TSA 10 Code B Heat Sink Question

Hi everyone & thank-you for this great forum, I have been reading and learning for a few years but I have a question that I couldn't find on this forum. I am working on a Seeburg USC-2 with a TSA 10 Code B amp and when I acquired it, two of the power transistors (Q5109,Q5110) on top of the heat-sink were missing. The other two are present. I am almost finished re-capping and replacing out of spec. resistors on it and I have 4 replacement transistors (2N457A) but I don't see any insulator or heat sink grease remnants where they were. I finished the DCC already.

My question is do they need some kind of insulator in between the transistor and the heat sink or heat sink thermal compound or nothing at all?

I am retired and have been repairing 40's & 50's radios, and 2 Rockola Jukeboxes so far. It's been a hobby for the last five years to keep the brain cells functioning, but the Seeburg is totally different than the Rockolas. I have Ron's microlog and mech. books as well as the service manuals for the USC 1,USC 2, and the parts catalog.

Thanks in advance for any help on this.....

Steve K.

They must have mica and compound. The final stages of these amps are DC coupled and if the finals are shorted or missing, it is a very good idea to place the amp in series with a 25 watt bulb when you first power it. The bulb should blink somewhat brightly as the main filters form and die down to very little glow.
There is a bias adjustment to set the offset level on the outputs. However, do not attempt to adjust it without first washing or injecting contact cleaner into the bias pot(s). It must then be powered through the bulb while you turn the pots a few degrees to check for dead spots. You may see the bulb flash brightly as you turn them indicating a dead point. These are cheap and notorious for killing the finals and their drivers.

i generally replace these pots with a 100-120 ohm fixed resistor.

Rob-NYC

Rob-NYC wrote:They must have mica and compound. The final stages of these amps are DC coupled and if the finals are shorted or missing, it is a very good idea to place the amp in series with a 25 watt bulb when you first power it. The bulb should blink somewhat brightly as the main filters form and die down to very little glow.
There is a bias adjustment to set the offset level on the outputs. However, do not attempt to adjust it without first washing or injecting contact cleaner into the bias pot(s). It must then be powered through the bulb while you turn the pots a few degrees to check for dead spots. You may see the bulb flash brightly as you turn them indicating a dead point. These are cheap and notorious for killing the finals and their drivers.

i generally replace these pots with a 100-120 ohm fixed resistor.

Rob-NYC

And don't forget the nylon shoulder washers!
I always test for continuity/isolation from the sink, just in case - before power is applied.

Matt, it is not a bad idea, but none of these old '60's-70's Seeburg (or any others) had them. They probably would have added 1/1000 of a cent

The continuity test is a good idea.

Rob

Thanks Rob & Matt, will get some Mica insulators before I connect them. I use a Dim-Bulb tester all the time for radios, and the DCC. Will use it for the amp as well. After the amp, it's on to the Mech......

Thanks again,
Steve K.

Hi Steve and all,
Thanks for purchasing the guides--
On the nylon shoulder washers--I don't think you should use them on this unit--the screw is actually used as a "contact"--
I don't know what happened in the USC-1 manual, but they left out a portion of the "write-up" that appeared in all earlier manuals that used the TSA series amps-- This page described the outputs, and the Mica insulators to be used along with the heat sink grease --they specified "Dow-Corning #5" be used liberally, on both sides of the mica--and of course, the mounting screws MUST be tight. You should check the two transistors that are not being changed for the Mica, and grease. Ron Rich

Hi Ron,
I'll check the two transistors that are installed, but just looking at them, it doesn't appear that there is any insulator under them. That's OK though, I will be changing out all 4 anyway. The screws used on the two are short hex-head machine screws that appear to be good and tight but I'll take a trip to the local "real" hardware store to get new non-rusty replacements. Is it necessary to use the "Dow Corning #5" or will Radio Shack silicone thermal grease work OK? I Checked on Amazon, the Dow #5 is $28.00 + shipping.
Thanks for the info. and I appreciate your compilation of knowledge in those books, great reference material for us non-professionals. Will keep in touch as I'm sure this won't be the only question as I move along on this project.

Thanks,
Steve K.

Any suitable transistor "heat sink grease" is ok.
A thin layer smeared on both sides of the mica insulator with a Qtip.

Great, thank-you Matt....
Steve K.

Steve, Matt,
RS heat sink grease, if you can find the "clear" type, it was DC#5, which IMHO, is much more efficient, then the "white" stuff, and does not dry up. ( BTW, Mattie--I use my fingers to apply it as sometimes using any fiber like a Q-tip, the fiber will get into the area it should not be in !) Ron Rich

Ron Rich wrote:Steve, Matt,
RS heat sink grease, if you can find the "clear" type, it was DC#5, which IMHO, is much more efficient, then the "white" stuff, and does not dry up. ( BTW, Mattie--I use my fingers to apply it as sometimes using any fiber like a Q-tip, the fiber will get into the area it should not be in !) Ron Rich

Stop buying those cheap Qtips!
LOL!

Hi Ron
I'll see if I can find some clear while I wait for the rest of the e-caps to get here. Gotta get the micas also. I try not to use Q-tips for that reason, unless it's the only thing that will work.
PS. Rob-NYC---What wattage for the 100 ohm resistor in case I decide to replace the pots?
Thanks,
Steve K.

Hi Steve,
1/2 ohm will work there--however unless "someone messed with the pots" they seldom need to be touched ! ( still "factory sealed"--leave-m-alone !!). Ron Rich

I think Ron means ½ watt and that is what I have used. Again, if you clean the pots and test with bulb in series it should be OK as-is. I tend to go a bit overboard as I am doing these amps for a return to commercial service and "I don' wanna' hear nuttin" from the locations

Rob

Hi Ron, Rob,

They still have the seal on them so I'll leave them alone and see how it goes with the dim-bulb test, when I get to that point. I just put a new power cord on the USC-2 (the DCC and AMP are NOT connected yet), I got power to the bulbs so that's a good sign. Spent some time cleaning it, yuk! Years of crud, nicotine etc. Maybe tomorrow I'll put the DCC in and see what happens. (I recapped it already and Dim-Bulb tested it)
Thanks for all of the support, it's nice to know there are folks out there that like to help solve problems with others.

Steve K.