Fender Hot Rod Deluxe failure, confused on source of the problem

[basisforaday]

I have a 1995 Fender Hot Rod Deluxe, it's one of the first 500 ever produced (so I was told my an amp repair tech years ago).  After years of it collecting dust, I have been gigging with it 1-2 times a month for the last 6 months.  It has had a recurring issue that I find very odd, and even an experience amp tech does not seem to be able to diagnose is.

What happens is while I am playing, always at least 30-45 minutes into a performance, it will suddenly cut silent.  This ONLY happens when it has a lot of gain going through it.  For example, the second I hit my tubescreamer pedal the sound will cut out, or as soon as I hit a really high note with the amp's overdrive on.  It generally will come back on after about 15-30 seconds, and this will happen maybe another 1-2 times throughout a performance.  During my last performance, the sound did NOT end up coming back, even when I plugged in directly, however it once again worked fine when I got home.

What the hell could be causing this?  I brought it in to an amp tech, he said he was not able to recreate the problem.  Does this have something to do with my pedals?  How/why would the pedals affect the amp like this?  Any insight is appreciated as I am clueless and I am afraid it is going to crap out on me for many gigs to come.

[Roly]

Intermittent faults are always curly coz your first problem is getting the fault to show itself.

In this case the times suggest that it's basically thermal, and it is likely to be something such as a valve pin losing contact with its socket after some period of operation.  (Does it show any response to a thump on the case?)

The general approach to a fault like this is to set the amp up down the end of the workshop with the radio burbling through it and wait for it to fail, then start prodding, poking, and measuring.

Does this have something to do with my pedals?

Well, given...

even when I plugged in directly

...no, it looks like an amp problem.

[J M Fahey]

I can truthfully say my customers: "I can solve any amp problem" ... if it happens before me" .... and I'm not bragging, just putting things in perpective.

What it really means is:  can't solve unseen problems.

If you can reproduce it at will, we'll be glad to help.

[galaxiex]

Not to de-rail your thread or get off topic but... hopefully some insight into how these amps are constructed may shed some light.
Please bear with me... I get a little long winded at times...

I happen to own one of these amps, but my Hot Rod Deluxe is a bit newer... but not by much.
I think I bought it around 1998.

My experience with it started with the brand new amp making a mechanical nasty buzzing noise *only* when playing the note "A" on the 7th fret of the D string at medium to high volume.
Took it back for warranty repair and was told the tech could not duplicate the problem. 

So I took it apart to sees what I could find...

These things have got to be a service persons nightmare.

Difficult to work on, weak ribbon cables everywhere, board mounted tube sockets and pots, "fast on" connectors that grip so tight you risk breaking something getting them off, etc...

The main circuit board is supported on plastic stand-offs and one end of the main board is "hanging in the breeze". 

The nasty buzz turned out to be that main circuit board vibrating in sync with the aforementioned "A" note. (what does THAT do for solder joints!!!)  :grr

Now try to find THAT when it ONLY makes the noise when the amp is all assembled and *of course* it won't make the noise when the chassis is removed from the cabinet where you could actually work on and observe the internal parts.

In the process of dis-assembly re-assembly of probably a dozen or more times... looking for the noise, I noticed many poor solder connections and those darn ribbon cables (which you HAVE to flex to work on it) started breaking where they are soldered to the boards. UGH! Self created repairs...

Not to mention removing/replacing the tubes stressed the board mounted sockets and cracked some solder joints there as well. Geezus!

I got lucky (after a dozen attempts!) finding the noise of the vibrating circuit board and ended up wedging a piece of foam between the circuit board and the chassis to damp the vibrations. Whew!

I have since modded the heck out of this poor thing and got it to the point of "mostly" reliable but if I took it on a gig I would be sure to bring a back-up amp. 

Anyways... my point is that your cutting out problem MAY have something to do with poor/cracked solder joints.

Fellow by the name of Justin Holton had a website that went into great detail about these amps "The Unofficial HRDx Owners Guide - a Source and Shrine" but unfortunately that website has been gone for quite some time... 

However... I luckily saved almost all of the website info on my comp.  :tu:

One particular problem area is the plate load resistors R57 R58 on the PI.

Quote from the info... "Most techs go ahead and replace every plate load (R4, R11, R16, R22, R57, R58), which is probably a good idea."

Another common problem is the plastic input jacks.

Quote... "The stock plastic jacks are notoriously unreliable. They are easily damaged if you tighten their nuts too tightly. This puts stress on the inside pieces, and eventually they begin losing their solid connection to the circuit board (PCB)"

Those might be good places to begin looking.... but be warned... this amp is not easy to work on and it's very easy to damage things just attempting to get it apart.

HTH and good luck!

HAH! I found Justin Holton's website info. You can download the entire thing here...

http://www.maxxplay.us/z-jp-hrdx.html

Here it is as individual pdf pages...

http://home.comcast.net/~bandweb2/justin-holton_files.htm

[galaxiex]

Oh yeah... here's a schematic...

[galaxiex]

Ok, it's just a WAG but I bet your cutting out problem is the input jack(s)...

See this...

http://home.comcast.net/~fredholz/Justin-Holton/Replacing%20Damaged%20Jacks.pdf

[Roly]

...and again here;

http://www.stratopastor.org.uk/strato/amps/hrdx/hrdx.html

[phatt]

Hi basisforaday
I had a Mesabugga turn up long time back (model escapes me) well cared for but left for a long time, Would run for about 10 minutes then the sound would go crap. The owner was surprised but happy to learn that it was only dirty valve sockets. <3)

Your issue might be rather more complex but pays to start at really simple  things before getting into a complete rebuild. (which often comes cheap) :tu:
Just remove and reinsert the valves can often fix these sorts of issues.
As mentioned by *galaxiex* these amps can be a pain to service and not something to take on without experience. xP

Hey galaxiex, I did find and fix the shocking hum (design flaw) in some models of those Pro Junior amps a year or so back,, so I understand your frustration. I found the volume return track (back to grid) runs right beside HT2 was the main issue.
Makes you mad that big names get away with such trash design. :grr
Phil.

[g1]

  One of the simplest things to try is a spare cord between the FX send and return jacks (or preamp out & pwr amp in).
  These jacks have internal switches that route the signal through.  They often cause problems like this and are a great place to begin trouble shooting.
  If that doesn't help, try plugging your guitar straight in to the FX return or pwr amp in jack.  If the problem stops, it is likely you have a preamp problem.  If the problem continues, you have isolated it to the power amp or speaker.
  Alternatively, you can run the FX send/preamp out to another amp and see if the problem is still there.