Sruddy's FM-200-B Restoration Thread

[dcgillespie]

C60/61 are in the audio output stages so they would have nothing to do with the AFC. Which caps in the RF section did you replace?

If the squeal is there in both FORCED stereo and mono, then the MPX section is eliminated from consideration. Turn the output level control full down and then turn the tuner on. Do you hear the squeal? If so, it must be originating in V10.

Dave

 

[sruddy]

C60/61 are in the audio output stages so they would have nothing to do with the AFC. Which caps in the RF section did you replace?

If the squeal is there in both FORCED stereo and mono, then the MPX section is eliminated from consideration. Turn the output level control full down and then turn the tuner on. Do you hear the squeal? If so, it must be originating in V10.

Dave

C210 and 214 I also replaced 71,85,and 86 but the AFC issue didn't show up until I replaced 210 and 214.

Will check squeal/static with volume down as soon I get home. THX!

 

[dcgillespie]

C210/214 are in the MPX section and would have nothing to do with the AFC function. However, make sure that C85/86 are installed correctly with regards to polarity, and also check C71 for the same concern for good measure.

Dave

 

[sruddy]

C60/61 are in the audio output stages so they would have nothing to do with the AFC. Which caps in the RF section did you replace?

If the squeal is there in both FORCED stereo and mono, then the MPX section is eliminated from consideration. Turn the output level control full down and then turn the tuner on. Do you hear the squeal? If so, it must be originating in V10.

Dave

Your a genius Dave! The squeal and static was due to the V10 tube. It tested very strong on both plates, had no shorts, but had a very slight bit of gas. I had a pair of unused new production tungsols and they are working well.

For some reason the AFC is working good now to so maybe there was some atmospheric stuff happening. I'll let you know if anything changes but for now it appears to be working well!!! I'm going to polish the tube shields and take some photos.

 

[dcgillespie]

Glad it's working well for you now! The 200-B is a wonderful tuner, with the same basic tuner circuits as used in the FM-1000, so enjoy!

Dave

 

[sruddy]

Glad it's working well for you now! The 200-B is a wonderful tuner, with the same basic tuner circuits as used in the FM-1000, so enjoy!

Dave

I know! I'm getting stations I didn't even know existed. I can barely turn the dial without getting something.Thank you and everyone else for all the help. I really appreciate it. Photos coming.

 

[sruddy]

OOPs! I realized this morning I put 12AX7's in last night instead of 12AT7's. I found a same type of Fisher labeled gray plate angled getter Telefunken from another unit I had. So I now have a pair that at least are the same type of tube. One tests 700/750 the other 825/700 Those numbers are all above the 625 minimum but they aren't matched and the sections aren't matching is this an issue for the tuner? Also do you all like the Telefunkens for this tuner? I see Tun Sol is making a new production 12AT7 and wonder how they stack up as I can probably get a matched set for not too much.

 

[larryderouin]

12ax7 isn't going to hurt it short term, and may not hurt it long term. the 12at7 has a gain(mu) of 70 while the 12ax7 has a gain(mu) of 100.The 1st one(700/750) isn't too shabby, but the 2nd (825/700) is a bit too far out for me. Go ahead and try it tho. It may sound fine. You always have the output pots you can adjust just for that reason. Watch for microphonic tubes tho in the 12at7's. I like JAN 6201's in place of the 12at7's where I use them. I wonder if a 5751 wouldn't be a better tube in this spot than the 12at7. Same mu. and usually better microphonic rejection.

 

[gadget73]

I believe the 12at7 will deal with more current than a 12ax7 will though, so you might do unfavorable things to the tube. The gain is not the only thing of consequence here. Different input capacitance really can make a difference in a tuner, depending where it is.

 

[larryderouin]

They are the output tubes for the tuner

 

[sruddy]

12ax7 isn't going to hurt it short term, and may not hurt it long term. the 12at7 has a gain(mu) of 70 while the 12ax7 has a gain(mu) of 100.The 1st one(700/750) isn't too shabby, but the 2nd (825/700) is a bit too far out for me. Go ahead and try it tho. It may sound fine. You always have the output pots you can adjust just for that reason. Watch for microphonic tubes tho in the 12at7's. I like JAN 6201's in place of the 12at7's where I use them. I wonder if a 5751 wouldn't be a better tube in this spot than the 12at7. Same mu. and usually better microphonic rejection.

