Lack of volume on a tweed champ

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Lack of volume on a tweed champ

Postby steve_p on Wed Feb 17, 2016 4:42 pm

Hi all,

I have been working on a Tube Amp Doctor tweed champ kit. When I plug it in it works but the volume level is pretty low, way lower than it should be. I have checked the voltages inside the amp and everything is well within spec except for the pins that are associated with the first triode of the ECC83. I get 0 volts on pin 3, and 299 volts on pin 1 (it should be 190 volts). I have tried swapping the valve, but get the same results, so the problem does not lie with the valve. The other triode is working fine, with a reading of 189 volts at pin 6 and 1.6 volts at pin 9.

I have checked and resoldered the wiring to and from this valve, and checked the values of all the components, so I am stumped. any ideas on what would cause the high anode voltage?
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Re: Lack of volume on a tweed champ

Postby Baron Von Machinenmann on Wed Feb 17, 2016 5:47 pm

Which version/schematic?
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Re: Lack of volume on a tweed champ

Postby steve_p on Wed Feb 17, 2016 6:21 pm

5F1. The schematic is in this document: http://www.tubeampdoctor.com/images/Fil ... .10.15.pdf
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Re: Lack of volume on a tweed champ

Postby Baron Von Machinenmann on Wed Feb 17, 2016 11:55 pm

steve_p wrote:
I have checked and resoldered the wiring to and from this valve, and checked the values of all the components, so I am stumped. any ideas on what would cause the high anode voltage?


Are you sure you have a 100k resistor for the plate load on the triode with the excessive B+?
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Re: Lack of volume on a tweed champ

Postby Papa Dog on Thu Feb 18, 2016 5:21 am

Baron Von Machinenmann wrote:
steve_p wrote:
I have checked and resoldered the wiring to and from this valve, and checked the values of all the components, so I am stumped. any ideas on what would cause the high anode voltage?


Are you sure you have a 100k resistor for the plate load on the triode with the excessive B+?


there is something amiss on the cathode circuit as well. Unless there were zero volts to the plate there should be something on the cathode...even with a very low plate voltage the cathode should be above ground if the resistor is there.

So,,,the Baron is right...you need to check the plate resistor, AND the cathode resistor. Not just the markings on them, but with an ohm meter. If you are till getting zero on the cathode you have a bad socket...
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Re: Lack of volume on a tweed champ

Postby steve_p on Thu Feb 18, 2016 12:01 pm

Thanks for the help guys. I checked both the grid and the cathode resistors before my original post and both read ok on my voltmeter. The amp has developed the characteristic crackle of of a dirty socket (though still passing a signal from the input to the speaker), so I think my problems lie with the socket. A new one has been ordered. Just have to wait for the mailman...
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Re: Lack of volume on a tweed champ

Postby Papa Dog on Thu Feb 18, 2016 1:20 pm

steve_p wrote:Thanks for the help guys. I checked both the grid and the cathode resistors before my original post and both read ok on my voltmeter. The amp has developed the characteristic crackle of of a dirty socket (though still passing a signal from the input to the speaker), so I think my problems lie with the socket. A new one has been ordered. Just have to wait for the mailman...


that still does not account for the higher-than-expected voltages on the plate. getting a good cathode connection will knock it down a little bit, but it will still be high...that should not give you LOW volume though...which is why I was thinking that there is an issue with the cathode...I mean zero volts is also a clue...

Oh, yeah, also be sure to check the "grid leak" and "grid stopper(s)" and the input jack wiring...(pics would be helpful)
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Re: Lack of volume on a tweed champ

Postby steve_p on Fri Feb 19, 2016 12:47 pm

Thanks for that PD. A bit of an update. Last night the new 6V6GT blew. Presumably the cracking that I had been hearing previously came from this tube. A replacement has been ordered.

A new socket for V1 arrived and has been fitted. This seems to have fixed the problem. Plate and cathode voltages on both halves of V1 are now the same and read about 235V for the plates and 1.75V for the cathodes. I am assuming that these voltages will drop when a functioning 6V6GT is in the circuit. Will find out early next week.

Thank again for your help.
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Re: Lack of volume on a tweed champ

Postby Baron Von Machinenmann on Sat Feb 20, 2016 1:04 am

Do yourself a favor and get a proper NOS or LNOS 6V6 GT for that amp, they made tens of millions of them so they aren't expensive,I haven't heard a new production tube that comes close. :wink:
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Re: Lack of volume on a tweed champ

Postby Unit_1 on Sat Feb 20, 2016 1:48 am

Here's a beautiful pair, black plate, copper posts, damn near new readings and since it's branded Hammond (made by GE) it's about half the price...

http://www.ebay.com/itm/2-x-6V6gt-G-E-H ... SwgQ9V7beb

I have at least 10 pairs in my private stash otherwise I'd probably get them, lol.... :mrgreen:
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Re: Lack of volume on a tweed champ

Postby Papa Dog on Sat Feb 20, 2016 6:46 am

steve_p wrote:Thanks for that PD. A bit of an update. Last night the new 6V6GT blew. Presumably the cracking that I had been hearing previously came from this tube. A replacement has been ordered.

A new socket for V1 arrived and has been fitted. This seems to have fixed the problem. Plate and cathode voltages on both halves of V1 are now the same and read about 235V for the plates and 1.75V for the cathodes. I am assuming that these voltages will drop when a functioning 6V6GT is in the circuit. Will find out early next week.

Thank again for your help.


Not a problem. Glad I could be of assistance. I must give credit where credit is due. I have learned a lot of valuable information from this site. the Baron has been particularly helpful, and Unit_1 has provided much valuable insight in private consultations. Many, many others here have good information and are usually happy to help.

Anyways, I will second (or third) the advice to find an NOS or LNOS tube. My preference would be for a JAN, but opinions vary. At any rate some of the modern makers build a version of that tube, but, IMHO, only because there is a demand and the quality is reputed to be questionable. I think that because there are still so many NOS tubes on the market they do not pay attention to detail as they would on more highly demanded tubes which are in much shorter supply (6550, KT88, EL34, and 12ax7, just to name some of the more popular offerings).
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