Help Saving 400-CX SA-100 and 100-R Tuner

[moondogtn]

Dave, I haven’t checked the can cap but just assumed it should be replaced? I’ve been doing some reading and it seems the EFB would definitely be a worthwhile addition. Should I do it now or get it running first?
I’d like to get this amp prepared for a longer, productive life.

So, I will do some more reading to see what all this entails. I’ve read threads by notdigital and ronton3. I think there was another that I was looking for but can’t find it. I’ll look again later.
I’ll get back here once I get it sorted out so that I can ask more relevant questions.
As always, thanks for help and suggestions.

Bill

 

[notdigital]

EFB is definitely worth doing since a significant ancillary reason is that the unit will no longer be a cooker! All those heat throwing wirewounds would be eliminated with the mod. Of course, the primary reasons for the mod are laid out in Dave's thread.

BTW: My opinion FWIW is that you should get it working first. Once you iron out the kinks, then you can enhance its performance with modification.

 

[larryderouin]

ALWAYS Repair, get it working, THEN Modify or update it.

 

[moondogtn]

I haven’t given up just been busy. I was finally able to spend some time with the SA-100 this evening. I replaced the small electrolytics. I used the axial te series by sprague.
50uF 50 volts like for like and the 25 uF 6 volt I used 25 uF 16 volts.
I don’t have a can cap just yet but will get one ordered. I’ll probably use Tom at Hayseed unless someone knows of a drop in replacement.

Just doing a preliminary visual, I noticed some wiring that may have gotten hot. I tried to capture this in first two attached pictures. Is this normal for this amp?
Last two are before and after replacing caps.

Bill

 

[moondogtn]

I was looking and notice that several folks have used this cap with success. Which is preferred? Cost is about the same for either option. https://www.tubesandmore.com/products/capacitor-ce-mfg-525v-40402020uf
I saw a post stating that some modification may be required using the CE cap.

I could also have Hayseed bump voltages slightly if it is a good idea?

Thanks.

Bill


Bill

 

[larryderouin]

I prefer Hayseed just for the Temp ratings. 105*C rating on Hayseed. 55*C on the Mallory copy from AES. The caps at AES aren't bad, but their temp rating is low.

 

[moondogtn]

Larry, thanks. I let them know to bump up voltages to 525 or so. Should have it ordered today. I plan to try and work on soldering all the grounding tabs this evening.

Bill

 

[moondogtn]

I was able to get all of the tabs grounded except one. Pic is prior to new cap being installed. It reads fine on meter but may go ahead and try to do it but I need to remove transformer leads to do it.

I’m using a good Weller with a chisel tip. This chassis is a brute to heat up.
Any tips?

I’m dreading the removal of that can cap. It will take some heat to few up that tab soldered to the chassis. I also have hakko 808 gun that may help.
If I break the wafer, I’ll have to drill out and mount new one but noticed that those rivers don’t go all the way through the chassis.

One step at a time....

Bill

 

[larryderouin]

Usually 2 irons or guns on either side will heat up a chassis joint in good time. When/if you have to replace the wafer, you can use 4x40x5/8" machine bolts.

 

[heyraz]

I used a 140 watt Weller gun, flux, braid and a lot of patience.
I applied heat only to the underside because I didn't want to damage the topside's paint finish.
Flux is messy, but I couldn't have done the job without it. I dipped the braid in flux, put the braid against the area to be de-soldered and applied heat to the top of the braid. The solder moved quickly from the chassis into the braid maybe 1/2 inch at a time. I snipped off the loaded braid and repeated the process until all was clean.

 

[moondogtn]

Thanks for all the advice. I worked and got the cap out. The new one is here and I hope to get that installed tomorrow.
I got a bit sidetracked working on the cosmetics. Painted transformers as they were pretty rough looking. I had lots of encouragement and guidance on this from a friend. Before and after Pics...

Any tips on cage? It’s pretty crusty as well...

Bill

 

[moondogtn]

I installed the cap and if time permits, would like to power up tomorrow...any words of wisdom? Do I need to have speakers connected? All tubes installed?
Thanks

Bill

 

[larryderouin]

USE A DBT with a 150W bulb on it. Disposable 8 ohms speakers, and ALL TUBES INSTALLED! No source until you've proven out voltages against schematic. Then add a source or the CX2 with a source.

 

[dcgillespie]

One thing I'd suggest: Check those two 680K resistors coming off the can cap to each 7247. Unless they're new, dollars to donuts they're closer to 1 Meg or more than to 680K.

Dave

 

[moondogtn]

Good call Dave! Those two resistors are going to need replaced. One was open and the other reads 3,3 Megohms. I’ll probably run through the others throughout and check. Anything known to be problematic I should pay any special attention to?
Thank you.

Bill

 

[moondogtn]

Questions regarding these 680kohm resistors. I ordered same type and rating.(Carbon composition 500mW).
What caused them to fail or drift so far from original spec?
Should I have upped power rating?
What are these (R11 and R28)used for here in the circuit?
Also, what type of resistors are preferred here?

I can always swap out later if needed.
I checked others and all seemed close but will replace if any are prone to failure.

Thanks for info here.

Bill

 

[dcgillespie]

The .5W power rating fine. It's no more complicated than that particular brand of resistor (whatever it is) is well known (by me at least anyway) to go very high in value over time. Particularly the higher value pieces. Therefore, it was an easy bet to make. Resistors of the same type manufacture (CC) from other manufacturers on the other hand have remained quite stable over time, so it seems to be the pieces manufactured by that particular manufacturer. They are easily identified by their blackish body appearance, rather than the bakelite brown body appearance that other manufacturers often used. Anytime you see a resistor of that type appearance, I'd replace it without hesitation. Many manufacturers used them. I think Fisher only did when their other sources (with better components) couldn't cover the need.

Dave

 

[moondogtn]

Dave, I didn’t even notice them being darker until you pointed it out. I will try to remember that for future reference. I should have those resistors here tomorrow, Friday. I hope to get them installed and check voltages. I’ll post up findings. Thank you.

Bill

 

[moondogtn]

I had everything in place and hooked up a pair of junk speakers to GRD and 8 ohm. I was hoping to fire it up tonight but my 150 watt bulb is nogo. I will search for a replacement tomorrow. They are difficult to find.

I am setting all controls to minimum? Meaning CCW? Once I do initial check on DBT, I will remove and begin taking voltage readings to post up. Thanks for all the help along the way. This project is moving very slow but summer means pool to care for as well as everything else so I am still chipping away.

Bill

 

[dcgillespie]

NO. Set all the chassis adjustment controls to their mid setting before applying power to the unit. The level controls can be set to minimum if you wish.

Dave