Fender Hot Rod deluxe

[JC@]

I have a problem with one of these.
Randomly, whem strumming a chord, a scratchy noise like a loose/cold solder joint comes out. It is very difficult to test because it shows up sometimes only.

I have noticed that while the noise is there, because it stays with the music like a tube's internal noise does, if I bump the top of the amp with my hand it goes away then maybe comes back as the chord sound decays away.
It dosen't matter how hard I hit the amp with my hand or on the components with the wooden stick probe, the noise does not show up. It only comes sometimes as I strum a chord, as previously mentioned.

I have replaced all tubes in the amp with fresh ones.
All solder points in the tube sockets boards have been remelted.
I haven't checked the back of the main board, but using the wooden stick does not reveal the problem for the moment.

Any help please?

[Sweetfinger]

Try a different speaker-

Maybe the voice coil has come unglued, or there might be a tiny piece of crud stuck in the gap. All it takes is ONE IMPOSSIBLY TINY strand of steel wool about 1 mm in length stuck on a jack to really drive you crazy as an outhouse rat.

[Amp Kat]

You know that makes sence because a lot of those Fender amps mainly twins will sound fine on the bench but when you put them back in the cab all hell breaks loose and these little noises start popping out at intermittent times. I have also seen the filter caps break loose from the solder joint causing them and I also believe that the cheapness of these new pcb's can attribute to cracks and cold solder joints if they are even looked at to hard but it is a over and over thing with almost all of these amps. Whats even stranger is that most of these amps have that little purple sticker from commercial consumer products which is probably why they got rid of it in the first place.

[JC@]

I guess will have to be patient then.
I have two of these amps, and both show a wrong value for a couple of resistors. R52 (180K on the schem, 200K on the amp), and R9 (220K on the schem, 180K on the amp). They are side by side on the board.

Another thing I would like to ask is which would be the best places to tweak because one of the owners want a cleaner clean channel. The trouth is that the clean channel sounds clipped on these amps even at low volume settings. It would be nice to have that clipped wave but a little bit further, at 7 or 8 on the clean pot, not right from the very begining.

JC@

[Amp Kat]

Hmm, seems to me like you have a problem with that amp. Could be an open plate resistor on the PI. That amp on the clean channel should be fender clean up to about 7 or 8. You can set the gain on the yellow channel and more gain on the red channel.

[Enzo]

So unplug the internal speaker and play the amp throough another speaker cab. That will tell you right away if it is the speaker or not. Of course that also removes the vibration from the chassis.

I would not worry about that small change in 200k resistor value.

I agree with KB, this amp should be clean most of the way up. This is not something to tweak, it is something to fix. I also agree that an open plate load resistor on the PI is the place to look first.

If whacking the amp affects the symptom, then it is a connection. There are a couple cement power resistors that a number of people have reported coming free of their solder. They are next to the bias twiddle pot.

[JC@]

>So unplug the internal speaker and play the amp throough another speaker cab. That will tell you right away if it is the speaker or not. Of course that also removes the vibration from the chassis.

I did that at a certain point, and the noise was still there.

>I agree with KB, this amp should be clean most of the way up. This is not something to tweak, it is something to fix. I also agree that an open plate load resistor on the PI is the place to look first.

Well the point is that for a casualty I have two amps from the same exact model, and both sound the same. It is not distortion really, it could be better called "too hot" to be clean. Lovely, but a bit too hot for clean.

>If whacking the amp affects the symptom, then it is a connection. There are a couple cement power resistors that a number of people have reported coming free of their solder. They are next to the bias twiddle pot.

I am going to remove the main board, the one with the pots, and have a look behind. And inspect the input jack sockets, maybe there's a tiny bit of conductive material in there as Sweetfinger mentioned before.

It's something quite annoying because I can't reproduce it by any means, just hitting big chords and wait until it happens.

It is so similar to a noisy tube... but I have replaced them all.

[Thorny]

Those amps sound much better with a 12AT7 in V1 instead of a 12AX7. That cleans things up somewhat.

