Posts: 147
Threads: 28
Joined: Nov 2005
re: The 37-650 Saga
I just pulled the 2nd IF coil can for a look-see, and
to clean up the trimmers, in case they are dirty.
While doing so, I took the following readings:
(#28 on the schematic, for those following the
proceedings here)
Readings made with all wires disconnected from
trimmers: trimmer number given for coil reference
only, ohmed circuit is the coil shown for each
trimmer. I made sure to clean ends of coil leads, in
case they had varnish, rosin, etc., throwing reading
off.
Trimmer 28P coil should have 12 ohms resistance. Reads
14 ohms
Trimmer 28S coil should read 8 ohms total, and 4 ohms
at tap. Actually reads 14 ohms total, with 10 ohms at
tap.
These sound high to me.
How may these readings be contributing to the
misery...er, mystery...
Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Posts: 1,703
Threads: 55
Joined: Sep 2005
City: Evanston, IL
Actual resistance is immaterial - you have continuity on both windings.. You're good.
Posts: 147
Threads: 28
Joined: Nov 2005
Ok- Here's the latest, boiled down:
I have reasonably good reception on both SW bands, could use more adjustment, but gets the point across well. I can pick up lots of stuff, depending on the time of day, so I think thats ok.
The BC band is still the issue. I have trimmed and tuned and adjusted until I can do it in my sleep. Here is the final result:
Everything above 900 is fine, maybe a little off freq, but quite acceptable. Everything below is pure crap- buzz and whistle and blatt and squeal, etc.
If I attach the antenna lead directly to the top of the 6A8G Det. Osc. tube, all magically works wonderfully- again, a need for more precise adjustment, but otherwise, I get almost full range(a little messy at the 540 end, but negligable.) If I touch the antenna lead with my finger, it improves even more. I remember there being a troubleshooting step being done this way but forget what this indicates as the problem!
Help?
Thanks!
Scott
So close....
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Posts: 80
Threads: 10
Joined: Sep 2005
City: Warren, Ohio
Open antenna coil on broadcast band? Antenna coil not properly wired into band switch? Something along these lines.
Steve Chambers
Posts: 1,703
Threads: 55
Joined: Sep 2005
City: Evanston, IL
An open winding on RF transformer coils 1 and 10.
Primary to sec. shorts/leakage in these RF transformers.
Bad bandswitch contacts (or sneak shorts/leakage) for these coils; contacts F10, F11, D10, D11, C12, B10, B11, A1, A11.
Two RF transformers and switches are all that stand in the way from the antenna connector to the grid cap of the 6A8 in BC band position.
Try changing the 6A8 tube.
BC band OSC coil 17 is probably ok, since you get the upper half of the BC band. Check resistor 23, cap 22. Check for leakage/shorts in the OSC coil 17.
Don't suspect the RF tube since both SW bands are fine. If that 6K7 is working at SW freqs, then it should also work in MW as well.
Try changing the 6K7 tube. Clrean the RF tube socket contacts. Looks for bad/loose/rusty/corroded grounding rivets.
Posts: 147
Threads: 28
Joined: Nov 2005
Thanks, Chuck- I'll start the "laundry list" with the tube swaps, and go from there...
Thanks again,
Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Posts: 147
Threads: 28
Joined: Nov 2005
Chuck- Quick question: RF coil 10?
Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Posts: 1,703
Threads: 55
Joined: Sep 2005
City: Evanston, IL
Robbie Roberts Wrote:Chuck- Quick question: RF coil 10?
Scott
Ok, part number 9 (the other 10). 
Mea Typo
Posts: 147
Threads: 28
Joined: Nov 2005
Cool- Thanks Chuck!
Scott
Old Cars, Old Radios, Old Pipes and Young Women... What more is there?
Users browsing this thread: 2 Guest(s)
|
|
Recent Posts
|
|
38-10T chassis Restoration begins
|
| Thanks for the info guys. I always wondered why the use of mica. Now I know.dconant — 01:52 PM |
|
38-10T chassis Restoration begins
|
| Most common plastics have a dielectric constant in the 3-4 range whereas mica is around 6. This means that even if you w...Steve D — 01:46 PM |
|
38-10T chassis Restoration begins
|
| It is acceptable but not desirable.
Plastic is not an approved cap dielectric, and even though a reasonably thick piece...morzh — 11:52 AM |
|
38-10T chassis Restoration begins
|
| I have a question about the mica sheets. I thought I saw somewhere on the Phorum where someone used thin plastic report ...dconant — 10:44 AM |
|
38-10T chassis Restoration begins
|
| Yes, you should carefully remove the mica sheets from the trimmers otherwise you risk trapping foreign material in the t...RodB — 10:34 AM |
|
American Bosch Model 802 auto radio
|
| Hi Joe, Thank you again. The American Bosch Model 634A has the same tube lineup as my Model 802 and the parts layout dia...Antipodal — 03:09 AM |
|
38-10T chassis Restoration begins
|
| hello everyone,
I know it has been a while since I have posted about this radio but finally got chance work on it .
I ...radiorich — 02:45 AM |
|
Rusty Tuning Condenser
|
| You could soak the fins in vinegar. You have to be careful if any pot metal is involved because the vinegar will dissolv...RodB — 09:20 PM |
|
Rusty Tuning Condenser
|
| Hello, I have a Philco 91 where the tuning condenser fins are rusty. I magnet sticks to them so they can't be aluminium....dconant — 05:50 PM |
|
American Bosch Model 802 auto radio
|
| I’ve found six United Bosch auto radio’s with the same 6-tube line-up as the 802, on NostalgiaAir. They are models 150, ...Joe Rossi — 02:52 PM |
|
Who's Online
|
There are currently 2835 online users. [Complete List]
» 1 Member(s) | 2834 Guest(s)
|
|
|
|
 
|
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
