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 Post subject: Re: Hammarlund SP-200
PostPosted: May Tue 28, 2019 9:29 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1769
Location: Eagan, Minnesota, USA
The AVC transformer, T-6, has five resistors and five capacitors inside of it. To access these parts, you need to get the shield off. There are four screws on the side of the shield, and two nuts beneath the chassis that will allow this shield to slide off and access the parts you want to change.

On my set, one of the screws was seized, and the pressure applied to attempt freeing it up caused the metal stand off attached to a phenolic tag board to break off of the board. I could have used this part without that one mount, but having a parts set available, I decided to just replace the T-6 assembly with the one from the parts set, which came apart easily and was undamaged.

I removed T-6 from the parts set, removed the shield, then made a list of the parts I would be replacing. I decided to replace all of the resistors and capacitors. It makes sense to me to do this now while it is easy to do rather than risk finding a problem later on and having to fight gaining accessibility for parts replacement later on. I also changed all of the wire leads for easier installation, as the old wire was stiff, and had not much color left for identification purposes later on.

I made notes of the replacement parts, and was able to compare my work with the other T-6 which was apart, but still attached to the chassis.
I was able to get it done, but did not install the shield yet, as I want to do another comparison with the old one just to make sure that everything has been replaced properly. There is a lot of parts overlay on this assembly, and it wouldn't take much to screw it up. So in a few days, I'll take some time and verify the work I did. Then install the shield, and then install the rebuilt T-6 to the chassis.

Resistor found: 2K, 5100 ohms (2), 24K, and 1 Meg. Capacitors found: .05 mfd, .01 mfd (3), and .005 mfd.

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Frank
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 Post subject: Re: Hammarlund SP-200
PostPosted: Jun Mon 10, 2019 10:29 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1769
Location: Eagan, Minnesota, USA
I installed AVC Transformer T-6. At this point, half of the main chassis has been rebuilt. From here, it looks like I need to get into the detector transformer to replace some resistors and capacitors that are internal to it. Also, I received another crystal phasing assembly that has a good shaft on the variable capacitor control. What I think I will do is rebuild this assembly and install it on my chassis. Both units look to be exactly the same, so there should not be any problems making the swap. I will be very careful to not damage this shaft, as I'm finding out that this is a pretty common issue on these sets.

The rest of the rebuild on the main chassis looks to be fairly straight forward, with just replacement of capacitors and resistors. There are a few can type capacitors that mount to the side of the chassis, and contain two capacitors each. I think I'm going to just place two new capacitors as neatly as possible in the area of each one, and just leave these can caps remain as they are for visual appearance. The new ones will fit easily in their areas. From what I can tell, the variable IF mechanism looks good, and after cleaning and lubrication, operates smoothly. So I don't see doing anything with that or the IF transformers associated with that mechanism.

So work will move onward as I can get the time for it. But progress is being made.

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Frank
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 Post subject: Re: Hammarlund SP-200
PostPosted: Jun Mon 24, 2019 7:39 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1769
Location: Eagan, Minnesota, USA
Completed T-4, second detector transformer, and the associated resistors and capacitors involving V8; 6H6 detector. T-4 is similar to working on T-6. You remove four screws on the side of the cover, then remove two nuts underneath the chassis. Then slide off the cover. I was keeping this part, so I worked with it wired to the chassis. There are three resistors inside, along with five capacitors. Three of the capacitors are mica, and two are paper. I replaced the three resistors, and just the two paper capacitors, and left the mica capacitors alone. After the parts were changed, I secured the cover using the four removed screws, and then re-attached the completed transformer to the chassis. This is not a difficult task. I did add some fish paper where the terminal strips looked like they might be close to the sides of the cover. May not have been necessary, but I added it anyway as a precaution.

I then replaced the resistors and capacitors around V8; 6H6 detector, working my way around the main chassis. From here, it looks like just more capacitor and resistor replacement underneath, and then swapping the crystal phaser assembly with the recently acquired one with a good control shaft.

Here are some parts notes I made:
R47 - 2K
R48 - 100K
R49 - 1MEG

C42 - .05 MFD @ 600V.
C43 - .02 MFD @ 600V. (Note: schematic shows .01 mfd, but actual part in T-4 was .02 mfd).

C41 - 5.5 pf mica.
C44 - 50 pf mica.
C45 - 50 pf mica.

L32 resistance readings: 10 ohms primary; 9.3 ohms secondary.

One comment I want to make is how helpful it has been to have a good parts chassis. So far, I have replaced the audio output transformer, T-6 AVC transformer assembly, switch, phones jack, and numerous small stuff I can't even remember. Thanks again to Warren, local guy who provided me with that chassis and the crystal phaser assembly. I'd be stuck right now without his help!

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Frank
KD0RUC


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 Post subject: Re: Hammarlund SP-200
PostPosted: Jul Tue 02, 2019 5:23 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1769
Location: Eagan, Minnesota, USA
Replaced the T-1 Crystal Selectivity/Phasing assembly. The original had a broken shaft on the variable capacitor. This assembly contains the phasing control variable capacitor, a six position switch, and two coil assemblies within the unit. There are four screws holding this to the chassis, and three wires to unsolder for removal and replacement. After cleaning it up, I replaced all of the resistors in it and one .01 mfd paper capacitor along with an 85 pf mica capacitor. I replaced the three wires that run underneath the chassis because of brittle insulation. Replacing two of them is a little tedious because they connect to points on a coil (L 26) that is within a shield. So I had to take caution not to hit the coil with the soldering tip or damage any of the fine wire connections around that area. One wire connects to a 10K resistor, and just runs out the bottom of the assembly.

The switch bypasses the crystal in the off and number one position, and is open to it in the other positions. The other section of the switch keeps adding resistance of four resistors and runs through L 27.

Parts found:

C21 - 120 pf mica.
C22 - 100 pf mica.
C23 - 100 pf mica.
C33 - 85 pf mica.
C34 - .01 mfd (actual part in unit was .02 mfd).

R42 - 25 ohms.
R43 - 50 ohms.
R44 - 300 ohms.
R45 - 2K.
R46 - 10K.

L26 - Primary 6 ohms; Secondary 1 ohm.

L27 - 6.5 ohms.


This completes replacement of parts in assemblies located on top of the chassis. What remains on this main chassis is replacement of resistors and capacitors along one side of it. At completion, the next phase will be to begin work on the RF deck unit that was removed from the main chassis earlier.

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Frank
KD0RUC


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