The Fisher 202-R Tuner

So today I touched up the AM alignment.

Wife and I went out this evening, and when we got home it was after dark so I fired up the 202-R for some evening AM listening.

It pulls in plenty of AM stations. It pulls in stations I would normally expect to hear only on a well restored 1930s Philco with multiple tubes and a longwire antenna. And, again, this is only with its built-in ferrite rod!

I am very pleased with how this one turned out. Now, to decide just how I am going to use it, since it requires an amp for normal operation...

Thanks to all who helped me get this going again, very much appreciated.
 
Ron; Mix up some ammonia and water (25% to 50% ammonia to water). Use a micro fiber cloth and wipe with the damped cloth in one direction. Don't scrub!!! And don't let this sit on the panel longer than a couple minutes. Rinse under cold water. Dry and wax it. The silkscreen is tougher than you think it is.

Hey Larry - as I was reassembling this tuner, I worked up the courage to try this. I can't really tell if it helped much, but it certainly did no harm. Thanks!
 
I will likely be getting my 202-R tomorrow according to the tracking information. I may try the ammonia & water method too. I am currently looking for the unique knobs used in this time period of Fisher products. I have one concentric set I ordered and another that is a plain knob normally used for tuning as it has no arrow on it.

One issue I am wondering about is whether the power transformer in the set would have enough filament current capability to operate 3 12AX7 tubes in a MX-65 to demodulate stereo. I have never seen any specifications on the transformer for this unit.

Joe
 
A quick note to let everyone know that the 202-R arrived today by FedEx. Package looks OK, will check shortly. I might have some pictures later.

Joe
 
Joe

Thanks to the Sams Photofact, I have complete specs for the 202-R's power transformer. I will post them in your new thread.

In the meantime - here's a question for anyone who can answer it:

Why does the FM signal drop slightly when Microtune is on?

I first noticed this when I initially had the tuner up and running after the recap but I forgot to ask at the time. After the alignment the phenomenon is barely noticeable on strong signals, but on medium to weak signals it is very noticeable.
 
Joe and Ron -- While the Sam's specs for specifically power transformers are certainly helpful, they are not a specification of the transformer itself but rather, what the circuit is drawing from the transformer. Again, certainly helpful, but not exactly the same thing.

Ron -- If you are finding that when you let go of the tuning knob to engage the Microtune circuit that the tuning then comes off of the peak meter indication you had tuned it to, that is an alignment problem in the IF strip. I had made mention of this concern way back in my post #12, as it is not uncommon for units with the Microtune feature to display this behavior when the alignment is off. A little bit of off-tuning can be tolerated. But in later tuners like the FM-200B, if it gets significant enough, it can knock the automatic stereo circuit back to mono due to the off-tuning when the Microtune circuit engages. The alignment on Microtune units needs to be very precise, with at least a crystal controlled IF signal used for alignment (what Fisher used), and preferably if possible, a digitally locked signal with counter readout for precise 10.7 mHz accuracy.

Dave
 
Joe and Ron -- While the Sam's specs for specifically power transformers are certainly helpful, they are not a specification of the transformer itself but rather, what the circuit is drawing from the transformer.

Just trying to help Joe out. The Fisher manual gives no info whatsoever on the power transformer.

Ron -- If you are finding that when you let go of the tuning knob to engage the Microtune circuit that the tuning then comes off of the peak meter indication you had tuned it to, that is an alignment problem in the IF strip. I had made mention of this concern way back in my post #12, as it is not uncommon for units with the Microtune feature to display this behavior when the alignment is off. A little bit of off-tuning can be tolerated. But in later tuners like the FM-200B, if it gets significant enough, it can knock the automatic stereo circuit back to mono due to the off-tuning when the Microtune circuit engages. The alignment on Microtune units needs to be very precise, with at least a crystal controlled IF signal used for alignment (what Fisher used), and preferably if possible, a digitally locked signal with counter readout for precise 10.7 mHz accuracy.

