Spyder - Retro Kit Amplifier

[vidarr]

I got a Spyder, kit amplifier from the 70-80s? that was popular in Brazil. It was built by my wife's dad.

The way I received it was with the transformer wires cut from the main board.  I cleaned the whole thing and checked both sides of the main board. The fuse and everything else seems to be in good order.

Last time I posted a repair, I started with the transformer and everyone asked why. Is this a case where I start with the transformer? Would her dad have cut the transformer off because it didn't work? Or maybe he cut it off because something on the board is broken? It would be awesome if I could fix this thing.

Most of Brazil is 110-120V, but there are many areas along the coast that are 220V and some areas have both in one house. Her dad built and used this amp only in 120V even though it has a 120/220V switch. We also live in a mostly 120V area. I bring this up because these transformers give me a headache. I have another transformer (12V) that has two lines out. Very simple. Suppose I use this alternate power supply, how does it match up with the three wires (red, red, black)? They are not labelled on the board other than "red, red, black", but in Portuguese. (The amp has all 16V capacitors, so I believe the 12V will be enough to test it.)

Thanks!

[vidarr]

OK, I've been reading about this transformer issue and noticed a few things. One, transformer posts asking questions are almost always everybody guessing. Two, a lot of people give up. Three, the people who get it solved always have a transformer not like mine.

So, I read that a three wire transformer like this is probably a center tap and would have two powers out (like +12v/-12v ---- Va and Vb) and a ground I think. In other situations, people would use one of the power wires and the ground and tape the other wire. In my case, all three wires connect to the main board. Next to the transformer is a bridge rectifier. I want to think the transformer is +12v/-12v but that cannot be right. It would have to be +12v, or +6v/-6v. That is because the capacitors on the board are rated 16v. I mean it could be a 16v transformer maybe, but is there such a thing. Anyway, that doesn't matter.

I have a "standard", 12vdc, power supply that I bought online. It only has positive out and negative out. How would I go about figuring out which of the main board wires to connect to? I hope I showed enough effort that someone sees I really am trying and will help me. Thanks.

[0xdeadbeef]

Wow, you must have sentimental reasons to attempt this but honestly just looking at this crusty mess give me a depression.

Anyway, I guess it's clear that the bipolar power supply to the board (red/black/red) was cut off. If there are no markings on the board, it should be possible to follow the traces to diodes or electrolytic caps to see which of the red wires is +V and which is -V. On the transformer only measuring will help but be aware that touching live wire is potentially lethal.
Anyway, I can't seem to find the bridge rectifier you're talking about. There are these two greenish things on the PCB close to the three cut off voltage supply lines which might be weird Brazilian diodes even though I never saw green ones. But this would be only a half wave rectifier. So where is this bridge rectifier you're talking about?

Besides, I'm puzzled by the amount of wires connected to the transformer. I would assume that the brown and black/blue are 110V line and neutral - where it's not 100% clear to me why it's three lines. Is this thing they're coming from a switch or a fuse holder? If this is the 110V/220V switch, then it could select e.g. either the blue or brown line to select the according (tap of the) primary winding. Then there is this white wire going to a lamp (?) which is also connected to two yellow wires coming from the transformer. Like a separate secondary winding only to power a lamp??? Last but not least there are two green wires, probably some additional unused secondary winding?

Last but not least: is this a stereo amplifier? Since there are four transistors but only four loudspeaker connectors (given that they are not coax). So probably some dual differential amplifier setup?

[Chris56000]

Hi!

This a simple basic stereo class B amplifier about 15W per channel output!

Can you tell me the value and voltage rating of the large yellow can capacitor mounted to the right hand side of the PCB please - this will help me select the correct transformer rating!

The green rectifier diodes were very common in the UK in the late 1960s/early 1970s and the BY126/BY127 were typically made in this style, although moulded in black rather than the light green here!

I would suggest a mains transformer of about 12V-0-12V at about 2A would be correct for this design, if you do an eBay search for "R Core Transformer" you should have no trouble finding something suitable!

The rectifier circuit is a simple bi-phase full wave-rectifier, as shown in the attached diagram!

Chris Williams

[vidarr]

0xdeadbeef - Thanks a lot. I am going to try. My wife's dad died and it would be really nice to bring this Amp back to life for her. You got a lot of that correct without knowing this amp. Yeah, the wires to the transformer are a big mess, but I spent some time sorting it out. There is a 120/220v switch, a light, a fuse, an electrical socket on back (for phono), a power on/off switch. That was all on the input side.

Chris56000 - You obviously know this amp, or very similar amps. I hope you can help me through this. That capacitor is rated 2500uF/35v.

I guess my first issue is to figure out the two AC input wires to the transformer to test it?

Thanks!

edit: I should state, her dad was an electrical engineer he did both design things and build them for a lot of companies. He built this when he was probably a teenager. The transformer being cut off was for a reason. I just don't know what. Could be a problem on either side.

I was wrong about the back switch - it is only an on/off - not a 110/220v switch (He switched the switch. The amp says "110/220" the switch says "on/off"). So, all four of the wires from one side of the transformer go to that switch. Brown and Blue together and Black and Green together. Plugging it in is that part that makes me nervous. The last one I did, it made a huge pop and its life came out. I put it outside and watched through a window while I plugged it in.

[Chris56000]

Hi!

Whilst I've not seen an exact model other than from the pictures you supplied, the circuit type is very very common, and a look in the UK's "Practical Wireless" and "Radio Constructor" magazine for the early to mid 1970s will turn up many similar designs, e.g., the P.W. "Texan" for example!

(All free to download from American Radio History!)

In the light of the yellow cap rating you gave me, a transformer rated at 18–0–18V 1.5A will give you a rectified voltage of 25V., which should provide the power output the amp was designed for!

The other winding, was probably about 6V 0.5A to operate a pilot lamp!

Searching "15W Stereo Amplifier" in Practical Wireless and Radio Constructor magazines should provide a variety of example circuits you can use, either directly or as a guide to draw your "Spyder" out from – I recommend you buy a new 18–0–18V 1.5A transformer from ebay or similar, wire the secondary according the diagram I provided, then connect a pair of 15 ohm speakers to your amplifier and let us know what happens?

Is there any chance you might still have the original documentation your Dad built it from, or has that long gone?

Unfortunately with the festive season coming up I can't do as much as I'd like from an electronics point of view, but I'll be keeping an eye open in this thread as and when I can!

Chris Williams

[vidarr]

C -

This is so very helpful! Thank you!

I have another transformer that is 24v with two wires out. I made a little test power supply with it. Is it possible to test the amp using it? Could I use the two red wires going into the amp and ground the black wire? It will be some time before I can get a new transformer. I would want/have to order any parts for the amp that might be needed at the same time. The capacitors could be stale, or who knows what. The little lamp works though. What a relief.

Thanks for the American Radio History tip. I am already checking it out.

Enjoy the holidays!