1965 Deluxe Reverb--Filter Cap Issue--Blowing Fuse

[wsscott]

A friend has this amp, original issue, 2 channels, etc., and has had it for about 3 years.  Its been re-capped before he got it, and has been playing fine, until recently, and its started blowing the fuse.  He asked if I was willing to look at it, mainly just to see if it was something obvious, and I said great opportunity.  So I've opened it up, and took the cover off the dog house to confirm that those 5 caps have been replaced, and they have, and checked their circuit, and find that the negative side of the 2nd A Node 22uf 450V cap is not going to Ground.  It's negative side is not connected to the other 22uf cap's Negative, and only soldered to its eyelet.  Not connected to anything.

Doesn't seem right to me.  How could it be working properly?  The only symptom it otherwise had before blowing the fuse is that the tremolo makes a loud thumping sound when its turned on.

Thoughts?  Thanks as always.  Stephen

[sluckey]

Doesn't seem right to me.  How could it be working properly?

The first two caps should be connected in parallel. But since they're not, rather than 44µF for the Node A cap, you only have 22µF for Node A. I would not expect any bad symptoms other than maybe a little more hum.

Need more details about blowing fuse.

[wsscott]

Yes, but he says its always sounded great. So I can at least connect them after I get the fuse issue resolved. So as to the fuse, I have taken all the tubes out, put in a new fuse, and hooked it up to a light bulb limiter connected to a Variac.  I turned on the power to the amp, Standby is ON, turned on the Variac and started to turn up the voltage, and the light bulb starts glowing at around 15 VAC.  So I shut everything off.  That's where I am.

[sluckey]

With the rectifier tube pulled the STBY switch does nothing. But STBY ON is a confusing statement. It's much clearer when you say the amp is in STBY mode or the amp is in operate mode. When you say it like that we don't have to guess if the switch contacts are open or closed.

Also, with the rectifier tube pulled, there's not much left. Just the PT, bias circuit, and ground switch death cap. Disconnect the death cap from the switch and disconnect the PT red/white wire from the bias board. What happens now?

[wsscott]

The light bulb begins glowing at the same low voltage when the Amp is on and in Standby mode, death cap previously removed, PT wire disconnected.

[sluckey]

Beginning to point to the PT. Disconnect the PT green wires from the indicator lamp assembly. Recheck.

Still no joy, disconnect all secondary wires. Use an ohm meter to check resistance of each winding, including primary winding. No winding should have continuity to any other winding. Post the resistance readings for each winding.

[wsscott]

Before I saw your post, I connected my ohm meter leads to the Red Primary and the Red/White secondary and it read 31 ohms.  Nothing else was disconnected.  Does this tell us anything?  I assume there should read OL, but maybe not since everything else is in circuit.

[wsscott]

I guess not since I realize the "Red Primary" is actually a Secondary winding.

[wsscott]

I disconnected and separated the green wires going to the indicator bulb, and the result is the same, ie. the test light bulb begins glowing at around 24 VAC.

[wsscott]

R/W--GRN--6.9 OHMS
R/W--RED--31.6
RED-GRN-32.3
R/W-YELLOW--0L
GRN-YEL-OL
RED-YEL-OL

I left the 2 center taps soldered to the chassis, and the 2 black primaries soldered to the fuse and the on/off switch.

[sluckey]

I left the 2 center taps soldered to the chassis

Well, take em loose and repeat measurements!

[wsscott]

Ok, the only combinations not reading OL are as follows:

R/W-R/Y--6.8 ohms
R/W-R--31.6
R/Y-R--32.4
G/Y-G--0.2

[sluckey]

OK. Now check each secondary wire for continuity to chassis. Should be infinity. Then tape up the ends of all the secondary wires so they can't short to each other or anything else. Repeat your lamp limiter test.

[wsscott]

Ok, all the wires test fine for continuity to chassis ground.  No Continuity, ie. no beeps.

The light bulb lights up just as before with the light bulb tester hooked up, and only the 2 black wires from the PT connected to the switch and the fuse.

I guess there's a short in the PT on the Primary Winding?

[sluckey]

I guess there's a short in the PT on the Primary Winding?

Kinda looks that way. Take your variac out of the circuit. IOW, plug the light bulb limiter into the wall and plug your amp into the LBL. Use a 40W or 60W bulb. How bright does it get?

