question on Hot Rod Deluxe

[ocguy106]

My Dad was having an issue with his Hot Rod Deluxe, actually 2 issuse.

First it was crackling alot and if you touched one of the tubes in the preamp stage it would get worse.

second the output was greatly reduced and sound was distorted. where as you could be nice and clean at 4 and start to break up nicly at 6 it was under powered and broken up at 4 and un-usable at 6.

I resoldered the socket tube. It was the second tube in the pre amp and that fixed the crackling problem.
I replaced all 5 tubes and that fixed the low out put problem and now it sounds great.

One problem now when you switch it to overdrive or the "dirty" channel you get an osolation kinda like the 60hrz 110v is back flowing into the circuit. It is loud and un usable in this state. He never uses this channel but I would like to fix it anyway. There is a ribbon cable that connects the Tube PCB to the Main PCB and I am thinking that maybe that got damaged some how.

Here is a link to the schematic for this amp:
http://www.blueguitar.org/new/schem/fender/hotrod_deluxe.pdf
it looks like the overdrive channel is connected to the second tube which is the one I was working on.
any sugestions?

Ken

 

[-CB-]

In any tube amp -

You want to discharge the circuit.  That schematic does not show any bleed down resistor that I can see.  Adding one is always a good idea.

After discharging, you want to make sure each socket contact is tight onto the pins of the tube by adjusting/bending them with a small instrument.  I use a machinists awl (thinner and longer than a punch awl).

You want to spray some contact cleaner on the tube pins and insert it into the socket a few times to de-grunge it.

You want to make sure the tubes themselves are not noisy or microphonic.  You can turn on the amp and give them the finger flick test - if they make a little scratch noise, like moving in the socket... that is ok.  If they continue on scratching, rumbling, howling etc... any noise that persists beyond the "flick", they're noisy and bad.

Ninety nine percent of the time - what you're describing is a dirty and loose socket, or a bad control.  Spray the pots too.

 

[Patrick from Davis]

That amp will hold 65 volts or so for a long time.  Make a bleed resistor doo-hickey and clip it across one of the big (roll of dimes sized) electrolytic caps to discharge the amp.  I have played in the insides of a hot rod deluxe a lot, it holds a charge for a while.  Also the chassis has rough edges and will scrape you up quickly.  You might want to vacuum the insides out if you are in there.  It is amazing what ends up in those things.  I had a ground loop in an amp I built and it was like a twelve string in a howling wind of feedback.  If you get a little short in the wrong spot, chaos ensues.

But, CB is probably right.  Clean up the tube sockets, and it will make a big difference.
Patrick

 

[-CB-]

The thing to do with the bleeder... is to permanently install it.

Its easy.  Just get a resistor that's 1megohm in value, by 1 watt.  Solder up some insulated leads to it, and enclose the whole thing in shrink wrap.  Now you can solder it across one of the big capacitors - from B+ (plus side) to ground (minus side).  When you're playing, and the amp is on, the amp wont notice the few milliamps that go thru the resistor.  When the amp is off, and the standby switch is in the PLAY mode, then it will drain off all residual voltage in a matter of a minute or so - and keep it there - since capacitors will "regrow" their voltage with the amp off!~

The 1 watt size and shrinkwrap are total overkill - but since the amp may be on for extended period of times, we overkill.  Also, if you cut a little square of corrugated cardboard, and super glue it to the shrinkwrap  where the resistor body is, and let that be the heat insulator - so the resistor doesn't contact the side of the capacitor, thats a good thing too.

 

[ocguy106]

That is a good idea CB I will def do that since I will have the amp apart anyway.

Thanks