There are not very many books out there for beginners to get started. The website AudioKarma is an excellent resource. You can also learn a great deal by watching others working on these things on KZfaq. If you are interested in vacuum tube electronics search “uncle doug”. Another great teacher is “xraytonyb”

Thanks for the notes! I misspoke when talking about the tuner, the low value tantalums were my primary concern, even the 1uF electrolytics in that board tested fine. Interesting tip on the SMD bypass. For the moment so use Nichicon low leakage caps for high value tantalum replacement. On the fan there is really not much room but it would be interesting to Mount a low noise fan and connect to the lamp supply. It’s really not necessary after these mods though. On the distortion on the amp side it could be anything, the speaker relay is still original, switch contacts in the speaker output, multiple banana connections on the way to the dummy load… on the preamp distortion I have already replaced the failure prone transistors and all of the tants and electrolytics. Could be a resistor but more likely that it’s a slightly dirty switch contact, or aging carbon volume or balance control.

@@NovaluxStereophonic I can't think of an example in vintage audio gear where a tantalum was used for 'low leakage'. Mainly, they have lower ESR at HF frequencies; the highest voltage electrolytic that will fit the lead spacing is usually OK with bypassing. (even X7R or Z5U .01uf ceramics are OK because there is only small signal voltage variation that could change the value enough to cause measurable audio distortion) EX: I noticed you did a video on Marantz 1122 preamp. There are tantalum's for emitter resistor bypassing in that model. 5 ohms ESR at 1 MHz makes a difference in the high frequency phase margin of those circuits. The value sets the low freq cuttoff, and a film or ceramic bypass on any electrolytic is sufficient to keep the ESR low >1MHz. Another place they might be found - power supply bypass in tuner circuits, and it's not for 'low leakage'. A nice trick to see if leakage current is important: 9v battery with 10 meg resistor is ~1ua. That's also a method to reform the dielectric of capacitors sitting in a parts bin for years before you use them in a circuit. Contact noise from oxidation on jacks (test equipment or device) and relays etc. could be the excess noise source. A couple years ago, a $50 gift card snuck into my wallet; sooo, I bought a bunch of gold plated RCA's and banana's for my bench... no more twisting and wiggling

@@NovaluxStereophonic On the fan: My buddy used a STA-2100D Realistic receiver as his primary power amp DJ'ing in the 80's. We put two 4" muffin fans on the top to keep it cool - worked flawlessly for years. (rebadged Pioneer SX1250) You could double sided sticky tape a thin fan underneath 🧐

What did you say ?