Also, there is (or was) a website that was dedicated to the repair and modification of hot rod and blues amps as I recall. There were some value switches on the 5w resistors from 470 to 330 ohms on those models, and check the solder joints (beef them up). I had one doing the something similar and there were some resistors in the phase inverter that I changed out to correct the problem as I recall as well.

Not sure if this helps or not... hope it does some.

Thorny

[JC@]

Yes sure it helps.
So I better check those PI plate resistors...
Thank you all.

[PedroC.]

Hi! (I'm new to this forum)

I have a Fender Deluxe 90 that had the exact same problems as yours. I changed the filter caps and showed some improvement, but thanks to R.G. Keen at Aron's DIY forum, I found the main cause:





Check to see if your PCB shows the same heat damage in the 470 resistors (mine were 330). The thing here is that, even replacing them won't be much of a long-term repair, since the resistors will continue to heat up from lowering the voltage from 41v to 16v.





A real (transistor based) voltage regulator would be the way to go, but I'm not very sure how to implement it with the existing PCB and chassis space. So, if anyone has a good idea, I'm all ears

Cheers!

-PedroC.

[gtech]

I never had any problem with my HRD, but I don't use it that much.

The clean channel is still clean (but warm), and the Drive channel is a bit too fuzzy for me.

But it's good to read about what can happen and how to fix it...

Btw, something that could help is one of these:

https://ssl.eurotubes.com/cart/index...category_id=32

I have the Blues #2 kit in mind. Looks good.

The info on the bias is also very interesting. I should try cranking the one on mine a bit. It should help the sound.

Gilles

[JC@]

This is the problem with copying and pasting.
Where I typed: Well the point is that "for a casualty"
I meant to say, "I happen to have two of them"
Poor casualty is one of the amps because I haven't found the cure for that noise for the moment.

[Mouthurst]

Dont suppose it would be something like an amp input resistor or a bad tone cap on the guitar?
Good luck with it, I just bought the working guts of one of these off ebay which Im putting in a 1x12 cab to lighten the load.
Ive never heard one. Can you describe how they lean...tweedy? Blackfacey..?
Unique of course but whats it sound like with everything at 12oclock?
Mouth

[tim]

You may as well pull the main board out and checkfor bad solder joints around the jacks, 470 doping resistors, filter caps, zener diodes etc etc....Also change the 470's to 330's.....30% less voltage drop across each one which means they run cooler and the solder joints under them last longer. Check and make sure that the 82k and 100k plate load resistors on the phase splitter tube are really that (they also get noisey sometimes). I would change the 100k plate load resistors on V1 and V2 while you have the board out as they can get noisy.
I have one of these amps that is an older "made in USA" models. I have done some mods on it over the years and I keep it as a loaner for my customers that need an amp to carry them through while their amp is in my shop. I usually have to pry it out of their hands to get it back! I had one guy back a month or so who was willing to trade straight for a Mesa Boogie Rect-o-Verb that I had just repaired for him. I was tempted but it wouldn't have been a fair deal for him and he is a good customer. They are workhorse amps with a few weak points (mostly poor soldering or not enough solder). That is easily fixed. I have seen a number of newer Hot Rod series amps across my bench that all have cracked solder joints on the power tube solder joints...if your amp is new and is acting very strangely (squealing, losing power, tube plates glowing, blowing fuses) check those solder joints on the circuit board under the power tube sockets...I'll betcha they're cracked.
Tim

[Enzo]

Pardon me? The rail in the drawing above is 42 volts. The 470/330 ohm resistors feed 16v zeners. They are current limiting resistors, not dropping resistors strictly speaking. That means ther will be 26 voltas across each resistor no matter what value you use. And that mean the 330 ohm will run even hotter than the 470. I do not recommend that change.

The two in Pedro's post are indeed the equivalents to the ones I mentioned. In the amp we are looking at, they are next to each other and beside the bias twiddle.

You could engineer a three leg regulator in there, but zeners work fine. These particular resistors just get a bit hot. At 470 ohms they dissipate about 1.4 watts. Change them to a 7 watt maybe, or mount them on standoffs.

In any case, do you have B+ on BOTH plates of the PI? Open plate load means no B+. since the back of the socket is exposed, it should be a snap to check, not that the resistors are hard to find either.