202-R Arrived

[fred soop]

The TFM-300 is almost exactly the tuner portion of the 600-T receiver. It uses the tube/nuvistor front end from the 500C (FETs were not yet ready for prime time, that would have to wait for the 700-T). The TFM-300 has no remote and no autoscan. The 440-T receiver was produced during the same time as the 600-T but had a bipolar transistor front end.

The TX-300 was not quite identical to the amplifier section of the 600-T. There were a few more features, including a second phono input, a microphone input, and a stereo-reverse position on the mode switch. Same fragile, load sensitive, heat sensitive, exploding, germanium output stage.

 

[dcgillespie]

Ah, the old CRT rejuvenator and brightener tricks to extent CRT life. It seemed to me that the improvements they generated never seemed to last very long.......

Dave

 

[audmod01]

Dave;

Yes that was my experience too. They sometimes helped for a while but would eventually go from bad to really bad.

Fred;

If the TFM 300 did not have the remote control, then that was not the model I was thinking about. I seem to remember it being a fully tube unit. I remember that what service information we had was like an addendum to a FM-200-B or something similar. It had no pre-sets and the remote had a tune up and a tune down button. I think it also had tune up and down buttons on the front panel. The model number may have been M-300. I can't remember for sure. It reminded me of automobile radios with search tuning. Like them it had an electric drive motor to move the dial. It also had a manual tuning knob.

Joe

 

[larryderouin]

Mom and Dad had this thing for everything in the house from Sears, Except for large Kitchen & Laundry appliances then Mom put her foot down and went GE! They are now on their 3rd TV since 1960. (Sears Silvertone 19" B&W tube) which lasted into the Late 80's but downstairs in the rumpus room for the kids once they got the Color TV. I would replace tubes in it when it would act up and get goofy on us. Going down to the Corner Drugstore for tubes was fun when they had a tube tester as it would read them all dead or close to it, even tho I knew they had some life left in them (Dad had at the time a Hickok 6000A that I would test them on, before it got lost in one of the moves(military and Westinghouse)). In 1968 he bought a Silvertone 19" Color TV. Surprisingly a real good TV too. He kept it running until last year when the flyback burned up (Mom called the Fire dept to respond on that one) while on his bench in the garage and took out the main board for it, and he'd replaced the CRT 2 yrs before. So they went and got a 42" Sony LED. He hates the damned thing!

Dad turned 85 last week and has now given up working on stuff as he has beginning stages of Alzheimer's and Mom won't let him near the bench except to get a screwdriver or a pair of pliers. So now I'm making weekly trips to Southern Del and doing stuff around the house that he can't do anymore. I was going to give them my 58' Contemporary, but since Dad has Alzheimer's now I don't want any tubes around the house. He's got a bunch of records, but nothing to play them on so I'm probably gonna give them a S.S. record player I have. That way he can listen to his Big Band stuff he hasn't listened to in years.

 

[audmod01]

Fred;

I was close to the mark on M 300, the model I remembered was the MF-300 and it was an all tube model which had the same front end as a FM-200-B and included the necessary parts for the remote control functions. There are a few images of some on the worthpoint site. I have not seen any service information on these since I left Berkman's Hi-Fi in 1966.

Joe

 

[audmod01]

Here is the test report from the Sept. 1963 issue of High Fidelity magazine for the Fisher MF-300 tuner.

 

[audmod01]

There is a bit of a learning curve on rebuilding electrolytic can capacitors. I have been dealing with that on this thread:
http://audiokarma.org/forums/index....-to-a-490-t-tuner.774128/page-2#post-10690088
so now with some valuable experience behind me I believe I can tackle the single electrolytic can capacitor on the 202-R. It turns out that even on a badly dried out electrolytic can that more heat can be applied if just a hair drier does not do the job.

I received the electrolytics that I ordered from Mouser Electronics on Saturday, so they are ready to be used for making a new capacitor. One thing that I did was to select new individual radial lead types that are narrow and tall like Ron described and with the needed value and voltage ratings. I also managed to get capacitors that have a higher temperature operating range up to 105 degrees C, so the new parts should last better than the originals.

Ron;

Did you find it necessary to use deoxit on the tuning capacitors of your 202-R? I am thinking I will have to do that. I have had to do it to much newer units than this one, so I sort of expect to need to do that. At the very least the pivot bearings need to be relubricated on the variable capacitor assemblies. I already applied some new lubrication to each dial string pulley and to the bearing surfaces of the flywheel weights of the tuning knob shafts. Those efforts made the tuning much smoother to the feel already.

Joe

Joe

 

[mrphilco]

Joe

No, the tuning condenser of my 202-R was (and is) fine, not noisy. Both AM and FM tuning seem to move just fine, no problems.

