[denny9167]

I searched the board to find a solution for the problem I'm having but couldn't find it, well I finally completed the upgrade on the Fm-1 with multiplex board installed. Turned it on and was able to tune some stations in,sounds pretty good before alignment. But after about halfway through the precedure,I lost everything,I couldn' t tune anything in,I may have thrown a kink in the rf stage,not sure any suggestions?

[rlee8394]

Denny,

What did the indicator tube show during the dead air time? Try gently pushing in and pulling out on the tuning knob to see if you get any RF reception. At which portion of the alignment procedure did you loose RF? I have the same board from Chauncey. Check to make sure you have a good electrical connection between L1 and ground. That hole in the PCB was a bit too small for the L1 lead. I had to enlarge it a bit and lost all RF.  I made a deliberate connection to the ground plane and then all was well. I mentioned this to Chauncey as well as a few addition PCB changes that needed to be made. I'll help out as much as I can.

Ron

[denny9167]

Denny,

What did the indicator tube show during the dead air time? Try gently pushing in and pulling out on the tuning knob to see if you get any RF reception. At which portion of the alignment procedure did you loose RF? I have the same board from Chauncey. Check to make sure you have a good electrical connection between L1 and ground. That hole in the PCB was a bit too small for the L1 lead. I had to enlarge it a bit and lost all RF.  I made a deliberate connection to the ground plane and then all was well. I mentioned this to Chauncey as well as a few addition PCB changes that needed to be made. I'll help out as much as I can.

Ron

It was during the adjustment of T1,is it possible that the adjustment of T1 is so far off that it makes reception impossible?

[rlee8394]

Yes, go back and read the DYNA alignment instructions. T1 was factory adjusted for 10.7 MHz. During alignment, T1 needs very little deviation from the factory setting. If you have adjusted it several turns, then it is way off and you need to have someone with accurate test equipment to set that back to 10.7 MHz. If you remember how many turns and in which direction, you may be able to set it back close enough to do an alignment. Check with Chauncey, he has replacement trannies for the FM-3. Maybe you can swap if he has one that is preset to the 10.7 MHz frequency.

Ron

[denny9167]

Yes, go back and read the DYNA alignment instructions. T1 was factory adjusted for 10.7 MHz. During alignment, T1 needs very little deviation from the factory setting. If you have adjusted it several turns, then it is way off and you need to have someone with accurate test equipment to set that back to 10.7 MHz. If you remember how many turns and in which direction, you may be able to set it back close enough to do an alignment. Check with Chauncey, he has replacement trannies for the FM-3. Maybe you can swap if he has one that is preset to the 10.7 MHz frequency.

Ron

Thanks Ron

[denny9167]

Well I'm finally receiving stations,but sensitivity is weak even with an indoor antenna, and I'm not getting any eye closure. Not sure if it's weak tube or what, reception is better with the leads loosely attached, as soon as I snug the leads, I just get white noise! Weird!

[baldrick]

Try this:
Pinch C12 with your fingertips.
Did the sensitivity improve?  If so then adjust the top of T2 in the opposite direction that you turned it when you were looking for maximum hiss between stations.

Then do the alignment again.  If your T1 transformer is completely shot in terms of deviation from the 10.7 MHz factory setting PM me - I can help.

Also, are you aligning with the shields on the tubes or off the tubes?  It's important to do the alignment (and listening) with the shields on.

[baldrick]

Hey Denny,

Have you had any luck with your alignment?

[denny9167]

Hey Denny,

Have you had any luck with your alignment?

Not much,I did pinch C12,It did help some. But I just finished the design on the new board for PC-7,it will be populated with new components and a few of the old,I have replaced C8 with a more modern trimmer cap,and adjustment will be from the top instead of the bottom,and I am seeing about having T1 properly aligned,I would love some help with this if possible.

[baldrick]

If you get a change in sensitivity when you pinch C12 then you have one of two problems:
1. your alignment is still not right.  Start the alignment from step 1.
2. you have a sensitivity issue somewhere between T1 and T2 or an internal oscillation.

I experienced #2 with an FM-1 rebuild I did a few years ago.  I found that de-tuning T2 a little bit helped.  While I was adjusting T2 there was a point where the sensitivity would increase to a point and then the signal would drop out altogether.  There is a bad component around V3 that I still think is causing an oscillation. 

You could also try changing C12 to a mica type and make sure that R9 R10 R11 and C14 are all within spec.  Then swap V3 and V4 and see if the problem improves.  This could indicate a bad valve.  (unlikely - V3 and V4 are pretty stout but always a possibility given the age of the valves themselves)

In any case if you think you took your interstage transformers way out of spec I can help you bring them back.  Just PM me.

[Brett Buck]

I experienced #2 with an FM-1 rebuild I did a few years ago.  I found that de-tuning T2 a little bit helped.  While I was adjusting T2 there was a point where the sensitivity would increase to a point and then the signal would drop out altogether.

  That's an interesting idea, but I am not so sure about the interpretation. I have something similar on a Zenith Transoceanic - I switched to a "solid state 1L6", i.e. Edward Allison's 1L6 replacement, and touched up the alignment. Fantastic, excellent sensitivity, vastly better than almost all real 1L6 tubes on high frequencies. But, for some reason, it will not generate local oscillator if you start it near the low end of the 19 meter band, i.e. no IF. As run the frequency up, it will suddenly start, and then continue to oscillate if you tune it back down. Works fine on all the other bands. The only way I can get it to work is by changing the oscillator tuning to be a little "off" peak, then it will start on it's own at the low frequency end. Note that in this case it uses the 1L6 for both the IF oscillator and the mixer, but your situation sounds similar, that might be why the signal is dropping out. So instead of a spurious internal oscillation, you might have *no* oscillation on either the IF or the resonant RF side.

    Brett

[denny9167]

If you get a change in sensitivity when you pinch C12 then you have one of two problems:
1. your alignment is still not right.  Start the alignment from step 1.
2. you have a sensitivity issue somewhere between T1 and T2 or an internal oscillation.

I experienced #2 with an FM-1 rebuild I did a few years ago.  I found that de-tuning T2 a little bit helped.  While I was adjusting T2 there was a point where the sensitivity would increase to a point and then the signal would drop out altogether.  There is a bad component around V3 that I still think is causing an oscillation. 

You could also try changing C12 to a mica type and make sure that R9 R10 R11 and C14 are all within spec.  Then swap V3 and V4 and see if the problem improves.  This could indicate a bad valve.  (unlikely - V3 and V4 are pretty stout but always a possibility given the age of the valves themselves)

In any case if you think you took your interstage transformers way out of spec I can help you bring them back.  Just PM me.

You are a life saver,I will get the new boards next Friday,I will let you know how things go,C12 will be a new ceramic,if this doesn't work I will see what's wrong on PC-8,or PM you on T1 Alignment,Thanks again!!!!