So I bought an amp that is a copy of a Matchless Lightning. It’s a 2 el84, 3 12ax7’
, treble bass and master volume, amp.
When I fire it up I get no sound from my guitar. Instead I get a prominent 60 cycle hum. Changing the volume makes no difference. It stops when I pull the phase inverter. It doesn’t stop when I pull the other two preamp tubes. Put new tubes in, no change.
I suspect it’s an issue in the power section. Tomorrow I’m going to check voltages.
Just posting for ideas of what to check?
Thanks in advance.
Les
PS - The turret board was not fastened to the chassis. Instead it sits on legs like a table on the kitchen floor. I’m sure in shipping it was bounced all over the chassis and somewhere there is a short.
Lightning Style Amp w/ 60 Cycle hum, no sound
Moderators: pompeiisneaks, Colossal
Re: Lightning Style Amp w/ 60 Cycle hum, no sound
You have to start from zero, and check every connection methodically.
I build and repair tube amps. http://amps.monkeymatic.com
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Stevem
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Re: Lightning Style Amp w/ 60 Cycle hum, no sound
Sounds to me like you have a bad coupling cap between gain stages up stream from the PI tube.
The problem could in fact be with the coupling cap right there at the input to the PI stage being bad.
The issue is how ever not a bad power supply filter should someone suggest that, as fully bad filter would either still allow audio to pass but with a hum, or blow the amps fuse!
The problem could in fact be with the coupling cap right there at the input to the PI stage being bad.
The issue is how ever not a bad power supply filter should someone suggest that, as fully bad filter would either still allow audio to pass but with a hum, or blow the amps fuse!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Lightning Style Amp w/ 60 Cycle hum, no sound
Thanks everyone.
Okay I found a broken ground and the PI tube socket was trashed. I bolted down the turret board, repaired the ground & replaced the PI tube socket. Voltages in V1 & V2 are high. The only sound I get is when I touch the phase inverter HV I get the usual crackle.
I'm going to check the coupling cap to the phase inverter.
Les
Okay I found a broken ground and the PI tube socket was trashed. I bolted down the turret board, repaired the ground & replaced the PI tube socket. Voltages in V1 & V2 are high. The only sound I get is when I touch the phase inverter HV I get the usual crackle.
I'm going to check the coupling cap to the phase inverter.
Les
Re: Lightning Style Amp w/ 60 Cycle hum, no sound
Ok I changed all the coupling and tone caps out. Voltages before AND after remain very strange. Here are the voltages:
Tube 1......2....3.....4......5..... 6....7.....8......9
V1 347...na...0...na....na.....347....na.....0....na
V2 347...na...0...na....na.....351....347....0....na
V3 345...0....0...na....na.....345.....0......0....na
V4 na....na..8.4...na....na...na....347.....na...243
V5 na....na..8.4...na....na..na.....347.....na...243
The ground scheme is a mess. I'm thinking I need to redo the grounds next.
Thanks,
Les
Tube 1......2....3.....4......5..... 6....7.....8......9
V1 347...na...0...na....na.....347....na.....0....na
V2 347...na...0...na....na.....351....347....0....na
V3 345...0....0...na....na.....345.....0......0....na
V4 na....na..8.4...na....na...na....347.....na...243
V5 na....na..8.4...na....na..na.....347.....na...243
The ground scheme is a mess. I'm thinking I need to redo the grounds next.
Thanks,
Les