51 Fender Deluxe 5b3 - clean-up advice needed

[martin manning]

Can you describe the remaining noise? Hiss, crackle, hum? Is it affected by the controls or not? If you pull the pre-amp or PI tube does it go away?

The 7k (now 2k5) resistor determines the balance of the PI's outputs. You might want to see how the two sides compare at this point, and of course it will vary with each particular tube that is installed.

MPM

[orrong65]

Completed stage 2 of the work now, replacing:

. 2 x 10k cc power resistors with 1W metal oxide resistors

. 2k2 PI resistor with correct 6k8 value

As a result, the noise level is much lower, to an extent where the amp noise is acceptable for recording use. Pic 1 shows the final components.

The power rail resistors looked "burned", and one easily disintegrated on removal (pic 2). My view is this is where most of the noise was. These two 10k resistors look like they were original 1951 vintage.

One last step is to replace the 250 ohm 5W bias resistor with a new component, which should add the last clean-up step.

Thanks to all who made useful comments along the way. Amp is now in the studio, and recording a new CD.....

[orrong65]

Well, I spoke too soon. Got it into the studio and the noise level was just a little too much, and could be heard in the background at some times.

Back onto the bench, and a bit of checking identified the remaining noise to mainly be in the pre-amp: it increased and decreased as both (pre-amp) volumes were increase and decreased. The guitar channel was also slightly noisier than the mic channel.

This time I decided to concentrate around the input stage of V1, and I cleaned the input jack sleeves and earth contacts, and replaced both 5 meg self-bias resistors with new cc's. I have often seen high value resistors being the cause of the noise. While I was at it, I also replaced the two 50k input resistors with new 33k and 68k cc's, to give low and high impedance guitar inputs.

The result - noise has now dropped by at least another 50%. The 5meg resistors looked awfully tired, and I think these were the culprit, even though they measured 5.5meg and 4.6meg.

Thanks for all the comments and messages.

[billyz]

Well, I spoke too soon. Got it into the studio and the noise level was just a little too much, and could be heard in the background at some times.

Back onto the bench, and a bit of checking identified the remaining noise to mainly be in the pre-amp: it increased and decreased as both (pre-amp) volumes were increase and decreased. The guitar channel was also slightly noisier than the mic channel.

This time I decided to concentrate around the input stage of V1, and I cleaned the input jack sleeves and earth contacts, and replaced both 5 meg self-bias resistors with new cc's. I have often seen high value resistors being the cause of the noise. While I was at it, I also replaced the two 50k input resistors with new 33k and 68k cc's, to give low and high impedance guitar inputs.

The result - noise has now dropped by at least another 50%. The 5meg resistors looked awfully tired, and I think these were the culprit, even though they measured 5.5meg and 4.6meg.

Thanks for all the comments and messages.

While your at it replace those plate load resistors in the preamp.

[Phil_S]

While your at it replace those plate load resistors in the preamp.

I am pretty sure this is rather irreverant, but...when you do the plate load resistors, use metal film or metal oxide. There is no tone running on those and the MF will be more stable and quiter. Use 1 watt resistors.

I figure, at this point, there are enough non-original parts that it isn't very important to use CC resistors. A zealot can always put them in later. Meanwhile, you'll improve the chances of getting the quiet you are seeking. It isn't as if I suggested the chassis need an extra hole or something.

[labb]

While your at it replace those plate load resistors in the preamp.

I have had good results with Vishay/Dale RN series resistors for the plate load resistors.

[Structo]

What is that component by the new Sprague cathode cap on the left?
The brown lumpy looking thing between the black Sprague and yellow Astron?

It always amazes me that some of these amps even work after all these years.

As long as the transformers are still good they keep chugging along.

An old amp I worked on recently didn't have one resistor that was within tolerance.
All the carbon comps had drifted upwards of 20% or more.
But after the cap job it sounded like heaven!
I only replaced two resistors that were critical to setting voltage levels in the supply.

[orrong65]

To structo,
that component, I guess, is a 1951 250ohm 5W wire wound bias resistor, all bubbled and lumpy in the middle. I measured it at close to 250 ohm, and it seems to work fine, but given its condition, I am waiting on a new 5W ceramic replacement.

I am happy to replace parts progressively, and my preference is not simply to rebuild the circuit completely (I'm halfway there already!), but to logically step through the segments.

I am surprised how much the noise dropped after replacing the 5meg grid resistors with new AB carbon comp 5meg resistors. The way in which the originals fell apart with only slight pressure on them must indicate significant deterioration.

The plate resistors are probably in the same condition - they all appear to be the same type and have the old value of 250k ohm.

To replace or not - the noise is OK now, but will the amp be reliable??

[billyz]

To structo,


The plate resistors are probably in the same condition - they all appear to be the same type and have the old value of 250k ohm.

To replace or not - the noise is OK now, but will the amp be reliable??

I see your dilemma. 250k is going to be hard to find in a CC. since you have gone this far though. Measure them and if they have drifted up you might be able to use a 270K( that measures low) . That is if you like the sound of the higher value, i.e.distortion.
since you want it as quiet as possible I would change them out. I find those early 50's CC's to be unreliable compared to later AB or Stackpole.
Then again, they might be fine, you can always change them later on, they have lasted this long.

[Noval_novice]

[quote="Structo"]What is that component by the new Sprague cathode cap on the left?
The brown lumpy looking thing between the black Sprague and yellow Astron?

Ohmite "brown devil?"

[Structo]

If you haven't already done it, I would rework the heater supply.
I think you can gain some more peace by isolating the heater wires to the tubes and not have them ground to the chassis. Sorry if you already did.

[67plexi]

Sprague TVA 1906 ??? why all the new spragues I have used failed.
And are noise sorce. Mallorys are #1 preformed and tested.
http://www.alliedelec.com/search/produc ... KU=8529100
Also all the power supplys I have rebuild with Mallorys have been dead silent
not so with the spragues.
Nice amp

[labb]

I just finished a clone of the 5B3 and it is dead quiet.. I'm cheap, I used Xicon Electrolytics and mostly Mallory 150 caps, Xicon 1/2 watt carbon comp resistors except for the power resistors and the bias resistor. I two wired the heaters with a center tap and I used a buss ground for the ground scheme. I grounded the buss right at the input jack. Still letting some players test it out but up to this point it is a sweet sounding little amp. Lots of control with the single knob tone control..One thing though, at about two on the volume it starts to get really loud.