Premier 90 Reverb Clone HUM
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FUCHSAUDIO
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Re: Premier 90 Reverb Clone HUM
I don't understand how that would change anything unless you had a bad tube or fixed a bad solder joint or something when you swapped .jon wrote:Switching to a 12ax7 seems to have done the trick
Thanks everyone
6euu and 12ax7 are the same tube with different pins.
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FUCHSAUDIO
- Posts: 1247
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Re: Premier 90 Reverb Clone HUM
The pin outs are f*cked enough that maybe (just maybe) things are close enough to cause an issue. Maybe the heater cathode differentials are different enough to make it hum....weird, but glad it worked out.
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Re: Premier 90 Reverb Clone HUM
i worked on one of these and found that the cathode resistors in some of the preamp tubes were not large enough (in value) to stop grid current from flowing in said preamp tubes. A lrager cathode resistance cleaned up quite a bit of the hum problems, especially in terms of the grid current flowing through the guitar pots (makes nasty scratching noise when the pot is turned).
Re: Premier 90 Reverb Clone HUM
Sorry for not replying but I've been in Saudi Arabia for work the past week, (still here in fact).
As it turned out I was a little premature in claiming all was fixed. It still has som hum, all 120hz at this point. One thing I did do when I built the reverb was include a .1uF cap on the input of the grid on v1 to stop back flow to the guitar. Currently I am running an ez80 in half wave form when I return I am going to convert it to hybrid full wave. Using two diodes to create other half of the bridge. As the unit has more than enough drive I have no issue increasing the cathode resistance to a mor standard 1.5k or so, hopefully it will help.
As it turned out I was a little premature in claiming all was fixed. It still has som hum, all 120hz at this point. One thing I did do when I built the reverb was include a .1uF cap on the input of the grid on v1 to stop back flow to the guitar. Currently I am running an ez80 in half wave form when I return I am going to convert it to hybrid full wave. Using two diodes to create other half of the bridge. As the unit has more than enough drive I have no issue increasing the cathode resistance to a mor standard 1.5k or so, hopefully it will help.
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Stevem
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Re: Premier 90 Reverb Clone HUM
How much ac ripple voltage are you seeing on the plate of the first gain stage ?
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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: Premier 90 Reverb Clone HUM
OK an update!
I have eliminated all the 120hz hum from the amp. It turned out I had a bad coupling cap and I was getting DC on the output jack. But I still have significant 60hz hum. I have checked all my filters I changed from a half wave to a full wave rectifier. I elevated my heaters (12VAC). Elevating the heaters has cut the level considerably.
Am I blatantly missing something?
I have eliminated all the 120hz hum from the amp. It turned out I had a bad coupling cap and I was getting DC on the output jack. But I still have significant 60hz hum. I have checked all my filters I changed from a half wave to a full wave rectifier. I elevated my heaters (12VAC). Elevating the heaters has cut the level considerably.
Am I blatantly missing something?
Re: Premier 90 Reverb Clone HUM
Update!
The hum is caused by the interaction of the two devices. Reverb alone has a beautiful signal in and out through a scope. Connect it to an amp and it hums. Any suggestions?
Ps lifting the ground on the reverb does not help.
The hum is caused by the interaction of the two devices. Reverb alone has a beautiful signal in and out through a scope. Connect it to an amp and it hums. Any suggestions?
Ps lifting the ground on the reverb does not help.
Re: Premier 90 Reverb Clone HUM
Don't know if this will help.
On the first amp I built from scratch, a 40 watt copy of an American Vox, everything worked fine, but there was a loud hum. I grabbed an insulated screwdriver to tap on the the components to see if something was loose. But, I noticed as I moved the tool near one spot on the chassis, the hum diminished. I ended up attaching a small aluminum "shield" at that spot, and the hum was completely gone.
On the first amp I built from scratch, a 40 watt copy of an American Vox, everything worked fine, but there was a loud hum. I grabbed an insulated screwdriver to tap on the the components to see if something was loose. But, I noticed as I moved the tool near one spot on the chassis, the hum diminished. I ended up attaching a small aluminum "shield" at that spot, and the hum was completely gone.