Hot rod deluxe problem

[blu4x5]

its a green board printed 1996.
issue: turn it on/standby i can feel it slightly vibrating. take off standby still slight vibrating and there is a slight crakling. just put in new 6L6s havent change preamp yet. where should i look. i know how to dissipate caps. not scared to poke around a little bit. got a chopstick and poked around didnt locate problem. not sure i'm looking in right area.

[paddy]

Hi there,

Can you tell if the noise is comming from the power transformer? Maybe loose laminations.
Also, these amps have a lot of trouble with dry joints on R78/79 which are the large white 5 Watt 470 Ohm resistors.

Cheers,
Paddy

[blu4x5]

i've read about R78/79 so i already took a chopstick and tried wiggling them around didn't hurt or help the situation. should these be replaced w/ the 5w 330k.

[xtian]

Vibration is typical, hum from vibration is not. Is it humming audibly?

The crackling is probably not related to the hum. Is it only on warmup or all the time? Could be dirty socket pins, bad tube, failing plate load resistors, poor solder joint, etc.

Divide and conquer by pulling preamp tubes; still crackling? Then you can move your attention to the power tubes.

[Markusv]

I had one on the bench with similar issues.
Not the vibrating. I agree that may be loose laminations

The crackling was due to shitty preamp tube sockets
Replaced all 3 though V1 was the culprit
Quiet as a mouse

M

[paddy]

I just checked my repair database and I had a similar issue with one of these amps. The cause of the crackling turned out to be the PI plate resistors. I also agree that you should check out the tubes/sockets.
I wouldn't worry too much about changing the 5 watters to 330 unless someone has come up with a good reason. What I have done with these in the past is change them to the type that have an aluminum heat sink. This requires mounting them on the chassis and running wires to the board. This greatly increases reliability and only cost a couple of bucks.

Cheers,
Paddy

[blu4x5]

ok before i was just poking around so i decided to take a systematic approach and follow the schematics. http://support.fender.com/schematics/gu ... ematic.pdf


question #1 WTF is this http://dl.dropbox.com/u/32815923/010113161849.jpg
and how do i fix it.

question #2 is this normal http://dl.dropbox.com/u/32815923/010113164541.jpg
seems more discolored then other parts of the board almost semi charred

[xtian]

question #1 WTF is this http://dl.dropbox.com/u/32815923/010113161849.jpg
and how do i fix it.

Someone's earlier mod. Don't know what it is.

question #2 is this normal http://dl.dropbox.com/u/32815923/010113164541.jpg
seems more discolored then other parts of the board almost semi charred

The big, white "cement" resistors in this photos are the notorious ones that often fail in this amp. The circuit board is getting baked and is discoloring. They are part of the DC supply for the channel and reverb switching circuit. If you lift the board, save yourself a headache and replace these.

There's lots of great info for the HRD here: http://www.justinholton.com/hotrod/

[blu4x5]

Someone's earlier mod. Don't know what it is.

i understand its a earlier mod more after what it is and what it does.

The big, white "cement" resistors in this photos are the notorious ones that often fail in this amp. The circuit board is getting baked and is discoloring. They are part of the DC supply for the channel and reverb switching circuit. If you lift the board, save yourself a headache and replace these.

i understand R78/79 are a trouble area that's why i showed a pic to get some feed back.

i may email justin w/ a link to the thread if we don't finger it out in a day or so

[ampdoc1]

++ on the PI plate resistors. While the circuit isn't identical, I saw these cause problems on a number of DeVilles back in my repair days. Replacing those, the switching FET and those large resistors fixed about 90% of the repairs on those models.

a'doc

[blu4x5]

++ on the PI plate resistors. While the circuit isn't identical, I saw these cause problems on a number of DeVilles back in my repair days. Replacing those, the switching FET and those large resistors fixed about 90% of the repairs on those models.

the plate resistors are R78/79 correct?


the switching FET is where?

[paddy]

The plate resistors for the PI are R57/58. I wouldn't be too concerned about the switching FET's at this stage.

Cheers,
Paddy

[husky]

i've read about R78/79 so i already took a chopstick and tried wiggling them around didn't hurt or help the situation. should these be replaced w/ the 5w 330k.

You need to do more than replace them but move them.
I've fixed at least 10 of those like that
Those solder joints unsolder and re-solder themselves due to the heat so many times they usually become cold joints. I replace them with chassis mount dale resistors and fly the wires to the board. This is so stupid they didn't spend $1 more for an extra tap on the PT.

[blu4x5]

i took it to rehearsal last nite can't hear the crackling w/ the drums and bass and its the only place i can open the amp up at since i live in an apartment. did good for about 2hrs then it went a little haywire. loud crackling and static as described by http://www.justinholton.com/hotrod/plateloads.html
turned it off for 10 min then finish rehearsal w/o a further problems. so i'm going w/ this answer for now and i have a little time 2moro to check it out. are those resistors available at radio shack?

[xtian]

No, you have to order from Mouser or such. I don't bother flying them off the board. Just leave enough lead to raise them away from the board about a half inch, then silicone them in place with hi-temp silicone from auto parts store.