'67 Deluxe Reverb, noise in Vibrato Channel

[drasp]

Recently acquired a lovely early '67 BF Deluxe Reverb. Came to me nearly perfectly original down to the tubes, 2-prong cord, speaker, etc. Had a vented Mallory in the dog pan, plan to keep the amp long-term so I decided to give it a solid "shotgun blast" right off the bat. I've done:

1) 3-prong cord, removed "death cap"
2) fresh electrolytic caps
3) all 100k CC resistors in the preamp section
4) grid resistors
5) bias resistor
6) checked/fixed phase on heaters, adjusted lead dress
7) biased fresh set of JJs 6V6S @ ~25mA
new Weber 12F150 50W, light dope
9) new AT7 for v3, fresh "vintage type" reverb cables & rebuilt US-made Accutronics tank (v3 was missing, cables were bad)
10) cleaned pots/jacks/tube sockets with DeOxit, blew out dust bunnies, etc.

The amp now works beautifully, sounds even better than it looks, and on the Normal channel idles as quiet as any vintage tube amp I've ever heard. Noise flow is VERY low. Very happy. BUT, the Vibrato channel is still a bit noisy. Now I know there is an extra gain stage amplifying noise & additional circuitry, so I'm not expecting it to be the same as the Normal channel, but I've had plenty of old Fenders & this is above what I'd consider normal - worth digging for & correcting. Can anyone suggest any "usual suspects" for buzz/noise in the Vibrato channel? I've pulled V3, no change. Swapped in known-good tubes in every preamp position, no change. Thinking the next step is to trace the from the input w/ an audio probe, but thought I'd ask for the inputs of some folks smarter than myself (Y'all!)

Any help greatly appreciated!!!

[img:800:600]http://delaraspelle.com/misc_pix/67_del ... verb-a.JPG[/img]

[img:800:676]http://delaraspelle.com/misc_pix/67_del ... verb-c.JPG[/img]

[img:729:800]http://delaraspelle.com/misc_pix/67_del ... verb-e.JPG[/img]

[img:800:600]http://delaraspelle.com/misc_pix/67_del ... verb-h.JPG[/img]

[pdf64]

Lucky chap, it looks lovely!
Please could you describe the noise? Do any of the controls affect it?

If hiss, are you sure you aren't chasing ghosts?
The vib channel has more gain and 2 levels of bright boost than the normal channel, so the noise floor, esp hiss is likely to be higher.

Did the 100k slope resistors get replaced along with the 100k plate loads?

What value are the 6k8 mid resistors?

Does the PT maintain a reasonable temperature with that degree of static current?

[Stevem]

Take the ground wire for the output tube screen grid filter from where it's landed and move it to the grounds over by the PT where the B+ and heater center tap are landed if it's 120 hz noise you may be dealing with!

You will likely need to lengthen that Wire or replace it to cover that distance.

Also note that since in these two channel amps the two channels are out of phase with each other you can actually turn up the normal channel and effect the 60hz and 120hz noise level of the whole amp while you are plugged into the vibrato channel!!

[Firestorm]

In the doghouse, the yellow wire running between the first two caps looks like it connects anode on the second cap to cathode of the first. Surely you don't want to series connect 16uF caps. (Maybe it just looks that way).

As to noise, if it's just hiss that's typically present. Three preamp gain stages and you're attenuation the third with a 3M3. You could try metal film there, but some resistor noise is a function only of resistance and temperature so composition won't affect it.

If it's hum, the wire bundle coming up out of the doghouse has the output plate supply which is very hammy. Dress that bundle as far away from the tone control leads as you can. You could try wrapping it with a grounded shield wire, silverface style.

[drasp]

Thanks to all VERY much, for these suggestions!!!

Family day w/ the in-laws today, but I should have a chance to try some of this over the weekend. . .will report back.

[drasp]

Finally got a little time to fuss with this some more - I'm quite convinced the noise level on the Vibrato channel is higher than it should be. Comparing to a '69 Super Reverb (that I went through a few years back & has since been my primary amp) its several times the noise - the Super is damn quiet in the Vibrato channel and Normal.

Anyhow, I think at least one issue with my work may have been found already, there is a lead connecting the first & second filter caps. Those caps had been replaced at some point long ago & I took pictures of that work which I copied - looks like perhaps I copied a mistake or "mod?" form the ancient past!?

Here is a more clear view of the filter caps (with the area in question circled in red):

[img:800:600]http://delaraspelle.com/misc_pix/67_del ... r_caps.jpg[/img]

Looking at other examples from the same era on a Google image search, I don't see anything connecting the anode & cathode of those two caps. Remove it!? Also looks like I've got the black wire going to the ground of the 2nd cap in the wrong spot supposed to land at the 1st cap, yes?

