mike stehr Posted October 12, 2017 Share Posted October 12, 2017 Okay, I read through the audiokarma thread. The one guy asked to pull the rectifier tube, (GZ34) to see if the hum/buzz went away. I recall you mentioned that you did that and the hum went away. He mentioned that if the hum went away, that it's possibly a wiring/grounding/layout issue. Judging by the way the amplifier is laid out and wired, it's a bit of a mess and wouldn't doubt that the wiring/grounding could be the problem. I can't recall if the Moth SET amplifiers of the day had kits, like Welborne labs. It appears to be wired like a kit, or other owners may have added different parts. (The Jupiter coupling caps were not around when this amp was new I'm guessing.) The output tubes, (2A3) are indirectly heated with DC, using some sort of voltage regulation. I have no idea if the pots are for hum nulling or not. Did you happen to see if those pots changed in the millivolt range when your turned them? Sometimes triode output tubes get a bit noisy getting to the end of their life as the emission lowers, that's why I asked if you had a way to test them. Even the driver tubes and rectifier could be tested. A guy can test them in circuit by confirming proper voltages/current, but one will have to probe around in a powered amplifier. The amplifier is a bit older, and there may be a dried up cap or two, but I don't really think that's the issue...maybe part of it... Without a schematic or some sort of manual be it assembly or operating, it's a bit of a chore to figure out the circuit from pictures of underside wiring, how it works, etc... There a forum member named Eric Mandaville (I hope I spelled his last name correct) who I'm pretty sure has a Moth audio amplifier...maybe it's pre-amp. He'd be the guy with most knowledge about Moth audio around here I would think. Maybe find the schematic or a manual and befriend someone locally who happens to be into tube audio, either a tech or enthusiast who can look over the amplifier. You can learn quite a bit that way. Quote Link to comment Share on other sites More sharing options...
theoman Posted October 12, 2017 Author Share Posted October 12, 2017 Here's from Craig at Eddie Current:All Moth amps had manuals with schematics. If you got the amp it should have been sent in a wooden crate with the manual. That amp is 17 years old and it is likely the electrolytic caps are dried out which would account for the buzz. I don’t have any documentation on the Moth amps, and don’t work on them.You need to measure the bias resistor to see what the bias voltage should read. The 45 tubes need about 36mA, so if the resistor is 1 ohm the meter should read 36mV. Make sure you have the correct tubes, I have not seen a 45 tube that looks like that. Quote Link to comment Share on other sites More sharing options...
theoman Posted October 12, 2017 Author Share Posted October 12, 2017 1 hour ago, mike stehr said: Okay, I read through the audiokarma thread. The one guy asked to pull the rectifier tube, (GZ34) to see if the hum/buzz went away. I recall you mentioned that you did that and the hum went away. He mentioned that if the hum went away, that it's possibly a wiring/grounding/layout issue. Judging by the way the amplifier is laid out and wired, it's a bit of a mess and wouldn't doubt that the wiring/grounding could be the problem. I can't recall if the Moth SET amplifiers of the day had kits, like Welborne labs. It appears to be wired like a kit, or other owners may have added different parts. (The Jupiter coupling caps were not around when this amp was new I'm guessing.) The output tubes, (2A3) are indirectly heated with DC, using some sort of voltage regulation. I have no idea if the pots are for hum nulling or not. Did you happen to see if those pots changed in the millivolt range when your turned them? Sometimes triode output tubes get a bit noisy getting to the end of their life as the emission lowers, that's why I asked if you had a way to test them. Even the driver tubes and rectifier could be tested. A guy can test them in circuit by confirming proper voltages/current, but one will have to probe around in a powered amplifier. The amplifier is a bit older, and there may be a dried up cap or two, but I don't really think that's the issue...maybe part of it... Without a schematic or some sort of manual be it assembly or operating, it's a bit of a chore to figure out the circuit from pictures of underside wiring, how it works, etc... There a forum member named Eric Mandaville (I hope I spelled his last name correct) who I'm pretty sure has a Moth audio amplifier...maybe it's pre-amp. He'd be the guy with most knowledge about Moth audio around here I would think. Maybe find the schematic or a manual and befriend someone locally who happens to be into tube audio, either a tech or enthusiast who can look over the amplifier. You can learn quite a bit that way. I will get the all tubes checked out Friday. Do you think the Amp is worth saving? if not I still can sent it back to the estate. I paid 1,100 for it. here's the deceased owner thread on the amp http://audiokarma.org/forums/index.php?threads/moth-s45-arrives.1079/ Quote Link to comment Share on other sites More sharing options...
sheltie dave Posted October 12, 2017 Share Posted October 12, 2017 Theo, if you want, I would be glad to buy it for the $1100. I was the one who strongly recommended you buy it, so I’ll back you up. there are a couple tube amps here in St. Louis for sale that can put you in a happy spot, both private and listed at Gateway Audio Society. check your private message here. Quote Link to comment Share on other sites More sharing options...
