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 Post subject: 1956 Premier 120 Guitar Amp Tremelo Pulsing The Speaker Cone
PostPosted: Oct Thu 17, 2019 3:02 pm 
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Joined: Aug Sun 23, 2015 6:01 pm
Posts: 1009
Location: South Jersey East of Philly
The tremolo on this 1956 amp pulses the speaker to a point where it can vibrate the cabinet. The cone really moves in and out to the trem speed. I have worked on many other vintage guitar amps, but the trem circuit on this one is different, and I need someone to explain how this circuit modulates the straight signal to the pulsed trem...and why the cone is moving so much, and would that be normal for this circuit. I replaced all caps in the circuit and checked resistor values. There are many variations of the Model 120 circuits out there, and this one is the closest one I found.....
https://www.jt30.com/premier/premier120schematic3.gif


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 Post subject: Re: 1956 Premier 120 Guitar Amp Tremelo Pulsing The Speaker
PostPosted: Oct Sat 19, 2019 3:49 am 
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Joined: Dec Sat 24, 2011 9:17 pm
Posts: 5012
Location: Vancouver Island, Canada
Hi, have you made sure that V2 and V3 are the right tubes, not reversed by mistake?
I'm thinking you can't turn the tremolo intensity down for some reason.

What you could do if you have a 12AU7, is put that in for V2 and replace the 12AX7 with the 12AT7, which will lower the intensity and maybe give you better control. Just a thought to help pinpoint the cause, not suggesting it will cure anything.

I wish I could explain the tremolo circuit but have trouble figuring it out myself. :lol:

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 Post subject: Re: 1956 Premier 120 Guitar Amp Tremelo Pulsing The Speaker
PostPosted: Oct Sat 19, 2019 5:57 am 
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Joined: Aug Sun 23, 2015 6:01 pm
Posts: 1009
Location: South Jersey East of Philly
Quote:
I'm thinking you can't turn the tremolo intensity down for some reason.

The tremolo beat control does vary the intensity...but if you turn down the intensity you lose the tremelo. The trem circuit must be making a variable low frequency signal that isn't being filtered out. I imagine a small value cap in the right spot might work to eliminate the pulse and let the higher frequency signal pass....but I need some idea of what the circuit is doing so I know where to place the cap.
The circuit is very sensitive and doesn't work at all with any tube changes with different 12XX7 tubes from what is in the schematic.


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 Post subject: Re: 1956 Premier 120 Guitar Amp Tremelo Pulsing The Speaker
PostPosted: Oct Wed 23, 2019 12:20 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 5362
Location: Sunbury, Ohio 43074
Check the three tremolo controls for opens on one end or the other, perhaps even the element not making proper contact with the terminals on the inside of the pot. Are you sure when you replaced the caps, you didn't get one in there of the incorrect value? That would be my second suspect... Also of course check the usual suspects like chassis grounds not being grounds anymore, very common with vintage guitar amps.

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 Post subject: Re: 1956 Premier 120 Guitar Amp Tremelo Pulsing The Speaker
PostPosted: Oct Wed 23, 2019 2:42 pm 
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Joined: Aug Sun 23, 2015 6:01 pm
Posts: 1009
Location: South Jersey East of Philly
All caps replaced correctly and the circuit looked untouched. The pulsing may be normal for this design, but I am really looking for an explanation of how this circuit works...It's different than the more common ones of the day.


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 Post subject: Re: 1956 Premier 120 Guitar Amp Tremelo Pulsing The Speaker
PostPosted: Oct Wed 23, 2019 3:34 pm 
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Joined: Sep Tue 15, 2015 1:16 am
Posts: 692
Location: 18424 PA
Go to https://music-electronics-forum.com/ind ... styleid=12 join and become a member. It will get explained to you there.


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