Next, the ground points. I believe the point that Stevem is suggesting I move is the ground that was soldered to the chasis (another weird part of the "repair" that I copied for lack of a better solution. I also grounded the plate for all the pots to the same point on the chassis. I DO have the correct type of grounding lug/washers to extend these lines over to the mounting stud where they probably should be, just haven't done that yet. Better to extend them even further to the 2nd circled area?

[img:800:677]http://delaraspelle.com/misc_pix/67_del ... rounds.jpg[/img]

Will also be moving the bundle of filter wires further from the EQ pots as recommended.

THANKS AGAIN!!!

[Firestorm]

The yellow wire circled connects the main filter caps in series giving you only 8uF of filtering rather than the 32uF the design intended. This will leave a lot of ripple on the B+. With well-matched tubes, you won't hear it in the output, but the amp should ghost like crazy when you drive it hard. It also will make that wire bundle hum more than usual. The yellow wire should go and the first two caps should have their cathodes connected together and their anodes connected together.

What Steve is talking about is the ground on the third cap. This is the screen supply and that ground should be over with the other power amp grounds. Fender tapped this node to feed the reverb driver and put the ground with the preamp filters (maybe to resolve a reverb fault). These connections are under the filter board.

You should unscrew the filter board and unsolder the two orangish wires in the middle so you can flip the board up to gain access to the back. DRAIN THE CAPS BEFORE DOING ANYTHING IN THIS AREA.

[drasp]

Beautiful!!!

Thanks for the clarification - will drain the caps, flip the board, ditch the yellow wire & report back with pix. . .

[Structo]

Make sure the first two 16uF are grounded together.

[drasp]

Alright! My apologies for the diminished quality of the "progress pic", but I wanted to show what I've done & ask for a little more clarification on grounding the set of three caps. . .

[img:800:600]http://delaraspelle.com/misc_pix/67_del ... ogress.jpg[/img]

I've removed the weird yellow wire connecting the first two caps (counting from left of picture) & wired the anodes & cathodes of each cap together (circled in red). Would obviously have been more correct to use the full length of the leads to tie them together under the boards, but they're already cut to length. Maybe next time.

I've also traced the ground for the other three caps, all of them are tied together under the board & grounded by the black wire that goes into the chassis in the lower right of the picture. Inside the chassis, it lands at the big ground plate all of the pots are attached to.

Is the suggestion that I ground the third/middle cap to the LEFT side caps instead of the RIGHT side caps?

edit - I didn't mess with re-routing the ground for now, until I'm more clear on it. Decided it would be good to re-evaluate my noise w/ only the changes in wiring on the first & second cap + moving the twisted set of wires further from the EQ section. My Son just went to bed, so I'll need to listen more in the AM, but so far it SEEMs like the jump in noise from Normal to Vibrato *IS* way better/more normal. . .

[drasp]

Update: well, I'm sure this was a step in the right direction, but its still hissier/buzzier than I think it SHOULD be. . .and I managed to pick up some nasty clicking/ticking w/ the vibrato on. D'oh!!!

Would sound samples comparing noise levels of the two channels be helpful?

Should I wrap the lines coming out of the dog box SF style?

[drasp]

Service Bulletin #9'd the trem ticking w/ a .01 cap, thats gone & sorted now. Ran the amp for a bit on the bench & used a plastic tool to nudge leads looking for anything that seemed to change - didn't really find anything. I *have* noticed that V2 is fairly microphonic regardless of which tube I have in that spot. Everything from a healthy old RCA 7025 to a brand new JJ AX7, especially when tapping the orange wire @ pin 2 (input, yes?) Doesn't seem to be an issue when the amp is cranked, though the Normal channel DOES sound better when cranked above 5 or 6, the Vibrato channel has some weird bass content - I still feel like I'm chasing *SOMETHING* & maybe just doing a poor job of describing it?

[pdf64]

I don't think that PT mounting bolts are a suitable location for the line cord safety ground to the amp chassis.
Transformers tend to be a bit squishy, perhaps due to the numerous laminations, which may compress together.
When opening old Fenders, I often find that the PT nuts need tightening, or are actually loose.
Modern standards require that a dedicated fastener be installed for the safety ground chassis connection.
If drilling another hole is a step too far, consider using a fastener that's subjected to less stress and isn't retaining something squishy.

[Stevem]

Lets try to pin this down to what gain stage the issue is starting with, if you pull out tube V2 does all of the Vibrato channel issues stop?

Also before you yank out V2 take a meter set for ac volt and measure the power supply ripple voltage on the plate side of V2a and V2b and report back with how many mv that is if you would?

[Structo]

The green earth wire on the power cord should have it's onw bolt and nut with lock washers or star washers.

The Center taps for the power transformer should grounded near the transformer.

The power supple should ground near the filter caps.

You want any noise to get quieter the closer you get to the input.

My 2c