Silvertone 1464 solid state 100 amp

[DrGonz78]

I have one of these amps on my bench right now and I pretty sure that there is a short between emitter/base on one of the 3155 transistors. Basically, I still need to pull the part out to test it out of circuit. Just wondering if anyone can provide a good substitute for a 3155? Searching for this part I have not really come across any data sheets to help source the part. Also, it would be a long shot but does anyone have a copy of the schematic for this amp? I did see a schematic for sale on musicparts, but pretty sure the client might not want to spend $15. Thanks.

Edit: Another question is regard to the amp having an output transformer. Do I need to worry about not having a load on the amp? I have not worked on a solid state amp that had an OT on the output section. I basically have followed the policy to not connect solid state amp to a load until no DC is on the output. Will this philosphy apply even if it has a an OT?

[52 Bill]

If I remember it correctly, that amp has a transformer in the driver stage not the output. I think that there was a schematic in the Pitman book, but I'll have to dig it out to see. The transformer may be causing the low readings.

The amp is rated at 50 watts RMS, has a power supply of maybe 30-40 volts, so it probably used 2N3055 output transistors. I'd say any basic MJ1500 series transistor will work.

What is the problem with the amp?

[g1]

If those are 2N3155 then they are germanium. To use silicon types will require circuit mods.

[52 Bill]

If those are 2N3155 then they are germanium. To use silicon types will require circuit mods.

Good call. For some reason I remember them as having NPN Silicon outputs, but it's been a while since I've seen one.

[DrGonz78]

Yeah I have read about the modding of amps where they were germanium outputs and changing them to silicon which involves changing a bias resistor. So it could be that the driver transformer is causing the low resistance readings on emitter to base on that one 3155. I will have to check the transistor out of circuit to be sure and find out. The problem with the amp is that it was making stange noises, but that is just what I was told. Before connecting a speaker to the amp, I was bringing it up to voltage with a variac in line with a light bulb limiter(40 watt bulb) and at 110vAC I see over 1 vDC on the output. I am just being cautious before just plugging it in to line voltage. I have cleaned it up good and re-flowed the solder joints to make sure it is connected well. Got to change AC plug from 2-prong to 3-prong as well, but I want to make sure exactly what is wrong with the amp first. I will do some more testing late today and check it out more closely. Thanks.

BTW here is a list of transistors that I found and if it is accurate then the 3155 is germanium. Funny thing is that all my research is telling me that 2n3155 are PNP types, which does not make sense.

[J M Fahey]

No, forget germanium, it's a 2N3055 .
52 bill suggestion of MJ150xx is excellent.

And on circuit you will always measure a short BE, that's where the driver transformer secondary is connected.

And no output transformer, so standard lamp bulb limiter and no load until repaired still apply.

[DrGonz78]

So I just thought reading the post from 52 Bill that I should go look at my Jack Darr book. There are several schematics for a 1465 in the book and of course they are NPN on the output, 9158 transistors used on that model. Juan thanks for that confirmation too on the explanation for a shorted B to E reading, that makes sense. MJ150xx types were replacements used on another thread I read here at MEF regarding a 1465 Silvertone.

I did read about 3055 transistors at first as I had typed it in wrong on my search and those made perfect sense as replacements. Then I went back out to my shop and the transistors are numbered 3155 which is confusing. I have seen other pics of the amp online and they also have 3155 as the transistor number. They might actually be fine and working, but still wondering why they are numbered 3155. Can't find any data sheet that says 3155 is NPN.

[52 Bill]

There are several schematics for a 1465 in the book and of course they are NPN on the output, 9158 transistors used on that model. Juan thanks for that confirmation too on the explanation for a shorted B to E reading, that makes sense. MJ150xx types were replacements used on another thread I read here at MEF regarding a 1465 Silvertone.

Every version of these amps can be different. Just because one uses NPN outputs, doesn't mean that yours does. The only real rest will be to remove them and test them. They are socketed correct? A simple meter test will tell you if they are NPN or PNP and if they are Silicon or Germanium and if they are shorted or not.

Then I went back out to my shop and the transistors are numbered 3155 which is confusing. I have seen other pics of the amp online and they also have 3155 as the transistor number. They might actually be fine and working, but still wondering why they are numbered 3155. Can't find any data sheet that says 3155 is NPN.

The 3155 is probably a Sears part number and not a generic one.

[g1]

Meter it out of circuit as the others suggested. Germanium will read around .3 where a silicon will read around .6.
I had incorrectly assumed you meant it said 2N3155 on it. If it does not say "2N" than it may be something else.
If JM says it's a 3055, I have no reason to doubt it.

[Enzo]

Yes, it can get confusing when we toss number shorthand around before we establish what it is shorthand for.

We wanted to assume 2N3155, but if just the digits 3155 are printed on it then it is more likely a house number.

Here is a Sears 1423, with a transformer driven output using "3155" types. They are PNP. So i would be thinking germanium myself.

http://www.webphix.com/schematic%20h...rtone_1423.pdf

[DrGonz78]

Well the verdict is that it is probably silicon and not germanium, based on what G1 had posted earlier. I think this means it is a PNP type, but I could be wrong there... Here are the numbers... Red probe and black probe on associate point on the transistor...



Thanks so much you guys for all the helpful info. I am pretty sure that this means the transistors is working and I will test the other one just for perspective. I am going to put a 3-prong grounded power plug on the unit too. There are two caps and I can clearly see where the quotum quote "Death Cap" is located and that is easy to just snip out. There is another cap .047uf 600 that is across hot and neutral as it feeds into the transformer. I have attached part of a similar schematic to illustrate which caps I am talking about. The pilot light is dead too so I will need to replace the bulb. On the schematic part it will show the lamp next to a resistor and I had to redraw the trace in the circuit where the lamp connects. My question is do I need to remove C47 too?

[The Dude]

Hey Doc,
Those readings look a bit "goofy". By chance did you use an auto-ranging meter and it was on the k-ohm range and not ohms? Does your meter have a diode check function? If these are all ohm readings and not K, it would appear your E-C junction is leaky/shorted.

[DrGonz78]

Yeah those are my readings using the diode check function. I will go check the other one too and then post those results as well. I will also post results using ohms metering too.

[The Dude]

Ah,......so what we have is voltage drop, not resistance. I assume these readings are in circuit? If so and if the schematic Enzo posted is similar, E-B should be a low resistance both ways. You may have an open resistor. If you follow the base, it goes through the tranformer 4.5 ohm coil, through a 2.7 ohm resistor, then through the emitter resistor to the emitter for a total of about 7.5 ohms. In your chart, you show emitter to base open one direction. The other possibility is that the schematic is not all that similar.

[DrGonz78]

Actually the readings are out of circuit. I just did readings on the other transistor for comparison and now I think your right about the first one being leaky. They are Germaniums after all if I can trust this other one as reading more correctly. Here's the readings for both...

First transistor I posted early...


Second transistor posting now for comparison...


Edit: Sorry you have to click the image to see better detail... I tried to enlarge the picture but it made thumbnails meat of me...