I inherited from a friend a Dynaco PAS 3 stereo preamp and a Dynakit stereo 70 amp. They have been in storage for a long time and needed cleaning. From the first time I turned the system on there was popping and static in both speakers. After spraying the balance pot I could not get any volume in the left speaker but the right speaker had no popping or static. I sprayed it again and rotated the control a hundred times and still could not get any volume to the left speaker. The balance control regardless of whether it is to the left or right channel I can only get volume in the right. Even after I reversed the input cables from left to right I still only get volume to the right channel. I interchanged the tubes on both boards and nothing changed. Whoever built the kit did a really nice job and all solder joints are tight and clean. Before I try to find a new pot to replace the existing pot does anyone have an idea as to what may be wrong. Thank you!
Dyna PAS preamp channel problems
- Thread starter shade23
- Start date
Firstly, can I assume that the Stereo 70 power amp is fine? Are you able to use that normally?
Assuming it works fine, then looking to the preamp, swapping valves made no difference, so from that at first assumption, we can work on those being OK.
That leaves all the other parts, and at this point, you'll need some instrumentation. Measure the voltage on all the valve pins, and compare them with the manual. You need at least a circuit diagram.
If that's not available, then with the data on the valves, which is always easily available on line, measure the volts and compare each channel. They should be identical, but even up to 10% difference should be OK insofar as it will work, even if not up to spec.
Bear in mind that valve circuits operate at hundreds of volts, which can be lethal, so if you're not comfortable with that, find a local tech to do it for you. Those units are really nice, so worth getting them working.
S
Assuming it works fine, then looking to the preamp, swapping valves made no difference, so from that at first assumption, we can work on those being OK.
That leaves all the other parts, and at this point, you'll need some instrumentation. Measure the voltage on all the valve pins, and compare them with the manual. You need at least a circuit diagram.
If that's not available, then with the data on the valves, which is always easily available on line, measure the volts and compare each channel. They should be identical, but even up to 10% difference should be OK insofar as it will work, even if not up to spec.
Bear in mind that valve circuits operate at hundreds of volts, which can be lethal, so if you're not comfortable with that, find a local tech to do it for you. Those units are really nice, so worth getting them working.
S
Thank you for your suggestions! I hooked the #70 amp to my big receiver and the problem is in the amp. The left channel still did nothing except light static regardless of where the volume was set.
I am a retired commercial electrician and collect older stereo equipment and I have good test equipment and know how to use it. Tonight I will check joints and inspect the wiring on the amp and see where to go from there. I want to keep it because of the fact it is all tube and both units have Dynaco tubes.
Thank you for your help!!
