51 Fender Deluxe 5b3 - clean-up advice needed

[orrong65]

I've just got hold of a 1951 Fender deluxe 5b2 with the serial No 45xx on the chassis and on the label. It has most of the original components and works OK. I came just as a wooden box, so I have had it recovered in tweed already.

Trouble is its very noisy, and I want to clean it up for studio use.

At the risk of sparking off the debate again about "keeping it original" vs "making it useful" again, I am looking for comments on this process.

From the pictures you can see that power and bypass caps have been replaced, and some 2W carbon comp resistors replaced, but the rest is close to 1951 vintage. Someone has added a top boost cap on the back of the No 1 volume switch pot, which I will probably remove.

My issue is this: I want to clean it up so it can be used for studio recording, but I dont just want to replace every component. I am trying to approach it in a methodical way by replacing certain parts every time - such as the power resistors - and then testing it out before moving on to the next stage.

Can I have your comments please on how to clean this sound up, while preserving as much of the original componentry?

[Cygnus X1]

Very nice!

Have you tried different octal preamp tubes yet?
Those have a rep for being noisy but there are plenty of great NOS ones to be found for a bargain.

I wouldn't touch the Astrons but those wax caps might need some attention.

I'm sure you know that you will get very little clean headroom out of this model.

[Gibsonman63]

I would replace the cardboard tube type capacitors. I have heard that some people keep the cardboard and put the new caps inside for a more origianl look.

There is not a great number of components. If you want to take the methodical approach, you can test each capacitor for leakage and replace the leaky ones, however some will leak in the circuit that don't leak when tested due to higher voltages. You can also lift a leg of each resistor and see if it is in tolerance.

If you are worried about value, keep every thing you replace in a plastic bag and tape or staple it to the inside of the cabinet.

I didn't notice, but changing to a grounded power cord would be a good idea for safety if it has not already been done. This is a widely accepted compromise for vintage amps that are actually being played instead of being turned into museum pieces.

[Phil_S]

At the risk of sparking off the debate again about "keeping it original" vs "making it useful" again, I am looking for comments on this process.

Unfortunately, this IS the crux of the discussion. Useful vs. original have a degree of mutual exclusivity that is fairly high in this example.

I think I would approach this by making a priority order list for "original" and a priority order list for "useful". See what shakes out. The stuff that doesn't appear on either list, that's the low fruit to pick first.

I'd agree that the Astron tone caps need to be kept, provided they aren't leaky, but those wax ones probably need to go.

I don't know much about restoration in an old one like this, but it strikes me that you don't have to keep things the way they were originally done if they don't serve your purposes. If it's going to be a working amp, in the end, you will probably choose to do certain things out of necessity. For example, the heater grounds at each tube socket aren't optimal, so you may have to give in on that one. See if you can find some original looking wire for that job. You don't need much. The point is, if you can make it look period correct, it may be more palatable to dig in and fix it.

Nice amp. Good luck.

[billyz]

I agree that you should check those Octal preamp tubes for noise. It can be hard to get a good set. But they do sound great when you get the right ones. As much as I like Carbon comp resistors, I find those early ones can be very noisey, check those Plate resistors and replace with more modern CC ones. And finally check the cathode resistor on the power tubes , it look fried.

If all that fails check those red waxy caps.

[orrong65]

Thanks for all the comments. Just to clarify a few things:

Ive already fitted a 3 prong power cord and centrally earthed it, and removed the "death cap" to earth. There is no ground switch on this model.

I have tried it with 6SL7s in the preamp - pins 3 and 6 are connected on the valve socket so you can use both cathode types. It sounds great, and 6SL7s are much easier to get.

Its definitely going to be a working amp, mainly for studio recording, so the requirement is to get the original (6SC7 type) tone AND low noise.

[labb]

orrong65, if you get a chance would you take some voltage reading on that amp and post them...I am in the process of building a clone of it right now. I started with the intent of building the Rickenbacker M11 which a friend has. Looking close at the M11 and the 5B3 they are basically the same circuit..The big difference is that the M11 is true P to P and the 5B3 is on a board. This made the Fender a lot eaiser for me to build..Big thing that I have seen is that the voltages for the M11 are lower than the 5B3..ie: plate voltages for the pre amp tube for the M11 is as measured 66 vdc, the same for the 5B3 is 92 vdc per the layout drawing. the plate voltage for the PI tube is 150 vdc for both the M11 and the 5B3. The plate voltage for the power tubes is 323 vdc for the M11 and shows to be 350 vdc for the 5B3. Would be really interested if these numbers track what you actually measure in the Fender..My guess in the difference of the two amps is that the Rick is going to break up a lot earlier than the 5B3. By the way, I have heard the M11 being played and it is really a nice amp. Got to think that the 5B3 would sound as good or better.