Yes, you did indeed mention that, and I also mentioned above that it is better after I performed an alignment but it is still not "there" yet. I'm using a Sencore SG165 generator, and I'm not inclined to go out and buy another generator. I do have a B+K frequency counter, and I suppose I should doublecheck the Sencore's 10.7 mc output.

When I replace that 75 ohm resistor I put in temporarily with the proper 100 ohm resistor in series with the silicon rectifier output, I will revisit the alignment.
 
Ron -- You're right. Fisher never does give the specs on their power transformers, and I certainly know you were trying to help Joe. The information Sams gives is great in determining an appropriate replacement transformer for a given unit, but doesn't give a clear picture as to actual ratings of the factory transformer. They are also quite bogus for equipment with Class AB amplifiers in them. Sams (again) rates the B+ winding based on the current draw of the unit under quiescent conditions, yet current draw rises quite significantly with power output in Class AB output stages.

One trick you can use on your 202-R if the alignment frequency is close enough is to slightly off-tune the primary of the ratio detector transformer (top slug) after the Microtune circuit engages and the peak is lost. Off tune it to regain the peak again, and then the Microtune circuit should work well enough -- again, as long as the alignment IF frequency is close enough. I imagine with the Sencore, it is.

Dave
 
Ah-HA! That's it! NOW I remember what I was going to ask about (but later forgot)!

I cannot properly tune the top slug of the ratio detector. When I try, the slug gets stuck and will not allow me to get to zero reading on my VTVM. It remains on the negative side of zero. I can adjust it a little, but not enough to get it to zero.

Thoughts?
 
Might be some ham handed idiot poo-poo'ed the instructions about using the correct tool when adjusting and broke the slug. If it's not broken, then it's possible it's cross threaded (not likely tho). Can you take off the cover and check the slug???
 
Often times it indicates that the slug has been in that position many, many years. Is this the type with a threaded slug down in the coil? Or the type with a larger slug threaded between two plastic uprights?

Dave
 
It felt like it was cross threaded or otherwise binding up as I began turning it in an attempt to get it closer to zero on the VTVM - it doesn't feel broken. But I will check this weekend, thanks.

(it wasn't this ham-handed idiot :rflmao: - I have the proper adjusting tools)
 
Dave

Oops, you posted as I was answering Larry, sorry.

The slug having been in the same position for decades seems quite plausible, as this unit did not show any signs of repair prior to my ownership. The only thing that is not original is the AC plug, which is a hardware store replacement for the original Fisher plug.

The ratio detector has two threaded slugs inside the coils, made to be adjusted with a small plastic hex tool.
 
Talk about IDIOT's. Ever sighted a b-1-rd or a GU-11 thru binoculars or the scope and had a sub pull the cork? Made the poor shmuck feel about 1-1/2ft tall. 2nd week out on a Missile boat patrol (70 days or so), We were at periscope Depth and the X.O. was on the periscope, we were up for nightly(we were in Northern lattitudes so it was light out) radio and housekeeping stuff(blowing sanitaries, trash,etc.). Anyway, he sights this plane about 5 miles off on the scope at wavetop height apparently headed right for us, and luckily we had a monitor on the scope. X.O. calls "Down Scope, make depth 400ft. and make it fast!" Skipper walks into Control about the same time and "belay that, stay at Periscope Depth, Scope UP!" He nudges the X.O. aside and about 10 seconds later, tells the X.O. to bone up on his Plane I.D. as the craft in question was a B-1-RD or a GU-11. (A Laysan Albatross skimming the air currents just above the waves, the skipper had seen it flap wings just as the scope went under but wanted a good look before we dumped the air.) IT took the X.O. about a minute to figure out(he was never the sharpest pencil in the box) what the Skipper meant. While he was pondering this, IT was all the Control room crew could do to keep from busting guts and it got around the boat faster than a dirty rumor gets around women! The crew definitely had a good time razzing him about that one! Even gave him a hard hat with wings on it during the 1/2way night party. The Navigation team gave him a Aircraft recognition book from early-mid '60's(this was 1976) full of obsolete military planes in it. About the only one currently used at the time was the P-3 Orion.
 
