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It’s been years since I could hear much in the way of high frequency. If your cousin is happy it’s time to move on. The ends are not a standard thickness. I made cardboard templates for both ends. I Plane wood to be the same as original and Forstner bits to make the counter sink holes for case...

Did you put it in parallel with C4 on Q2 EB? Do the Capacitive Reactance .005uF at 20 kHz = 1,581 Ohms .022uF at 20 kHz = 362 Ohms Look at C7 at 0.022 uF that couples the audio from Q4 base to Q3 base. I'm not an audio designer. I would want at minimum of an order of magnitude less and even...

A good cross check is looking at the RS 660. Most of it is the same. It has some bells and whistles and other minor differences. The RS660 has the same value for R31 and R31 is also missing in the RS660s I have pictures of and the one on my desk.

P6 is Point 6 on the PCB layout xRay view. If you mean #2 on the terminal board at the bottom you can trace it to P6. Right side of the PA schematic it is marked as 56K and shows it in series with the junction of R31 & R32 feeding other side to incoming audio R9 &R 10 feeding the drivers. It...

P2 on the PA layout that I think is the collector of Q8?

My first guess is PA high frequency oscillation. Matching won't help with the high current. Look for a burr(s) on the heatsinks that punches through the mica insulator(s).

I believe what peteCWA is referencing I think of as transfer curves. The ONSEMI sheets have Typical Output Characteristics fig 7&8 and Typical Base Emitter Voltage fig 11&12. You what Base Emitter V (i.e. base current) to be high enough above the start of collector current to be in the linear...

You're correct I like my little Pan-Vise a lot. I think I got it about 1971. Along with 2 extra sets of plastic jaws and the card holder that inserts into the base when the vise is pulled out. My only complaint has been it doesn't stay well attached to my Formica desk top so it's often on one...

I'm a long retired EE and Journeyman auto mechanic among others. Most of the differences in degrees in Physics, ME, EE CEME etc is the constants in front of the equations. It's what you do after the paper that's different. The only thing I can think of that would affect both PAs is a power...

You shouldn’t need to change the finals in both sides. You shouldn’t need any more than matched characteristics for the PNPs / NPNs in each amp. Doubt a dim bulb would have helped with the short. Too many MFD in the rail caps. A dim bulb say 25W could save you from destructive oscillations...

This is not unique to any amp or any frequency. Amps like to oscillate as well as amplify. Carbon / ceramic resistors have negligible inductance. Wire wound resistors do and can be problems in signal and feedback paths in amp circuits. Germaine only if it is oscillating: In a few LR 9090 and...

Let’s see L1 / R30 is a filter. A spike still sees 10 Ohms while audio sees low X sub L. You can see how it works looking at Inductive reactance vs frequency. 2.5 uH at 20 kHz has XL of 0.31 Ohms - at 200kHzits 3.14 ohms - a 1 us pulse is 15.7 Ohms Have you gotten the SM such as it is. It’s...

Well now we see the forest and it’s time to go back to looking at the trees. Essentially zero idle current says we’re biased into Class C instead of AB. The popping may well be a byproduct of part failure. Class C is good for CW but not analog audio so that’s likely the distortion. Class C...

Sounds like you know your way around. The pop kind of sounds like the DIP plug on ribbon cable looking down from the front on the left edge of the tone board. When it's unplugged you get that reaction. Not sure about a bad connection on one pin. There's a cut trace on the tone board right of...

I think I gave a representative mV AC ripple on each of the power supply voltages. They are low. That would be an early point to consider. I have found almost no HV power supply caps bad. You will also notice that the WVDC on the RS rail caps is mighty close to PS voltage. Consider its been...

DC offset is OK and I don't see how that could cause hum. Is the hum the same in all positions SELECTOR (input selector) switch? I did presume you have slid the rear Phono Mag sensitivity switch up and down a few times. It rarely matters. Check the PA board common connections. Make sure...

Most of the time I've had that problem it is a bad cable or poor RCA plug connection between the TT and amp. I think 1 time I found a ground wire for the patch cable broken under the TT on a terminal strip. You might also check that the Gnd terminal on the back of the 660 is connected to the 660...

I got the schematic from HiFiengine. Is your SX550 a 120V? Did you remember to remove the 0.01mF across the switch? It would only matter in the OFF position and I haven't had TRIAC trigger because of the current through the cap BUT I would also remove the 0.01 across the primary. I remember...

you can put a jumper across the switch for test purposes

I can't see how you can get a switch arc. There is around 100 Ohms in series the gate lead and the TRIAC switches just over 1 volt past the zero crossing and has 1 diode junction drop (0.6V) while it is ON in that quadrant (direction). If you use a current probe on the AC line the current is of...

As important to me, is the power switches on the amps I have also trigger the protection circuit. I really dislike the rail caps discharging through my woofs and whatever else happens in a noncontrolled shut down until voltages fall enough to trigger the protection circuit or relay(s) drops...

There are no direct replacement LED or incandescent replacement to the best of my knowledge. Most of the time the old lamps will pull out of the rubber holders they are inserted in. The adapters are old and tired so work carefully. Somewhere back in this thread I detailed how I did the LED...

your correct R19 sorry for typo. Commons are not constant and often vary by mV in low level circuits. Test equipment setup sometimes will reference where the common point to be used for a setting / reading. In industrial control equipment common can vary by volts. Sometimes a lot (nice...

For the AM question Try folding the loop stick ant away from the back panel Try adding a 2 to 4 foot piece of wire to the AM post on the back Look for broken wires from the loop stick to the MB posts Other thought is mute signal is present. Selector SW S1d +12V wire 14 to switch term 14 AM is 1...

What scope did you get? I recommend you find a 1:1 isolation transformer for it. Electrical junk yards often have Control Power Transformers (CPT). As long as you can set jumpers for 1:1 marked voltage is not a problem. Rating is in KVA or VA. If rating is for a transformer rated 220V that...