<off topic> Now, I do have a vintage 1960 Rittenhouse whole house intercom with AM-FM radio...their first solid state unit of this type...it was in our house when we bought the place. I recapped it a few years ago, replaced its 120V to 16V step-down transformer in the basement...and I think it is good to go for several more years. But its tuning condenser makes terrible scratching noises through the speakers when tuning, when it is set to FM. I tried lubricating the pivot bearings on the tuning condenser assembly and that worked for a while, then the scratchiness came right back. I had always read to not use DeoxIT or any other spray contact cleaner on tuning condensers. What are your thoughts on my situation? </off topic>

 

[audmod01]

What I have done is to spray a small amount in the cap that goes on the can and use a small screwdriver to dip into that and transfer a drop just to the pivot points and grounding clips, then run the tuning capacitor end to end multiple times and recheck. I had one case in a Kenwood KT-7500 that was stubborn and I had to resort to inserting some silver particle heatsink compound made for CPU chips into two of the shaft grounding clips to silence it. There was corrosion down in there that I could not get at and I did not want to completely disassemble the front end to correct it. I used a small amount on the tip of a chisel blade X-acto knife to work the compound into the grounding clip and shaft area. That corrected the problem and it has not come back. Previously every application of Deoxit did the same as you described - temporary correction of the noise and the noise came back after it dried out well.

Joe

 

[mrphilco]

That's a great idea, thanks! I will get some of the silver particle CPU heatsink compound and try it...

 

[audmod01]

Ron;

The brand I used was Dynex and it came in a hypodermic syringe and was just labeled Silver Thermal Compound.
Good luck!

Joe

 

[audmod01]

Today after I set aside the Electra IV/VI mating project pending arrival of new tubes, I turned to looking at the 202-R again. I decided to start by measuring resistance to chassis ground on each electrolytic cap section of C26. I saw less than 20K ohms to ground on each section of C26. This was measured using the 20K ohm function of my Fluke 8600A Digital Multi-Meter. I started disconnecting components from each section of C26. Section A receives the +DC output of the selenium bridge rectifier. It measured well over 20K and I switched to the 200K function and it rose in resistance until It exceeded 200K ohms. I moved to Section B of C26 and with its lead disconnected it measured a little over 16K ohms. I looked at Section C with its leads disconnected and it rose to over 200K ohms with its leads and components disconnected. With Section B showing resistance to chassis ground with the wire disconnected from it, I don't trust this can electrolytic. I have seen enough smoke rise from turning on suspect equipment over the years and even though the person who sold the unit said it was working, I always take any such statements with a grain of salt.

I have on hand a complete set of 40uF@350VDC individual electrolytics that I ordered at the same time I ordered electrolytics for the Electra chassis set. So the next step will be to remove C26 and take its guts out, then reassemble with new electrolytics inside. The bridge rectifier will eventually be replaced, but appears to be OK for now. When new rectifiers are installed in place of the selenium bridge I will install the recommended resistor to keep B+ in line with the design.

Joe

 

[gadget73]

its hard reading those things accurately with a DVM. Not enough voltage. If you've got a source of HVDC and say a 10K resistor, you can work out the leakage easy enough. Old cap testers with leakage functions will do this for you too.

Or you can change it and not have to worry about it.

 

[audmod01]

Gadget;

Yes, I am aware that readings of such conditions vary depending on the circuitry inside a given meter. The leakage does indicate a problem inside that particular section. I prefer to replace rather than apply power and wait for something to happen. If I know there are good parts in the power supply, then I do not have to worry. There are also a couple of 20uF@300V caps that are not part of the can electrolytic. Those will get changed too before power is applied.

One thing that is nice about this design is that none of the tubes or other parts are being subjected to very high DC voltages. That helps to extend tube life and the life of other components too. Over the years I saw far too many radios and televisions with tube circuitry that ran everything right at its limits. This practice leads to frequent failure of parts and tubes. I like to see comfortable margins of operation compared to the ratings of the parts.

I should be able to get this electrolytic can rebuilt today and installed. I am eager to try this tuner out and see how it performs if at all. In particular I want to check the AM section to verify my repair of the loop antenna. The loop I used from an Electra 610-ST had its winding spread out over the same length as the original with some turn spread and one area more compressed, so I hope it will track well against the dial.

Joe

 

[gadget73]

A lot of audio gear pushed the limits pretty hard too. Just depends what the goal was and who designed it. If you need just 5 more watts than the other guy, adding voltage is an easy way to get it.

 

[audmod01]

Gadget;

Yes, and often engineers are pushed into areas they would prefer not to go because of sales staff and management - such is life!

