Hey guys
I recently purchased a used 1974x. It is a sweet amp overall. Channel with tremolo has couple of issues.
First, the two inputs on the tremolo channel have lower volume than the normal channel. Second, When I dime the channel with my guitar plugged into the normal channel I find that tremolo channel has very low volume with lower input and buzzing noise with the top input. When I dime with my guitar into the tremolo channel, it works better. It seems like the lower input on the tremolo channel has much lower volume than top input.
I changed the preamp tubes but the problem doesn't go away. I have attached a video for you to hear what I mean by farting noise. The channels are dimed with my guitar plugged into top input of normal channel with volume cranked. I have also attached photos of the circuit.
I was also able to measure voltages for the valves if that helps.
V1
Pin 1 = 133 VDC
Pin 2 = 50 mVDC
Pin 3 = 1.1 VDC
Pin 4 = 3.1 VAC
Pin 5 = 3.1 VAC
Pin 6 = 133 VDC
Pin 7 = 50 mVDC
Pin 8 = 1.1 VDC
Pin 9 = 3.1 VAC
V2
Pin 1 = 198 VDC
Pin 2 = 50 VDC
Pin 3 = 73 VDC
Pin 4 = 3.1 VAC
Pin 5 = 3.1 VAC
Pin 6 = 202 VDC
Pin 7 = 51 VDC
Pin 8 = 71 VDC
Pin 9 = 3.1 VAC
V3
Pin 1 = 138 - 142 VDC (fluctuating because of tremolo I guess)
Pin 2 = -30 - 40 mVDC (fluctuating because of tremolo I guess)
Pin 3 = 1.05 VDC
Pin 4 = 3.1 VAC
Pin 5 = 3.1 VAC
Pin 6 = 89 VDC
Pin 7 = 25 mVDC
Pin 8 = 1.05 VDC
Pin 9 = 3.1 VAC
V4
Pin 2 = 0.70 VDC
Pin 3 = 9.5 VDC
Pin 4 = 3.1 VAC
Pin 5 = 3.1 VAC
Pin 7 = 310 VDC
Pin 9 = 294 VDC
V5
Pin 2 = 0.70 VDC
Pin 3 = 9.6 VDC
Pin 4 = 3.1 VAC
Pin 5 = 3.1 VAC
Pin 7 = 305 VDC
Pin 9 = 294 VDC
V6
pin 1 = 305 VAC
pin 7 =305 VAC
pin 4 = 86 VAC
pin 5 = 81.8 VAC
pin 3 = 316 VDC
Here is a video of the buzzing sound that I observe.
https://www.youtube.com/watch?v=wp-RPjnNWXU
HELP! 1974x issues with trem channel
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Daviedawg
- Superior Amp Tech
- Posts: 750
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Re: HELP! 1974x issues with trem channel
Welcome to 18 watt.com.
First thing is two easy answers. Your voltages are a little lower than I would expect but only by a small margin so not relevant to your issues. The volumes you describe in relation to each other sound correct. The Normal channel inputs if built as the traditional design are the same but the hi and lo on the trem channel are different with the hi noticeably louder than the lo.
It is always hard to reference volume from a video.But I know if I put my 18 watt to full volume in a domestic context it would be unbearably loud and there would be some noise too. Even from this it does not sound right basically. But it is hard to diagnose from the information here.
Can you do another video or sound clip moving the volume of the normal channel from around 1 up to as high as the noise starts so we can hear the tone and volume change? And another in the trem channel?
Dd
First thing is two easy answers. Your voltages are a little lower than I would expect but only by a small margin so not relevant to your issues. The volumes you describe in relation to each other sound correct. The Normal channel inputs if built as the traditional design are the same but the hi and lo on the trem channel are different with the hi noticeably louder than the lo.
It is always hard to reference volume from a video.But I know if I put my 18 watt to full volume in a domestic context it would be unbearably loud and there would be some noise too. Even from this it does not sound right basically. But it is hard to diagnose from the information here.
Can you do another video or sound clip moving the volume of the normal channel from around 1 up to as high as the noise starts so we can hear the tone and volume change? And another in the trem channel?
Dd
0 x