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Post subject: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Wed Feb 06, 2019 10:46 am
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So i have a number of Fenders in my collection, and always do my own repairs, this amp had some Hum as soon as i hit the power switch on (EVEN BEFORE I FLIP ON THE STANDBY) so that was a concern. So I figured since it was an older USA model, and there were some crusty caps (leaking) id change them out and be done. I changed caps an the noise was still there.

After looking closer at the main LARGE board I noted R63 right next to the bright switch was FRIED, no problem, I swapped out many R78/R79 and have it down to a science, so i dropped the board, changed R63 and power up and SMOKE/FRIED again and obviously i still got noise. And yes I have changed power tubes.

Im lost on why? And where to go from here, any input from anyone would be appreciated.


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Wed Feb 06, 2019 1:50 pm
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We'll look at this;

It is a 10 ohms resistor between the common / ground on pots and amp chassis ground .
There are a short -circuit somewhere

Remove all tubes and look if resistor burn.

Any mods on the amp ?



Image[url=https://flic.kr/p/2exuuJf]Image[url=https://flic.kr/p/2exuuJf]


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Wed Feb 06, 2019 2:32 pm
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You have a AC voltage going thru the Output Transformer = hum.
AC for heater are there if Power is On and Stanby is at Off. That is why Stanby don't need to be in Play position.

So there are any mod on amp ?


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Wed Feb 06, 2019 5:43 pm
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stratele52 wrote:
We'll look at this;

It is a 10 ohms resistor between the common / ground on pots and amp chassis ground .
There are a short -circuit somewhere

Remove all tubes and look if resistor burn.

Any mods on the amp ?


Aa noted in the original post, yes R63 was burnt. No Mods on the amp.



Image[url=https://flic.kr/p/2exuuJf]Image[url=https://flic.kr/p/2exuuJf]


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Wed Feb 06, 2019 7:28 pm
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To reiterate what stratele52 posted, remove ALL tubes, replace resistor and retry. If the resistor doesn’t burn with all tubes removed, it could possibly be a shorted preamp or PI tube.

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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Wed Feb 06, 2019 10:01 pm
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shimmilou wrote:
To reiterate what stratele52 posted, remove ALL tubes, replace resistor and retry. If the resistor doesn’t burn with all tubes removed, it could possibly be a shorted preamp or PI tube.



I will do that, I never knew a shorted pre or pi could create this symptom.


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Thu Feb 07, 2019 2:40 am
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Ryan41018 wrote:
shimmilou wrote:
To reiterate what stratele52 posted, remove ALL tubes, replace resistor and retry. If the resistor doesn’t burn with all tubes removed, it could possibly be a shorted preamp or PI tube.



I will do that, I never knew a shorted pre or pi could create this symptom.


Yes it is a very strange issue. In tubes amp we must always check tubes first


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Thu Feb 07, 2019 9:25 am
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R63 goes from ground to the pot brackets. These are connected to ground at the chassis by nuts.
The only way there can be enough current to blow r63 is if the Green ground wire is not doing its job.
Even then, there shouldn't be any current flowing through ground. Make sure the ac cord is connected to the right board terminals.
I would confirm that the AC receptacle you're using be checked for proper grounding and polarity. A $4.00 tester is available at hardware stores.
If that all checks out, there could be leakage in the power transformer.


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Thu Feb 07, 2019 9:51 am
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stratele52 wrote:
Ryan41018 wrote:
shimmilou wrote:
To reiterate what stratele52 posted, remove ALL tubes, replace resistor and retry. If the resistor doesn’t burn with all tubes removed, it could possibly be a shorted preamp or PI tube.



I will do that, I never knew a shorted pre or pi could create this symptom.


Yes it is a very strange issue. In tubes amp we must always check tubes first



I did pull the pre amp tubes and the PI and still noise with a quick flip of the power on switch, but i looked close at the board and THIS DOESNT LOOK STOCK???


[url]https://ibb.co/qgzKr5V/url]


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Thu Feb 07, 2019 9:54 am
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We can't see the picture :(


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Thu Feb 07, 2019 10:11 am
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stratele52 wrote:
We can't see the picture :(



which photo hosting does everyone use?


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Thu Feb 07, 2019 10:42 am
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stratele52 wrote:
We can't see the picture :(


[img]https://imgur.com/a/91n7xfg/img]

https://imgur.com/a/91n7xfg


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Thu Feb 07, 2019 11:54 am
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TimsAudio wrote:
R63 goes from ground to the pot brackets. These are connected to ground at the chassis by nuts.
The only way there can be enough current to blow r63 is if the Green ground wire is not doing its job.
Even then, there shouldn't be any current flowing through ground. Make sure the ac cord is connected to the right board terminals.
I would confirm that the AC receptacle you're using be checked for proper grounding and polarity. A $4.00 tester is available at hardware stores.
If that all checks out, there could be leakage in the power transformer.


There was broken solder joint on the rear of the board on the green wire that mounts to the chassis as a ground, so now the hum only appears when the standby switch goes ON, not before while POWER SWITCH gets flipped on .


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Thu Feb 07, 2019 1:43 pm
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That's good. I would still check the AC polarity both in the amp and the outlet.
On the AC outlet, the black wire should go to the small slot on the receptacle.
On the amp, trace the black AC cord wire to black wires on the switch, switch, fuse, and thermistor. Then it connects to the black transformer wire at CP3.
if the hot and neutal are the wrong polarity, it can cause hum. if the hot and ground are interchanged, this will give you a hot chassis that can shock you.


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Post subject: Re: Hot Rod Deluxe MYSTERY could use some HELP!
Posted: Thu Feb 07, 2019 2:06 pm
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TimsAudio wrote:
That's good. I would still check the AC polarity both in the amp and the outlet.
On the AC outlet, the black wire should go to the small slot on the receptacle.
On the amp, trace the black AC cord wire to black wires on the switch, switch, fuse, and thermistor. Then it connects to the black transformer wire at CP3.


I will check those.
if the hot and neutal are the wrong polarity, it can cause hum. if the hot and ground are interchanged, this will give you a hot chassis that can shock you.


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