my fm-3 woes

I started modding my fm-3. So far i've done a few caps and resistors, 2 out of the 3 pec boards and finally swapped the cap can out for a cap board, all sheldons boards. Everything went fine up until the cap board. Now I have a hum on my speakers , didn't with the can. I had it grounded to the same point as the transformer, the same common ground as before. I switched it to a slot where the can was, still have a hum. Any ideas?

Are the caps to close to the transformer? Other than the hum it works flawlessly.

Tried it with case on, same result. Caps are all new as well. Thanks Bob.

Hi:
Although you did not mention it. It looks like you are using the original or at least older tubes in there. I had one tuner that did this when I put a cap board in and found a bad tube was the problem.
Have you tried replacing the tubes one at a time? Worth a try as it may be the easiest and quickest solution.
I had all my original tubes tested and most of them were not up to spec but still worked. Replacement Chinese tubes were not so great in there either. I replaced my tubes with quality NOS stuff I bought on the net.
You should also do a very careful re-alignment and be extra careful with the multiplex section of the alignment and T-5. I hope you have the special tool to do this as using a metal screw driver can create some bits of carbon to dislodge inside the transformers and minute shorts occur or even worse you can easily damage them and not see it from looking in the top and looking in the bottom is almost impossible.
I still have a few transformers if you need one or two. PM me if you need to.
You can get one of these tools from Chauncey Epperson at the FM-3 Zone site for $7.00 this is a must IMHO.
I used compressed air to clean the transformers in the tuner and I cleaned them thoroughly before installation on the tuners I did from scratch. You can buy compressed air in cans for this purpose.

The alignment process is supposed to be easy and Dynaco says so way too many times in the manual but it is also very ticklish and can cause a hum if not done very carefully in several of the steps especially in the MPX and T-5 alignment sections.
After doing the T-5 you should try minute adjustments of the other transformers (1-4)again one at a time and mark where you started from so you can re-set it before going on to the next one. just make very small adjustments here.
These thing are 50 years old and somehow go out of spec from the slightest adjustment or change. Overall good alignment turns out to be a bit of an art.
Since you did not replace all the board parts there may also still be a bad cap or resistor that is suffering from effects of the new stuff. C-74 on PC-12 is usually bad. I had to replace it on all my tuners.
Good luck

Here is the complete parts list with "Mouser" part numbers. Locations are exactly the same as the Dynaco list.
P.S.
I forgot to mention that it looks like you are still using the old style carbon resistors. I would replace them with the ones on this list. Some of the values are a little different but work fine.
Baddog1946