Davecv41 Posted October 12, 2017 Share Posted October 12, 2017 4 hours ago, theoman said: here's the deceased owner thread on the amp http://audiokarma.org/forums/index.php?threads/moth-s45-arrives.1079/ Such flowery writing. He could make knob-and-tube wiring sound attractive. Quote Link to comment Share on other sites More sharing options...
theoman Posted October 12, 2017 Author Share Posted October 12, 2017 Bingo! 2 Quote Link to comment Share on other sites More sharing options...
theoman Posted October 13, 2017 Author Share Posted October 13, 2017 why am I only able to load one picture only? Quote Link to comment Share on other sites More sharing options...
sheltie dave Posted October 13, 2017 Share Posted October 13, 2017 It is the Klipsch site, one and done. Did the hum go away after you lifted the grounded wire? Quote Link to comment Share on other sites More sharing options...
theoman Posted October 13, 2017 Author Share Posted October 13, 2017 From Craig at Eddie Current (moth) You need to measure the bias resistor to see what the bias voltage should read. The 45 tubes need about 36mA, so if the resistor is 1 ohm the meter should read 36mV. Make sure you have the correct tubes, I have not seen a 45 tube that looks like that. I don't understand what he's talking about! Quote Link to comment Share on other sites More sharing options...
Davecv41 Posted October 13, 2017 Share Posted October 13, 2017 2 hours ago, theoman said: From Craig at Eddie Current (moth) You need to measure the bias resistor to see what the bias voltage should read. The 45 tubes need about 36mA, so if the resistor is 1 ohm the meter should read 36mV. Make sure you have the correct tubes, I have not seen a 45 tube that looks like that. I don't understand what he's talking about! The picture posted at 10:07pm yesterday shows a 2A3 tube in someone's hand. Does Craig at Eddie Current think you're using 45s or 2A3s? Quote Link to comment Share on other sites More sharing options...
theoman Posted October 18, 2017 Author Share Posted October 18, 2017 he knows I'm using 2A3s. Quote Link to comment Share on other sites More sharing options...
justinsweber Posted October 18, 2017 Share Posted October 18, 2017 Where do you live? Close to LA? If so I can look at it. Criag of NOS valves could too if he is closer. Either way, we can pop the top and figure out whats going on. Quote Link to comment Share on other sites More sharing options...
theoman Posted October 20, 2017 Author Share Posted October 20, 2017 Im in Houston not much service out here Quote Link to comment Share on other sites More sharing options...
Marvel Posted October 22, 2017 Share Posted October 22, 2017 On 10/17/2017 at 11:31 PM, justinsweber said: Where do you live? Close to LA? If so I can look at it. Criag of NOS valves could too if he is closer. Either way, we can pop the top and figure out whats going on. Craig is in Michigan... The amp would need to be wired differently for a 45 (slightly). Erik Mandaville on here built some Moth amps from kits if I remember correctly. He lives in the Southwest. Bruce Quote Link to comment Share on other sites More sharing options...
seti Posted October 22, 2017 Share Posted October 22, 2017 There was a tech in Austin who worked on tube amps but can't remember who it was. I remember being in there shop years ago. They had lots of tube gear for sale. Quote Link to comment Share on other sites More sharing options...
theoman Posted October 23, 2017 Author Share Posted October 23, 2017 I blew out my diaphragms on my horns in my Altecs and replaced them with the ones from china. is there much difference in the US models? Quote Link to comment Share on other sites More sharing options...
sheltie dave Posted October 24, 2017 Share Posted October 24, 2017 Generally,a lot. Quote Link to comment Share on other sites More sharing options...
theoman Posted October 24, 2017 Author Share Posted October 24, 2017 has anyone compared the ones made in china and the states? not saying they are made here. Quote Link to comment Share on other sites More sharing options...
seti Posted October 24, 2017 Share Posted October 24, 2017 I would ask over on the audio heritage forum. They have likely tested them already. Quote Link to comment Share on other sites More sharing options...
jazzmessengers Posted November 23, 2017 Share Posted November 23, 2017 I will suggest asking at Headfi since Moth Audio made many headphone amps, so there might be some owners that have their speaker amps over there. Quote Link to comment Share on other sites More sharing options...
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