[wsscott]

Only have a 100W bulb, might be a 150, and it almost blinds you.  REALLLLLLLY Bright.

[sluckey]

One last thing. Disconnect the PT primary leads and remove the PT from the chassis. Now connect the PT primary leads directly to the LBL. No need to be fancy. Just stick the bare ends of the PT primary leads into the convenience outlet on the LBL. Still bright?

[wsscott]

I’ll have to try it in the morning since I’ve had a cocktail and don’t want to take any chances. Thanks Sluckey.

[wsscott]

What does LBL stand for?

[mresistor]

Light Bulb Limiter

[wsscott]

How obvious! 

[wsscott]

It glows really BRIGHT!!  I guess not a good thing?

[sluckey]

Sure it's a good thing. Now you know what's wrong. Not your dime, right?   

[wsscott]

Right.  So now I'll let my buddy know the bad news, and then figure out what replacement PT he should get.  As I indicated this is a 1965 Fender Deluxe Reverb.  Sluckey, do you have any recommendations on what you think would be good.  I know he, and the musicians that record in his studio really love its sound, but that might be more "psychological" than reality, at least in part because one of the filter caps wasn't even connected.  Thoughts?

I guess after I get this going, then I've got to look at the tremolo thumping issue.  It really sounds like a bass drum beating when its turned on!

Thanks again.  Best.

[sluckey]

Hammond 290BX is a drop in replacement. AES and Hawk both have it. Hawk is best price...

     https://www.hawkusa.com/manufacturers/hammond-mfg/enclosures/290bx

[sluckey]

You say "1965 Fender Deluxe Reverb". Please clarify. This is a real DR, not the '65 Reissue, right? I ask because the reissue DR PT is not the same physical size as the original DR PT.

[wsscott]

Yes Original 1965 DR, not a reissue.

[wsscott]

My friend is going to order a PT, and I just want to be really sure the PT is bad.  Is there any other test I can do to make sure, like with a DMM? Seems like the LBL is definitive, but I don't want him to spend the money on a new PT if I missed something.  Thanks.

[sluckey]

My friend is going to order a PT, and I just want to be really sure the PT is bad.  Is there any other test I can do to make sure, like with a DMM? Seems like the LBL is definitive, but I don't want him to spend the money on a new PT if I missed something.  Thanks.

Sure. Since you have pulled the PT, plug it straight into the wall and see what happens.   

[labb]

might try this:  https://www.premierguitar.com/the-super-secret-transformer-tester

[PRR]

> plug it straight into the wall and see what happens

On the driveway. Video to YouTube.

[wsscott]

As an old lawyer I once saw say to a judge: "Your Honor, I may be dumb, but I'm not stupid"!

[sluckey]

Well my last suggestion will absolutely tell you if the PT is shorted. But if you ain't brave enough to try it, then plug the PT straight into your variac and slowly bring the voltage up. Surely your variac has a fuse. Bet you can't get the voltage up to 120.

[thetragichero]

don't call him shirley!

[wsscott]

Finally the USPS delivered the new PT.  It had been sitting at the PO with a bunch of other mail waiting to be sorted and delivered.  I'm still waiting on something I ordered that should have been delivered on Sept. 10!!  Anyway, I hooked up the new PT to the Light Bulb Tester, and NO LIGHT!!!!  Hooray.  I then hooked up the old PT to the LBT just to be sure and BRIGHT LIGHT!!  Hooray.  So at least we know the old PT has issues.  So I'm starting back up today, and see how far I get.  I'm replacing the 8 pin sockets while I'm at it, since 2 of them show cracks.  Will keep you all posted.  Thanks.

[sluckey]

I'm a believer.   

[wsscott]

Question about the 6.3 V filament wiring.  Does it matter if the wiring on the 6V6's between their sockets connects to the same pins on each socket, ie. pin 2 to pin 2, pin 7 to pin 7, etc? 

[sluckey]

Makes no difference functionally, but I always connect pin 2 to pin 2 and pin 7 to pin 7 just because I like symmetry. 

[pdf64]

Question about the 6.3 V filament wiring.  Does it matter if the wiring on the 6V6's between their sockets connects to the same pins on each socket, ie. pin 2 to pin 2, pin 7 to pin 7, etc?