FM-3 Parts with Mouser #'s
PC-7
CF1- Part or Jumper
L2 – original or 3.9uh choke (netminer@juno.com)
R1 – (68r) 273-68-RC
R2 – (10k 1w) 281-10K-RC
R3 – (10k 1w) 281-10K-RC
R4 – (390r) 273-390-RC
R5 – (10k) 273-10K-RC
R6 – (47k 1w) 281-47K-RC
R7 – (1k 1w) 294-1K-RC
R8 – (1k 1w) 294-1K-RC
Led module
1 x 273-75-RC (75r)
1 x 859-LTW-2S3D7 (White led)
1 x 604-WP7113MBD (Blue led)
1 x (4007 Diode)
PC-8
R09 – (100k 1/2w) 273-100K-RC
R10 – (33r resistor) 273-33-RC
R11 – (10k 3w) 588-43F10KE
R12 – (100k 1/2w) 273-100K-RC*
R13 – (10k 3w) 588-43F10KE
R14 – (100k 1/2w) 273-100K-RC*
R15 – (330k) 273-330K-RC
R16 – (220k) 273-220K-RC*
R17 – (62k) 273-62K-RC*
R18 – (100k 1/2w) 273-100K-RC*
R19 – (3.3m) 660-CF1/2C335J*
R20 – (100k 1/2w) 273-100K-RC*
R21 – (100k 1/2w) 273-100K-RC
R22 – (47k 1w) 281-47K-RC*
R23 – (47k) 273-47K-RC
R24 – (3.9k) 273-3.9K-RC*
R25 – (62k) 273-62K-RC
R26 – (62k) 273-62K-RC
R27 – (1.2m) 660-CF1/2C125J
R28 – (390r) 273-390-RC*
R29 – (8.2k) 273-8.2K-RC
R30 – (12k) 273-12K-RC*
R31 – (100k 1/2w) 273-100K-RC*
R32 – (100k 1/2w) 273-100K-RC
R33 – (330k) 273-330K-RC*
R34 – (1k) 273-1K-RC
PC-12
R71 – (18k) 273-18K-RC*
R72 – (240r) 273-240-RC
R73 – (22k) 273-22K-RC
R74 – (47k) 273-47K-RC
R75 – (150k) 273-150K-RC
R76 – (1.2m) 660-CF1/2C125J
R77 – (3.3m) 660-CF1/2C335J
R78 – (2.2k) 273-2.2K-RC
R79 – (220k) 273-220K-RC
R80 – (150k) 273-150K-RC
R81 – (47k) 273-47K-RC*
R82 – (47k) 273-47K-RC
R83 – (47k) 273-47K-RC
R84 – (47k) 273-47K-RC
R85 – (100k 1/2w) 273-100K-RC
R86 – (100k 1/2w) 273-100K-RC
R87 – (1k) 273-1K-RC
R88 – (1k) 273-1K-RC
R89 – (100k 1/2w) 273-100K-RC
R90 – (100k 1/2w) 273-100K-RC
R91 – (470k) 273-470K-RC
R92 – (470k) 273-470K-RC
R93 – (470k) 273-470K-RC
R94 – (1.2m) 660-CF1/2C125J (alignment resistor)
PEC Modules
R95 – (10k) 273-10K-RC*
R96 – (10k) 273-10K-RC*
R97 – (10k) 273-10K-RC*
R98 – (10k) 273-10K-RC*
R99 – (10k) 273-10K-RC*
R100–(10k) 273-10K-RC*
R101–(250k Pot) 313-2420F-250K
R102–(22k) 273-22K-RC
R103–(22k) 273-22K-RC
PC-7
C02 – (180pf) 598-CD10FD181JO3F
C03 – (180pf) 598-CD10FD181JO3F
C04 – (47pf NPO) 140-500N5-470J-RC
C05 – (.0047uf) 140-500P5-472K-RC
C06 – (10pf NPO) 140-500N2-100J-RC
C07 – (2.55pf) N2200 Surplus sales dogbone
C08 – (1 to 10pf trimmer) 659-GAA10006
C09 – (.0047uf) 140-500P5-472K-RC
C10 – (.0047uf) 140-500P5-472K-RC
C11 – (2.2pf) 140-500N2-2R2C-RC
C12 – (47pf NPO) 140-500N5-470J-RC
C13 – (180pf) 598-CD10FD181JO3F
C38 – (180pf) 598-CD10FD181JO3F
C39 – (180pf) 598-CD10FD181JO3F
PC-8
C14 – (.0047uf) 140-500P5-472K-RC
C15 – (47pf NPO) 140-500N5-470J-RC
C16 – (.0047uf) 140-500P5-472K-RC
C17 – (47pf NPO) 140-500N5-470J-RC
C18 – (.0047uf) 140-500P5-472K-RC
C19 – (.0047uf) 140-500P5-472K-RC
C20 – (47pf NPO) 140-500N5-470J-RC
C21 – (.01uf) 140-PF2G103K
C22 – (.0047uf) 140-500P5-472K-RC
C23 – (.0047uf) 140-500P5-472K-RC
C24 – (47pf NPO) 140-500N5-470J-RC
C25 – (47pf NPO) 140-500N5-470J-RC
C26 – (.01uf) 140-PF2G103K
C27 – (.0047uf) 140-500P5-472K-RC
C28 – (.0047uf) 140-500P5-472K-RC
C29 – (.47uf) 5989-400V.47-F
C30 – (27pf) 598-CD10ED270JO3F
C31 – (.22uf) 5989-400V.22-F
C33 – (.02uf) 140-PF2G203K
C34 – (.0047uf) 140-500P5-472K-RC
C35 – (.0047uf) 140-500P5-472K-RC
C36 – (.0047uf) 140-500P5-472K-RC
C37 – (.0047uf) 140-500P5-472K-RC
PC-12
C71 – (500pf) 5982-15-500V500
C72 – (220pf) 598-CD19FD221JO3F
C73 – (.012uf) 5989-1KV.012-F
C74 – (.0068uf) 75-715P400V0.0068
C75 – (500pf) 5982-15-500V500
C76 – (.001uf) 75-225P400V0.001
C77 – (.0033uf) 75-715P600V0.0033
C78 – (.0015uf) 75-715P600V0.0015
C79 – 140-PF2G103K (.01uf)
C80 – (500pf) 5982-15-500V500
C81 – (100pf) 5982-10-500V100
C82 – (1uf) 5989-400V1.0-F
C83 – (1uf) 5989-400V1.0-F
C84 – (18pf) 598-CD5CC180JO3F
PEC Modules
C85 – (100pf) 5982-10-500V100 (100pf)
C86 – (510pf) 598-CD15FD511J03F
C87 – (510pf) 598-CD15FD511J03F
C88 – (510pf) 598-CD15FD511J03F
C89 – (100pf) 5982-10-500V100
C90 – (510pf) 598-CD15FD511J03F
C91 – (510pf) 598-CD15FD511J03F
C92 – (510pf) 598-CD15FD511J03F
C93 – (510pf) 598-CD15FD511J03F
PC-12
D71-74 - original or (Diodes) 526-NTE110MP
L71 - Original or 434-03-563J
* Stands on end

Wow thats great info baddog. I will dig into it some more and shotgun all resistors to see if it makes a difference, i need the tool to do the alignment.

I pulled the rectifier tube and turned it on, hum is almost nil. So a tube might be bad. I swapped the 12ax's for known good, still there. What tube was causing your issue?

The 6B8A (V-1) and the 6V4 rectifier both caused hum on a couple of mine. I also had to match the (V3-V4)and the (V5-V6) pairs to get the last bit of hum out. I went with NOS RCA's.