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Post by paradisecs on Feb 14, 2018 16:55:27 GMT
I have three units, LS2, USC1, and STD160 that I've been working after being in storage untouched for nearly 15 years. The LS2 and 160 mechanically are working great but there is a very pronounced hum when a record is not playing. The USC1 has a slight hum but only the younger hear it. Is there something, capacitor or resistor, or something else that could be causing this? I relate this to the sound of an old guitar amp turned up way to loud, but adjusting the volume doesn't seem to make the level of the hum changed.
I just started reading through the SHP amp book but I don't have anything specific to the TSA amps.
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Post by Ron Rich on Feb 14, 2018 17:32:43 GMT
On all Seeburg (and any brand) first thought is the power supply filters. Specifically on Seeburgs from the TSA-1 (except the -2's)if the hum "builds up", after sitting for a few seconds, look at the mute relay --either it's dirty, or not being held, energized. Ron Rich
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Amp hum
Feb 14, 2018 18:24:27 GMT
via mobile
Post by grizzlydude on Feb 14, 2018 18:24:27 GMT
Ron my shp1 amp u have been walking me through also hums , what pins on relay should I check for the voltage to see if is being "held" like u say
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Post by Ron Rich on Feb 14, 2018 18:31:22 GMT
Use your eyes ! simple---
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Post by robnyc on Feb 15, 2018 6:49:43 GMT
......adjusting the volume doesn't seem to make the level of the hum changed. I just started reading through the SHP amp book but I don't have anything specific to the TSA amps. D-L and listen to this file of two types of hum: www.fileconvoy.com/dfl.php?id=gc5b9f41c851b9fa010000596418cd406c947b89be6The first is 60Hz. It is caused primarily by defective shielding. The second, higher pitched hum is poor filtering of a full wave poser supply such as used in most amps. This can be due to dried out filter caps (likely in your case) or excessive drain on the power supply. A representative schematic of the later TSA series is here: www.verntisdale.com/Seeburgschem.htm Use TSA5. From TSA5-through TSA10 the architecture is essentially the same. The main filters are C5135 & C5133 -but ALL electrolytic caps should be replaced in an amp this old. FWIW: the main differences between the TSA and SHP, aside from the finals being silicon in SHP, is the bipolar power supply in SHP and single rail in TSA. The preamp and AGC are essentially the same. RobNYC |
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Post by paradisecs on Feb 19, 2018 18:27:17 GMT
I thought it might be some EM interference and I believe the sound is more like the 60hz you posted, thank you for that. I've read a few things about 60 vs 120hz hums but wasn't sure what the difference really was. As for bad shielding what would you recommend checking?
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Post by robnyc on Feb 19, 2018 21:47:58 GMT
If the level of hum is not affected by volume control setting, it is likely that the actual hum is 120Hz and the result of either excessive drain or failing filters. The reason I suspect this is because the volume control pretty much divides the low vs high signal levels in these (and most other) amps. In the low signal level we find the areas most susceptible to 60Hz hum pickup due to their high amplification. Shielding is more critical there. The later stages which are primarily designed to boost power -not gain are less likely to pick up 60HZ -though it can happen in certain cases.
Other than the fluorescent ballasts, there isn't much that can induce hum in those machines.
Does the heatsink get warm even with no signal-?
If possible, post a recording of the hum...but I suspect it is amp repair time.
RobNYC
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Post by paradisecs on Feb 20, 2018 17:13:25 GMT
Thanks for the info. I'll see about a video of the hum. I've been avoiding the rebuild amp method yet, I haven't felt ready to do so. But I'm getting there and looking at a new soldering iron to replace my ancient Weller to get me that much closer. My father-in-law purchased a lot of 15 Seeburgs from LS1 up to STD160s and I've been working on getting them up and running. Most just needed some basic TLC and we either gave them away or sold them super cheap to friends. I'm to the point now where I just tore down a mech on a USC-2 and cleaned every component and I'm putting it back together today. Once that is done I'll focus on what you said here and see what happens. I should have torn one down first, I've learned more this week than I have the last two months just by doing so. I suspect the amp will be the same.
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