Today I finished installing new electrolytics throughout the 202-R. The B+ was running around 200VDC at the first filter capacitor and began to drop the longer it was on. I went back into the unit and took out the bridge rectifier. It showed high resistance, so I built up a bridge rectifier using a terminal strip and individual 1N4007 diodes. The B+ is now running about 250VDC so I need to add a resistor on the input to that first filter as Dave recommended.

The FM is working but not the AM so far. I had to replace two dial lamps, one for FM on indicator on the front panel and one for the light on the AM tuning meter. The AM meter does not move off of its resting place either, so I have some more work to do. Next step will be adding the resistor to B+ and then testing all the tubes.

Joe

 

[gadget73]

make sure the antenna is good too. Some things had the antenna as part of the RF amp circuit and not having a good one will make it not work even with an external. My Pilot had a couple dead AM tubes in it. I suspect it was rarely used in AM and they died from a lack of B+ after long hours.

 

[mrphilco]

Joe

On my 202-R, the B+ was 252 VDC at the first filer cap until I added a 75 ohm dropping resistor temporarily; that only dropped it to 243 or so VDC. So when my most recent parts order came in yesterday, I changed the 75 ohm resistor for a 270 ohm 7W resistor. Now the B+ is at 210 VDC going into the first filter.

The Fisher service data calls for 226 VDC at this point.

I think a 200 ohm or, better yet, 150 ohm resistor would be a better choice. 100 ohms isn't enough to drop the B+ to factory specs. At 243 VDC, many of my tubes were running hot. In fact I removed the shield from the ECC85/6AQ8 in the FM tuner section because it was running so hot. Dropping the B+ has reduced the fever of the tubes noticeably.

Dave G. will probably have a better idea on this and I will defer to his Fisher expertise.

Now as to the AM section...check those tubes. Mine was barely receiving any AM, and I found that three tubes were weak and one had significant H-K leakage. I replaced all four. Then AM came back with a vengeance!

But do check the ferrite antenna as Gadget suggested. The ferrite antenna's coils are in use even with the AM antenna switch set to the external antenna position.

 

[audmod01]

It pays to rest a bit and take another look at things. I pulled out my B&K tube tester and tested all the tubes. I found a couple of 6AU6 IF tubes that tested weak, so I replaced them with some that at least showed in the ? area on the tester. I always take a grain of salt with tube testers, as the only really good test is a new or known good tube. I did, however, find a bad tube in the AM section. I replaced that one and the AM came to life I now get stations all up and down the dial on am with signal levels rising to around 5.5 on the signal level meter.

On FM it is another story. No stations rise to above about a 2.3 and certainly not over 2.5. The 6AV6 used in the microtune circuit has one diode reading significantly lower than the other diode in the tube. The microtune circuit does not work. I get no change in signal levels when adjusting the muting circuit - nothing changes. I am not certain I have audio from either output. I have been feeding the audio output via cables to the Fisher Electra I just got up and running using its Aux inputs. There is a loud hum on that input and no audio. I plan to try again tomorrow and feed audio cables to my normal audio system which is Dynaco all the way. If I still get loud hum there then I know the problem is in the 202-R.

I did find a 100 ohm 10W wirewound resistor on hand and installed it in the feed from the bridge rectifiers to the first capacitor filter. That dropped the B+ from +250VDC to +233VDC. That is within 5V of what Fisher called for on the schematic, so that is close enough.

I did pass some paper through the contacts on the relay a few times in case the relay contacts have a problem. There could still be a problem there. I see not indication that the relay activates when touching the FM tuning knob. I have not changed any of the brown molded capacitors. I may do that as I have plenty of new capacitors of various values all rated at 630VDC. There are still a lot of things I need to do, such as make a chart for each tube and measure B+ on each plate and/or screen grid, cathode and signal grid for reference. Some problems become obvious when making voltage checks.

I have a suspicion that at least one IF transformer in the FM IF has the dreaded silver mica disease. The fact that no station's signal rises above 2.2 to 2.5 on the signal level meter indicates a problem there somewhere. I have no idea what someone else may have done to IF tuning. It is possible that the IF tubes testing in the questionable area on the tube tester is an indication of weak tubes, but I tend to have my doubts, as I have seen tubes in other receivers testing about the same that nevertheless still worked well in the set. I may order some new tubes, especially the 6AV6 and some 6AU6 tubes. I note that Fisher used one 6BA6 in the FM IF while the others are all 6AU6 and one 6BN6 limiter tube (which checks quite strong).

I will know more tomorrow after I try connecting the tuner to another audio system.

 

[mrphilco]

I have found that the relay does not want to activate when the tuner is upside down on the bench, but then works fine when right side up. I think that is simply a matter of the laws of gravity.