillation birdie in the audio that only goes away at absolute center of tuning. Most Fisher receivers I remember working with years ago would lock well to the MPX signal even before reaching absolute center of tuning and there was no audible oscillation birdie in the audio.
I suppose I should measure the smaller knobs on my TA-600 - now I am curious about them.
Oy vey. Mine does not go above 4. However, I did align it Sunday afternoon and, wow, does the FM side ever pull in the stations! I can even receive WUOL - 90.5 MHz from Louisville, a classical music station that should not even reach my area although I can easily receive it in my vehicle and on the 600-T in the living room which has an amplified antenna in the attic. Mind you, WUOL is very weak, but that is still better than any other receiver in the house will do (again, without being connected to the attic amplified antenna). No birdies, just good, clean FM reception.
I still haven't tested the tubes, and I really need to. Alignment did not help the AM side. I'm betting there is a tube in the AM tuner or AM IF stage that is nearly dead. But on FM...this tuner is everything that I have read about. Simply amazing.
Joe -- Besides Ron's amplified antenna, remember too that the 202-R runs with 6 IF stages, with likely four of them acting as limiters -- lots of gain there to cover any one stage that might be weak.
To clarify, I did not have the 202-R connected to my amplified attic antenna. I had it connected to a couple of wires that are stretched across a short portion of my basement ceiling. This is why I was so amazed that it picked up WUOL. Yes, very weak, but it was there.
Nothing else in the house will pick up WUOL unless it is connected to the attic antenna...and that is set up to output to the living room only.
Ah! Thanks for setting me straight!
If you're pulling in signals like that, I'd be tempted to ignore what the signal meter shows and say that its working pretty well.
Yes the extra limiting stages of the 202-R can overcome shortcomings elsewhere. I remember sharing an apartment with several other students in my college years and one of them had a FM-200-B. We were in Austin, TX and he regularly picked up a classical music station in Houston which was about 160 airline miles away. Of course that was when the equipment was new, early to mid 1960s. He was using rabbit ears or the folded dipole twin-lead antenna.
Here are the results of testing all of the tubes:
1st AM IF - 6BA6 - significant H-K leakage
2nd AM IF - Det-AVC - 6DC8/EBF89 - weak diodes, pentode OK
FM Muting Osc-Det - 6AV6 - weak diodes
3rd FM Limiter - 6BN6 - weak
All other tubes tested good.
I have a scan of the factory manual but I used a Sams Photofact to restore the tuner; it was from this Photofact that the functions of the tubes above were taken.
Dave/Larry/Gadget/anyone...I suppose H-K leakage could all but kill AM reception...in effect partially shorting that tube's cathode and upsetting the tube's bias, and/or introducing AC into the tube (I did not hear any significant hum on AM)...your thoughts?
If FM reception was excellent with a weak 6BN6 3rd FM Limiter...imagine how much better it will be with a good tube in that position...
I will find out in the near future - I will order some tubes this week.
I suppose its possible. The tubes in my Pilot tuner that were killing the AM were the mixer/oscillator tubes. That one happens to use a 6U8 triode/pentode in that spot. I forget which section was bad, possibly both, but it barely moved the needle on the tube tester. None of them had any noticeable leakage as I recall.
Quick look at the schematic shows the cathode of the first AM IF goes to ground through a 100 ohm resistor. Honestly I don't know that H-K leakage would have any significant effect on how that tube works, though you might get some funky hum modulation. I don't believe it would cause the tuner to be dead. Bad detector diodes would, but they'd have to be very weak to have no life at all.
The solid state units have a meter adjustment. So, if you are in an area with poor reception, "What would you like the meter to read?".
My antenna is 2 folded dipoles at right angles (omnidirectional) connected in parallel in the attic. That combination then goes to a 300 Ω to 75 Ω transformer (mismatch with the 2 300 Ω sections in parallel), then 2 splitters (-6 dB total) then a 75 Ω to 300 Ω transformer, then to the receiver. I tried an amplifier once, but it actually made things worse. This was a $20 special from All Electronics and I have heard that cheap amplifiers are garbage.
Ron -- Check the continuity of the Antenna circuit. It usually supplies bias to the RF Amplifier from the AVC line -- but the Fisher antenna is easily broken either on the antenna mount, its connecting leads, or otherwise. If that circuit is open, that will really kill the AM. The bias for the RF amplifier stage is largely provided by the AVC voltage. The 100Ω cathode resistor is basically a stop-gap when no AVC voltage is present. I've seen plenty of H/K compromised tubes that otherwise still work fine in both AM and FM tuners.
If the antenna is good, the tubes are good, and the operating voltages are otherwise good as well, then I'd go after the IF transformers and check for silver mica disease. Having just one resonant cap go south will really kill performance, and if there's more than one, then it will really be compromised.
I have no doubt that you'll find the issue in no time though!
My attic antenna is actually a TV/FM directional which I had bought to try and pick up TV stations but now that we have basic cable (and never watch it), the antenna is only being used for FM reception on my 600-T which is in the living room. The amplifier is a Radio Shack unit made for outdoor TV/FM antennas; the actual amplifier mounts under the antenna and goes to a power injector/splitter as it has two outputs. One output is still connected to our HDTV, the other output to the 600-T. It does pick up FM very well. Using this antenna, WUOL usually comes in quite well.
Thanks. As it happens, you sort of read my mind. I was thinking earlier this evening while finishing up the mowing from yesterday - I need to start checking coils and taking voltage readings. Your suggestion is a great place to start; thank you again, very much appreciated!
I just sent an inquiry to Jim McShane for the tubes that I need. While I wait for them, I'll start checking the antenna circuit and go from there.
Jim will likely have the AM tubes -- I recently had to get some from him for Rob's TA-800.....
I am happy to report this morning that I have the amber and the red jewels for the front panel of the 202-R which I have coming from eBay. The one I bought has its green jewel, so now I will not need to order extra jewels. I had these from restoration of my X-101-C integrated amp.
I also ordered some Fisher 1961 era knobs from eBay this morning. One is the .813" X .725" with the brown cap and brass arrow and the other one is a two-piece knob for treble or bass for the concentric shaft controls. Matt and I are working on exchanging some knobs for the 202-R as he has the correct type for the AM Antenna selector knob. That one on my tuner is present, but missing the cap.
Sounds good, Joe. I just heard from Jim McShane and have ordered the tubes that I need for my 202-R.
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