Hot Rod Deluxe Problem

[draperjojo]

My Hot Rod Deluxe is popping, and cutting out with the drive light on the top of the amp flashing in synch with the pops. It does it whether the footswitch is plugged in or not. Doesn't matter which cord I use, or which tube set. Currently the amp has a Celestion Vintage 30 speaker and a Torres Forever Tube set in it. Ideas????? I saw a thread about R57 or R58 being a weak spot?????

[e_c_mccollum]

Check for cold solders. There are small transistors that control the relays which switch the channels. Heat really affects these amps and they can be a pain to work on. Good Luck...........

[draperjojo]

I did check R57 and R58 and they are within tolerance.

[Robert M. Martinelli]

The HRD problem on R57 and R58 can be related to the resistors getting out of tolerance, if this is not your case, then I would check the solder joints, because R57-R58 get so hot that solder joints can melt, and, time after time, heating up and cooling down the solder joints can fail. These resistors drop the voltage to supply the channel switching and the preamp section, so, if the solder joints are defective you get the symptoms you're describing. Searching the forum you' ll find similar threads, and some advice on mods or fixes.

Check also this thread : http://music-electronics-forum.com/s...81516#poststop

I think issues like yours to be caused by a rather poor/flawed design aimed at cutting costs.

My advice would be to either increase the resistors' rated W to keep them from overheating or, better yet put in voltage regulators in their place.


Hope this helps

Best regards

Bob

[Enzo]

I don;t worry so much here about R57,58. They are the plate load resistors for the phase inverter. They do go open or off value, but they don;t usually pop and wouldn;t blink the pilot lamp.


Bob is thinking the same resistors I am - the 5 watt droppers for the zener supplies, but those are R79,79. Bottom center onteh main board, they are next to the bias adjuster. Tap on them adn see if that triggers the pop.

But even that doesn;t affect the pilot light.

Thinking about it a minute, I'd check the inrush limiter. SInce the pilot is wired right off the power transformer, I want to think the mains are being interrupted. It is part TH1 and is a black disc in the lower left of the main board - it sits at a bit of an angle. Poke it with something insulated (like a chopstick) and see if the pop happens. Also check the main AC wiring down in that area and wiggle test the power switch, the fuse holder.

Turn the reverb down, then ball up your fist and whack the top of the amp hard. If that makes the pop or other response, there is a loose connection somewhere. The amp shouldn't respond to a whacking - it won;t hurt it.

[draperjojo]

All good ideas. I had an IR camera here tonight so I snapped a couple pics of the amp and put them in an album.

[Robert M. Martinelli]

Bob is thinking the same resistors I am - the 5 watt droppers for the zener supplies, but those are R79,79.

Enzo, you're right, I was referring to the zener droppers, but I didn' t have the schematic at hand, but being the dropper resistors a fairly common issue on HRDs I assumed them to be R57-58. OTOH I think it's still worth checking the droppers IMHO, because draperjojo says the channel switching circuit acts strange ( the "drive channel" light goes on and off in sync with the popping ). The channel switching circuitry gets its supply from the droppers and the zeners so.....

Best Regards

Bob

[Enzo]

Oh.

And now you've got me back. I saw "drive light" and my head couldn't think anything but pilot light. Yes, then all the more reason to poke those resistors. if the pilot light stays on steady, forget the inrush limiter stuff.

[52 Bill]

When you're checking for loose parts, also check the led itself, if it breaks loose it can also cause the problem that you describe

[Marc]

I've got one of these beastys on my bench right now and it came in with similar issues.
It also was really down on volume-like not very loud with the MV on 5.
Initially I found the footswtich jack had loose solder joints.
So I'm thinking easy fix yea!
I buttoned it back up and now almost no sound.
I found one plate resistor on the PI open, replaced it.
Still just a little sound.

Measured the bias and B+ at the power tube plates screens and the preamp voltages seem to be OK.
Tried the preamp out into my champ and the amp sounds good, switching and all.

I am suspecting the OT is bad.
The owner said he had suddenlylost power and volume recently and had at least one power tube failure.

I measured the OT DCR and found one leg at 86 ohms and the other at 113 from the CT. Does anybody know if this a normal resistance spread or too large?

Sorry for the thread hijackk, but it is sort of related....

thanks,
Marc

[Marc]

Oh yeah the two wire ribbon cable also had broken solder joint and the zener dropping resistors appear to have been replaced, and the speaker tag card had the riviet busted off and the speaker wires were dangling. Yep it's a players amp....

[Marc]

Hold the phone!
I'm guilty of a stupid.
(sure am glad I caught it before Enzo did) Yep, I plugged in to the wrong speaker jack with my test speaker.
Now why would Fender put the extension speaker jack where they did? Just to make sure we're paying attention.
I was thinking logically the closest jack to the tubes would be the main jack, but nope it's not and now the amp is too loud for me to test without annoying the wife and waking the kids.

Thanks for reading this far and I'm off to have a glass of wine.

Marc

[Enzo]

The jacks are shown on the tube chart inside the cab. Also, since the back was off - I hope - while you were working inside, the main jack is the one with the cutout contact.

[bnwitt]

When you say the drive light is flashing could you give a little more detail? Are you playing in clean mode or drive mode when this happens. What color(s) is the drive light in both working and acting up mode when it flashes

[Marc]

Now Enzo, I do know the speaker jack has a cut off!
but both jacks have cut off switches-the ext jack just has more....somehow I knew you couldn't resist the poke. and I swear that chart wasn't there last night!

Back to the original thread, again. This amp had the blinking drive light and it stopped afer I remelted the footswitch jack solder .

Marc