Sounds like my right channel is a bit lower since I replaced the squealing tube. I don't see any instructions in the service manual for adjusting the output. Also what will a tube with bad miss matched sections sound like?

thx

 

[larryderouin]

In most cases you won't notice any difference, except on a scope. In an extreme case you may notice a slight distortion or a reduced gain. There should be 2 pots on the back with output level marked on them. You can adjust them until the balance is correct. Make sure the amp is set in mono 1st. 99% of the time some adjustment of the level controls will be necessary due to variances in component parts. Build two amps with Identical parts, and there will be slight differences between them, especially in tube gear where the tolerances are greater than solid state.

 

[sruddy]

In most cases you won't notice any difference, except on a scope. In an extreme case you may notice a slight distortion or a reduced gain. There should be 2 pots on the back with output level marked on them. You can adjust them until the balance is correct. Make sure the amp is set in mono 1st. 99% of the time some adjustment of the level controls will be necessary due to variances in component parts. Build two amps with Identical parts, and there will be slight differences between them, especially in tube gear where the tolerances are greater than solid state.

Not on the back but I did see two boxes on the schematic with output level printed inside. I will have to investigate as they didn't appeare to be a component of the schematic only some kind of indicator. I'll let you know what I find.

 

[dcgillespie]

That is simply labeling the front panel level control shown on the schematic.

Dave

 

[sruddy]

That is simply labeling the front panel level control shown on the schematic.

Dave

So how does one adjust output level per channel. I guess I will put on a pink noise record and record the level of both channels to confirm my claim.

 

[dcgillespie]

There are no provisions for individual channel output adjustments on the FM-200B. Try this:

1. Operate the tuner in mono mode. If the imbalance is there, it is due to some issue in the output amplifier circuits.

2. If the imbalance is there with the Output Level Control at a mid-range setting, then the problem could be the control itself. Operating the tuner (still in mono) with the Output Level Control up full will eliminate the control as a possibility. Any imbalance with the control in this position then must be due to some issue/component in the immediate vicinity of the output amplifiers -- or the following amplification/speaker equipment.

If the imbalance is only there in stereo mode, then the MPX decoder becomes ground zero for the hunt.

Dave

 

[sruddy]

There are no provisions for individual channel output adjustments on the FM-200B. Try this:

1. Operate the tuner in mono mode. If the imbalance is there, it is due to some issue in the output amplifier circuits.

2. If the imbalance is there with the Output Level Control at a mid-range setting, then the problem could be the control itself. Operating the tuner (still in mono) with the Output Level Control up full will eliminate the control as a possibility. Any imbalance with the control in this position then must be due to some issue/component in the immediate vicinity of the output amplifiers -- or the following amplification/speaker equipment.

If the imbalance is only there in stereo mode, then the MPX decoder becomes ground zero for the hunt.

Dave

Thanks Dave, I'll check it out.

 

[sruddy]

12ax7 isn't going to hurt it short term, and may not hurt it long term. the 12at7 has a gain(mu) of 70 while the 12ax7 has a gain(mu) of 100.The 1st one(700/750) isn't too shabby, but the 2nd (825/700) is a bit too far out for me. Go ahead and try it tho. It may sound fine. You always have the output pots you can adjust just for that reason. Watch for microphonic tubes tho in the 12at7's. I like JAN 6201's in place of the 12at7's where I use them. I wonder if a 5751 wouldn't be a better tube in this spot than the 12at7. Same mu. and usually better microphonic rejection.

Larry for the heck of it I just tried a pair of new production Tun Sol 12AT7 in place of the original Fisher Telefunken with the angled getters. The Tung Sols had great detail and were quieter but just like a pair of Tun Sol 12AX7 I have, the mid range is harsh. So back in with the Telefunkens for now. They are still good but so darn expensive to replace. I wish I could find something I would like as well that were cheaper. So far Telefunken are my tube of choice.

 

[larryderouin]

Try a Sylvania 12at7 or JAN Sylvania 6201's. They tend to have a smooth mid. And FISHER switched to the Sylvania's from the Tele's in about 1965-66 Check with local HAM or radio clubs and see when a hamfest (fleamarket) is. Most of these guys are pretty good about tubes with decent prices.

 

[sruddy]

Try a Sylvania 12at7 or JAN Sylvania 6201's. They tend to have a smooth mid. And FISHER switched to the Sylvania's from the Tele's in about 1965-66 Check with local HAM or radio clubs and see when a hamfest (fleamarket) is. Most of these guys are pretty good about tubes with decent prices.

Thanks, I'll try them out.