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Lafayette LR-1500T - need help ID'ing these transistors

tabpat

tabpat

Member
This receiver sounds like either the outputs are failing or the driver transistors are weak. Being that it's a 1968 era machine, the transistors are pretty foreign to me. The outputs are SanKen DF2 and the drivers are marked on the schematic as DF3 and BF3. I'm guessing that someone has replaced the DF3's with 2SC485 (TO39's) at some point. Of course, the only cross reference to the outputs that I can find are NTE130's (ugh) and a brief mention of 2N3055's. After a full re-cap the receiver plays for a while then gradually gets grittier sounding and fades to near nothing with one channel being about 25% of the other.


 
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How are the supply voltages? Have you monitored them while the issue is occurring?

If I were to replace the drivers, I would look at a different style, like the TIP41C, TIP42C. Looks
like there's plenty of room to add heat sinks if necessary.

Rob
 
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Hello tabpat, Welcome to AK. Looks like a previous owner had the DF3s replaced with the 1500ta equivalent parts. The Service Manual for the 1500ta does have a replacement parts for the transistors listed. You replaced all of the caps?. Would like to see the pics after that since in the pic posted, some caps on the right side looked like they got real warm (shrinking, hot spots).
 
some capacitors look likely shot . change all of them . check resistors too .. i cant zoom in but one or 2 looked burned .
p.s you left gps on .. this might not bother you but does some folk .
 
I'll re-take another photo with the new caps as soon as I can. I'll also deoxit the trimpots and try again. Also, I forgot to add that there is the occasional weird noise that this thing makes - kind of like a very faint heterodyne whine at times - on all inputs. I've back-burnered this to work on another "more modern" 1974 quad receiver because looking at this thing makes me feel like it was made on another planet from what I'm used to. I'm not a pro and I'll be the first to admit it.
 
Here it is, re-capped. I cleaned the pots to no effect. I did a quick thermal reading on the outputs. The left channel outputs were warm after a few minutes (87 degrees), but the right channel outputs were near room temperature. Didn't have time to mess with it any further. However, this leads to another question... There are 4 pots per channel - which I'm sure control bias current and dc. I've only ever seen 2 per channel. How would this be adjusted once I get the problem solved?

 
According to schematic, the pots are for bias, DC, and two for current limiting. The 1500TA manual (available from hifiengine.com - free but have to register) has the adjustment procedures for them, and looks like the same design. Outputs are the same, driver are 2SA485, 2SC485.
 
UPDATE. So, I replaced the driver transistors and the outputs. I still have a dead channel, but now it makes noise. There is a rumbling/fluttering of sorts on the channel that was once dead. I grabbed a portable CD player and clipped onto the amplifier board inputs and both channels are there, so that part is now working... The preamp board is now suspect. I recapped it with no improvement. It has three germanium transistors per channel. 2SB178 - 2SB324 - 2SB348 (2SB178s are what's in it). The only thing I can find to replace 2 of them are NTE102A's. Holy crap are NTE102A's expensive! They're like 8 bucks each and it takes 4 of them!! Can any of these be replaced with regular silicon transistors?
 
UPDATE to the UPDATE. I got both channels working. Turns out it was a bad solder joint somewhere on the board and I touched up the whole side. That's the good news. The bad news is that one channel is definitely lower and muddier than the other, except in mono mode. When I tested the pairs of transistors against each other, the 2SB348s were not even closely matched. One had an hfe = 8 and uf = 151, the other had an hfe =209 and uf = 118. So, they still need to be changed out.
 
tabpat said:
This receiver sounds like either the outputs are failing or the driver transistors are weak. Being that it's a 1968 era machine, the transistors are pretty foreign to me. The outputs are SanKen DF2 and the drivers are marked on the schematic as DF3 and BF3. I'm guessing that someone has replaced the DF3's with 2SC485 (TO39's) at some point. Of course, the only cross reference to the outputs that I can find are NTE130's (ugh) and a brief mention of 2N3055's. After a full re-cap the receiver plays for a while then gradually gets grittier sounding and fades to near nothing with one channel being about 25% of the other.


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I have a complete unit I’ll donate if you would like spare parts. The outputs work. For that matter all of it worked just needed new caps. Let me know
 
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