Best new production 5Y3 (and filter cap!) for a Fender Champ

springhead

I'm reparing a 70's silver face Champ for a friend.  Dead mains transformer.  It arrived with the valves out and the 5Y3 has it's locating spigot snapped off.  I'm wondering if it was put in the wrong way round and maybe killed the transformer, or could be coincidence and the spigot broke after the transformer event.  I can put it in my valve tester and find out but even if it's working it's probably not great to give him the amp back with a mechanically faulty valve that could end up in the wrong orientation. 

He's on a limited budget and won't be shelling out for a vintage NOS 5Y3.  I don't have any spare so what's the best of the currently available new replacements?

ICBM

Just mark the broken one and use it if it tests ok. The spigot has no electrical function at all.

If you really don’t want to use it, just buy an old-production one - they’re not expensive, and any is better than any new one.

springhead

I don't mind using it but would feel more comfortable without him having the possibility of disaster.  Quick eBay search shows plenty of NOS 5Y3's at decent prices.  I'll get one ordered.

kreggs

I have had good luck with a NOS Raytheon 5Y3 in one of my builds. Also got a couple of  new JJ 5Y3 in other builds which are holding up well and provide the correct output. NOS is still so cheap though.

springhead

5Y3 on the way.

Next question.  This Champ, from 1974, has it's original (1973 date stamped) 3 section filter cap: 40, 20, 20 @450V. ; I've bought a 40,20,20,20 JJ replacement for it but just discovered the JJ is larger diameter by a few mm.  To fit it will involve filing out the hole in the chassis, perhaps just around the connection lugs and also drilling mounting holes for a clamp as the original uses bent over tags which also form the ground connection to the cap. 

So go ahead and mod the chassis?  Or is there a better fitting replacement (I can't find one, apart from in the US but that's 20,20,20).  Alternative is to leave the original  in place.  It's not swollen but hasn't been used for at least 5 years.  I don't have a variac but do have a lamp limiter.  I could run it up on that, maybe with a series resistor who's value I could reduce over some hours in order to re-form.

ICBM

I would leave it until you're sure it needs replacing. You've very little to lose by powering it up on the lamp limiter - with a valve rectifier, especially run at reduced voltage via the lamp, the voltage will rise quite slowly, and if the cap fails it was almost certainly going to anyway. You don't need hours, even with a Variac - I raise the voltage by 10% every minute or so when I do this. The cap cans in these amps are actually quite a bit less failure-prone than the 'stick of dynamite' ones in the larger models too, even at the same age - I'm not sure why, but I've had to replace very few.

If it does need replacing, I would fit the new one with a proper clamp, and cut away whatever you need to in order to fit it. DO NOT use a Dremel or similar on any of the old solder though, without at least wearing a proper dust mask - it creates fine lead dust which is extremely toxic if inhaled, even in tiny quantities.

springhead

I'll try running it up on the limiter and let it sit for a while.  I'd rather not hack the chassis.

Thanks for the warning on the solder dust.  I wouldn't have thought of that, and given that the old cap is held in place by two tags soldered flat with large amounts of solder to the chassis it would be hard not to make dust.  Top tip, thank you!

RiftAmps

Modulus stocks the correct fitting Cap can - https://modulusamplification.com/Capacitor-Electrolytic-20202020-uF-475-VDC-P5375685.aspx

springhead

Wow!  Thank you, that would do it. Didn't find that when I was searching earlier.   Quite spendy though, £47.88! I guess if you've got a vintage amp and want to keep the original appearance then that's what you have to do. 

I've got the original one running with just the rectifier on the lamp limiter and no drama so far, but then I'm not pulling any current yet.  I'll let it sit for a while and then put the 12AX7 in to load it a little and if that looks ok I'll try the 6V6 as well. 

This Champ has a very buckled eyelet board.  I'd heard old Fender boards could do this but not seen it.  It's got the insulating board underneath it and nothing is touching the chassis so guess it's ok, unless the board is conducting within itself.  Looks odd though.

Edit:  thought I'd check, I can measure 1V or just over in a couple of places on the board.  Not great.