For push pull amps, there's a potential, theoretical advantage in regard of hum rejection, but I doubt it makes a difference.
I wouldn't bother re-working the heater wiring if the output valve sockets were wired 2 to 7.

[PRR]

Hum comes from the stages with 0.050V signals. If you can make hum in a stage with 50V-500V signals you have strong gremlins.

[wsscott]

Okay, looking good!  Without tubes in, and plugged into the Light Bulb Limiter and the Variac, I turned it on, took it off Standby, and no smoke or pops, NO LIGHT BULB SHINING, Pilot light burning, and no blown fuse.  So it looks like I need to move to the next step of checking the bias and putting in the tubes.  Its running 6V6's and a GZ34S rectifier.  The new PT is 350V on the secondary.  I would appreciate guidance on what to do next.  Thanks as always.

[sluckey]

Remove the LBL and plug straight into the wall socket. With no tubes plugged in... set the bias pot for maximum negative voltage on pin 5 of each 6V6. Be sure you have negative voltage on each tube. Now measure the B+ on every filter cap. They should all be high. Next, measure voltage on the plate and screen of ALL tube sockets. They should all be high.

If you got this far, connect a speaker and plug in all tubes and listen for a scream or howl, and watch for smoke. Shut down if either, otherwise, plug in a guitar and play for a while. Once you think the amp is working properly, set the bias and measure B+ voltages and tube voltages for all pins (including grids even if zero).

[wsscott]

So, with no tubes in, and my DMM set to VDC, Neg. connected to chassis, and Pos. connected to + side of each filter capacitor, each of the 5 caps measure in the 320 MV range.  Could this be correct?

I measured 6.8 VAC on the filaments for the 6V6's connected at pins 2 and 7, and also on down the line on the remaining 9 pin tube sockets at pins 4/5 and 9.

I measured 5.3 VAC on the rectifier tube at pins 2 & 8.

The hot wires each read 356 VAC.

So I put in the tubes in, and only the rectifier glows and gets warm.  All the other tubes are not glowing and are cool.

So what's going on?

[wsscott]

Could there be a problem with the rectifier tube?

[wsscott]

I was able to set the maximum neg. bias to a reading of -65 on both 6V6's.

[sluckey]

So, with no tubes in, and my DMM set to VDC, Neg. connected to chassis, and Pos. connected to + side of each filter capacitor, each of the 5 caps measure in the 320 MV range.  Could this be correct?

That's correct if the GZ34 ain't plugged in.

I measured 6.8 VAC on the filaments for the 6V6's connected at pins 2 and 7, and also on down the line on the remaining 9 pin tube sockets at pins 4/5 and 9.

I measured 5.3 VAC on the rectifier tube at pins 2 & 8.

Both probes are on the sockets, one probe on one filament pin, the other probe on the other filament pin. Right?

So I put in the tubes in, and only the rectifier glows and gets warm.  All the other tubes are not glowing and are cool.

So what's going on?

What you said above must not be true.

This is easy. Should be able to spot the problem with your eyes. Look for a problem between the PT filament wires and the first tube. Especially around the power indicator.

[wsscott]

FOUND IT!  Sluckey was right on the spot.  One of the filament wires at one side of the power light was not a good solder joint.  Fixed that, and everything is working.  Sound and all.  Will need to work on bias tomorrow.  Then when that's all settled in, I'll need to deal with the tremolo that sounds like Helicopters landing in VietNam.  Not good.  Thanks.

[wsscott]

I was looking at the wiring of the 3 prong power cord that has been added by someone, and checked to see if it was wired correctly.  It doesn't appear to be correct.  The Neutral wire of the power cord comes into the chassis, and then through the Ground Switch then to the Line side of the aux. power receptacle, and then goes from there to the ON/OFF Power Switch.  The Line side of the power cord goes through the Ground switch and connects to the Neutral side of the aux. receptacle, and then goes to the Bottom of the Fuse holder. Am I correct that this needs fixing?

I can switch the wires at the Aux. Receptacle and that should fix the mix-up with the feeds from the Mains Supply?  Is the wiring at the fuse holder ok like it is with the feed from the power cord going into the bottom of the fuse holder?

[mresistor]

Take a look here http://www.sluckeyamps.com/misc/Amp_Scrapbook.pdf at the last page   (page 19)

[wsscott]

I guess since the amp has the Ground Switch, it really doesn't matter.