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 Post subject: Squeal/Ugly Distortion
PostPosted: Sun Feb 19, 2012 2:45 pm 
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I am finally able to get back to my Tramp build from last summer and need to address a couple of issues. First, when the amp is on the 'Tude" setting and the power, volume and master dimed, I get a squeal (only with the RCA 6L6) and a very ugly distortion and volume drop using the RCA, Sovtek 5881, or a EH 6V6. This does not happen in the 'tweed" mode. Overall, I am satisfied with the amp's sound on either setting until I turn up the 'Tude' channel. I have read previously that there was a modification to the 'Tude' setting to solve this but I am using the latest schematic. Has anyone else experienced this?

Secondly, when I lower the VRM/Power control, I cannot get a clean sound on any setting. Is this normal for the VRM? I have read that the VRM will "brown" the sound a bit when it is turned down but it is not the tone/sound I was hoping for. I usually leave this maxed. Am planning on using this at rehearsal tomorrow for the first time and since we mike everything, I will not need to turn this all the way up.

I have tried a couple of pre-amp tubes, including a TAD 70205WA, with no change.

Any suggestions?

Thanks,

Dan


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PostPosted: Mon Feb 20, 2012 4:02 pm 
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Is the 10K grid resistor attached to the tube pin socket. That was one change we made.
Check the latest posted layout.
You should be good on the VRM to about 5-6 on the dial. Browning ocurrs with the dial at about 7

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PostPosted: Wed Feb 29, 2012 2:53 pm 
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I checked the latest schematic and I do have the 10K grid resistor connected to the pin. I moved the MV ground to the input jack ground and changed out the preamp plate resistors to carbon comp. Still getting the squeal on the 'tude setting when the MV is dimed even with the volume up half way or more. Swapped out the preamp tube with a NOS GE 12ax7 and put in a Sovtek 5881 WXT and this has improved the overall tone and sound. I ordered a WGS 10" G10C and will see how that affects the sound/tone. I am currently using a Jensen C10Q that I need to put back in my '57 Bassman clone. Other than the squeal on the 'tude setting, I am satisfied with tone on all settings. I still get a browned out sound at any setting except 10 on the Power setting so I will keep this turned up. The Tramp sounded good at the last rehearsal and am planning on using it for gigs also. Any other suggestions/tweaks that would solve the squeal sound?

Thanks,

Dan


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PostPosted: Fri Mar 02, 2012 12:34 am 
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Squealing suggests you need to carefully tidy up your lead dress. Have you tried moving wires around with a chopstick, to see which make the squeal increase or decrease? Maybe also use a bit more shielded wire in critical places. This amp doesn't squeal when built neatly.

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PostPosted: Tue Jul 24, 2012 11:41 pm 
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I had the same problem in 'Tude mode and found the following solution by poking around the preamp tube wires with a wood pencil:

Pushing the wire connected to pin 6 towards pin 2 & 3 will INDUCE squeal. When the wires almost touch, the squealing starts. Pulling the pin 6 wire as far from pins 2 & 3 wires as possible eliminated the squealing. Suggest shortening these wires and securing them so they won't move around during transit and end up moving and repeating the squeal conditions.

Of course be very careful with this test as the amp is live and you could electrocute yourself. WOOD pencil only without any metal parts or a drumstick also works.


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PostPosted: Thu Jul 26, 2012 9:41 am 
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I've read that pencils are to be avoided for this purpose as the lead in them is conductive carbon. Wooden or plastic chopsticks are recommended.

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PostPosted: Wed Aug 29, 2012 4:20 pm 
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I shortened the wire from pin 6 on the preamp tube and moved the wire on pin 2 until the squealing stopped. This seemed to solve the squealing problem but am still getting a rather ugly distortion with the gain and MV dimed. Backing off a bit seems to solve that also. I will play with the amp over the next few days to see if what I have is acceptable. Thanks for you suggestions about the preamp tube wires.

Dan


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PostPosted: Mon May 20, 2013 5:10 am 
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Bumping this because it is a useful thread. Helped me reduce squealing in 'tude mode. Hope this helps others.


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PostPosted: Thu Jul 11, 2019 3:12 pm 
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I just built a Tramp head that squealed. I practically rebuilt the entire front end before I came up with this which should stop any remaining squealing.

Put a .001uF - .0015uF poly cap (Mallory 150) between grid pin 2 to the ground lug of the terminal strip.

At maximum volume & power, the squeal was gone.

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