Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

37-660 Alignment Issue
#1

Well I've rewound the OT and it works fine. Began the alignment and all was going fine until the last SW tuning range 2 (2.3-7.4 mc). The first part of this stage you peak at 7 mc by adjusting the oscillator (30B)(no problem) and then you are to go to 2.35mc (closing the tuning cap plates) and peak there (30C) where I don't hear the sig gen signal.

If I set the sig gen to 6 mc the radio dial has to be set to about 6.65 mc to hear the tone (this is after peaking at 7 mc). To me it seems like it is short on capacitance. I note that across 30C (the 2.5 mc osc trim) there is what appears to be a large mica. According to the schematic this is 30x and is a 1150 uufd (I didn't change this one). The parts list does not say it is mica whereas it does state other small ones as mica. I am wondering if this cap might not be mica and could be causing my problem? Looking to you experts for help and suggestions.

http://www.nostalgiaair.org/PagesByModel...013220.pdf
#2

Hello, Marv: The best way to align is to connect a volt meter to the voice coil leads of your speaker and use min sig gen amplitude when adjusting your set.

This prevents your AVC circuit from interfering with your alignment.
#3

If I had to guess (and I do) Icon_wtf you are on the wrong peak. ie if the LO is to be at 6.53MHz when you tune 7Mhz, you have it peaked at 7.47 Mhz on the LO

turn the signal generator level down, and try to find a peak at 7MHz with the trimmer turned in tighter.

I would also assume the 1150 pF cap would be paper, you could try putting 2 .0022uF caps in series (1100pF) and see if the situation improves.

John
Las Vegas, NV USA
#4

Still have problem on range 2. Changed 1150pfd cap, no difference. Close inspection of coils noted that one lead of RF range 2 primary broke off wafer switch. (Probably happend when replacing caps deep within). Soldered lead back on to D3, still cannot align this range correctly.

Before I remove the RF section from chassis again to check this coil closer can someone please confirm that when the radio range lever is in range 2 I should read 12 ohms of the primary between D3 and D6 of the wafer. I read open. Getting to these coils is nearly impossible.

marv




Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Philco Model 80 Transformer resistance
The DC resistance of the primary is 8 to 9 Ohm.morzh — 07:54 PM
Philco Model 80 Transformer resistance
I have a feeling the primary winding on the power transformer is bad. My resistance reading on the primary side is 9 ohm...Mike L — 07:48 PM
Rusty Tuning Condenser
I would try Naval Jelly and use a soaked pipe cleaner to get it where it needs to go.RossH — 06:56 PM
38-10T chassis Restoration begins
Hello Dconant , they sold mica to use as a insulator between transistors and their heatsinks too. Rob I will remove th...radiorich — 02:52 PM
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

[-]
Who's Online
There are currently 4035 online users. [Complete List]
» 1 Member(s) | 4034 Guest(s)
Avatar

>