Fender Hotrod -- partial volume drop problem

Z

Zhangliqun

Questionologist
I'm no amp tinkerer but I've been inside this amp a bunch of times biasing and making the part replacements recommended by the Unofficial Fender Hotrod site (great place). I replaced R4, R11, R16, R22, R57 and R58 and they are all still checking out with the multimeter. Also replaced the input jacks.

But now the problem is something not mentioned there -- the volume drops a bit at times when the output from the guitar is low (not playing or playing softly) then pops back up when you hit the strings harder.

Anyone know what that could be?
 
Re: Fender Hotrod -- partial volume drop problem

The biggest thing i have seen with hotrods is both joints coming loose on the tube sockets, and the plate resistors beginning to cook. Have a good look at those and while you've got it open, do yourself a favor and reheat the joints at the tube sockets anyway!
 
Re: Fender Hotrod -- partial volume drop problem

astrozombie said:
tubes.
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yep me too - definitely eliminate that possibility before you open the amp and stary looking for trouble. When a light globe blows in your house, it doesnt mean you need to call the electrician - at least not until you have replaced the globes and checked the fuse box.
 
Re: Fender Hotrod -- partial volume drop problem

I'd be looking for a bad/dry joint or bad connections or maybe dirty valve pins.
maybe even a faulty pot.
Valves are a bit more expensive than light globes so I wouldn't go buying more valves until I was sure it wasn't any of the above.
Effed light globes are pretty obvious,; Shot valves aren't.
 
Re: Fender Hotrod -- partial volume drop problem

gibson175 said:
hey golden vulture...where in aus are you?
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Over at Rainbow in the Land of OZ
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Nth west victoria, about 100k from the S.A. border. Nearest large town/city/traffic lights, Horsham. SwanHill is a little bit further away but "near ".
<<<<<<<<
Rainbow is at one end of Lake Hindmarsh. Jeparit [ the birth place of Robert Menzies ] at the other end. The lake is about 35 km long. It's just filled up with all the water from the floods. First time in 15 years. Most of the last twenty five years it has been empty. Until recently you could drive onto the lake bed.:bandit:
 
Re: Fender Hotrod -- partial volume drop problem

The power tubes are fine. When they go bad it's a very different quality -- the punch is gone and the tone starts to get fuzzy and you keep turning the volume up and up to replace what's lost. The amp still has plenty of punch, even when the volume does the slight drop.
 
Re: Fender Hotrod -- partial volume drop problem

Take a look at the 2) 5 watt ceramic resistors R78 & R79. If you notice a burnt orange ring around the traces? This could be your problem? Let us Know.
 
Re: Fender Hotrod -- partial volume drop problem

No orange traces, both read about 330 ohms.

Will check tube sockets...
 
Re: Fender Hotrod -- partial volume drop problem

I know this is going to sound dumb, but check the input jack for corrosion. i HAD THIS HAPPEN ON MY Marshall's effect loop send jack and the volume would go up & down. I took some emory paper (800) rolled it up like a pencil ans pushed it in and out of all the jacks. Worked great! The other thing is to check for any scratchy pots. Obviously you can't do the same thing but spraying them all out with contact cleaner will do the amp wonders.
 
Re: Fender Hotrod -- partial volume drop problem

I reheated the socket solder joints on both power and preamp tubes. That seems to have solved the problem -- no crackling, no volume drops, The End.

Gentlemen: Thanks for your assistance, I feared a long hard slog bent over the PC board with nothing but frustration to show for it, followed by an expensive trip to the repair shop, followed in turn by a month-long wait without my main amp for evaluating pickups. Thanks be to God for providing this info through you...
 
Re: Fender Hotrod -- partial volume drop problem

Zhangliqun said:
I reheated the socket solder joints on both power and preamp tubes. That seems to have solved the problem -- no crackling, no volume drops, The End.

Gentlemen: Thanks for your assistance, I feared a long hard slog bent over the PC board with nothing but frustration to show for it, followed by an expensive trip to the repair shop, followed in turn by a month-long wait without my main amp for evaluating pickups. Thanks be to God for providing this info through you...
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This is what would have dreaded too. Glad it worked out for you David.
 
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