Ah-HA! That's it! NOW I remember what I was going to ask about (but later forgot)!

I cannot properly tune the top slug of the ratio detector. When I try, the slug gets stuck and will not allow me to get to zero reading on my VTVM. It remains on the negative side of zero. I can adjust it a little, but not enough to get it to zero.

Thoughts?

Careful. If it is stuck, you could end up turning the coil and breaking off all the wires. Been there, done that. Fortunately, the Elenco AM-FM radio kit uses a similar ratio detector circuit and I was able to improvise. It ended up being 2 coils, one for the top of the original, the other for the bottom.

12421646254_2d850a46a6_b.jpg
 
Nice setup, Fred...but I want to keep mine looking and functioning as original. I have not tried to force that slug, nor will I do so.

I have done nothing more to the 202-R, having been distracted by a quick recap and rectifier replacement of an FM-50-B multiplex tuner. It surprised me...it is almost as sensitive as the 202-R. Stereo also works even though I did not replace the 1 uF electrolytic (the only electrolytic I did not replace, only because I didn't have one on hand).

But I digress...

During this time I also found and bought a NOS J.W. Miller 1465 ratio detector transformer. It arrived today. Unlike the original Fisher rat det coil, this one has the large iron cores that go over the coils. And it does not have built-in diodes as does the original. I'm tempted to go ahead and install it in place of the original, add two outboard germanium diodes, and try again to get this unit properly aligned.
 
Ron; a 1uf 400v film works as well and you don't have to worry about it 20 years down the road.
 
Excellent, Larry, thanks!

(of course I'll still have to buy one...)

I checked out the Miller 1465 ratio detector today. It's never been soldered. All coils show good continuity. I found a source for 1N541s so I'm thinking I will replace the ratio detector with the Miller coil so I can easily adjust this circuit.
 
With this post, I can report that following a long streak of work that began last night and lasting most of the day today, I believe that I finally have my 202-R all tuned up and performing at its best.

I installed the Miller 1465 ratio detector last night. This called for external germanium diodes as the original has diodes built into the unit. The terminals of the Miller 1465 are arranged differently than the original coil also, which led to some longer lead lengths which I do not feel was a good thing.

What followed was performing the FM alignment more times than I can count, with OK but less than stellar results.

Long story short - I put the original ratio detector back in this evening and performed yet one more FM alignment. After having consulted the Fisher service manual as well as Sams, I discovered that I had made a serious error which was probably my main FM alignment problem all along.

IF YOU ARE USING THE SAMS PHOTOFACT DATA TO ALIGN THIS TUNER:

Be sure you note that the first FM alignment point, A14, is not the upper slug - it is the lower slug. A25 is the upper slug. (The Sams Photofact data is correct in this regard, and the Fisher manual confirms this. Dummy me somehow managed to transpose the two.) :oops: Which is why the upper slug was getting stuck - I was turning the wrong slug at the wrong time, and the two had become very close together inside.

Here is another tidbit which may prove helpful:

A25 (again, the upper slug of the ratio detector coil) should be adjusted for a zero reading on your VTVM with its high side connected to point <C> and common lead to chassis. This is done after the remainder of the FM IF alignment is complete. Now, having done that, disconnect your signal generator, connect an antenna and tune in a fairly strong station. Now turn on Microtune. If the signal strength drops, leave Microtune on and readjust A25 very slightly and very carefully until the signal level on the FM tuning meter is the same as it was with Microtune off. Now tune in other FM stations and see if Microtune is still working correctly. If so...your alignment is complete.

Now, my 202-R is rock solid and Microtune is working perfectly. It is now capturing and holding both strong and weak FM stations. :thumbsup:

Tomorrow evening, I will reassemble it (again) and it will be finished.
 
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