ICBM

springhead said:

I've got the original one running with just the rectifier on the lamp limiter and no drama so far, but then I'm not pulling any current yet.

Don't do that!! Although too late now... it does sound like you've got away with it, and it at least proves that the cap is probably unlikely to fail now. But whatever you do, don't do that without the limiter.

You should not run an amp with the *preamp* valves out, exactly since that will stop the current draw and mean that the lower stages of the B+ chain rise to the full HT, which puts a lot more stress on the filter caps than they've been used to, which can make them fail.

Running with the *power* valves out is fine.

springhead said:

This Champ has a very buckled eyelet board.  I'd heard old Fender boards could do this but not seen it.  It's got the insulating board underneath it and nothing is touching the chassis so guess it's ok, unless the board is conducting within itself.  Looks odd though.

Edit:  thought I'd check, I can measure 1V or just over in a couple of places on the board.  Not great.

Buckling means nothing, but they do very commonly develop leakage. In fact, it's quite often the underlayer which causes the trouble, and it can be fixed by inserting another cardboard spacer between the two - Cornflake packets are ideal .

springhead

Oops! 12AX7 now inserted and volts dropped.  It was sitting unloaded below the rating of the cap but point understood and noted.

If it's noisy, scratchy pots or whatever then I'll try some additional insulation and see what happens.

Thank you!

DJH83004

If you do have to fit a new multi-section cap, you will need a big soldering iron for the lugs that are soldered to the chassis. But like IC, I have never had to change one, other than when a customer has insisted a full cap job be done irrespective of the condition of the originals.   

ICBM

DJH83004 said:

If you do have to fit a new multi-section cap, you will need a big soldering iron for the lugs that are soldered to the chassis. But like IC, I have never had to change one, other than when a customer has insisted a full cap job be done irrespective of the condition of the originals.   

I've had a couple with one cap element having obviously failed, and I'll confess to cheating, since the others were fine - simply by disconnecting the faulty one and adding a new single cap. This was before proper replacements were readily available, admittedly.

I've also replaced a couple, but I've never even tried to solder the new one to the chassis - just cut the old one away, using an old wood chisel, which will chop through solder and aluminium with no trouble at all (just don't use one of your nice ones ) - then fitted a clamp.

springhead

Well, the old cap seems to work so hopefully won't have to get brutal with replacment.  The 6V6 was dead so I've put one of mine in for now.  Seems to be running a bit cold, all the volts are a bit high.  Bit noisy and scratchy which may be the eyelet board conducting I suppose.  Looks all original apart from one mod - small ceramic cap from 6V6 G1 to cathode - unless you chaps have seen that in factory fresh examples?

ICBM

springhead said:

Looks all original apart from one mod - small ceramic cap from 6V6 G1 to cathode - unless you chaps have seen that in factory fresh examples?

Yes, that’s original.

springhead

Thanks for that.  Can’t see it on the versions of the schematic I’ve found. 

RiftAmps

springhead said:

Thanks for that.  Can’t see it on the versions of the schematic I’ve found. 

That's because they added it later on, it's on the Bronco schematic which is the same amp but came part of the Bronco starter pack (gtr + amp)

https://en.wikipedia.org/wiki/Fender_Bronco_Amp

http://vintageampguide.com/schematics/bronco_ab764_schem.gif

springhead

That's interesting, thank you.  Not heard of the Bronco.  This one is the basic Champ, no tremolo and apart from the dead mains transformer I've replaced it looks untouched since being built ('74).

jpfamps

I've had a few Champs with failed can caps, and as there is enough space in the chassis you can fit modern electrolytics on a piece of tag strip.

In my experience can caps do seem more durable than regular caps; I expect due to greater thermal mass, and hence they don't get as hot.

NOS 5Y3s can be found cheaper than current production. 

gringopig

.

ICBM

gringopig said:

I had my Champ repaired and renovated a wee while ago at Time Travel Audio in Edinburgh. Leith actually:

https://imgur.com/a/wlLvVDn

Bit naughty to leave the voltage selector operational!