Silvertone 1484 Hiss issue

[emresound]

Hi everyone,

I've recently acquired a twin twelve from someone else.

It has a really noticeable hiss that just stays constant at all volumes, even when nothing is plugged in.
I was wondering if anyone had any pointers as to what could be the problem. I've tested the 12ax7 valves and the problem still persists when I change it to fully working ones.

I've attached a video of the hiss.

Another issue is the tremolo only works on input 2 of the 2nd channel. Works perfectly but not with any other channel (and the reverb is dead as it is often the problem).

[Enzo]

The tremolo is only supposed to work on channel 2, channel 1 is "plain". I cannot imagine how the trem would know which of the two channel 2 jacks you were using though. it should work on both or neither, because they are wired together one resistor in.

Turn the reverb all the way down and click it off, still hiss?

[emresound]

The tremolo is only supposed to work on channel 2, channel 1 is "plain". I cannot imagine how the trem would know which of the two channel 2 jacks you were using though. it should work on both or neither, because they are wired together one resistor in.

Turn the reverb all the way down and click it off, still hiss?

I tried the reverb but it doesn't do anything. Click it on or off doesn't make any difference. I'll look at Ch2 as to why it doesn't engage the trem in input 1 of channel 2.


Still trying to track that hum.

[Enzo]

Hum now? or do you still mean the hiss?

Ok then we now know the reverb path is not the noise source.


What schematic are you using? I am using this copy:
http://bmamps.com/Schematics/Silvert...ertone1484.pdf

Does the hiss go away if you turn the standby switch to standby mode?

Note the V numbers for the tubes. Since turning the volumes down does not kill the hiss, I will ignore V1. SO pull V2, does the hiss go away or stay? If it stays, pull V3, same question. if neither kills the noise, then it is coming from the power tubes. If pulling V2 kills it, it is the likely point, maybe not the tube itself, but the stage circuit the tube is in. If V2 no effect but V3 kills it, then the V3 stage is suspect.

Just for science, you can pull ONE of the 6L6 power tubes and fire it up. His or no hiss?, now put the tube back in and pull the other one. Hiss or no hiss now? V3 phase inverter and the two power tubes for two parallel circuits, we wanted to find if both or only one carries the hiss.

[emresound]

Hum now? or do you still mean the hiss?

Ok then we now know the reverb path is not the noise source.


What schematic are you using? I am using this copy:
http://bmamps.com/Schematics/Silvert...ertone1484.pdf

Does the hiss go away if you turn the standby switch to standby mode?

Note the V numbers for the tubes. Since turning the volumes down does not kill the hiss, I will ignore V1. SO pull V2, does the hiss go away or stay? If it stays, pull V3, same question. if neither kills the noise, then it is coming from the power tubes. If pulling V2 kills it, it is the likely point, maybe not the tube itself, but the stage circuit the tube is in. If V2 no effect but V3 kills it, then the V3 stage is suspect.

Just for science, you can pull ONE of the 6L6 power tubes and fire it up. His or no hiss?, now put the tube back in and pull the other one. Hiss or no hiss now? V3 phase inverter and the two power tubes for two parallel circuits, we wanted to find if both or only one carries the hiss.

Thanks Enzo, I will try the 1 power tube trick as I have currently 12ax7s only (no 6cg7s).
I say hum but I meant hiss my bad, sorry!

[Enzo]

You don't need another 6CG7 to just remove it and see what happens.

Also, you have two 6CG7 in the amp, one for the phase inverter and one for driving the reverb. They can be traded places. If nothing changes, then both tubes are probably OK. But if exchanging them makes any change in your hiss, then they or their circuits are involved.

The tests I just described above are for removing a tube and running the amp without it to see the effect. That is a different thing from using a new tube in one's place.

[soundmasterg]

Silvertone 1484's always have some level of hum and hiss due to the poor layout. That said, the amount in your video is too much. Enzo's method of pulling tubes and swapping tubes will help to narrow down the scope of the problem and help you identify the source of the issue. There are a couple errors on the schematic, including a ground where there shouldn't be and incorrect pinout on the trem tube. Also interesting about these amps is that their standby shorts the grids together of the power tubes, which gives a sort of incomplete standby.

If this amp still has the original Planet 'Guaranteed for one Year' filter caps then you should replace them along with the can cap. There aren't exact replacement can caps around anymore but you can enlarge the hole and use a dual cap and then attach a terminal strip inside the chassis to mount the third cap from the can.

Greg

[severedlim]

Ever determine the source of the hiss

Thanks Enzo, I will try the 1 power tube trick as I have currently 12ax7s only (no 6cg7s).
I say hum but I meant hiss my bad, sorry!

Hey, I'm having the same issue. Did you ever solve the issue? I'll probably try the workflow that Enzo mentioned to see if I can narrow down the issue.

[severedlim]

Question

Hum now? or do you still mean the hiss?

Ok then we now know the reverb path is not the noise source.


What schematic are you using? I am using this copy:
http://bmamps.com/Schematics/Silvert...ertone1484.pdf

Does the hiss go away if you turn the standby switch to standby mode?

Note the V numbers for the tubes. Since turning the volumes down does not kill the hiss, I will ignore V1. SO pull V2, does the hiss go away or stay? If it stays, pull V3, same question. if neither kills the noise, then it is coming from the power tubes. If pulling V2 kills it, it is the likely point, maybe not the tube itself, but the stage circuit the tube is in. If V2 no effect but V3 kills it, then the V3 stage is suspect.

Just for science, you can pull ONE of the 6L6 power tubes and fire it up. His or no hiss?, now put the tube back in and pull the other one. Hiss or no hiss now? V3 phase inverter and the two power tubes for two parallel circuits, we wanted to find if both or only one carries the hiss.

Hey Enzo,

I had the same problem as @emresound. I pulled V2 and V3 individually and it killed the hiss. What schematic were you using? I used the one from this site: http://www.silvertoneworld.net/ampli...schematic.html

Also for science, I removed the power tubes one by one and the hiss persisted. Since removing both V2 and V3 removed the hiss, it's probably R28 right?