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Need 18 watt help

Dishimyuh

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Nov 4, 2005
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1,206
I have an 18 watt "clone" that was built by a friend. I am having a big problem with "grid clamp" or "blocking". It is a TMB circuit with an EZ81 recto. Does this design have an inherent problem or is there a cure?
 

Richie

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Sep 1, 2004
Messages
173
It depends on what is used,or what values are used in the circuit. There are many tweaks that people use,so one would have to know what layout is in your amp before they could make a suggestion as to what to look for,or tell you how to go about fixing it. lead dress is very important.. There shouldn't be any problems if it is built right,you will not have the noises or problems..

Richie
 

wineredlespaul

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Feb 21, 2004
Messages
140
Like Richie said, if the lead dress is done well, and someone didnt try to overdo gain early on in the amp, they behave very well, and sound killer when done well. Layout is also pretty sensitive. If you know what you are doing in the amp, try going into it with wood sticks, and moving wires around, esp plate and grid leads, to se eif you can make it better or worse. I also would suggest pulling 1 tube at a time, to isolate where the issue is. Start with v1, pull it. If it goes away completely you know where to look, if not, put it back and try v2. Sometimes you can isolate a trouble area this way.
Bob
 

Dishimyuh

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Nov 4, 2005
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I really can't ship it out. The amp was built by a friend who is an amp tech.This was the prototype of a TMB circuit that he was working on. I really don't want to sacrifice my friendship over an amp. I wound up taking it back to him and we discussed the design problems which he wants to rectify. I think that it is just a process of working out the bugs.
Richie and Bob, thanks for the input. Considering your respective reputations it was very kind of y'all to take the time to respond to my post. Btw, Bob I love the Greg Martin clips on your site.
 

59Vampire

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Feb 1, 2005
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4,223
you dont have to sacrafice a friend ship. dont tell him. I paid a lot of money fora clone that was down right awful. Iposted ont he 18 wat board and GOD SHINED DOWN on me and Richie hooked me up. Seriously, if you want it to be what it should be contact the man. if you feel uncomfotable with the whole situation contact me at loml4eva@aol.com seriously, Richie is THE MAN
 

Dishimyuh

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Nov 4, 2005
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Vamp, this guy is not just somebody that I know, he is a F R I E N D. Eventually he would find out and that would be very hurtful for him. Did I fail to mention that he is the only decent tech that I know of in this town. It just would not be advantageous for me to insult this cat.
 

wineredlespaul

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Feb 21, 2004
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140
If he has any questions, please post em here, or email me offline, I will try to help out if possible.
Bob


BTW, you are doing the right thing going with him to see if he can fix it. Friendship is more important than a temporary problem.
 

59Vampire

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Feb 1, 2005
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i did not mean to insult you or your friend. But sit down with him and a few coldones and maybe suggest it should get a second opinion. A good friend should understand
 

Dishimyuh

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Nov 4, 2005
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Bob,
Thank you for the kind offer, I will certainly contact you if I need help.
 

JoeV

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Mar 14, 2006
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598
Blocking distortion comes from too much signal driving the grids of the power tubes positive. You either need more interstage attenuation or a lower gain phase inverter tube, or both. FWIW.
 

BluesForDan

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Aug 31, 2002
Messages
6,798
could some one tell me what blocking distortion is? How do you know when it is the culprit? I am investigating things 18 watts and would like to know about the various pitfalls. This sounds like one of them.

thanks in advance
 

Richie

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Sep 1, 2004
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173
any way you could post a pic of the inside of the amp? It might help see what or where a problem might be. Does this amp have an 18 channel also..is it ok,or suffer the same problems?
Richie
 

Dishimyuh

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Nov 4, 2005
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Richie, I don't have it in my possession at this time. It is a two channel/ four holer. One channel is TMB and the other is the regular vol/tone setup. It also (IIRC) has the same problem. I will try to get a pic posted if I can. The circuit works fine clean. When the amp is turned up and starts to saturate is when the problem occurs. It starts to sound metallic and it almost seems to be flanging.
 

marT

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Jul 18, 2006
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Why can't you tell him that its great BUT it has a few small problems. If he is your friend I don't see why it would be a problem for him to fix it?
 
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