[selloutrr]

Approach it as a restoration even though you are keeping most of it stock.

if it doesn't have a 3 prong AC add one
take the board out and clean between the insulation board and the traces
remove the parts one by one and test them.
replace as needed
If you want to keep the cool vintage look of the wax caps new electrolytics can fit inside the housings. I've had luck with epoxy and wax.
clean and lubricate all pots and switches
tighten and clean tube sockets.

what is referred to as the "studio mod" was to replace all ceramic caps with orange drops" and new filter caps.
after the amp is clean and all solder points are good and the grounds are solid it's all about voicing the amp with the right tube combination. the more you have to tryout the better.

[Teleguy61]

+1 to selloutrr.
The amp is no longer original that I can see, so that's pretty much off the
table.
Make it work for you, keep all the "original" parts bagged.
If it's not "original", its greatest value is as a great sounding amp.
George

[roadkingbluzs]

As it is not totally original ,maybe install complete new board and leave the original board intact . I am sure there is some value to a collector? BTW who recovered your cab. I have a '52 Pro that needs new tweed.

[orrong65]

Thank to everyone for the further comments.

Answers to a few question:
. I have already fitted a 3 prong power cord and removed the death cap
. It was recovered by Phil Bowen of Melbourne, Vic Australia, including brown silk speaker cloth

I will start testing parts in sequence, and replacing as necessary. I intend to replace the power drop resistors with new 2W carbon comps, and the look at the input input caps. Then I will retest for noise levels. the amp is full of dust so I will clean that out as well.

But before I do all this I will measure some voltages for labb.

[orrong65]

OK labb, I have taken some voltage readings from it, in the state that its currently in:

Mains 117 VAC (through stepdown here)

DC
B+ 418 V
B1 345 V
B2 317 V

V1a/b plate 85/84 V
V2a/b plate 88/237 V all DC ref to ground

Well, right there I can see a few issues - the old schematic showed a B+ of 350V for a 5Y3GT, so thats a bit off (im using a Sovtek 5Y3GT).

There must also be a dud V2b plate resistor giving the 237v, when all the other 3 plate voltages, each after a 250k plate resistor, is around 85V (schematic says 150V).

I guess Im seeing an awful lot of drift in these old carbon comp resistors.

Amp distorts rather nicely at high volume levels though!

[Structo]

In my experience the old carbon comp resistors drift up in value, sometimes by quite a margin.

[labb]

Thanks for taking the readings..If I remember correctly the Sovtek 5Y3GT will give you Voltages that are about 30 to 40 volts higher than a NOS 5Y3. From what I see from your readings it looks as though Fender did in fact run his voltages higher than Rickenbacker did for this amp. When I get this put together I am going to play with the rail voltages and see how much difference there is. If you take 40 volts off of the 418 B+ reading and remember that mostly mains at that time were 110 VAC you would be pretty close to the 350 VDC. Thanks again for taking the time to measure and post the readings.

[orrong65]

Thanks to all the comments received. I have completed stage 1 clean-up of this amp. Work completed is:

. replaced the three .05uf paper caps with molded caps (two Black Cats, one Sangamo 33, all tested before installation);

. added a 100pf ceramic cap across the PI plates - this is present in the 5A3 schematic and the 5B3 layout diagram.

. replaced cathode bypass electrolytics with Sprague atoms (25uf/50V)

The result: Noise has reduced noticeably, but not enough.

At each opportunity I have measured the resistance or capacitance of parts on the eyelet board, with the result that all are close to stated values. The 250k plate resistors have measured at 263, 274, 272 and 280k, all OK. The paper and electrolytics were all close. The 5W wire wound resistor on the 6V6 cathode is a bit bubbled, but measured spot on.

To labb, I was intrigued by your comments on the Sovtek 5Y3 voltages, so I replaced it with an RCA 5Y3GT, black plate, 1957 date code, tests new. Voltages are now:

DC
B+ 397
B+1 327
B+2 300
V1a/b plates 83/84
V2a/b plates 176/186

So it looks like some of the previous issues with V2 voltages have been sorted out.

Having done this, its on to the next phase. My plan is to replace the 10k power resistors and the 250 ohm bias resistor. I have also realised that the 7k resistor is actually 2.2k in the amp. I am awaiting a 7k replacement.

Comments please.