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Post subject: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 5:17 am
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currently trying to fix a hotrod deluxe that has about half normal volume and is heavily distorted on the clean channel. have replaced r57 r58 and plate load resistors for the phase inverter aswell as preamp plate resistors. new filter cap for the b+ supply aswell. as far as i can tell the tubes are all getting the right voltage and there is a signal getting to both power tubes.checked the speaker and cable for faults both are okay. am getting about .3ohm for the main speaker wires from the output transformer which i think is about right. i have plugged the guitar into the power amp in and the distortion is still there so it has to be in the power stage. anybody got any ideas?


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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 6:07 am
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Did you replace the power tubes? Sounds like you checked everything but the tubes. You may have lost a power tube.

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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 6:08 am
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brand new power tubes and preamp tubes that i know work


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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 7:37 am
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Did you check for cold/fractured solder joints on the PCB? That's a real problem with these amps. They may be hard to spot. On mine, all I had to do wiggle the tube in the socket a little and they showed up. Man, I'm glad I sold my HRDlx. Mine was a constant reliability headache. Did you clean and retention the power tube sockets? I'm getting close to running out of ideas. Maybe Arjay or Shimm will chime in.

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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 8:48 am
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yeah man its trippin me out.i had a very long look for anydry joints and resoldered all tube sockets just in case. i had found several dry on the tone controls but not the tube sockets. what is the method for retensioning the sockets? from what i understand the symptoms say one of my power tubes is off but the data shows they are on. im going insane


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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 8:48 am
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If all other suspected causes have been examined I think the only thing left is a possible defective output tranny.

Arjay

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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 8:51 am
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Yes, the solder joints are the usual suspects, check them all carefully, including the main PCB. Just a couple of other thoughts. What is the idle bias current setting? If the bias is low, could cause distortion. What about the screen grid resistors for the output tubes? (470 ohm) They can open and still look OK. :idea:

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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 9:08 am
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i have -47 volts on the power tube bias pins which ends up being about 60mv at the test point.
i did check those 470ohm resistors and they are not open and making good contact with the board.


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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 11:14 am
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Turn your bias up to about 85 to 90 mV at the test point and see if it is better (assuming approx 430 VDC Plate voltage, check yours to be sure). Unlikely that the tube sockets need re-tensioned, but it's possible, and if you want to try it, check here for instructions.

http://billmaudio.com/wp/?page_id=171

I shouldn't assume, so make sure that the caps are discharged by measuring for voltage before sticking anything into the tube sockets. :!:

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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 1:53 pm
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What you can do in order to isolate the culprit circuit is:
Plug you instrument directly in Power In input or use another preamp connected on Power In --> If still distorded then the amp is the culprit;
Plug you Preamp out in another amp --> If no distortion, you confirm that the amp is the culprit otherwise the culprit is the preamp and the first measurment has shown distortion.
:wink:

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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 2:25 pm
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Tis-san wrote:
What you can do in order to isolate the culprit circuit is:
Plug you instrument directly in Power In input or use another preamp connected on Power In --> If still distorded then the amp is the culprit;
Plug you Preamp out in another amp --> If no distortion, you confirm that the amp is the culprit otherwise the culprit is the preamp and the first measurment has shown distortion.
:wink:


I think the gentleman already did that......

"i have plugged the guitar into the power amp in and the distortion is still there so it has to be in the power stage. anybody got any ideas?"

(from his initial post)

Arjay

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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 3:22 pm
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I owned a Blues Deluxe (1 speaker jack out), so this is a shot in the dark. What happens if you plug the speaker into the extension jack instead of the main jack?

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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 4:36 pm
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okay so here are some numbers.
v3
pin1 250vdc
pin2 24v
pin3 36v
pin4 0
pin5 0
pin6 241v
pin7 23v
pin8 36v
pin9 0

v4
pin1 0
pin2 0
pin3 422v
pin4 421v
pin5 -4
pin6 0
pin7 0
pin8 0

v5
pin1 0
pin2 0
pin3 421v
pin4 422v
pin5 -40v
pin6 0
pin7 0
pin8 0


i tried to get the bias to 90mv but it only goes to 75 at max. im using jj 6l6gc's so maybe they need a higher bias?
had a thourough look for dry joints and none i can find.
thansk heaps for the help guys even if i cant find the problem


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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 6:22 pm
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Are you sure that you have no filament voltage at any of your tubes? This will be an AC voltage. Are the tubes not "lit up" (glowing orange)? :idea:

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Post subject: Re: hotrod deluxe loss of power
Posted: Fri Jul 22, 2011 8:10 pm
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They are orange but i have not checked the ac voltage on them


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