HH Scott LK-48 troubleshooting

[beefkabob]

My parents gave me the old HH Scot LK-48 that my mom built back in the '60s and that has been in the closet and then the garage for decades. I think they took it out of use in the mid-80s they got a Fisher component stereo.

I have plugged in through the extra input. I have two old Canton speakers wired up. I'm actually listening right now.

I think I'm only getting one channel of input, the right channel. I can move that to the left speaker with reverse stereo or with mono playing the right channel to both outputs.

There are five tubes across the back. Looking from the back at the back from left to right, it goes big tube and then four small tubes, and the second to the right small tube does not light up. Is this likely just a case of needing to replace a tube?

Thanks!

 

[beefkabob]

 

[beefkabob]

Those wires are just RCA cables I had. The yellow is plugged in to the right output on my receiver, and it's the one that works.

 

[cavedriver]

given the age of that unit you need to look at replacing all the capacitors. You fry one and there'll be more than a bad tube on your amp. Best to find a stereo repair store that has experience repairing tube equipment. There are (were) things called tube testers that you can use to check each tube, but other than finding one on ebay or at a yard sale it's not an easy thing to come across. Also, on my old Scott the volume control and some of the switches developed corrosion spots that needed to be cleaned off or you can have channel dropping and noise.

 

[beefkabob]

I ordered four tubes from China so I will replace them together. I'll start there. Corrosion is likely but I'm not sure I want to pour too much into this.

 

[sergeauckland]

I volunteer at a Museum of Home Entertainment, doing repairs and refurbishing vintage equipment. What you have there is a lovely item, with nicely generous output transformers, so should give very decent bass. Output level would be about 10-12 watts, as the output valves look like EL84s or the US numbered equivalents.

Apart from replacing the valve that doesn't light up (most likely just a simple heater failure), you really need to check the coupling capacitors, as ANY leakage there will affect the bias of the following valves with anything from minor to catastrophic consequences. After changing the coupling caps, check the cathode bias on the output tubes just to make sure they're running at their normal level.

You can get the tubes tested by a competent techie, but generally, valves (valves, tubes...whatever) will work even if 50%, even 70% down on specification. I generally only replace tubes if their emission drops below 50%. I would check or just replace the coupling capacitors and the faulty valve, then try again. If it works and sounds fine, leave it alone until it doesn't. If it hums at 120Hz, then and only then replace the reservoir and smoothing caps.

Do try and get a Service Manual, or at least a Circuit Diagram if you can.

S